Characterization of a Pearl Dace (Margariscus sp.) Hybrid Zone in Western New York

Two species of Pearl Dace are known to occur in New York State. The Allegheny Pearl Dace (Margariscus margarita) is found in the Hudson River watershed and those of the Southern Tier, while the Northern Pearl Dace (M. nachtreibi) is found in the watersheds of the Saint Lawrence drainage and direct tributaries to Lake Ontario. Although these two species are recognized as distinct, the descriptions and morphological characters used to tell them apart are currently insufficient as many of these characters overlap, making positive identifications unnecessarily difficult. During a routine morphological study to identify consistent diagnostic traits for these species, we discovered that individuals from several locations in the Eastern Lake Ontario Basin showed characteristics that were intermediate between Allegheny and Northern Pearl Dace, indicating that these specimens were of hybrid origin. This has necessitated an expansion of this project to include genetic data and specimens from throughout the two species' ranges in New York, in order to fully delimit and characterize the range and population genetics within this hybrid zone, as well as to fulfill our original objective of being able to reliably identify Pearl Dace Specimens from New York. Because the hybrid zone occurs at the nearest margins of the two recognized species’ ranges, our genetic studies also have the potential to generate significant insights into the processes leading to the isolation and speciation of these two forms.