Midwest Partners in Amphibian and Reptile Conservation

Midwest PARC Species List Additional Information

Unisexual Ambystomatids

Description of unisexual members of the Ambystoma jeffersonianum complex, by Christopher A. Phillips and Jennifer Mui. [From: Amphibian Declines, Edited by M. J. Lannoo , 2005. University of California Press]

The occurrence of all-female morphs of salamanders associated with Jefferson salamanders (Ambystoma jeffersonianum) and blue-spotted salamanders (A. laterale) has been recognized for over 50 years.  Two distinct forms of these all-female morphs were distinguished based on the same morphological characters that separate the two diploid species, suggesting that the all-female morphs resulted from a post-Wisconsin hybridization between A. jeffersonianum and A. laterale.   Subsequently, it was demonstrated that the all-female morphs and their offspring are triploid and, based on observations of lampbrush chromosomes, it was proposed that pre-meiotic chromosomal duplication and gynogenesis was a mechanism explaining the perpetuation of the all-female triploid lineages.  Under this hypothesis, sperm from spermatophores deposited by males activate the unreduced eggs, but normally do not fertilize them.

Several exceptions to this scenario have been reported, including unisexual tetraploid and pentaploids that result from fertilization rather than simple activation of unreduced triploid ova. Diploid unisexual salamanders also occur.

In the United States, unisexual hybrids are distributed sporadically throughout east-central Illinois, Indiana, most of Ohio, northern Kentucky, Wisconsin, southern Michigan, Connecticut, Massachusetts, New York, northern New Jersey, northern Minnesota, Maine, Vermont, and New Hampshire.

Unisexual hybrids will breed in fishless ponds in a variety of wooded and semi-wooded habitats including ponds, wetlands, ditches, and sloughs.

Unisexual hybrid adults are found in upland forests as well as bottomland forests, often associated with sandy soils.  They may remain near the surface most of the year until late autumn.

Because of their genetic complexity, these animals are not accommodated under either biological or evolutionary species concepts.  However, as of 2002, unisexual hybrids continue to be recognized as animals Of Special Concern in Connecticut and as Endangered in Illinois and New Jersey.