Mortality and morphology in egg masses of unisexual and Jefferson Salamanders

Unisexual Ambystoma salamander egg masses have often been observed to exhibit very high rates of embryo mortality. The ecological consequences and underlying mechanisms are of great concern to researchers and managers studying these and other members of the species complex, all of which are listed as rare species throughout much of their range. Substantial embryo mortality is commonly used by field ecologists as an indicator that unisexual salamanders are present in a pond; egg masses of unisexual salamanders appear otherwise very similar to those of A. jeffersonianum (Jefferson Salamander). Early researchers suggested that elevated mortality among unisexual salamanders was due to lack of fertilization caused by sperm limitation. However, recent work has suggested that embryo failure is due to genetic errors particular to the unisexual salamander lineage. Our goals in this study were to (1) identify when during development embryonic mortality occurs in unisexual salamanders, and (2) to ...