The role of maternal effects on life history variation in a polyphenic salamander

Background/Question/Methods

Maternal effects form a flexible 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 plastic life history variation through adulthood. Facultatively paedomorphic salamanders are a potentially instructive system in which to examine 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. We investigated how experimentally manipulated embryo size differences regulated larval growth trajectories, phenotype production, and first-year reproduction of mole salamanders. We predicted that larger embryo sizes would influence larvae towards rapid growth, paedomorphosis, and high investment in first year reproduction, while smaller embryo sizes would direct larvae towards slower growth, metamorphosis, and lower investment in reproduction. Individuals were reared at one of three conspecific densities (low, medium, high) in experimental mesocosm ponds by embryonic treatment (control vs ~20% embryonic yolk storage reduction). Individuals from each tank were captured five times throughout the 2012 season to assess growth rates, and tanks were emptied in mid-November at which point adult phenotypes of each individual were observed.

Results/Conclusions

Embryos subjected to the experimental yolk reduction were significantly smaller at hatching, but demonstrated rapid compensatory growth during the first 30 days of the larval period, when initial size differences were no longer significant. After 105 days, larval growth exhibited negative density dependence with context dependent effects of embryonic treatment, where reduced treatment larvae were smaller at low densities but larger at high densities than control treatment larvae. Embryonic treatment and density interacted in the production of metamorphic individuals, with more metamorphs being produced at high densities of the reduced treatment than the control treatment. Embryonic treatment did not influence rates of paedomorphosis. Experimental animals are currently being mated to sample for embryo size and number based on embryonic treatment and rearing density. These data are a strong indication of the context dependent fitness consequences of maternal effects and suggest that embryonic yolk stores act as a signal of previous environmental conditions that maximize fitness when matched to offspring environmental conditions. Further research will focus on the longitudinal effects of density dependence on reproduction and subsequent offspring life history variation.