Polyphenisms are an extreme form of phenotypic plasticity where two or more alternative, enivronmentally-cued phenotypes can arise from a single genotype. Facultatively paedomorphic salamanders are polyphenic in that adults can exhibit either a metamorphosed terrestrial phenotype or a paedomorphic aquatic phenotype. The adult phenotype is largely determined by various ecological conditions experienced during larval development. We conducted a series of mesocosm experiments with the salamander Ambystoma talpoideum to investigate 1) density-dependent thresholds 2) lethal and non-lethal effects of three fish predators and 3) local adaptation to hydroperiod.
Results/Conclusions
Density had strong effects on growth and phenotype. Low densities produced large individuals that became paedomorphic while high densities stunted growth preventing individuals from reach sexually maturity. Fish predators varied in their effects with high salamander mortality occurring with large-gaped Lepomis and substantially less mortality with moderately-gaped Aphredoderus and small-gaped Fundulus. Variations in body size and phenotype proportions largely reflected changes in density via predator-induced mortality. Hydroperiod and source pond had variable effects on body size and phenotypes, but, interestingly, no effect on larval period. Body size once again reflected changes in density, but individuals from a historically temporary pond performed better in short hydroperiods than individuals from historically permanent ponds. Paedomorphs were more common in long, as opposed to short, hydroperiods. All the tested factors had strong effects on growth and phenotype, but changes in density (even when induced via the other factors) seems to have an overriding effect that can lead to predictable variation in size and phenotype proportions.