CiteULike: Tag symbiosis

Specialization and Resource Trade: Biological Markets as a Model of Mutualisms

Mark Schwartz — 2007-09-27T06:58:53-00:00

Ecology, Vol. 79, No. 3. (1998), pp. 1029-1038.

Most ecological theory suggests that the conditions that would give rise to the evolution of mutualisms are rare. In contrast, empirical evidence suggests that mutualisms are common. Thus, there appears to be a need for additional theory to describe conditions under which mutualisms may evolve. Furthermore, there is a need for theory to predict the conditions under which we expect interactions to remain mutualistic once established. We adopt a biological market approach to present a model for the evolution of resource exchange mutualisms, using the relationship between plants and mycorrhizal fungi as an example. We apply the economic theory of relative advantage to investigate the conditions under which species ought to specialize and trade. A simple economic analogy demonstrates that, in a two-resource model, a species that is relatively efficient at acquiring one resource would benefit from specialization on acquisition of that resource accompanied by trade for the other resource. The theory of relative advantage extends this prediction to show that specialization and trade confer an advantage even for species that are relatively poor resource competitors for both resources. Under the assumptions of our model, we show that two species ought to specialize in the acquisition of one resource and trade for a second resource as long as each species perceives different relative acquisition costs for the two resources. We also describe the conditions under which changing resource availabilities will benefit, or harm, both partners in a mutualism. We predict conditions conducive to mutualisms to occur when the costs of resource exchange are low, the opportunity to ensure fair trade is high, or the cost of tolerating cheaters is low. Market models such as ours may help to explain the conditionality often observed in mutualisms.

Evolution of Marine Symbiosis--A Simple Cost-Benefit Model

Jonathan Roughgarden — 2007-09-27T02:17:02-00:00

Ecology, Vol. 56, No. 5. (1975), pp. 1201-1208.

A simple cost-benefit analysis of symbiosis from the guest's point of view is developed for (1) the conditions under which symbiosis should form, (2) the extent to which the association should be facultative or obligatory for the guest, (3) the conditions for the evolution of mutualistic activity by the guest, and (4) the optimum amount of mutualistic activity by the guest. Some predictions are that: rate species and species with short life-spans in a taxon of potential hosts should have fewer coevolved parasites; facultative parasites on unpalatable or well-protected hosts should be more deleterious to their hosts than those on comparatively vulnerable hosts; and mutualism should only evolve in hosts of intermediate survival ability. The use of the theory is illustrated with data on the damselfish-sea-anemone associations.

Contextualizing bodies: human infants and distributed cognition

Stephen Cowley — 2007-02-06T03:25:18-00:00

Language Sciences, Vol. 26, No. 6. (November 2004), pp. 565-591.

Linking a distributed view of cognition to an integrational perspective on language, learning to talk is presented as an ontogenetic achievement. Examining this as an epigenetic process permits an innovative sketch of how infants come to be heard as producing grammatical utterances. Appealing to `shallow' or content-free cognition, I show how adjustments by contextualizing bodies allow adult overinterpretations to shape infant doings. Far from needing `representations', the baby uses joint activity, affect, and self-directed anticipative learning. Humans, then, use affective co-ordination to develop neurophysiological biases for speaking/hearing vocalizations around syllabic structures. This promotes a kind of agency that allows a 2 year old human, like an encultured bonobo, to act in ways that appear to be self-implicating, self-directing, self-regulating and self-serving. Both species can use (what we hear as) abstracta in novel and coherent behaviour. Unlike its wild counterpart, however, a human needs no external computational hardware. Rather, her achievement derives from strategic use of contextualizing bodies to gradually discover the rewards that accrue from taking part in utterance-activity.

Complete genome of the uncultured Termite Group 1 bacteria in a single host protist cell

Yuichi Hongoh — 2008-04-28T21:06:57-00:00

Proceedings of the National Academy of Sciences, Vol. 105, No. 14. (8 April 2008), pp. 5555-5560.

Termites harbor a symbiotic gut microbial community that is responsible for their ability to thrive on recalcitrant plant matter. The community comprises diverse microorganisms, most of which are as yet uncultivable; the detailed symbiotic mechanism remains unclear. Here, we present the first complete genome sequence of a termite gut symbiont--an uncultured bacterium named Rs-D17 belonging to the candidate phylum Termite Group 1 (TG1). TG1 is a dominant group in termite guts, found as intracellular symbionts of various cellulolytic protists, without any physiological information. To acquire the complete genome sequence, we collected Rs-D17 cells from only a single host protist cell to minimize their genomic variation and performed isothermal whole-genome amplification. This strategy enabled us to reconstruct a circular chromosome (1,125,857 bp) encoding 761 putative protein-coding genes. The genome additionally contains 121 pseudogenes assigned to categories, such as cell wall biosynthesis, regulators, transporters, and defense mechanisms. Despite its apparent reductive evolution, the ability to synthesize 15 amino acids and various cofactors is retained, some of these genes having been duplicated. Considering that diverse termite-gut protists harbor TG1 bacteria, we suggest that this bacterial group plays a key role in the gut symbiotic system by stably supplying essential nitrogenous compounds deficient in lignocelluloses to their host protists and the termites. Our results provide a breakthrough to clarify the functions of and the interactions among the individual members of this multilayered symbiotic complex. 10.1073/pnas.0801389105

Evolving together: the biology of symbiosis, part 1.

GG Dimijian — 2007-01-03T10:37:13-00:00

Proc (Bayl Univ Med Cent), Vol. 13, No. 3. (July 2000), pp. 217-226.

Symbioses, prolonged associations between organisms often widely separated phylogenetically, are more common in biology than we once thought and have been neglected as a phenomenon worthy of study on its own merits. Extending along a dynamic continuum from antagonistic to cooperative and often involving elements of both antagonism and mutualism, symbioses involve pathogens, commensals, and mutualists interacting in myriad ways over the evolutionary history of the involved "partners." In this first of 2 parts, some remarkable examples of symbiosis will be explored, from the coral-algal symbiosis and nitrogen fixation to the great diversity of dietary specializations enabled by the gastrointestinal microbiota of animals.

Evolving together: the biology of symbiosis, part 2.

GG Dimijian — 2007-01-03T10:36:50-00:00

Proc (Bayl Univ Med Cent), Vol. 13, No. 4. (October 2000), pp. 381-390.

Symbiotic trade-offs dominate the world of biology and medicine in colonist-host relationships and between separate, mutually dependent organisms of different species. Infectious and parasitic diseases can be better understood by exploring the dynamic continuum between pathogenicity and mutualism, between antagonism and cooperation-the sliding scale along which microorganisms can move in a moment's notice with a single nucleotide substitution. Organisms practicing piracy or pastoralism may be close genetic relatives. Mergers occur not only between cells but also between genomes; viruses co-opt host genes and in turn insert themselves into host genomes. Separate organisms, from ants to fungi to plants, establish symbiotic ties with each other that bind over deep time, generating much of the diversity we see in nature.

When mutualists are pathogens: an experimental study of the symbioses between Steinernema (entomopathogenic nematodes) and Xenorhabdus (bacteria).

M Sicard — 2007-01-03T10:34:33-00:00

J Evol Biol, Vol. 17, No. 5. (September 2004), pp. 985-993.

In this paper, we investigate the level of specialization of the symbiotic association between an entomopathogenic nematode (Steinernema carpocapsae) and its mutualistic native bacterium (Xenorhabdus nematophila). We made experimental combinations on an insect host where nematodes were associated with non-native symbionts belonging to the same species as the native symbiont, to the same genus or even to a different genus of bacteria. All non-native strains are mutualistically associated with congeneric entomopathogenic nematode species in nature. We show that some of the non-native bacterial strains are pathogenic for S. carpocapsae. When the phylogenetic relationships between the bacterial strains was evaluated, we found a clear negative correlation between the effect a bacterium has on nematode fitness and its phylogenetic distance to the native bacteria of this nematode. Moreover, only symbionts that were phylogenetically closely related to the native bacterial strain were transmitted. These results suggest that co-evolution between the partners has led to a high level of specialization in this mutualism, which effectively prevents horizontal transmission. The pathogenicity of some non-native bacterial strains against S. carpocapsae could result from the incapacity of the nematode to resist specific virulence factors produced by these bacteria.

Ancient Tripartite Coevolution in the Attine Ant-Microbe Symbiosis

Cameron Currie — 2006-02-24T05:11:41-00:00

Science, Vol. 299, No. 5605. (17 January 2003), pp. 386-388.

Coevolved Crypts and Exocrine Glands Support Mutualistic Bacteria in Fungus-Growing Ants

Cameron Currie — 2006-01-06T00:12:40-00:00

Science, Vol. 311, No. 5757. (6 January 2006), pp. 81-83.

Attine ants engage in a quadripartite symbiosis with fungi they cultivate for food, specialized garden parasites, and parasite-inhibiting bacteria. Molecular phylogenetic evidence supports an ancient host-pathogen association between the ant-cultivar mutualism and the garden parasite. Here we show that ants rear the antibiotic-producing bacteria in elaborate cuticular crypts, supported by unique exocrine glands, and that these structures have been highly modified across the ants' evolutionary history. This specialized structural evolution, together with the absence of these bacteria and modifications in other ant genera that do not grow fungus, indicate that the bacteria have an ancient and coevolved association with the ants, their fungal cultivar, and the garden parasite.

A Virus in a Fungus in a Plant: Three-Way Symbiosis Required for Thermal Tolerance

Luis Marquez — 2007-01-26T15:35:03-00:00

Science, Vol. 315, No. 5811. (26 January 2007), pp. 513-515.

A mutualistic association between a fungal endophyte and a tropical panic grass allows both organisms to grow at high soil temperatures. We characterized a virus from this fungus that is involved in the mutualistic interaction. Fungal isolates cured of the virus are unable to confer heat tolerance, but heat tolerance is restored after the virus is reintroduced. The virus-infected fungus confers heat tolerance not only to its native monocot host but also to a eudicot host, which suggests that the underlying mechanism involves pathways conserved between these two groups of plants. 10.1126/science.1136237

In the Ant's Garden, Fungal Parasites Are Closely Matched to Their Fungal Hosts

Richard Robinson — 2007-01-26T18:00:53-00:00

PLoS Biology, Vol. 4, No. 8. (1 August 2006), e259.

Pathogenic fungus harbours endosymbiotic bacteria for toxin production

Laila Partida-Martinez — 2005-10-05T22:35:20-00:00

Nature, Vol. 437, No. 7060., pp. 884-888.

Overlay Network Symbiosis: Evolution and Cooperation

Naoki Wakamiya — 2007-06-27T01:40:03-00:00

Bio-Inspired Models of Network, Information and Computing Systems, 2006. 1st (2006), pp. 1-5.

Simultaneous overlay networks compete for physical network resources and disrupt each other. If they could establish cooperative relationships, the collective performance can be improved and they can coexist peacefully and comfortably. Taking inspiration from biology, in this paper we present a model of symbiotic overlay networks. Coexisting overlay networks dynamically evolve, interact with each other, and change their internal structures. Overlay networks in a symbiotic condition, i.e., mutualism, eventually establish the strong relationship and finally fuse into one. We first analyze characteristics of an overlay network which evolves based on three different models, i.e., the preferential attachment, random, and combination of them, by using mathematical analysis and simulation experiments. Next, we evaluate the effect of interconnecting two overlay networks from the viewpoint of the cost and the benefit

Cleaner production and industrial ecosystems, a Dutch experience

Leo Baas — 2005-05-09T22:28:26-00:00

Journal of Cleaner Production, Vol. 6, No. 3-4. (September 1998), pp. 189-197.

This article opens briefly with the recent discussions about the effectiveness of pollution prevention. As pollution prevention and cleaner production are important elements of industrial ecology, the different definitions and approaches of industrial ecology as a term also need clarity. The major part of this article reflects the first results of the cleaner production and industrial ecology concepts, applied in an industrial ecosystem project (INES) in the Rotterdam harbour area. In this industrial area with many refineries and (petro)chemical facilities, the possibilities for companies to reuse waste streams, by-products and energy from each other was researched. The project was initiated by an industrial association. Sixty-nine members of the industrial association joined the INES project and provided confidential information about their resources, products and waste streams to the research team. Based on this information, 15 projects were designed. The selected three projects for further feasibility studies showed the potency to reduce the use of energy, water and bio sludge significantly.

Experiences from early stages of a national industrial symbiosis programme in the UK: determinants and coordination challenges

Murat Mirata — 2005-05-09T22:26:35-00:00

Journal of Cleaner Production, Vol. 12, No. 8-10. ( 2004), pp. 967-983.

This paper reviews the factors influencing the development and sustained operation of regional industrial symbiosis (IS) networks and discusses the roles a coordination body can play to alter these factors so as to catalyse the development and functioning of such networks. These are analysed within the context of experiences gained in the early stages of three regional IS programmes under development in the UK, and of the recently launched national IS programme (NISP) that they are part of. It is stated that the policy framework in the UK has elements supportive of such networks to evolve, and the regional public bodies are favouring their development. Based on differences among studied cases, it is argued that the nature of companies' operations and industrial history in the regions, the extent of peer pressure, the positioning of the coordinating body in the region, and its approach to awareness raising and recruitment have major influence on the progress of the programmes. Finally, the paper emphasises the importance of aligning the characteristics of emerging operations with the longer-term sustainability requirements. If accepted, this challenge assigns additional responsibilities to the coordinating parties.

Implementing nature's lesson: The industrial recycling network enhancing regional development

Erich Schwarz — 2005-05-09T22:25:44-00:00

Journal of Cleaner Production, Vol. 5, No. 1-2. (1997), pp. 47-56.

While biological systems are centrally characterized by the rate of composition and decomposition being practically equal, industrial systems show a primary focus on production. The industrial recycling network integrates the re-use of 'former waste' by an inter-company matching of production processes. In this way it helps to reduce material and energy throughput in the economic system to sustainable levels. This article identifies central characteristics of this concept. Conclusions for further enhancement are drawn based on two observed recycling systems. The industrial recycling network is also shown to foster development within regions.

Industrial symbiosis networks and the contribution to environmental innovation: The case of the Landskrona industrial symbiosis programme

Murat Mirata — 2005-05-09T22:21:27-00:00

Journal of Cleaner Production, Vol. 13, No. 10-11. ( 2005), pp. 993-1002.

This paper considers the potential contribution of Industrial Symbiosis (IS) networks in fostering environmental innovation at the local or regional level. Drawing on literature from innovation studies and innovation in spatial proximity, we outline three factors that are important for the innovation process and identify where the effects from IS networks can be explored. We use observations from the first IS programme in Sweden to provide examples of previously hypothesised effects. The implications of this inquiry are discussed in terms of design and development of IS programmes and for further research into the innovation effect of IS networks.

Industrial Ecology of the Paper Industry

T Pento — 2004-12-28T15:31:03-00:00

Water Science and Technology, Vol. 40, No. 11. (1999), pp. 21-24.

Integrating waste, manufacturing and industrial symbiosis: an analysis of recycling, remanufacturing and waste treatment firms in Texas

Donald Lyons — 2004-12-28T16:30:47-00:00

Local Environment, Vol. 10, No. 1., 71.

Zero Pollution for Industry : Waste Minimization Through Industrial Complexes

Nelson Nemerow — 2005-05-02T17:38:12-00:00

(06 November 1995)

Increased Effectiveness of Competitive Rhizobium Strains upon Inoculation of Cajanus cajan.

B S Hernandez — 2008-06-06T23:17:45-00:00

Applied and environmental microbiology, Vol. 53, No. 9. (September 1987), pp. 2066-2068.

A field study was conducted in lysimeters containing N-enriched soil to determine the effects of four competitive rhizobium strains upon yield parameters of pigeon peas (Cajanus cajan). The greatest differences observed were in seed yields; strain P132 effected the highest seed yield (121 +/- 20 g per plant), and the control strain (indigenous rhizobia) effected the lowest yield (43.9 +/- 8 g per plant). With the exception of seeds and pods, the dry matter weights were not different. Although there appeared to be no effect by inoculum strains on the fractional content of N derived from biological nitrogen fixation when the total plant biomass was considered, strains P132 and 401 partitioned more of the N derived from fixation into seeds and leaves than did the other strains. Because the seeds comprised the major portion of plant N, more total N and more N derived from biological nitrogen fixation (about half of total N) were found in plants inoculated with P132, whereas the smallest amount was found in the uninoculated controls. P132 was also the best competitor with respect to indigenous rhizobia and acounted for all of the nodules found on the plants in which it was inoculated.

A pyrF auxotrophic mutant of Sinorhizobium fredii HH103 impaired in its symbiotic interactions with soybean and other legumes.

JC Crespo-Rivas — 2008-06-06T23:02:00-00:00

International microbiology : the official journal of the Spanish Society for Microbiology, Vol. 10, No. 3. (September 2007), pp. 169-176.

Transposon Tn5-Mob mutagenesis allowed the selection of a Sinorhizobium fredii HH103 mutant derivative (SVQ 292) that requires the presence of uracil to grow in minimal media. The mutated gene, pyrF, codes for an orotidine-5 - monophosphate decarboxylase (EC 4.1.1.23). Mutant SVQ 292 and its parental prototrophic mutant HH103 showed similar Nod-factor and lipopolysaccharide profiles. The symbiotic properties of mutant SVQ 292 were severely impaired with all legumes tested. Mutant SVQ 292 formed small ineffective nodules on Cajanus cajan and abnormal nodules (pseudonodules) unable to fix nitrogen on Glycine max (soybean), Macroptitlium atropurpureum, Indigofera tinctoria, and Desmodium canadense. It also did not induce any macroscopic response in Macrotyloma axillare roots. The symbiotic capacity of SVQ 292 with soybean was not enhanced by the addition of uracil to the plant nutritive solution.

A computational model of symbiotic composition in evolutionary transitions

RA Watson — 2007-05-25T10:36:31-00:00

pp. 187-209.

Several of the major transitions in evolutionary history, such as the symbiogenic origin of eukaryotes from prokaryotes, share the feature that existing entities became the components of composite entities at a higher-level of organization. This composition of pre-adapted extant entities into a new whole is a fundamentally different source of variation from the gradual accumulation of small random variations, and it has some interesting consequences for issues of evolvability. Intuitively, the pre-adaptation of sets of features in reproductively independent specialists suggests a form of 'divide and conquer' decomposition of the adaptive domain. Moreover, the compositions resulting from one level may become the components for compositions at the next level, thus scaling-up the variation mechanism. In this paper, we explore and develop these concepts using a simple abstract model of symbiotic composition to examine its impact on evolvability. To exemplify the adaptive capacity of the composition model, we employ a scale-invariant fitness landscape exhibiting significant ruggedness at all scales. Whilst innovation by mutation and by conventional evolutionary algorithms becomes increasingly more difficult as evolution continues in this landscape, innovation by composition is not impeded as it discovers and assembles component entities through successive hierarchical levels.

The chimeric eukaryote: Origin of the nucleus from the karyomastigont in amitochondriate protists

Lynn Margulis — 2007-05-25T10:30:31-00:00

PNAS, Vol. 97, No. 13. (20 June 2000), pp. 6954-6959.

10.1073/pnas.97.13.6954

How far do birds disperse seeds in the degraded tropical landscape of Hong Kong, China?

Weir — 2007-01-24T10:42:18-00:00

Landscape Ecology, Vol. 22, No. 1. (January 2007), pp. 131-140.

The persistence of ripe fleshy fruits in the presence and absence of frugivores

Alvin Tang — 2007-06-21T11:45:07-00:00

Oecologia, Vol. 142, No. 2. (17 January 2005), pp. 232-237.

A trade-off between antimicrobial defences and palatability to dispersers may place limits on fruit persistence in nature. The retention times of ripe fruits on 34 wild plant species under natural conditions (unbagged persistence) and when fruits had been bagged with nylon mesh to exclude frugivores (bagged persistence) were compared in Hong Kong, China (22°N). Bagged persistence is a measure of the effectiveness of fruit defence while unbagged persistence is an inverse measure of attractiveness to vertebrate frugivores. Bagged fruits persisted significantly longer than unbagged fruits in 30 species, with half the species tested persisting for more than 2 months. There was a significant positive relationship between the median persistence times of bagged and unbagged fruits, suggesting that species with a high resistance to microbial infection are also less attractive to frugivores. Both bagged and unbagged fruits persisted significantly longer at lower temperatures. There was a significant positive relationship between bagged persistence time and fibre content of the fruit pulp, but no significant relationships between unbagged persistence and the six fruit traits tested (diameter, pulp as a percentage of fruit fresh weight, and lipid, total soluble carbohydrate, nitrogen and fibre as percentages of pulp dry weight). Mechanical damage significantly decreased the bagged persistence time for half of the species. Although some fruits decayed or dried up while attached to the plant, fruits of 53% of the species remained visually attractive until they fell off.

Fig-eating by vertebrate frugivores: a global review.

M Shanahan — 2007-06-21T11:44:19-00:00

Biol Rev Camb Philos Soc, Vol. 76, No. 4. (November 2001), pp. 529-572.

The consumption of figs (the fruit of Ficus spp.: Moraceae) by vertebrates is reviewed using data from the literature, unpublished accounts and new field data from Borneo and Hong Kong. Records of frugivory from over 75 countries are presented for 260 Ficus species (approximately 30% of described species). Explanations are presented for geographical and taxonomic gaps in the otherwise extensive literature. In addition to a small number of reptiles and fishes, 1274 bird and mammal species in 523 genera and 92 families are known to eat figs. In terms of the number of species and genera of fig-eaters and the number of fig species eaten we identify the avian families interacting most with Ficus to be Columbidae, Psittacidae, Pycnonotidae, Bucerotidae, Sturnidae and Lybiidae. Among mammals, the major fig-eating families are Pteropodidae, Cercopithecidae, Sciuridae, Phyllostomidae and Cebidae. We assess the role these and other frugivores play in Ficus seed dispersal and identify fig-specialists. In most, but not all, cases fig specialists provide effective seed dispersal services to the Ficus species on which they feed. The diversity of fig-eaters is explained with respect to fig design and nutrient content, phenology of fig ripening and the diversity of fig presentation. Whilst at a gross level there exists considerable overlap between birds, arboreal mammals and fruit bats with regard to the fig species they consume, closer analysis, based on evidence from across the tropics, suggests that discrete guilds of Ficus species differentially attract subsets of sympatric frugivore communities. This dispersal guild structure is determined by interspecific differences in fig design and presentation. Throughout our examination of the fig-frugivore interaction we consider phylogenetic factors and make comparisons between large-scale biogeographical regions. Our dataset supports previous claims that Ficus is the most important plant genus for tropical frugivores. We explore the concept of figs as keystone resources and suggest criteria for future investigations of their dietary importance. Finally, fully referenced lists of frugivores recorded at each Ficus species and of Ficus species in the diet of each frugivore are presented as online appendices. In situations where ecological information is incomplete or its retrieval is impractical, this valuable resource will assist conservationists in evaluating the role of figs or their frugivores in tropical forest sites.

Frugivory and seed dispersal by vertebrates in the Oriental (Indomalayan) Region

Richard Corlett — 2007-06-21T11:43:58-00:00

Biological Reviews, Vol. 73, No. 4. (1998), pp. 413-448.

ABSTRACT Current knowledge of frugivory and seed dispersal by vertebrates in the Oriental Region is summarized. Some degree of frugivory has been reported for many fish and reptile species, almost half the genera of non-marine mammals and more than 40% of bird genera in the region. Highly frugivorous species, for which fruit dominates the diet for at least part of the year, occur in at least two families of reptiles, 12 families of mammals and 17 families of birds. Predation on seeds in fleshy fruits is much less widespread taxonomically: the major seed predators are colobine monkeys and rodents among the mammals, and parrots, some pigeons, and finches among the birds. Most seeds in the Oriental Region, except near its northern margins, are dispersed by vertebrate families which are endemic to the region or to the Old World. Small fruits and large, soft fruits with many small seeds are consumed by a wide range of potential seed dispersal agents, including species which thrive in small forest fragments and degraded landscapes. Larger, bigger-seeded fruits are consumed by progressively fewer dispersers, and the largest depend on a few species of mammals and birds which are highly vulnerable to hunting, fragmentation and habitat loss.

Plant invasions - the role of mutualisms

David Richardson — 2007-06-21T11:43:33-00:00

Biological Reviews, Vol. 75, No. 1. (2000), pp. 65-93.

ABSTRACT Many introduced plant species rely on mutualisms in their new habitats to overcome barriers to establishment and to become naturalized and, in some cases, invasive. Mutualisms involving animalmediated pollination and seed dispersal, and symbioses between plant roots and microbiota often facilitate invasions. The spread of many alien plants, particularly woody ones, depends on pollinator mutualisms. Most alien plants are well served by generalist pollinators (insects and birds), and pollinator limitation does not appear to be a major barrier for the spread of introduced plants (special conditions relating to Ficus and orchids are described). Seeds of many of the most notorious plant invaders are dispersed by animals, mainly birds and mammals. Our review supports the view that tightly coevolved, plant-vertebrate seed dispersal systems are extremely rare. Vertebrate-dispersed plants are generally not limited reproductively by the lack of dispersers. Most mycorrhizal plants form associations with arbuscular mycorrhizal fungi which, because of their low specificity, do not seem to play a major role in facilitating or hindering plant invasions (except possibly on remote islands such as the Galapagos which are poor in arbuscular mycorrhizal fungi). The lack of symbionts has, however, been a major barrier for many ectomycorrhizal plants, notably for Pinus spp. in parts of the southern hemisphere. The roles of nitrogen-fixing associations between legumes and rhizobia and between actinorhizal plants and Frankia spp. in promoting or hindering invasions have been virtually ignored in the invasions literature. Symbionts required to induce nitrogen fixation in many plants are extremely widespread, but intentional introductions of symbionts have altered the invasibility of many, if not most, systems. Some of the world's worst invasive alien species only invaded after the introduction of symbionts. Mutualisms in the new environment sometimes re-unite the same species that form partnerships in the native range of the plant. Very often, however, different species are involved, emphasizing the diffuse nature of many (most) mutualisms. Mutualisms in new habitats usually duplicate functions or strategies that exist in the natural range of the plant. Occasionally, mutualisms forge totally novel combinations, with profound implications for the behaviour of the introduced plant in the new environment (examples are seed dispersal mutualisms involving wind-dispersed pines and cockatoos in Australia; and mycorrhizal associations involving plant roots and fungi). Many ecosystems are becoming more susceptible to invasion by introduced plants because: (a) they contain an increasing array of potential mutualistic partners (e.g. generalist frugivores and pollinators, mycorrhizal fungi with wide host ranges, rhizobia strains with infectivity across genera); and (b) conditions conducive for the establishment of various alienalien synergisms are becoming more abundant. Incorporating perspectives on mutualisms in screening protocols will improve (but not perfect) our ability to predict whether a given plant species could invade a particular habitat.

Functional ecology of soil organisms in tundra ecosystems: towards the future

ID Hodkinson — 2007-06-29T08:31:08-00:00

Applied Soil Ecology, Vol. 11, No. 2-3. (1 February 1999), pp. 111-126.

The need to understand the functional linkages between Arctic/alpine soil communities and the major soil processes is stressed. Soil organisms are classified into broad functional groups and it is suggested that the functional success of any organism can be defined by its position along four axes, namely population responsiveness, dispersability, ecophysiological flexibility and resource use flexibility. Each of these axes is defined by reference to a spectrum of relevant ecological attributes. The resilience and response of tundra communities to change are discussed and the possible alteration in community structure and function that may result from shifting climate patterns are reviewed. The interrelationship between the spatial distribution patterns of organisms and their dispersability is highlighted and the significance of the thermal environment in moderating the competitive interaction between species is emphasised. The advantages and disadvantages of various approaches to studying the effect of climate change on Arctic/alpine community structure and function are contrasted. In particular, the manipulative experimental approach is distinguished from the comparative approach that makes use of measurements taken along geographical/ecological transects as analogues for climate change.

Cooperation, conflict, and coevolution in the attine ant-fungus symbiosis

Natasha Mehdiabadi — 2006-02-07T19:30:55-00:00

Behavioral Ecology, Vol. 17, No. 2. (March 2006), pp. 291-296.

Biodiversity and drug discovery -- a symbiotic relationship

Geoffrey Cordell — 2007-06-29T08:13:43-00:00

Phytochemistry, Vol. 55, No. 6. (November 2000), pp. 463-480.

The profound developments in natural products drug discovery in the past few years are discussed, and the importance of a global approach to biodiversity and drug discovery involving natural products for the early part of the 21st century is presented.

Population dynamics of defensive symbionts in aphids.

KM Oliver — 2008-04-17T04:01:24-00:00

Proceedings. Biological sciences / The Royal Society, Vol. 275, No. 1632. (7 February 2008), pp. 293-299.

Vertically transmitted micro-organisms can increase in frequency in host populations by providing net benefits to hosts. While laboratory studies have identified diverse beneficial effects conferred by inherited symbionts of insects, they have not explicitly examined the population dynamics of mutualist symbiont infection within populations. In the pea aphid, Acyrthosiphon pisum, the inherited facultative symbiont, Hamiltonella defensa, provides protection against parasitism by the wasp, Aphidius ervi. Despite a high fidelity of vertical transmission and direct benefits of infection accruing to parasitized aphids, Hamiltonella remains only at intermediate frequencies in natural populations. Here, we conducted population cage experiments to monitor the dynamics of Hamiltonella and of another common A. pisum symbiont, Serratia symbiotica, in the presence and absence of parasitism. We also conducted fitness assays of Hamiltonella-infected aphids to search for costs to infection in the absence of parasitism. In the population cages, we found that the frequency of A. pisum infected with Hamiltonella increased dramatically after repeated exposure to parasitism by A. ervi, indicating that selection pressures from natural enemies can lead to the increase of particular inherited symbionts in insect populations. In our laboratory fitness assays, we did not detect a cost to infection with Hamiltonella, but in the population cages not exposed to parasitism, we found a significant decline in the frequency of both Hamiltonella and Serratia. The declining frequencies of Hamiltonella-infected aphids in population cages in the absence of parasitism indicate a probable cost to infection and may explain why Hamiltonella remains at intermediate frequencies in natural populations.

Evolutionary Relationships of Three New Species of Enterobacteriaceae Living as Symbionts of Aphids and Other Insects

Nancy Moran — 2008-03-09T23:18:44-00:00

Appl. Environ. Microbiol., Vol. 71, No. 6. (1 June 2005), pp. 3302-3310.

Ecological studies on three bacterial lineages symbiotic in aphids have shown that they impose a variety of effects on their hosts, including resistance to parasitoids and tolerance to heat stress. Phylogenetic analyses of partial sequences of gyrB and recA are consistent with previous analyses limited to 16S rRNA gene sequences and yield improved confidence of the evolutionary relationships of these symbionts. All three symbionts are in the Enterobacteriaceae. One of the symbionts, here given the provisional designation "Candidatus Serratia symbiotica," is a Serratia species that has acquired a symbiotic lifestyle. The other two symbionts, here designated "Candidatus Hamiltonella defensa" and "Candidatus Regiella insecticola," are sister groups to one another and together show a relationship to species of Photorhabdus. 10.1128/AEM.71.6.3302-3310.2005

Evidence for a symbiosis island involved in horizontal acquisition of pederin biosynthetic capabilities by the bacterial symbiont of Paederus fuscipes beetles.

J Piel — 2006-09-25T15:54:05-00:00

J Bacteriol, Vol. 186, No. 5. (March 2004), pp. 1280-1286.

Pederin belongs to a group of antitumor compounds found in terrestrial beetles and marine sponges. It is used by apparently all members of the rove beetle genera Paederus and Paederidus as a chemical defense against predators. However, a recent analysis of the putative pederin biosynthesis (ped) gene cluster strongly suggests that pederin is produced by bacterial symbionts. We have sequenced an extended region of the symbiont genome to gain further insight into the biology of this as-yet-unculturable bacterium and the evolution of pederin symbiosis. Our data indicate that the symbiont is a very close relative of Pseudomonas aeruginosa that has acquired several foreign genetic elements by horizontal gene transfer. Besides one functional tellurite resistance operon, the region contains a genomic island spanning 71.6 kb that harbors the putative pederin biosynthetic genes. Several decayed insertion sequence elements and the mosaic-like appearance of the island suggest that the acquisition of the ped symbiosis genes was followed by further insertions and rearrangements. A horizontal transfer of genes for the biosynthesis of protective substances could explain the widespread occurrence of pederin-type compounds in unrelated animals from diverse habitats.

The Evolution of the Heat-Shock Protein GroEL from Buchnera, the Primary Endosymbiont of Aphids, Is Governed by Positive Selection

Mario Fares — 2007-09-03T20:02:54-00:00

Mol Biol Evol, Vol. 19, No. 7. (1 July 2002), pp. 1162-1170.

The heat-shock protein GroEL is a double-ring-structured chaperonin that assists the folding of many newly synthesized proteins in Escherichia coli and the refolding in vitro, with the cochaperonin GroES, of conformationally damaged proteins. This protein is constitutively overexpressed in the primary symbiotic bacteria of many insects, constituting approximately 10% of the total protein in Buchnera, the primary endosymbiont of aphids. In the present study, we perform a maximum likelihood (ML) analysis to unveil the selective constraints in GroEL. In addition, we apply a new statistical approach to determine the patterns of evolution in this highly interesting protein. The main conclusion derived from our analysis is that GroEL has suffered an accelerated rate of amino acid substitution upon the symbiotic integration of Buchnera into the aphids. It is most interesting that the ML analysis of codon substitutions in the different branches of the phylogenetic tree strongly supports the action of positive selection in the different lineages of Buchnera. Additionally, the new sliding window analysis of the complete groEL sequence reveals different regions of the molecule under the action of positive selection, mainly located in the apical domain, that are important for both peptide and GroES binding.

Parasitic inhibition of cell death facilitates symbiosis

Bart Pannebakker — 2008-04-17T03:24:09-00:00

Proceedings of the National Academy of Sciences, Vol. 104, No. 1. (2 January 2007), pp. 213-215.

Symbiotic microorganisms have had a large impact on eukaryotic evolution, with effects ranging from parasitic to mutualistic. Mitochondria and chloroplasts are prime examples of symbiotic microorganisms that have become obligate for their hosts, allowing for a dramatic extension of suitable habitats for life. Out of the extraordinary diversity of bacterial endosymbionts in insects, most are facultative for their hosts, such as the ubiquitous Wolbachia, which manipulates host reproduction. Some endosymbionts, however, have become obligatory for host reproduction and/or survival. In the parasitoid wasp Asobara tabida the presence of Wolbachia is necessary for host oogenesis, but the mechanism involved is yet unknown. We show that Wolbachia influences programmed cell death processes (a host regulatory feature typically targeted by pathogens) in A. tabida, making its presence essential for the wasps' oocytes to mature. This suggests that parasite strategies, such as bacterial regulation of host apoptosis, can drive the evolution of host dependence, allowing for a swift transition from parasitism to mutualism. 10.1073/pnas.0607845104

Parallel genomic evolution and metabolic interdependence in an ancient symbiosis.

John P McCutcheon — 2007-12-02T20:44:15-00:00

Proc Natl Acad Sci U S A (28 November 2007)

Obligate symbioses with nutrient-provisioning bacteria have originated often during animal evolution and have been key to the ecological diversification of many invertebrate groups. To date, genome sequences of insect nutritional symbionts have been restricted to a related cluster within Gammaproteobacteria and have revealed distinctive features, including extreme reduction, rapid evolution, and biased nucleotide composition. Using recently developed sequencing technologies, we show that Sulcia muelleri, a member of the Bacteroidetes, underwent similar genomic changes during coevolution with its sap-feeding insect host (sharpshooters) and the coresident symbiont Baumannia cicadellinicola (Gammaproteobacteria). At 245 kilobases, Sulcia's genome is approximately one tenth of the smallest known Bacteroidetes genome and among the smallest for any cellular organism. Analysis of the coding capacities of Sulcia and Baumannia reveals striking complementarity in metabolic capabilities.

Mutation rate and genome reduction in endosymbiotic and free-living bacteria.

Gabriel Marais — 2008-03-31T15:56:47-00:00

Genetica (29 November 2007)

Genome reduction has been considered the hallmark of endosymbiotic bacteria, such as endocellular mutualists or obligatory pathogens until it was found exactly the same in several free-living bacteria. In endosymbiotic bacteria genome reduction is mainly attributed to degenerative processes due to small population size. These cannot affect the free-living bacteria with reduced genomes because they are known to have very large population sizes. It has been proposed that selection for simplification drove genome reduction in these free-living bacteria. For at least one of them (Prochlorococcus), genome reduction is associated with accelerated evolution and we suggest an alternative hypothesis based on increase in mutation rate as the primary cause of genome reduction in free-living bacteria.

Interactions among multiple genomes: tsetse, its symbionts and trypanosomes.

S Aksoy — 2008-03-16T14:46:51-00:00

Insect Biochem Mol Biol, Vol. 35, No. 7. (July 2005), pp. 691-698.

Insect-borne diseases exact a high public health burden and have a devastating impact on livestock and agriculture. To date, control has proved to be exceedingly difficult. One such disease that has plagued sub-Saharan Africa is caused by the protozoan African trypanosomes (Trypanosoma species) and transmitted by tsetse flies (Diptera: Glossinidae). This presentation describes the biology of the tsetse fly and its interactions with trypanosomes as well as its symbionts. Tsetse can harbor up to three distinct microbial symbionts, including two enterics (Wigglesworthia glossinidia and Sodalis glossinidius) as well as facultative Wolbachia infections, which influence host physiology. Recent investigations into the genome of the obligate symbiont Wigglesworthia have revealed characteristics indicative of its long co-evolutionary history with the tsetse host species. Comparative analysis of the commensal-like Sodalis with free-living enterics provides examples of adaptations to the host environment (physiology and ecology), reflecting genomic tailoring events during the process of transitioning into a symbiotic lifestyle. From an applied perspective, the extensive knowledge accumulated on the genomic and developmental biology of the symbionts coupled with our ability to both express foreign genes in these microbes in vitro and repopulate tsetse midguts with these engineered microbes now provides a means to interfere with the host physiological traits which contribute to vector competence promising a novel tool for disease management.

The endosymbionts of tsetse flies: manipulating host-parasite interactions.

C Dale — 2008-03-16T14:46:49-00:00

Int J Parasitol, Vol. 31, No. 5-6. (1 May 2001), pp. 628-631.

Through understanding the mechanisms by which tsetse endosymbionts potentiate trypanosome susceptibility in tsetse, it may be possible to engineer modified endosymbionts which, when introduced into tsetse, render these insects incapable of transmitting parasites. In this study we have assayed the effect of three different antibiotics on the endosymbiotic microflora of tsetse (Glossina morsitans morsitans). We showed that the broad-spectrum antibiotics, ampicillin and tetracycline, have a dramatic impact on tsetse fecundity and pupal emergence, effectively rendering these insects sterile. This results from the loss of the tsetse primary endosymbiont, Wigglesworthia glossinidia, which is eradicated by ampicillin and tetracycline treatment. Using the sugar analogue and antibiotic, streptozotocin, we demonstrated specific elimination of the tsetse secondary endosymbiont, Sodalis glossinidius, with no observed detrimental effect upon W. glossinidia. The specific eradication of S. glossinidius had a negligible effect upon the reproductive capability of tsetse but did effect a significant reduction in fly longevity. Furthermore, elimination of S. glossinidius resulted in increased refractoriness to trypanosome infection in tsetse, providing further evidence that S. glossinidius plays an important role in potentiating trypanosome susceptibility in this important disease vector. In the light of these findings, we highlight progress made towards developing recombinant Sodalis strains engineered to avoid potentiating trypanosome susceptibility in tsetse. In particular, we focus on the chitinase/N-acetyl-D-glucosamine catabolic machinery of Sodalis which has previously been implicated in causing immune inhibition in tsetse.

Heritable Endosymbionts of Drosophila

Mariana Mateos — 2008-03-09T23:36:01-00:00

Genetics, Vol. 174, No. 1. (1 September 2006), pp. 363-376.

Although heritable microorganisms are increasingly recognized as widespread in insects, no systematic screens for such symbionts have been conducted in Drosophila species (the primary insect genetic models for studies of evolution, development, and innate immunity). Previous efforts screened relatively few Drosophila lineages, mainly for Wolbachia. We conducted an extensive survey of potentially heritable endosymbionts from any bacterial lineage via PCR screens of mature ovaries in 181 recently collected fly strains representing 35 species from 11 species groups. Due to our fly sampling methods, however, we are likely to have missed fly strains infected with sex ratio-distorting endosymbionts. Only Wolbachia and Spiroplasma, both widespread in insects, were confirmed as symbionts. These findings indicate that in contrast to some other insect groups, other heritable symbionts are uncommon in Drosophila species, possibly reflecting a robust innate immune response that eliminates many bacteria. A more extensive survey targeted these two symbiont types through diagnostic PCR in 1225 strains representing 225 species from 32 species groups. Of these, 19 species were infected by Wolbachia while only 3 species had Spiroplasma. Several new strains of Wolbachia and Spiroplasma were discovered, including ones divergent from any reported to date. The phylogenetic distribution of Wolbachia and Spiroplasma in Drosophila is discussed. 10.1534/genetics.106.058818

Diversifying selection and host adaptation in two endosymbiont genomes

Jeremy Brownlie — 2007-05-01T04:38:39-00:00

BMC Evolutionary Biology, Vol. 7 (30 April 2007), 68.

The Wolbachia genome of Brugia malayi: endosymbiont evolution within a human pathogenic nematode.

J Foster — 2006-07-25T08:58:25-00:00

PLoS Biol, Vol. 3, No. 4. (April 2005)

Complete genome DNA sequence and analysis is presented for Wolbachia, the obligate alpha-proteobacterial endosymbiont required for fertility and survival of the human filarial parasitic nematode Brugia malayi. Although, quantitatively, the genome is even more degraded than those of closely related Rickettsia species, Wolbachia has retained more intact metabolic pathways. The ability to provide riboflavin, flavin adenine dinucleotide, heme, and nucleotides is likely to be Wolbachia's principal contribution to the mutualistic relationship, whereas the host nematode likely supplies amino acids required for Wolbachia growth. Genome comparison of the Wolbachia endosymbiont of B. malayi (wBm) with the Wolbachia endosymbiont of Drosophila melanogaster (wMel) shows that they share similar metabolic trends, although their genomes show a high degree of genome shuffling. In contrast to wMel, wBm contains no prophage and has a reduced level of repeated DNA. Both Wolbachia have lost a considerable number of membrane biogenesis genes that apparently make them unable to synthesize lipid A, the usual component of proteobacterial membranes. However, differences in their peptidoglycan structures may reflect the mutualistic lifestyle of wBm in contrast to the parasitic lifestyle of wMel. The smaller genome size of wBm, relative to wMel, may reflect the loss of genes required for infecting host cells and avoiding host defense systems. Analysis of this first sequenced endosymbiont genome from a filarial nematode provides insight into endosymbiont evolution and additionally provides new potential targets for elimination of cutaneous and lymphatic human filarial disease.

Genome Size Determination and Coding Capacity of Sodalis glossinidius, an Enteric Symbiont of Tsetse Flies, as Revealed by Hybridization to Escherichia coli Gene Arrays

Leyla Akman — 2008-03-05T21:27:52-00:00

J. Bacteriol., Vol. 183, No. 15. (1 August 2001), pp. 4517-4525.

Recent molecular characterization of various microbial genomes has revealed differences in genome size and coding capacity between obligate symbionts and intracellular pathogens versus free-living organisms. Multiple symbiotic microorganisms have evolved with tsetse fly, the vector of African trypanosomes, over long evolutionary times. Although these symbionts are indispensable for tsetse fecundity, the biochemical and molecular basis of their functional significance is unknown. Here, we report on the genomic aspects of the secondary symbiont Sodalis glossinidius. The genome size of Sodalis is approximately 2 Mb. Its DNA is subject to extensive methylation and based on some of its conserved gene sequences has an A+T content of only 45%, compared to the typically AT-rich genomes of endosymbionts. Sodalis also harbors an extrachromosomal plasmid about 134 kb in size. We used a novel approach to gain insight into Sodalis genomic contents, i.e., hybridizing its DNA to macroarrays developed for Escherichia coli, a closely related enteric bacterium. In this analysis we detected 1,800 orthologous genes, corresponding to about 85% of the Sodalis genome. The Sodalis genome has apparently retained its genes for DNA replication, transcription, translation, transport, and the biosynthesis of amino acids, nucleic acids, vitamins, and cofactors. However, many genes involved in energy metabolism and carbon compound assimilation are apparently missing, which may indicate an adaptation to the energy sources available in the only nutrient of the tsetse host, blood. We present gene arrays as a rapid tool for comparative genomics in the absence of whole genome sequence to advance our understanding of closely related bacteria. 10.1128/JB.183.15.4517-4525.2001

Mealybug [beta]-proteobacterial endosymbionts contain [gamma]-proteobacterial symbionts

Carol von Dohlen — 2008-03-16T15:44:04-00:00

Nature, Vol. 412, No. 6845. (26 July 2001), pp. 433-436.

Bacterial Endosymbionts: Genome Reduction in a Hot Spot

Christopher Lane — 2008-03-05T21:27:07-00:00

Current Biology, Vol. 17, No. 13. (3 July 2007), pp. R508-R510.

Prokaryotic symbionts are common in invertebrates and play an essential metabolic role in deep-sea hydrothermal vent communities. Complete genome sequences of bacterial endosymbionts of two deep-sea clams are providing new insights into evolutionary genome reduction.

From Endosymbiont to Host-Controlled Organelle: The Hijacking of Mitochondrial Protein Synthesis and Metabolism.

Toni Gabaldón — 2007-11-13T10:52:33-00:00

PLoS Comput Biol, Vol. 3, No. 11. (2 November 2007)

Mitochondria are eukaryotic organelles that originated from the endosymbiosis of an alpha-proteobacterium. To gain insight into the evolution of the mitochondrial proteome as it proceeded through the transition from a free-living cell to a specialized organelle, we compared a reconstructed ancestral proteome of the mitochondrion with the proteomes of alpha-proteobacteria as well as with the mitochondrial proteomes in yeast and man. Overall, there has been a large turnover of the mitochondrial proteome during the evolution of mitochondria. Early in the evolution of the mitochondrion, proteins involved in cell envelope synthesis have virtually disappeared, whereas proteins involved in replication, transcription, cell division, transport, regulation, and signal transduction have been replaced by eukaryotic proteins. More than half of what remains from the mitochondrial ancestor in modern mitochondria corresponds to translation, including post-translational modifications, and to metabolic pathways that are directly, or indirectly, involved in energy conversion. Altogether, the results indicate that the eukaryotic host has hijacked the proto-mitochondrion, taking control of its protein synthesis and metabolism.

Genome history in the symbiotic hybrid Euglena gracilis.

N Ahmadinejad — 2008-02-04T13:20:30-00:00

Gene, Vol. 402, No. 1-2. (1 November 2007), pp. 35-39.

Euglena gracilis has a chimeric gene collection in which some genes were inherited from its heterotrophic host and others were acquired from a photoautotrophic endosymbiont during secondary endosymbiosis. The evolutionary reconstruction of such a hybrid genome poses a challenge for standard phylogenetic tools that produce bifurcating trees because genome evolution by endosymbiotic gene transfer is a non tree-like process. We sequenced 2770 ESTs from E. gracilis, of which 841 have homologues in a sample of other eukaryotes. Most of these homologues are found in all of the eukaryotes in our sample, but 117 of them are specific to photoautotrophic eukaryotes. A phylogenetic tree fails to account for this observation but the distribution of homologues and a phylogenetic network clearly show the common origin of E. gracilis from both kinetoplastid and photoautotrophic ancestors.

Wolbachia genome integrated in an insect chromosome: Evolution and fate of laterally transferred endosymbiont genes.

Naruo Nikoh — 2008-01-25T21:24:49-00:00

Genome Res (11 December 2007)

Recent accumulation of microbial genome data has demonstrated that lateral gene transfers constitute an important and universal evolutionary process in prokaryotes, while those in multicellular eukaryotes are still regarded as unusual, except for endosymbiotic gene transfers from mitochondria and plastids. Here we thoroughly investigated the bacterial genes derived from a Wolbachia endosymbiont on the nuclear genome of the beetle Callosobruchus chinensis. Exhaustive PCR detection and Southern blot analysis suggested that approximately 30% of Wolbachia genes, in terms of the gene repertoire of wMel, are present on the insect nuclear genome. Fluorescent in situ hybridization located the transferred genes on the proximal region of the basal short arm of the X chromosome. Molecular evolutionary and other lines of evidence indicated that the transferred genes are probably derived from a single lateral transfer event. The transferred genes were, for the length examined, structurally disrupted, freed from functional constraints, and transcriptionally inactive. Hence, most, if not all, of the transferred genes have been pseudogenized. Notwithstanding this, the transferred genes were ubiquitously detected from Japanese and Taiwanese populations of C. chinensis, while the number of the transferred genes detected differed between the populations. The transferred genes were not detected from congenic beetle species, indicating that the transfer event occurred after speciation of C. chinensis, which was estimated to be one or several million years ago. These features of the laterally transferred endosymbiont genes are compared with the evolutionary patterns of mitochondrial and plastid genome fragments acquired by nuclear genomes through recent endosymbiotic gene transfers.