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University of Michigan Biological Station

The University of Michigan Biological Station (UMBS) was founded in 1909.

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Experimental evaluation of the freshwater genus Stagnicola (Gastropoda:Lymnaeidae): ecomorphs or valid species?

Animal Population
Aquatic
Project Abstract: 
Pleistocene glaciations had great impacts on freshwater biota of Neartic ecosystems, although the evolutionary impacts of the forced retreats and subsequent recolonizations of freshwater populations are still poorly understood. The freshwater gastropod genus Stagnicola is comprised of 21 nominal species endemic to Nearctic regions, with a metropolis of members concentrated within the Great Lakes region, was likely strongly impacted by the glaciation cycles of the Pleistocene. Taxonomic evaluations of this genus, based solely on shell morphology, have long been disputed. The few molecular studies within this genus have revealed several small but distinct clades comprising of multiple species with little regards to geographic origin, implying (i) high degrees of ecophenotypic plasticity (making shell-based identifications unreliable), or (ii)recurrent hybridization between nominal species (confounding attempts to properly reconcile stagnicoline relationships). This study attempts to dissect the relationships between 3 nominal species present at UMBS through breeding experiments, analysis of parasite composition, and DNA sampling from individuals for future population genetics studies. Proper evaluation of Stagnicola is important for insight into the largely disputed relationships of freshwater gastropods, biodiversity and conservation effors, as well as having implications for understanding parasite-host relationships and ecological impacts of Pleistocene glaciations.
Investigator(s): 
Liesl Oeller
Status of Research Project: 
Complete (archive)
Years Active: 
2013
Research sites: 
Douglas Lake
Methods: 
Localities for sampling include Douglas Lake (Grapevine Point, Marl Bay, Sedge Point, North Fishtail Bay), Burt Lake, Maple River, and Sugar Island – all of which have been reported to contain members of Stagnicola, with most areas containing sympatric populations of nominal species. Snails will be collected and identified in the field using keys by Burch (1989). A previous study by Burch (1973) attempted to test for hybridization between S. elodes and S. emarginata using morphological markers and has provided an adequate protocol for this experiment. Mating trials will be performed in the Lakeside Laboratory using small glass tanks or similar holding containers for individuals. A diet of lettuce will be provided for all snails, and water replaced weekly. Crosses will be arranged based on nominal species or “morphs”, locality, and previous data concerning mitochondrial relationships. Test crosses will be set up between sympatric members of different nominal species, species who have shown high similarity in mitochondrial DNA sequences but differ in morphology, conspecifics from different localities who may differ in mtDNA haplotype, and as controls conspecifics from the same locality who have similar mtDNA haplotypes. Each cross will have four replicates. Two snails will be placed within the mating tanks for 1-2 weeks OR after multiple coitus attempts have been observed. Snails will then again be separated into individual containers. F1 juveniles will be phenotypically assessed. I will extract foot tissue from each crossed parent and the resulting offspring for DNA analysis to test for actual hybridization, as all Stagnicola are hermaphroditic and capable of self-fertilization. At the close of the experiment, all snails will be preserved in 70% ethanol for future anatomical studies. I also plan to assay individual snails for parasite loads. After collection, specimens will be separated and exposed under fluorescent light for 1-2 hours to induce emergence of cercariae in infected snails. Any observed cercariae will be identified using morphological markers and preserved in 70% ethanol. Information from the snail host will be recorded to correlate with parasite infection, including species name, shell length, and aperture width.