Geographical variation in life history response to stress in the Freshwater Snail, Lymnaea stagnalis.

Life histories are known to vary across geographic ranges in response to a number of factors, both biotic and abiotic. Environmental calcium availability has been shown to affect freshwater gastropod life histories due to its fundamental requirement in shell formation. Adaptation of life histories to local environmental conditions may cause the response to novel pollutants to vary across populations within a species due to trade-offs between and among traits but very few studies have examined wide scale variation in life history response to stress across geographic ranges. A long term study was conducted and aimed to expand on current understanding by rearing populations of the great pond snail, Lymnaea stagnalis sampled from across the UK, for two generations in high and low calcium environments. A comprehensive suite of life histories was recorded throughout the study and traits were compared between populations and treatments, and across generations to distinguish between environmental, plastic and heritable sources of variation. Further work focussed on life history trade-offs under different environmental conditions before utilising a stage-classified matrix model to derive population growth rates (λ) and compare effects across populations and calcium treatments. Finally, acute and chronic effects of exposure to nanoparticulate carbon black were assessed before using matrix models to investigate the combined effects of environmental calcium with nanoparticulate carbon black on λ for three populations of snails. Significant intra-specific variation was recorded in the majority of life history traits, which were shown to display high levels of phenotypic plasticity as the norm. Intergenerational comparisons revealed that traits more directly linked to fitness, such as size at reproduction and reproductive output, showed higher heritabilities than those pertaining to growth, such as growth rates and age at first reproduction. Both generalised and population specific responses to calcium availability were shown in life history traits across the study populations. These effects tended to be subtle but suggest that environmental calcium plays a role in shaping life history strategies across the UK distribution. Life history trade-offs between traits tended to be conserved across populations, and showed little response to environmental calcium, although differential investment in life history traits across calcium treatment was detected in some cases. A strong trade-off between age and size at first reproduction was detected across all generations and calcium treatments. Size at first reproduction was also shown to correlate with reproductive output, wherein a trade-off between eggs per mass and number of egg masses was detected. Traits involved in trade-offs appeared to more strongly associate with fitness and these findings suggest that trade-offs between key life history traits are of importance in understanding population specific life history strategies. Stage-classified matrix modelling showed a trend towards reduced λ in low calcium but this trend was not significant. A significant reduction in λ across generations was recorded which was most likely to be the result of inbreeding. Local adaptation to calcium availability was shown to influence the life history response to nanoparticulate carbon black, and was mirrored in predicted population growth rates obtained from matrix models. Intraspecific differences in response to carbon black nanoparticles only became apparent when calcium concentrations were low. These findings would support the view that in order to be better able to predict the response of species to the presence of novel stressors such as nanoparticles, it is necessary to account for intraspecific adaptation of life history traits as well as geographical variation in the environmental context.