Meeting Abstract
Differences in dispersal can allow coexistence when competition is high, such as between sexual species and sexual parasites. Among vertebrates, sexual parasites are often all-female lineages that require sperm from sexual species to reproduce. Unisexual Mole Salamanders (Ambystoma sp.) are the oldest known parasitic lineage in vertebrates, which are evolutionary and ecologically successful. However, whether differences in dispersal contribute to their long-term coexistence with sexual species is unknown. The geographic range of unisexuals includes a wide area of fragmented, agricultural land. In terms of dispersal, unisexuals could be wide-spread because they are superior dispersers in these landscapes, exploiting ephemeral breeding habitats and naïve males. We test this hypothesis by using indirect genetic methods and direct physiological measurements to compare dispersal ability between sympatric sexual and unisexual salamanders. Specifically, we used genetic assignment tests based on DNA microsatellite data to estimate dispersal distances between populations within an agricultural area of Ohio. We then measured walking endurance of wild-caught animals on a treadmill under standardized conditions. Contrary to predictions, sexual salamanders disperse on average twice as far and have 1.5 times the walking endurance compared to unisexuals. We conclude that differences in dispersal cannot account for coexistence between sexual and unisexual salamanders, as theoretical models designed for sexual/asexual coexistence indicate an extinction scenario for unisexual Ambystoma. We predict that the frequent introgression of nuclear DNA from sexual salamanders into the unisexual lineage requires new theory to match the uniqueness of this unusual reproductive mode.
