Iowa Pleistocene Snail


The Iowa Pleistocene Snail (Discus macclintocki) is a small terrestrial snail (5–8 mm in diameter) that is included on the US list of endangered species. Discus macclintocki is endangered mainly due to its dependence on rare algific (cold-air) talus slopes adjacent to stream-beds in northeastern Iowa and northwestern Illinois. Algific talus slopes were formed during the Wisconsin period of the Pleistocene Epoch along major river drainages where glacial runoff and large amounts of ice accumulated. D. macclintocki appears to have a limited temperature tolerance that prevents its expansion into the areas between slopes, which have harsher climates. Because of these temperature requirements, D. macclintocki is believed to be a relict species, surviving only on these isolated algific talus slopes since the last glacier receded and the temperatures increased approximately 16,500 years ago. Several surveys documenting the location of colonies of D. macclintocki have been conducted as well as demographic studies. These surveys indicate that variation in recruitment appears to be driving fluctuations in population growth and that snails are highly subdivided within sites.

My lab is conducting a genetic survey of D. macclintocki populations using hypervariable microsatellite markers and single nucleotide polymorphisms (SNPs).  Because they are co-dominant markers and evolve quickly, microsatellites and SNPs have advantages over mitochondrial DNA in resolving population structure, even at fine geographic scales.  Improving our understanding the population structure of D. macclintocki will provide information to conservation managers on gene flow within and between populations, effective population size, sustainability and other genetic attributes of extant populations.  The information obtained from this study will provide managers with the necessary population genetic data to make appropriate decisions on the listing status and future management of D. macclintocki.