Phenotypic plasticity can manifest itself as polyphenisms, where two or more alternative, environmentally-cued phenotypes are produced from the same genotype. Facultatively paedomorphic salamanders are polyphenic in that they can forego metamorphosis into terrestrial adults and instead reproduce as aquatic paedomorphs. Prevailing theory proposes that facultative paedomorphosis offers advantages over fixed developmental trajectories when aquatic conditions are favorable. Since metamorphosis is typically initiated in response to environmental stressors (deteriorating aquatic conditions), we investigated whether the stress hormone corticosterone (CORT) alters the probability of paedomorphosis. To do this, we examined the effects of exogenous application of CORT on the development and post-larval phenotype of mole salamanders, Ambystoma talpoideum. We utilized 32 large mesocosms (1200L) arranged into eight replicates (n=8) of four different treatments (k=4) where all mesocosms were identical except for differing doses of exogenous CORT repeatedly applied to the water (Control = 0mg CORT, Low = 6mg, Medium = 30mg, High = 60mg).
Results/Conclusions
We found strong effects of treatment on phenotype, with the highest proportion of paedomorphs occurring in Control and incrementally smaller proportions of paedomorphs found with increasing CORT dosage. High CORT produced no paedomorphs. Though survivorship, time to metamorphosis, mass at metamorphosis and mass of paedomorphs typically differ between the two life history strategies, we found no effect of treatment. These results show that stress hormones play an integral role in regulating the expression of paedomorphic and adult phenotypes. The endocrine mechanisms influencing life history transitions provide insights into how multiple environmental cues may influence the same process, thereby synthesizing theoretical models of metamorphosis and paedomorphosis.