CiteULike: jimmithy's library [90 articles]

Productivity, individual-level and colony-level flexibility, and organization of work as consequences of colony size.

I Karsai — 2007-05-24T05:34:47-00:00

Proc Natl Acad Sci U S A, Vol. 95, No. 15. (21 July 1998), pp. 8665-8669.

In social insects, colony-level complexity may emerge from simple individual-level behaviors and interactions. Emergent global properties such as colony size, which can be viewed as a consequence of life history traits, may influence individual-level behaviors themselves. The effects of colony size on productivity, body size, behavioral flexibility, and colony organization are examined here by considering colony size as an independent variable. Large colony size commonly corresponds with complex colony-level performance, small body size, and lower per capita productivity. Analyzing the construction behavior of various wasp societies reveals that complexity of individual behavior is inversely related to colony size. Parallel processing by specialists in large colonies provides flexible and efficient colony-level functioning. On the other hand, individual behavioral flexibility of jack-of-all trades workers ensures success of the small and early societies.

Normalized mutual entropy in biology: quantifying division of labor.

R Gorelick — 2007-05-24T05:24:33-00:00

Am Nat, Vol. 164, No. 5. (November 2004), pp. 677-682.

Division of labor is one of the primary adaptations of sociality and the focus of much theoretical work on self-organization. This work has been hampered by the lack of a quantitative measure of division of labor that can be applied across systems. We divide Shannon's mutual entropy by marginal entropy to quantify division of labor, rendering it robust over changes in number of individuals or tasks. Reinterpreting individuals and tasks makes this methodology applicable to a wide range of other contexts, such as breeding systems and predator-prey interactions.

Gigantism in honeybees: Apis cerana queens reared in mixed-species colonies.

Ken Tan — 2006-11-02T16:01:45-00:00

Naturwissenschaften, Vol. 93, No. 7. (July 2006), pp. 315-320.

The development of animals depends on both genetic and environmental effects to a varying extent. Their relative influences can be evaluated in the social insects by raising the intracolonial diversity to an extreme in nests consisting of workers from more than one species. In this study, we studied the effects of mixed honeybee colonies of Apis mellifera and Apis cerana on the rearing of grafted queen larvae of A. cerana. A. mellifera sealed worker brood was introduced into A. cerana colonies and on emergence, the adults were accepted. Then, A. cerana larvae were grafted for queen rearing into two of these mixed-species colonies. Similarly, A. cerana larvae and A. mellifera larvae were also grafted conspecifically as controls. The success rate of A. cerana queen rearing in the test colonies was 64.5%, surpassing all previous attempts at interspecific queen rearing. After emergence, all virgin queens obtained from the three groups (N=90) were measured morphometrically. The A. cerana queens from the mixed-species colonies differed significantly in size and pigmentation from the A. cerana control queens and closely approximated the A. mellifera queens. It is inferred that these changes in the A. cerana queens reared in the mixed-species colonies can be attributed to feeding by heterospecific nurse bees and/or chemical differences in royal jelly. Our data show a strong impact of environment on the development of queens. The results further suggest that in honeybees the cues for brood recognition can be learned by heterospecific workers after eclosion, thereby providing a novel analogy to slave making in ants.

A computational model of oxygen transport in skeletal muscle for sprouting and splitting modes of angiogenesis

James Ji — 2006-11-02T15:58:13-00:00

Journal of Theoretical Biology, Vol. 241, No. 1. (7 July 2006), pp. 94-108.

Oxygen transport from capillary networks in muscle at a high oxygen consumption rate was simulated using a computational model to assess the relative efficacies of sprouting and splitting modes of angiogenesis. Efficacy was characterized by the volumetric fraction of hypoxic tissue and overall heterogeneity of oxygen distribution at steady state. Oxygen transport was simulated for a three-dimensional vascular network using parameters for rat extensor digitorum longus (EDL) muscle when oxygen consumption by tissue reached 6, 12, and 18 times basal consumption. First, a control network was generated by using straight non-anastomosed capillaries to establish baseline capillarity. Two networks were then constructed simulating either abluminal lateral sprouting or intraluminal splitting angiogenesis such that capillary surface area was equal in both networks. The sprouting network was constructed by placing anastomosed capillaries between straight capillaries of the control network with a higher probability of placement near hypoxic tissue. The splitting network was constructed by splitting capillaries from the control network into two branches at randomly chosen branching points. Under conditions of moderate oxygen consumption (6 times basal), only minor differences in oxygen delivery resulted between the sprouting and splitting networks. At higher consumption levels (12 and 18 times basal), the splitting network had the lowest volume of hypoxic tissue of the three networks. However, when total blood flow in all three networks was made equal, the sprouting network had the lowest volume of hypoxic tissue. This study also shows that under the steady-state conditions the effect of myoglobin (Mb) on oxygen transport was small.

Mechanics and Chemotaxis in the Morphogenesis of Vascular Networks

A Tosin — 2006-10-30T00:00:49-00:00

Bulletin of Biology, Vol. V68, No. 7. (12 October 2006), pp. 1819-1836.

Fluctuation in the physical environment as a mechanism for reinforcing evolutionary transitions

Richard Boyle — 2006-10-29T23:57:42-00:00

Journal of Theoretical Biology, Vol. 242, No. 4. (21 October 2006), pp. 832-843.

We hypothesize a mechanism for reinforcing transitions between levels of selection, involving physiological homeostasis and amplification of variation in the physical environment. Groups experience a stronger selection pressure than individuals for homeostasis with respect to reproductively limiting variables, because their greater longevity exposes them more often to suboptimal physical conditions, and greater physical size means they encompass a larger fraction of any resource/nutrient gradient. Groups achieve homeostasis by differentiation into microcosms with specialist functions, e.g. cell types. Such differentiation is more limited in individuals due to their smaller size and shorter lifespan. Hence tolerance of fluctuation in certain physical variables is proposed to be weaker in individuals than in groups. We show that a trait providing increased tolerance ([alpha]) to fluctuation (V-Vopt) in a limiting abiotic variable (V), at relative fitness cost (C), can increase from rarity if the condition [alpha][middle dot]|V-Vopt|>C is met. Groups also sequester larger absolute quantities of resource than individuals, and group death is less frequent, hence the population dynamics of groups cause resource/nutrient availability to fluctuate with greater amplitude than that of individuals. Increasing the amplitude of fluctuation in a reproductively limiting environmental variable is proposed as a mechanism by which a group can limit reproduction of parasitic "cheat" individuals. Enhancing physical fluctuation is frequency dependent, hence only an increase in tolerance to fluctuation can explain the group's increase from rarity. However, once groups reach intermediate frequencies, a positive feedback process can be initiated in which a differentiated group enhances physical fluctuation beyond the tolerance of any "cheat", and in so doing enhances the selection pressure it experiences for homeostasis. This may help explain the persistence of transitions in individuality, and the coincidence of some such transitions with periods of change and oscillation in global scale environmental variables.

The Coupled Evolution of Breathing and Locomotion

Perry — 2006-10-29T23:46:35-00:00

Physiological and Biochemical Zoology

http://www.journals.uchicago.edu/PBZ/journal/issues/v79n6/060028/060028.html

Sexual size dimorphism in a Drosophila clade, the D. obscura group

Raymond Huey — 2006-10-29T23:09:56-00:00

Zoology, Vol. 109, No. 4. (14 November 2006), pp. 318-330.

The Drosophila obscura clade consists of about 41 species, of which 20 were used for analyses of wing and thorax length. Our primary goal was to investigate the magnitude of sexual size dimorphism (SSD) of these traits within this clade and to test Rensch's Rule [when females are larger than males, SSD (e.g., female/male ratio) should decrease with body size]. Our secondary goal was methodological and involved evaluating for these flies alternative measures of SSD (female/male ratio, female/male absolute difference, female/male relative difference), developing a bootstrap method to estimate the magnitude of intraspecific variation in SSD, and applying a new method of estimating allometric relationships that is phylogenetically based and incorporates error variance in both traits. All indices of SSD were strongly correlated for both size traits. Nevertheless, female/male ratio is the best index here: it is easily interpretable and essentially independent of size. For both traits, SSD (F/M) varied interspecifically, showed a strong phylogenetic signal, but did not differ for the main phylogenetic subgroups or correlate with latitude. Factors underlying variation in SSD in this clade are elusive and might include genetic drift. SSD (wing) tended to decrease with increasing size, as predicted by Rensch's Rule, though not consistently so. SSD (thorax) was unrelated to size. However, analysis of published data for thorax length of Drosophila spp. (N=42) with a larger size range showed that SSD decreased significantly with increasing size (consistent with Rensch's Rule), suggesting our ability to detect SSD-size relations in the D. obscura data may be limited by low statistical power.

Respiratory flow in obstructed airways

XL Yang — 2006-10-29T23:04:47-00:00

Journal of Biomechanics, Vol. 39, No. 15. (2006), pp. 2743-2751.

Chronic obstructive pulmonary disease (COPD) is one of the most common diseases in human community. The COPD always results in inflammation that leads to narrowing and obstruction of the airways. The obstructive airways have significant effect on respiratory flow. In order to understand the flow phenomenon in such obstructive airways, four three-dimensional four-generation lung models based on the 23-generation model of Weibel [1963. Morphometry of the Human Lung. Springer, Academic Press, Berlin, New York] are generated. The fully three-dimensional incompressible laminar Navier-Stokes equations are solved using computational fluid dynamics (CFD) solver on unstructured tetrahedral meshes. Therein, a symmetric four-generation airway model is served as the reference, the other three models are considered to be obstructed at each generation, respectively. The calculation results show that the obstructive airway has significant influence on the air flow in both up- and down-stream airways and it even results in flow separation in the conjunction region. The re-circulation cell blocks the air from entering the downstream branches. This may be the reason why COPD patients should breathe gently, and this also provides some valuable information for medicine powder deposition.

The effects of carbon dioxide anesthesia and anoxia on rapid cold-hardening and chill coma recovery in Drosophila melanogaster

Theresa Nilson — 2006-10-29T23:02:21-00:00

Journal of Insect Physiology, Vol. 52, No. 10. (October 2006), pp. 1027-1033.

Carbon dioxide gas is used as an insect anesthetic in many laboratories, despite recent studies which have shown that CO2 can alter behavior and fitness. We examine the effects of CO2 and anoxia (N2) on cold tolerance, measuring the rapid cold-hardening (RCH) response and chill coma recovery in Drosophila melanogaster. Short exposures to CO2 or N2 do not significantly affect RCH, but 60 min of exposure negates RCH. Exposure to CO2 anesthesia increases chill coma recovery time, but this effect disappears if the flies are given 90 min recovery in air before chill coma induction. Flies treated with N2 show a similar pattern, but require significantly longer chill coma recovery times even after 90 min of recovery from anoxia. Our results suggest that CO2 anesthesia is an acceptable way to manipulate flies before cold tolerance experiments (when using RCH or chill coma recovery as a measure), provided exposure duration is minimized and recovery is permitted before chill coma induction. However, we recommend that exposure to N2 not be used as a method of anesthesia for chill coma studies.

Analysis of the hypoxia-sensing pathway in Drosophila melanogaster.

N Arquier — 2006-10-23T20:07:10-00:00

Biochem J, Vol. 393, No. Pt 2. (15 January 2006), pp. 471-480.

The mechanism by which hypoxia induces gene transcription involves the inhibition of HIF-1alpha (hypoxia-inducible factor-1 alpha subunit) PHD (prolyl hydroxylase) activity, which prevents the VHL (von Hippel-Lindau)-dependent targeting of HIF-1alpha to the ubiquitin/proteasome pathway. HIF-1alpha thus accumulates and promotes gene transcription. In the present study, first we provide direct biochemical evidence for the presence of a conserved hypoxic signalling pathway in Drosophila melanogaster. An assay for 2-oxoglutarate-dependent dioxygenases was developed using Drosophila embryonic and larval homogenates as a source of enzyme. Drosophila PHD has a low substrate specificity and hydroxylates key proline residues in the ODD (oxygen-dependent degradation) domains of human HIF-1alpha and Similar, the Drosophila homologue of HIF-1alpha. The enzyme promotes human and Drosophila [(35)S]VHL binding to GST (glutathione S-transferase)-ODD-domain fusion protein. Hydroxylation is enhanced by proteasomal inhibitors and was ascertained using an anti-hydroxyproline antibody. Secondly, by using transgenic flies expressing a fusion protein that combined an ODD domain and the green fluorescent protein (ODD-GFP), we analysed the hypoxic cascade in different embryonic and larval tissues. Hypoxic accumulation of the reporter protein was observed in the whole tracheal tree, but not in the ectoderm. Hypoxic stabilization of ODD-GFP in the ectoderm was restored by inducing VHL expression in these cells. These results show that Drosophila tissues exhibit different sensitivities to hypoxia.

Progress in Functional Neuroanatomy: Precise Automatic Geometric Reconstruction of Neuronal Morphology From Confocal Image Stacks

JF Evers — 2006-10-23T20:01:34-00:00

J Neurophysiol, Vol. 93, No. 4. (1 April 2005), pp. 2331-2342.

Dendritic architecture provides the structural substrate for myriads of input and output synapses in the brain and for the integration of presynaptic inputs. Understanding mechanisms of evolution and development of neuronal shape and its respective function is thus a formidable problem in neuroscience. A fundamental prerequisite for finding answers is a precise quantitative analysis of neuronal structure in situ and in vivo. Therefore we have developed a tool set for automatic geometric reconstruction of neuronal architecture from stacks of confocal images. It provides exact midlines, diameters, surfaces, volumes, and branch point locations and allows analysis of labeled molecule distribution along neuronal surfaces as well as direct export into modeling software. We show the high accuracy of geometric reconstruction and the analysis of putative input synapse distribution throughout entire dendritic trees from in situ light microscopy preparations as a possible application. The binary version of the reconstruction module is downloadable at no cost. 10.1152/jn.00761.2004

In vivo modulation of morphogenetic movements in Drosophila embryos with femtosecond laser pulses.

W Supatto — 2005-01-27T03:55:46-00:00

Proc Natl Acad Sci U S A, Vol. 102, No. 4. (25 January 2005), pp. 1047-1052.

The complex biomechanical events associated with embryo development are investigated in vivo, by using femtosecond laser pulse-induced ablation combined with multimodal nonlinear microscopy. We demonstrate controlled intravital ablations preserving local cytoskeleton dynamics and resulting in the modulation of specific morphogenetic movements in nonmutant Drosophila embryos. A quantitative description of complex movements is obtained both in GFP-expressing systems by using whole-embryo two-photon microscopy and in unlabeled nontransgenic embryos by using third harmonic generation microscopy. This methodology provides insight into the issue of mechano-sensitive gene expression by revealing the correlation of in vivo tissue deformation patterns with Twist protein expression in stomodeal cells at gastrulation.

Ultrastructure of Insect and Spider Cocoon Silks.

Osnat Hakimi — 2006-10-23T19:50:27-00:00

Biomacromolecules, Vol. 7, No. 10. (9 October 2006), pp. 2901-2908.

Despite much interest in the extraordinary mechanical properties of silks, the structure of native silk fibers is still not fully understood. In the present study, the morphology, topography, and organization of insect and spider cocoon silks were investigated using a range of imaging methods. Field emission scanning electron microscopy was used to observe transverse and longitude structures in silk fibers subjected to tensile fracturing, freeze fracturing, or polishing. In addition, ultrathin sections of silk brins embedded in resin were examined using transmission electron microscopy. Finally, dry silk brins were examined by confocal microscopy. The results confirmed the existence of well-oriented bundles of nanofibrils in all the silks examined and gave an indication of a hierarchical construction of the brin. Observed separation of the microfibrils in fractured brins suggests that the multifibrillar structure of the silk fiber contributes to toughness by allowing dissipation of energy in the controlled propagation of cracks.

Whole insect and mammalian embryo imaging with confocal microscopy: Morphology and apoptosis.

Robert M Zucker — 2006-10-23T19:47:36-00:00

Cytometry A, Vol. 69A, No. 11. (18 October 2006), pp. 1143-1152.

BACKGROUND:: After fluorochromes are incorporated into cells, tissues, and organisms, confocal microscopy can be used to observe three-dimensional structures. LysoTracker Red (LT) is a paraformaldehyde fixable probe that concentrates into acidic compartments of cells and indicates regions of high lysosomal activity and phagocytosis, which both correlate to apoptosis activity. LT has been shown to be an indicator of apoptotic cell death which is correlated to other standard apoptotic assays. METHODS:: The mammalian samples were stained with LT, fixed with paraformaldehyde/glutaraldehyde, dehydrated with methanol (MEOH), and cleared with benzyl alcohol/benzyl benzoate (BABB). Following this treatment, the tissues were nearly transparent. Mosquitoes were fixed with MEOH and stained with propidium iodide. Next the tissues were dehydrated with MEOH and cleared with BABB. RESULTS:: Tissues as thick as 500 mum can be visualized after clearing with BABB. LT staining revealed apoptotic regions in mammalian limbs, fetuses, and embryos. Morphological observation of insect tissue consisted of combining autofluorescence with either nucleic acid staining (either propidium iodide or ethidium bromide). CONCLUSIONS:: The use of BABB matches the RI of the tissue within the suspending medium. It helps in increasing the penetration of laser light in a confocal microscope by reducing the amount of light scattering artifacts and allows for the visualization of morphology in thick tissues. LT is a probe that stains the acid regions of tissues and cells and has been correlated to apoptosis. Morphological features of a tissue or organism (embryo, mosquito larvae) can be elucidated by fixation aldehydes, autofluorescence, and red-emitting probes. This sample preparation procedure with optimization of confocal laser scanning microscopy allowed for the detection and visualization of apoptosis in fetal limbs and embryos which were approximately 500-mum thick. (c) 2006 International Society for Analytical Cytology.

Isolation and characterization of chitin from bumblebee (Bombus terrestris).

Juraj Majtán — 2006-10-23T19:42:59-00:00

Int J Biol Macromol (1 August 2006)

Insect chitin possessing shell-like structure was prepared from the bumblebee corpses by a consequent treatment with 1M HCl and 1M NaOH. The bumblebee chitin was compared with crustacean (shrimp) chitin by using elemental analysis, Fourier-transform infrared (FT-IR) and solid-state (13)C cross-polarization magic angle spinning nuclear magnetic resonance (CP/MAS)-NMR spectroscopy and confocal microscopy. Both chitins (bumblebee and shrimp) exhibited identical spectra, while the bumblebee chitin had a 5% lower degree of acetylation and was characterized by a fine membrane texture.

On connecting large vessels to small. The meaning of Murray's law

Tf Sherman — 2006-01-17T20:23:39-00:00

J. Gen. Physiol., Vol. 78, No. 4. (1 October 1981), pp. 431-453.

Discontinuous gas-exchange in centipedes and its convergent evolution in tracheated arthropods

Jaco Klok — 2006-01-13T23:42:37-00:00

J Exp Biol, Vol. 205, No. 7. (1 April 2002), pp. 1019-1029.

We have examined the gas-exchange characteristics of five southern African centipede species from three orders. Two scolopendromorph species exhibit discontinuous gas-exchange cycles (DGCs) identical to those recorded for several insect and chelicerate species. Another scolopendromorph and a lithobiomorph species exhibit weak periodic patterns, and a scutigermorph species shows continuous gas exchange. A crucial component for DGCs in tracheated arthropods is the presence of occludible spiracles. However, on the basis of studies of temperate centipedes, most recent invertebrate biology texts hold the view that centipedes, as a group, cannot close their spiracles. Using flow-through normoxic and normoxic--anoxic--normoxic respirometry and electron microscopy, we conclusively demonstrate that at least one of the scolopendromorph species, Cormocephalus morsitans L., can close its spiracles fully, thus accounting for its DGCs. Homologies in spiracular structure and DGCs suggest that several other tracheated arthropod taxa probably have this ability too and that DGCs have evolved convergently at least four times in the Arthropoda. Spiracular closure and discontinuous gas-exchange cycles are probably more widespread in arthropods than has previously been suspected.

Upper thermal tolerance and oxygen limitation in terrestrial arthropods

Jaco Klok — 2006-01-13T23:40:16-00:00

J Exp Biol, Vol. 207, No. 13. (1 June 2004), pp. 2361-2370.

The hypothesis of oxygen limitation of thermal tolerance proposes that critical temperatures are set by a transition to anaerobic metabolism, and that upper and lower tolerances are therefore coupled. Moreover, this hypothesis has been dubbed a unifying general principle and extended from marine to terrestrial ectotherms. By contrast, in insects the upper and lower limits are decoupled, suggesting that the oxygen limitation hypothesis might not be as general as proposed. However, no direct tests of this hypothesis or its predictions have been undertaken in terrestrial species. We use a terrestrial isopod (Armadillidium vulgare) and a tenebrionid beetle (Gonocephalum simplex) to test the prediction that thermal tolerance should vary with oxygen partial pressure. Whilst in the isopod critical thermal maximum declined with declining oxygen concentration, this was not the case in the beetle. Efficient oxygen delivery via a tracheal system makes oxygen limitation of thermal tolerance, at a whole organism level, unlikely in insects. By contrast, oxygen limitation of thermal tolerances is expected to apply to species, like the isopod, in which the circulatory system contributes significantly to oxygen delivery. Because insects dominate terrestrial systems, oxygen limitation of thermal tolerance cannot be considered pervasive in this habitat, although it is a characteristic of marine species.

Insect gas exchange patterns: a phylogenetic perspective

Elrike Marais — 2006-01-12T22:13:47-00:00

J Exp Biol, Vol. 208, No. 23. (1 December 2005), pp. 4495-4507.

Most investigations of insect gas exchange patterns and the hypotheses proposed to account for their evolution have been based either on small-scale, manipulative experiments, or comparisons of a few closely related species. Despite their potential utility, no explicit, phylogeny-based, broad-scale comparative studies of the evolution of gas exchange in insects have been undertaken. This may be due partly to the preponderance of information for the endopterygotes, and its scarcity for the apterygotes and exopterygotes. Here we undertake such a broad-scale study. Information on gas exchange patterns for the large majority of insects examined to date (eight orders, 99 species) is compiled, and new information on 19 exemplar species from a further ten orders, not previously represented in the literature (Archaeognatha, Zygentoma, Ephemeroptera, Odonata, Mantodea, Mantophasmatodea, Phasmatodea, Dermaptera, Neuroptera, Trichoptera), is provided. These data are then used in a formal, phylogeny-based parsimony analysis of the evolution of gas exchange patterns at the order level. Cyclic gas exchange is likely to be the ancestral gas exchange pattern at rest (recognizing that active individuals typically show continuous gas exchange), and discontinuous gas exchange probably originated independently a minimum of five times in the Insecta.

Cross-testing adaptive hypotheses: Phylogenetic analysis and the origin of bird flight

Kevin Padian — 2006-01-12T21:18:03-00:00

American Zoologist, Vol. 41 (2001), pp. 598-607.

Origin of flightCould ‘four-winged’ dinosaurs fly?

Kevin Padian — 2005-11-17T05:28:48-00:00

Nature, Vol. 438, No. 7066. (16 November 2005), pp. E3-E3.

How dinosaurs grew so large--and so small.

JR Horner — 2006-01-12T21:02:54-00:00

Sci Am, Vol. 293, No. 1. (July 2005), pp. 56-63.

Mandibular Mechanisms and the Evolution of Arthropods

SM Manton — 2005-12-19T09:08:58-00:00

Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, Vol. 247, No. 737. (1964), pp. 1-183.

(1) A functional and comparative study has been made of the jaw mechanisms of representatives of the major classes of arthropods, covering, where appropriate, the whole endoskeletal systems of the head and the form and function of other mouth parts, hypopharynx, etc. (2) Mandibles are developed embryologically, and presumably phylogenetically also, in one or other of two ways. Type A, in which the biting structures are developed from a proximal endite or gnathobase (Crustacea, Chelicerata), and type B, in which the mandible is developed from a whole limb, the tip of which and not the base is used for gnathal purposes (Onychophora, Myriapoda, Hexapoda). (3) Two types of movement typical of the more primitive ambulatory trunk limbs have been exploited in mandibular evolution. Type I mandibular movement uses the promotor-remotor swing of an ambulatory or swimming coxa on the body, but the axis of swing may be shifted in various ways (Crustacea, Thysanura), and type II mandibular movement uses the prehensile action in the transverse plane of a coxa or coxa and telopodite. Type II is found in Myriapoda, where segmentation of the whole-limb mandible is essential, and direct transverse gnathobasic biting is employed by Limulus. Mandibles of types I and II appear to have evolved independently in the named examples. (4) The more primitive examples of type II mandibles suit fine food feeding and the scratching of food surfaces. The gape is small, biting, if any, is weak, and added hydraulic efficiencies enable fine particles to be sucked up by terrestrial types (Chirocephalus, Hemimysis, Paranaspides, Petrobius). (5) Biting in the transverse plane is not a primitive attribute of the Arthropoda outside the Chelicerata and certain Myriapoda. In the more primitive Crustacea and Hexapoda transverse biting is absent and there is little basic adduction and abduction. Transverse muscles primarily serve promotor-remotor rolling movements. No example has been found of a so-called monocondylic mandible of a crustacean or of a hexapod which exhibits freedom of movement in all directions from this point and a basic power of transverse adduction, whether or not the mandible possesses a formed dorsal articulation. (6) Strong biting in the transverse plane suiting hard or large food is a repeated end term in arthropodan evolution. The examples considered are: some Decapoda, Peracarida, Pterygota, Diplopoda and Symphyla. Adduction in the transverse plane is mechanically simple, but abduction presents great problems, hitherto not appreciated, which have had to be resolved by every group of animals attempting to evolve such mandibles. The resolutions of the difficulty are various, mutually exclusive, and independently evolved by mandibles of all types. (7) The feeding mechanism of Limulus is described. The jaw mechanisms of Limulus and of Crustacea are fundamentally different and have probably been evolved in independence. (8) The validity of the evidence for the existence of a pre-coxal segment in Xiphosura needs reconsideration. (9) The rolling whole-limb mandibles of Petrobius are not far removed from a central type which could have given rise to the various mandibles occurring throughout the Hexapoda. It is shown in some detail how this mechanism is parallel to but different from that of the rolling gnathobasic mandibles of the more primitive Crustacea. Differences between the mandibles of Hexapoda and Crustacea concern mandibular form, musculature, movement and derivation; the head endoskeleton, and the form and movements of maxilla 1 are also different. The superficial resemblances are considered to be due to convergence between mandibles of unlike origin which utilize the same type of movement of an ambulatory limb. (10) Present-day animals show how the Petrobius-type of jaw mechanism could have given rise to (i) the strong transverse biting of the Lepismatidae and Pterygota with loss of hydraulic efficiency of the Petrobius type and to (ii) a further development of the rolling movement, together with protrusibility of mandibles, which has been made possible by entognathy in the Apterygota. These two trends are mutually exclusive. (11) Entognathy is a condition permitting great proximal mobility of the mandible and hence confers the powers of mandibular protrusion which are absent in strong closely articulated mandibles. Entognathy in essentially similar form, but differing in details, has been evolved in Onychophora, Chilopoda, Pauropoda, Collembola, Diplura and Protura. The `Entognatha' is not considered to be a valid taxonomic group but one of convergence. (12) A basic pattern of: mandibular structure, musculature, movements, associated head endoskeleton, and of the structure and movements of maxilla 1 is recognizable throughout the less specialized Pterygota, Thysanura, Collembola and Diplura, so linking these groups together by characters having nothing to do with the possession of three pairs of legs. This basic pattern of mandible and maxilla 1 is not found in the Myriapoda. (13) A unified system of skeletal tendons and apodemes exists within the Arthropoda which has hitherto been imperfectly described. Anterior and posterior tentorial apodemes are present throughout the less specialized of the Hexapoda in essentially similar form. The segmental tendon system, present embryologically in all body segments in many animals, occurs in the adult hexapod head except where strong transverse biting has been evolved, and its presence then is consequently not required. Hexapod-like tentorial apodemes are absent in Crustacea, but homologous anterior tentorial apodemes are present in Myriapoda where their mobility is enhanced. Rigidity of tentorial apodemes is found in hexapods where strong transverse biting has been evolved (Pterygota). (14) The details of the feeding mechanism of a chilopod are described. The mandibular mechanism has clearly been derived from the same basic transversely moving mandibles of the type seen in Diplopoda and Symphyla, but modified by the development of entognathy to give a highly specialized mechanism suiting carnivorous feeding and crevice living, and not found in any other group. (15) The Chilopoda, Diplopoda and Symphyla all appear to have obtained direct transverse biting without any preliminary rolling mandible such as seen in Thysanura, but segmentation of their mandibles is essential. All have used the mobility of the anterior tentorial apodemes to provide (Diplopoda) or enhance (Symphyla and Chilopoda) the abductor force which opens the jaws. The differences between the mandibular mechanisms of Chilopoda, Diplopoda and Symphyla indicate independent evolution from a common type and no one of these three classes could readily give rise to the mandibular mechanisms present in either of the other two. The term Myriapoda, indicating affinity between Chilopoda, Diplopoda, Symphyla and Pauropoda deserves to be reinstated. (16) The symphylan mandibular mechanism, together with the structure and use of maxilla 1, the mobility of the anterior tentorial apodeme, and the presence of the myriapodan maxilla 1 salivary gland, are so entirely opposed both to the thysanuran condition and to the directions of evolutionary change seen in the Pterygota and entognathous Apterygota (whose basis appears to lie in the Thysanura) as to make the symphylan theory of insect origin untenable. (17) It is concluded that jaws have evolved independently in (i) the Chelicerata, (ii) the Crustacea and (iii) the Onychophora-Myriapoda-Hexapoda series. Within the latter the jaws in the Onychophora must have evolved very early, before much cephalization had taken place. The mandibular mechanisms of the Myriapoda and Hexapoda are so different as to indicate that there can be no close connexion between these two groups of classes apart from a very distant common origin. The parallel evolution of jaws in arthropods must date from the earliest differentiation of the major classes. The Mandibulata cannot be regarded as a related group, but the term may serve to indicate a Grade of advancement. The bearing of these results on taxonomic systems is discussed.

Evolution and Bioluminescence

Newton Harvey — 2005-12-19T09:07:45-00:00

The Quarterly Review of Biology, Vol. 31, No. 4. (1956), pp. 270-287.

The Evolution of Flightlessness in Insects

Derek Roff — 2005-12-19T09:04:30-00:00

Ecological Monographs, Vol. 60, No. 4. (1990), pp. 389-421.

Many pterygote (winged) insects have secondarily become flightless; why has this occurred? In this paper I test for an association between the frequency of flightlessness and (1) environmental heterogeneity, (2) geographic variables, (3) gender, (4) alternate modes of migration, and (5) taxonomic variation. Various authors have predicted that decreased environmental heterogeneity will favor the evolution of flightlessness. This hypothesis is consistent with a number of studies on the variation of wing dimorphism and flightlessness and with data analyzed in the present paper on the relationship between habitat type and wing morph in the North American Orthoptera. The incidence of flightlessness is also exceptionally high in woodlands, deserts, on the ocean surface, in specific habitats on the seashore (dunes and rock crevices but not the foreshore), in aquatic habitats, in the winter months, in hymenopteran and termite nests, and among ectoparasites of endotherms and parasites of arthropods. It is low in habitats bordering rivers, streams, ponds, etc. and in arboreal habitats. Some of these habitats can be classified as persistent, but others cannot be so designated or are too vaguely defined. The incidence of flightlessness increases with altitude and latitude but, contrary to @'conventional@' wisdom, it is not exceptionally high on oceanic islands compared to mainland areas. Several authors have hypothesized that the clinal variation in flightlessness is a consequence of clinal variation in habitat persistence. Though the available data are consistent with this hypothesis, other factors such as impairment of flight by low temperatures cannot be rejected, though considered unlikely. Flightlessness is more frequent than expected by chance among parthenogenetic species and more frequent among females than males. Furthermore, there is a significant negative association between female mobility and flightlessness in males. I suggest that loss of flight is favored in females because it permits greater allocation of resources to egg production, but that flight is retained in males because it increases the probability of finding a mate. In some species alternate modes of migration, viz phoresy and ballooning, have evolved. Phoretic transport (i.e., via other animal species) may be important in those species in which it occurs, but it appears to have evolved relatively rarely. Among the Insecta ballooning occurs only in the larvae of Lepidoptera. Aptery (winglessness) is unusually frequent among Lepidoptera that eclose in the fall and winter months and live in woodlands and forests. I hypothesize that larval migration by ballooning, the large-scale spatiotemporal stability of woodlands, and the small-scale unpredictability of spring bud burst are primary factors favoring the evolution of flightlessness in these Lepidoptera. The mode of metamorphosis is correlated with the frequency of flightlessness; hemimetabolous and holometabolous insects are rarely flightless, while it is common among paurometabolous insects. Two factors that may favor such an association are differences in relative mobility of the larvae and niche shifts between the adult and larval stage. In the holometabolous insects taxonomic families with at least one flightless species have more species than those with only winged species. A possible explanation for this is that the occurrence of the appropriate ecological conditions favoring flightlessness in holometabolous insects and the requisite mutations are both very rare events.

Evolution and Classification of Beetles

John Lawrence — 2005-12-19T08:48:48-00:00

Competition among Body Parts in the Development and Evolution of Insect Morphology

HF Nijhout — 2005-12-19T08:42:10-00:00

Proceedings of the National Academy of Sciences of the United States of America, Vol. 95, No. 7. (1998), pp. 3685-3689.

Changes in form during ontogeny and evolution depend in large measure on changes in the relative growth of the various parts of the body. The current consensus in developmental biology is that the final size of appendages and internal organs is regulated autonomously, within the structure itself. Size regulation of body parts typically requires no external control and is thought to be relatively insensitive to signals from the developmental environment. We show in two very different systems, butterfly wings and beetle horns, that experimentally induced changes in the allocation of developmental resources to one trait produces compensatory changes in the relative sizes of other traits. These findings illustrate that interaction among body parts in development is part of the mechanism of size regulation of those parts. Furthermore, in the case of beetle horns, we show that the tradeoff in size is manifest as a significant negative genetic correlation among the involved body parts and, therefore, constitutes a developmental source of genetic constraint on the evolution of body form.

Biochemistry at 100 degrees C: Explosive Secretory Discharge of Bombardier Beetles (Brachinus)

Daniel Aneshansley — 2005-12-19T08:40:45-00:00

The defensive chemical spray of bombardier beetles is ejected at 100 degrees C, with a heat content of about 0.2 calorie per milligram.

Living in a physical world II. The bio-ballistics of small projectiles

Steven Vogel — 2005-12-17T21:24:02-00:00

Journal of Biosciences, Vol. 30, No. 2. (March 2005), pp. 167-175.

Many animals jump; many plants shoot their seeds. While ‘many’ may not imply ‘most’, terrestrial life is rife with examples of ballistic motion, motion in which a projectile gets all of its impetus prior to launch. For most of us, the trajectories of projectiles appeared briefly early in a basic physics course. Some tidy equations emerged in unambiguous fashion from just two facts. A projectile moves horizontally at constant speed; only the downward acceleration of gravity (g) alters its initial vertical speed. Where launch and landing heights are the same, a simple formula links range (d) with launch speed (vo) and projection angle (Q0) above horizontal: g v d o o sin 2q 2 = . (1) So, for a given initial speed, a projectile achieves its greatest horizontal range when launched at an upward angle of 45°. That maximal range is simply g v d o 2 max = . (2) Thus an initial speed of 40 m s–1 (144 km h–1) could take a projectile 163 m. Enroute, the projectile reaches a maximum height, hmax, of a quarter of that best range, or g v h o 4 2 max = . (3) The trajectory forms a nicely symmetrical parabola, and the loss of range at angles above 45º exactly mirrors the loss at lower angles – as shown in figure 1. Such tidiness gives (as once said) the biologist severe physics-envy. In promoting these expressions, text or teacher may mutter, sotto voce, something about an assumed absence of air resistance, about the presumption that drag exerts a negligible effect. Nevertheless the scheme generates significant errors even for a cannon ball. It gives still worse errors for golf balls – drag can halve the range of a well-driven golf ball (Brancazio 1984). The errors are tolerable only because golfers, however fanatic, rarely turn for help to physics. What keeps a projectile going is inertia; whether we view its consequences in terms of momentum or kinetic energy, mass provides the key element. Ignoring, to take a broad-brush view, variation in both density and shape, mass follows volume. What slows a projectile are two factors, gravity and drag. The standard equations deal with the downward force of gravity and produce their nice parabolas. Drag, the force that acts opposite the direction of motion, manifests itself in deviations from such simple trajectories; its magnitude varies in proportion either to surface area or diameter, depending on the circumstances. The smaller the projectile, the greater are both surface area or diameter relative to volume. So the smaller the projectile the less adequately that idealized, dragless trajectory should describe its motion. Since gravitational force, kinetic energy, and momentum all depend on mass, the less dense the projectile, the greater will be the relative influence of drag. The upshot is that biological projectiles will be poorly served by these simple equations. Few are very large and none very dense, so their performances pale besides those of long-travelling and damage-inducing chunks of rock or iron. Still, life’s projectiles are diverse in ancestry, size, and function. Sports, hunting, and warfare, uses that come first to mind, matter least often to species other than our own. Instead, two functions dominate. Some organisms jump, forming single, whole-body projectiles; others shoot propagules – fruits, seeds, spore clusters, even individual spores.

Living in a physical world I. Two ways to move material

Steven Vogel — 2005-12-17T21:21:54-00:00

Journal of Biosciences, Vol. 29, No. 4. (December 2004), pp. 391-397.

The diversity of life on earth dazzles all of us – the rich profusion of its designs, the wide size range of its organisms, the complexities of its hierarchical levels, and so forth. Undaunted, we life scientists seek broadly applicable rules, common patterns of organizations, and order beneath the perceptual chaos; we look for alternatives to the easy answers of revealed truth. Biology, no less than the physical sciences, treads this bumpy path – indeed the overt diversity of life puts especially bad bumps in its way. Perhaps its special difficulty underlies the gradual estrangement of biology from the more obviously successful physics of the post-Newtonian era and its awkward reintegration into the larger world of science in the twentieth century. That process remains incomplete; blame, if leveled, rests on the untidiness and distinctiveness of the subject. The tidy formulas of Newtonian physics work even less well for us than they do for, say, practicing engineers. Life directs its chemistry with sets of governing molecules and carries it out with the aid of catalysts of breathtaking specificity. And biology enjoys a strange organizing principle, evolution by natural selection, barely hinted at elsewhere in science. No aspect of this reintegration has been (and continues to be) more successful than what we have come to call molecular biology – a statement at once fashionable and incontrovertible, one with which I have no grounds to take issue. What matters here, indeed the entire justification for the essays that begin with the one here, comes down to the following. The very success of this chemically-reductionist biology too easily diverts us from other conjunctions of physical science and biology. This series will explore aspects of biology that reflect the physical world in which organisms find themselves. Evolution can do wonders, but it cannot escape its earthy context – a certain temperature range, a particular gravitational acceleration, the physical properties of air and water, and so forth. Nor can it tamper with mathematics. The baseline they provide both imposes constraints and affords opportunities. I mean to explore both. And I will take what other biologists might find an unfamiliar approach – one, by the way, that I have found productive enough to recommend. Instead of asking about the physical science behind a specific biological system, I will consider aspects of the physical world and ask what organisms, any organisms, make of each, both how they might capitalize on them and be in some fashion limited by them. In effect, this will be a search for commonalities and patterns, the only unusual feature being the physical rather than biochemical or phylogenetic bases. If this approach to science were a dart game, I would be thrown out – for throwing darts at a wall first and only subsequently painting targets around the points of impact. The series will concern itself mainly (but not exclusively) with organisms rather than ecosystems or organelles. It will follow the author’s bias and personal experience toward mechanical matters, doing less than equal justice to radiations and electrical phenomena. It will be speculative, opinionated, and idiosyncratic, aiming to stimulate thought and perhaps even investigation, to open doors rather than just describing them. When I began to do science, over forty years ago, I wondered first whether and then where I would get ideas worth pursuing. Now, on the cusp of retirement, I wonder what I am going to do with my accumulated headand notebooks-full of questions. Maybe we need something like a patent expiration date – if one does nothing with a hypothesis for some number of years, it should somehow revert to the public domain. I am not an unequivocal advocate of a strict rule, inasmuch as I have, on occasion, resurrected one of my old ideas, applying some additional insight or new tool in my experimental armamentarium – or just responding to a renewed interest. Still, these essays should, if nothing else, provide an opportunity to air untested ideas with some hope that others might care to pursue them.

Living in a physical world III. Getting up to speed

Steven Vogel — 2005-12-17T21:19:37-00:00

Journal of Biosciences, Vol. 30, No. 3. (June 2005)

Generalizations in biology come hard, so we treasure any that cut through life’s overwhelming diversity. In his famous essay, “On Being the Right Size,” J B S Haldane (1926) notes that jumping animals of whatever size should reach the same maximum height; Haldane attributes the insight to Galileo. Other iconic figures make the same assertion— Giovanni Alphonso Borelli (1680), grandfather of biomechanics; D’Arcy Thompson (1942), godfather of biomechanics; and then A V Hill (1938), father-figure for muscle physiologists. The basic reasoning is straightforward. The force of a muscle varies with its cross-sectional area. The distance a muscle can shorten varies with its length. So the work a muscle can do will vary with the product of the two, in effect with its mass. All mammals have about the same mass of muscle relative to mass, about 45%, and other jumping animals differ only a little more. Thus the work available for a jump should be proportional to body mass. At the same time, the energy, mgh, required to achieve a given height, h, should also be proportional to body mass, m (gravitational acceleration, g, of course, stays constant). Put in slightly different terms, launch speed, vo, sets height for a projectile shot upward, and kinetic energy at launch is 1/2 mv2 0 . So the energy required to achieve a given launch velocity, like the work available, will be proportional to body mass. Either way, height should not depend on body mass. As Borelli (1680), in the first great treatise on biomechanics, put it “…if the weight and mass of a dog is a fiftieth of those of a horse [ ] the motive force of the dog would be a fiftieth of that of the horse. Therefore, if the other conditions are equal [ ], the dog will jump as far as the horse.” (‘Force’ for Borelli meant something close to what we recognize as work or energy.)

Evolution of water conservation mechanisms in Drosophila

Allen Gibbs — 2005-12-17T21:01:35-00:00

J Exp Biol, Vol. 206, No. 7. (1 April 2003), pp. 1183-1192.

Flies of the genus Drosophila inhabit a wide range of habitats, from the tropics to deserts to boreal forests. The primary physiological mechanism allowing Drosophila and other insects to survive in arid habitats is a reduction in rates of water loss. To understand mechanisms of water retention in greater detail, we investigated the three main routes by which Drosophila lose water: excretion, cuticular transpiration and respiratory loss through the spiracles. Excretory losses comprised <6% of total water flux and did not differ between xeric (cactophilic) and mesic species. No consistent relationship was observed between water-loss rates and the composition, physical properties or amounts of cuticular hydrocarbons, suggesting that cuticular transpiration did not differ among species from different habitats. Metabolic rates and water-loss rates were highly correlated. Cactophilic Drosophila were less active, and female cactophiles had lower metabolic rates than female mesic species of the same size. They were also more likely to exhibit a pattern of cyclic CO2 release that may help to conserve water. We conclude that lower overall rates of water loss are achieved primarily by reduction of respiratory losses.

The role of the subelytral spiracles in respiration in the flightless dung beetle Circellium bacchus

Marcus Byrne — 2005-12-17T21:00:35-00:00

J Exp Biol, Vol. 206, No. 8. (15 April 2003), pp. 1309-1318.

The role of the subelytral cavity in flightless beetle species as an adaptation to water saving in arid habitats is still in dispute. We found that relatively little CO2 was released from the subelytral cavity of a large apterous beetle Circellium bacchus during simultaneous measurements of CO2 emission from the anterior mesothoracic spiracles and posterior body, which included the subelytral spiracles. However, when we sampled air directly from inside the subelytral cavity, we discovered that this pattern was reversed. A discontinuous gas exchange cycle (DGC) was recorded from the posterior body half, revealing a flutter phase that had been absent from the anterior mesothoracic DGC. The anterior mesothoracic and posterior subelytral spiracles act in synchrony to maintain high CO2 and water vapour levels inside the subelytral cavity. In addition, the O2 concentration of the air within the subelytral cavity is lower than the air around the elytral case, irrespective of the time of sampling. These findings lead us to conclude that the subelytral spiracles work in a coordinated fashion with the anterior spiracles to create a DGC, which allows us to extend the hypothesis of the function of the subelytral cavity as a respiratory water-saving device.

Discontinuous gas exchange and the significance of respiratory water loss in scarabaeine beetles

Steven Chown — 2005-12-17T21:00:21-00:00

J Exp Biol, Vol. 206, No. 20. (15 October 2003), pp. 3547-3556.

Respiratory water loss in insects is a controversial topic. Whilst earlier studies considered respiratory transpiration a significant component of overall water loss, to the extent that it was thought to be responsible not only for the evolution of discontinuous gas exchange cycles (DGCs) but also for variation in DGC patterns, later work repeatedly questioned its importance. In particular, investigations of the proportional contribution of respiratory transpiration to total water loss in species showing DGCs suggested that respiratory transpiration was unlikely to be important in these species. In turn, these studies have been criticized on analytical grounds. In this study we investigated variation in cuticular and respiratory water loss rates in five Scarabaeus dung beetle species, all of which show discontinuous gas exchange cycles, to ascertain the significance of respiratory water loss using modern analytical techniques. In particular, we determined whether there is variation in water loss rates amongst these beetles, whether both respiratory and cuticular water loss rates contribute significantly to variation in the former, and whether metabolic rate variation and variation in the duration of the DGC periods contribute significantly to variation in respiratory water loss rate. Total water loss rate varied such that species from arid areas had the lowest rates of water loss, and both cuticular and spiracular transpiration contributed significantly to variation in overall water loss rate. Moreover, variation in metabolic rate and in the duration of the DGC periods contributed significantly to variation in respiratory water loss rate. By contrast, examination of proportional water loss revealed little other than that it varies between 6.5% and 21%, depending on the species and the temperature at which it was examined. Cuticular water loss scaled as mass0.721, but did not differ from that expected from geometric considerations alone. By contrast, respiratory water loss scaled as mass0.531, suggesting that gas exchange takes place by diffusion and convection. Our results provide direct evidence that respiratory water loss forms a significant component of water balance, and that changes in both metabolic rate and DGC characteristics contribute to modulation of respiratory water loss.

The role of the mesothoracic spiracles in respiration in flighted and flightless dung beetles

Frances Duncan — 2005-12-17T21:00:05-00:00

J Exp Biol, Vol. 208, No. 5. (1 March 2005), pp. 907-914.

The relative role of the mesothoracic and abdominal spiracles in respiration was examined using flow-through respirometry in four dung beetle species from different habitats. Two species of flightless beetles, Scarabaeus (Pachysoma) gariepinus and Scarabaeus (Pachysoma) striatum, from the arid western region of southern Africa and a large flighted species, Pachylomerus femoralis, from a more mesic habitat were compared with Circellium bacchus, a flightless beetle from a low rainfall eastern area. All species showed a form of the discontinuous gas exchange pattern at rest. The mesic flighted species used a closed, flutter, open, cycle (CFO) while those species from more arid habitats used a closed, ventilation, cycle (CV) or a closed, burst cycle (CB). The relative importance of the mesothoracic spiracles in CO2 emission varied between the species, even between those from the same genus and habitat. C. bacchus and P. femoralis represent extremes of CO2 emission from the mesothoracic spiracles; from almost total to almost none, respectively. Overall, mesothoracic CO2 emission and convection were more pronounced in the dry habitat species, supporting the hypothesis that both strategies aid in the reduction of water loss.

Matching Spiracle Opening to Metabolic Need During Flight in Drosophila

Fritz-Olaf Lehmann — 2005-12-17T20:58:51-00:00

Science, Vol. 294, No. 5548. (30 November 2001), pp. 1926-1929.

Augmented respiration in a flying insect

Y Komai — 2005-12-17T20:58:19-00:00

J Exp Biol, Vol. 201, No. 16. (1 August 1998), pp. 2359-2366.

Extreme impact and cavitation forces of a biological hammer: strike forces of the peacock mantis shrimp Odontodactylus scyllarus

SN Patek — 2005-12-17T20:57:52-00:00

J Exp Biol, Vol. 208, No. 19. (1 October 2005), pp. 3655-3664.

Mantis shrimp are renowned for their unusual method of breaking shells with brief, powerful strikes of their raptorial appendages. Due to the extreme speeds of these strikes underwater, cavitation occurs between their appendages and hard-shelled prey. Here we examine the magnitude and relative contribution of the impact and cavitation forces generated by the peacock mantis shrimp Odontodactylus scyllarus. We present the surprising finding that each strike generates two brief, high-amplitude force peaks, typically 390-480 micros apart. Based on high-speed imaging, force measurements and acoustic analyses, it is evident that the first force peak is caused by the limb's impact and the second force peak is due to the collapse of cavitation bubbles. Peak limb impact forces range from 400 to 1501 N and peak cavitation forces reach 504 N. Despite their small size, O. scyllarus can generate impact forces thousands of times their body weight. Furthermore, on average, cavitation peak forces are 50% of the limb's impact force, although cavitation forces may exceed the limb impact forces by up to 280%. The rapid succession of high peak forces used by mantis shrimp suggests that mantis shrimp use a potent combination of cavitation forces and extraordinarily high impact forces to fracture shells. The stomatopod's hammer is fundamentally different from typical shell-crushing mechanisms such as fish jaws and lobster claws, and may have played an important and as yet unexamined role in the evolution of shell form.

Two sniffing strategies in palinurid lobsters

JA Goldman — 2005-12-17T20:57:36-00:00

J Exp Biol, Vol. 205, No. 24. (15 December 2002), pp. 3891-3902.

Most studies of lobster chemoreception have focused on the model systems of Panulirus argus (Palinuridae) and Homarus americanus (Nephropidae). We compare antennule morphology across lobsters and conduct the first kinematic study of antennule flicking in a palinurid species other than P. argus. High-speed video analysis shows that Palinurus elephas flicks at a rate more than an order of magnitude higher than in P. argus. However, both species flick their antennular flagella at a Reynolds number (Re) of approximately one, such that an asymmetry in the speed of the flick phases causes both species to have a leaky closing flick phase and a non-leaky opening phase. The antennular flagella of P. argus are nearly seven times longer than those of P. elephas, and, when compared across palinurid genera, Panulirus species sample far greater areas of water over greater spatial and time scales than do any other palinurid genera. Palinurid lobsters appear to have two sniffing strategies: low flick rates over a large area of water (e.g. P. argus) or high flick rates over a small area of water (e.g. P. elephas). P. argus is a highly informative model system in which to study aquatic chemoreception; however, its antennule anatomy and kinematics suggest a separate strategy, unique to Panulirus species, for sensing chemical plumes in fluid environments.

Squeaking with a sliding joint: mechanics and motor control of sound production in palinurid lobsters

Sheila Patek — 2005-12-17T20:57:16-00:00

J Exp Biol, Vol. 205, No. 16. (15 August 2002), pp. 2375-2385.

The origin of arthropod sound-producing morphology typically involves modification of two translating body surfaces, such as the legs and thorax. In an unusual structural rearrangement, I show that one lineage of palinurid lobsters lost an antennal joint articulation, which transformed this joint from moving with one degree of freedom into a sliding joint with multiple degrees of freedom. With this sliding joint, `stick-and-slip' sounds are produced by rubbing the base of each antenna against the antennular plate. To understand the musculo-skeletal changes that occurred during the origin and evolutionary variation of this sound-producing mechanism, I examined joint morphology and antennal muscle anatomy across sound-producing and non-sound-producing palinurids. Plectrum movement and antennal muscle activity were measured in a sound-producing species, Panulirus argus. The promotor muscle pulls the plectrum over the file during sound-producing and non-sound-producing movements; a higher intensity of muscle activity is associated with sound production. The promotor muscle is larger and attaches more medially in sound-producing palinurids than in non-sound producers. In Panulirus argus, each shingle on the file has an additional ridge; in Palinurus elephas, the shingle surfaces are smooth. These differences in shingle surface features suggest variation in the stick-and-slip properties of the system. Translational motion permitted by the sliding joint is necessary for sound production; hence, the construction of a sliding joint is a key modification in the origin of this sound-producing mechanism.

WHEN DOES MOTION RELATIVE TO NEIGHBORING SURFACES ALTER THE FLOW THROUGH ARRAYS OF HAIRS?

C Loudon — 2005-12-17T20:52:34-00:00

J Exp Biol, Vol. 193, No. 1. (1 August 1994), pp. 233-254.

Sniffing by a silkworm moth: wing fanning enhances air penetration through and pheromone interception by antennae

C Loudon — 2005-12-17T20:52:15-00:00

J Exp Biol, Vol. 203, No. 19. (1 October 2000), pp. 2977-2990.

Induced airflow in flying insects I. A theoretical model of the induced flow

Sanjay Sane — 2005-12-17T20:50:54-00:00

J Exp Biol, Vol. 209, No. 1. (1 January 2006), pp. 32-42.

A strong induced flow structure envelops the body of insects and birds during flight. This flow influences many physiological processes including delivery of odor and mechanical stimuli to the sensory organs, as well as mass flow processes including heat loss and gas exchange in flying animals. With recent advances in near-field aerodynamics of insect and bird flight, it is now possible to determine how wing kinematics affects induced flow over their body. In this paper, I develop a theoretical model based in rotor theory to estimate the mean induced flow over the body of flapping insects. This model is able to capture some key characteristics of mean induced flow over the body of a flying insect. Specifically, it predicts that induced flow is directly proportional to wing beat frequency and stroke amplitude and is also affected by a wing shape dependent parameter. The derivation of induced flow includes the determination of spanwise variation of circulation on flapping wings. These predictions are tested against the available data on the spanwise distribution of aerodynamic circulation along finite Drosophila melanogaster wings and mean flows over the body of Manduca sexta. To explicitly account for tip losses in finite wings, a formula previously proposed by Prandtl for a finite blade propeller system is tentatively included. Thus, the model described in this paper allows us to estimate how far-field flows are influenced by near-field events in flapping flight.

Effects of age and blood sugar levels on the proboscis extension of the blow fly Phormia regina.

T Amakawa — 2005-12-17T14:27:05-00:00

J Insect Physiol, Vol. 47, No. 2. (1 February 2001), pp. 195-203.

In some insects the proboscis is extended to imbibe a sugar solution if the concentration of sugar applied to the chemosensilla exceeds the behavioural threshold value. Recently, I found a reversal of the threshold values of this "proboscis extension reflex" (PER) in the blow fly (Phormia regina M.) for glucose and fructose. It depended on maturation and physiological conditions, both of which are explicable in terms of changing concentration of haemolymph trehalose. The direct injection of trehalose into the fly haemocoele brought about a dramatic shift of the threshold values of PER measured on tarsi or labellar sensilla, suggesting a strong dependence of PER on the blood sugar level. Using the tip-recording method, the dose-response (impulse frequency) curves for glucose and fructose were obtained on individual largest labellar chemosensilla. The curves for glucose and fructose crossed at one point because the former had a steeper gradient and higher maximum response than the latter. Injection experiments with trehalose were also carried out to test for changes in gustatory response. The shifting of the behavioural dose-response curves for glucose and fructose two hours after injection of 1 M trehalose (2 µl) into the haemocoele of the fly was associated with significant reduction in responsiveness of labellar chemosensilla to glucose, but less so to fructose. No change in responsiveness was found following injection of mannose. A hypothesis to explain the reversal relation of the PER thresholds, based on a shift in the firing rate in gustatory sensilla and possibly also interneurons, is discussed.

Unconventional mechanisms control cyclic respiratory gas release in flying Drosophila

Fritz-Olaf Lehmann — 2005-12-17T14:24:18-00:00

J Exp Biol, Vol. 208, No. 19. (1 October 2005), pp. 3645-3654.

The high power output of flight muscles places special demands on the respiratory gas exchange system in insects. In small insects, respiration relies on diffusion, and for elevated locomotor performance such as flight, instantaneous gas exchange rates typically co-vary with the animal's metabolic activity. By contrast, under certain conditions, instantaneous release rate of carbon dioxide from the fruit fly Drosophila flying in a virtual-reality flight arena may oscillate distinctly at low frequency (0.37+/-0.055 Hz), even though flight muscle mechanical power output requires constant metabolic activity. Cross-correlation analysis suggests that this uncoupling between respiratory and metabolic rate is not driven by conventional types of convective flow reinforcement such as abdominal pumping, but might result from two unusual mechanisms for tracheal breathing. Simplified analytical modeling of diffusive tracheal gas exchange suggests that cyclic release patterns in the insect occur as a consequence of the stochastically synchronized control of spiracle opening area by the four large thoracic spiracles. Alternatively, in-flight motion analysis of the abdomen and proboscis using infra-red video imaging suggests utilization of the proboscis extension reflex (PER) for tracheal convection. Although the respiratory benefit of synchronized spiracle opening activity in the fruit fly is unclear, proboscis-induced tracheal convection might potentially help to balance the local oxygen supply between different body compartments of the flying animal.

Structure of the insect head in ontogeny and phylogeny: a view from Drosophila.

BT Rogers — 2005-12-17T14:20:05-00:00

Int Rev Cytol, Vol. 174 (1997), pp. 1-84.

Evolutionary, developmental and insect biologists are currently using a three-pronged approach to study the evolution and development of the insect head. First, genetic manipulation of the fruit fly Drosophila melanogaster has led to the identification of many genes, including the segmentation and homeotic genes, that are important for embryonic pattern formation and development. Second, a comparison of orthologous gene expression patterns in other insects reveals that these regulatory genes are deployed in similar, yet distinct, patterns in different insects. Third, comparisons of embryonic morphology with gene expression patterns suggest that in general these genes promote a common insect body plan, but that variations in gene expression can often be correlated to variations in morphology. Here, we present a detailed review of the development of the cephalic ectoderm of Drosophila and extrapolate to development of a generalized insect head. Our analysis of the variations among insect species, in both morphology and gene expression patterns, conducted within an evolutionary framework supported by traditional phylogenies and paleontology provides the basis for hypotheses about the genetic factors governing morphologic and developmental evolution.

The Drosophila proboscis is specified by two Hox genes, proboscipedia and Sex combs reduced, via repression of leg and antennal appendage genes

Arhat Abzhanov — 2005-12-17T14:16:35-00:00

Development, Vol. 128, No. 14. (15 July 2001), pp. 2803-2814.

The proboscis is one of the most highly modified appendages in Drosophila melanogaster. However, the phenotypes of proboscipedia (pb) mutants, which transform the proboscis into leg or antenna, indicate a basic homology among these limbs. Recent genetic studies have revealed a developmental system for patterning appendages and identified several genes required for limb development. Among these are: extradenticle (exd), homothorax (hth), dachshund (dac), Distal-less (Dll) and spalt (sal). These limb genes have not been well studied in wild-type mouthparts and their role if any in this appendage is not well understood. Here we demonstrate that the homeotic gene products Proboscipedia (Pb) and Sex combs reduced (Scr) regulate the limb genes in the labial disc to give rise to a unique type of appendage, the proboscis. Pb inhibits exd, dac and sal expression and downregulates Dll. This observation explains the ability of Pb to inhibit the effects of ectopically expressed trunk Hox genes in the proboscis, to suppress leg identity in the trunk and to transform antenna to maxillary palp. Scr suppresses sal expression and also downregulates Dll in the labial discs; discs mutant for both pb and Scr give rise to complete antennae, further demonstrating appendage homology. In the labial disc, Pb positively regulates transcription of Scr, whereas in the embryo, Scr positively regulates pb. Additionally, our results suggests a revised fate map of the labial disc. We conclude that the proboscis constitutes a genetically distinct type of appendage whose morphogenesis does not require several important components of leg and/or antennal patterning systems, but retains distal segmental homology with these appendages.

Self-assembly at all scales.

GM Whitesides — 2005-12-17T14:15:26-00:00

Science, Vol. 295, No. 5564. (29 March 2002), pp. 2418-2421.

Self-assembly is the autonomous organization of components into patterns or structures without human intervention. Self-assembling processes are common throughout nature and technology. They involve components from the molecular (crystals) to the planetary (weather systems) scale and many different kinds of interactions. The concept of self-assembly is used increasingly in many disciplines, with a different flavor and emphasis in each.

How animals move: an integrative view.

MH Dickinson — 2005-12-17T14:14:00-00:00

Science, Vol. 288, No. 5463. (7 April 2000), pp. 100-106.

Recent advances in integrative studies of locomotion have revealed several general principles. Energy storage and exchange mechanisms discovered in walking and running bipeds apply to multilegged locomotion and even to flying and swimming. Nonpropulsive lateral forces can be sizable, but they may benefit stability, maneuverability, or other criteria that become apparent in natural environments. Locomotor control systems combine rapid mechanical preflexes with multimodal sensory feedback and feedforward commands. Muscles have a surprising variety of functions in locomotion, serving as motors, brakes, springs, and struts. Integrative approaches reveal not only how each component within a locomotor system operates but how they function as a collective whole.