COS 49-8
Maternal investment mediates offspring life history variation with context-dependent fitness consequences in an amphibian
Maternal effects form a transgenerational linkage between maternal and offspring environments. In amphibians, maternal effects such as investment in embryo size are known to have strong context-dependent larval fitness consequences, however relatively little is known about their influence on adult life history traits. Facultatively paedomorphic salamanders are a potentially instructive system for exploring the role of maternal effects on offspring life history variation, as the discrete adult phenotypes (aquatic paedomorphs and terrestrial metamorphs) are induced by variation in environmental condition. Using an experimental technique that removes ~20% of an individual’s embryonic yolk stores, we investigated how embryo size differences regulated growth trajectories, phenotype production, and first-year reproduction of mole salamanders. We predicted that large embryo sizes (Control) would influence larvae towards rapid growth, paedomorphosis, and high first year reproductive output. In contrast, we hypothesized that small embryo sizes (Reduced) would direct larvae towards slower growth, metamorphosis, and low first year reproductive output. Individuals were reared by embryonic treatment at one of three larval densities in experimental ponds. Individuals from each pond were captured six times from May until November to assess growth rates and phenotypic expression, and were dissected the following March to analyze reproductive investment.
Results/Conclusions
Embryos subjected to the experimental yolk reduction were significantly smaller at hatching, but caught up in size after the first 30 days of the larval period. After 105 days, Reduced larvae were significantly smaller than Controls at low densities but the same size at high densities. While embryonic treatment did not influence paedomorph production, there was an interactive effect of embryonic treatment and density in the production of metamorphs, with more Reduced animals undergoing metamorphosis at high densities than Controls. Furthermore, Reduced females produced larger clutches for a given body size than Controls. However, mean egg size increased with body size for Controls only. Reduced females produced an average egg size that was larger than Controls at small body sizes but similar at large body sizes. These differences in reproductive output mediated strong context-dependent fitness consequences, whereby Reduced females had lower fitness than Controls at low densities but higher fitness at high densities. These data are a strong example of the context-dependent fitness consequences of maternal effects, and suggest that condition-dependent maternal investment in embryo size may adaptively mediate offspring life history patterns to maximize fitness.