Summary 1 Life span, an essential component of fitness, can be affected by traits such age at first reproduction, as well as by the mortality regime imposed by the environment. In a long-term experiment under controlled conditions, we studied life span in an iteroparous plant species, the sea beet Beta vulgaris ssp. maritima (L.), from 104 wild populations sampled in France, Belgium, Great Britain and the Netherlands. We estimated the intensity of selective pressures on life span and the specific effects of age at first reproduction (first or second year, depending on vernalization requirement) and of environmental disturbance. 2 Mean life span (measured in glasshouse conditions) increases with latitude from about 2 years in inland habitats of south-western France to at least 11 years in north Brittany, before decreasing to about 5 years in the northernmost populations. 3 Comparison of spatial autocorrelograms for life span and cytoplasmic neutral markers showed there is strong selection for life span. 4 Within populations the effect of age at first reproduction on life span proved to be marginal. No causal relationship was detected among populations, although, in the southern part of the study area, a strong association between reproduction in the first year and short life span suggests common selective pressures. 5 Life span appeared to be highly associated with habitat type, as defined by mortality regimes. Populations with the longest-lived individuals occurred in the most stable habitats and populations with the shortest-lived individuals in the most disturbed locations.
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