Genetic Identification of the Origin of the Lake Ontario Deepwater Sculpin Population

Deepwater sculpin (Myoxocephalus thompsonii) were considered to be extirpated from Lake Ontario since the 1970s.  However, since 1998, individuals have been caught in southern Lake Ontario, in increasing numbers.  Our objectives were to determine whether the current population in Lake Ontario could be a remnant of the once-abundant native population in the lake, or if it could be a result of recolonization from the Upper Great Lakes.  Genetic data were collected at 10 microsatellite loci to identify the probable source of the current Lake Ontario deepwater sculpin population.  Lake Ontario samples collected in 2009 (n=66) and 2010 (n=43) were compared to museum specimens collected in 1942 from the south shore of Lake Ontario (average n=10) and to samples from 15 sampling sites in the Upper Great Lakes (total n=614).  Population structuring within Lake Ontario was not observed; instead, the collected individuals represent a single population. Genetic differentiation was lower between the recent Lake Ontario samples and the museum specimens (F_ST=0.09) than between the recent Lake Ontario samples and the Upper Great Lakes (F_ST=0.15), indicating the possibility that deepwater sculpin were not extirpated in Lake Ontario.  The current Lake Ontario population does not appear to have experienced a genetic bottleneck (i.e., no heterozygosity excess; p=0.5) and has genetic diversity levels similar to populations in the Upper Great Lakes.  Mitochondrial DNA will also be used in an effort to obtain data from additional museum specimens.  Based on preliminary microsatellite analyses, the current Lake Ontario deepwater sculpin population appears to significantly contribute to the Great Lakes-wide genetic diversity of the species.