PERSISTENT HIGH-LEVELS OF TETRAPLOIDY IN SALAMANDERS OF THE AMBYSTOMA-JEFFERSONIANUM COMPLEX

Almost all unisexual members of the Ambystoma jeffersonianum complex o f salamanders are triploid, although occasional tetraploid individuals have been observed in a few populations. A population characterized b y a high percentage of tetraploids (7-27%) exists at Kickapoo State Pa rk, Vermilion Co, Illinois. This high frequency of tetraploids has bee n maintained over a period of 12 years. Tetraploids in this population were originally formed by fertilization of unreduced A. platineum ova by A. texanum sperm. Tetraploids at Kickapoo State Park are, however, capable of obtaining sperm from the sexual host, Ambystoma texanum an d producing tetraploid offspring. Because tetraploids can be produced two ways, they might be expected to out-reproduce and replace triploid s. However, these tetraploids also produce abundant pentaploid offspri ng as a result of fertilization of their ova by A. texanum sperm. A hi gh incidence of physical abnormalities among pentaploid larvae and the ir scarcity as breeding adults suggests that pentaploids have reduced viability. Production of pentaploid larvae may thus be the selective m echanism that prevents tetraploids from replacing triploids in this po pulation. Higher than normal water temperature may be causing increase d fertilization rates in this population; this would account for its h igher frequency of tetraploids compared to other populations, as well as for the high number of pentaploid larvae that tetraploids produce.