Cottus cognatus and Cottus bairdi are small, benthic, freshwater fish species native to southeastern Minnesota. Current conservation efforts conducted by the Minnesota Department of Natural Resources (MNDNR) have included reintroducing sculpin to rehabilitate the native fish fauna in streams historically impacted by agricultural land-use. These restoration activities have provided diverse opportunities to study aspects of sculpin ecology in southeastern Minnesota.
The MNDNR reintroduction plan did not attempt to differentiate between C. cognatus and C. bairdi, in part because the two are morphologically similar and difficult to identify in the field. The two species are known to occur syntopically in some areas, and hybridization between the two has been documented. Fish survey data from the Minnesota Pollution Control Agency along with personal observation were used to identify sites in southeast Minnesota with syntopic populations. Fin clips were taken from fish in syntopic populations and genotyped using three species-specific microsatellite DNA markers. Habitat data were collected from syntopic sites to further understand conditions that allow for species co-occurrence. There was no evidence for hybridization in syntopic C. cognatus and C. bairdi populations in southeastern Minnesota, even though there was no spatial or temporal separation during breeding season. Syntopy occurred only in areas where a 1st- 2nd order spring-fed tributary flowed into a larger stream. Temperatures in syntopic locations were intermediate to temperatures recorded in allopatric locations for both species. The results of this study suggest that differences between the species limit or prevent hybridization in southeastern Minnesota. Sculpin reintroduction efforts should take into account the different preferences of each species to increase success in introduced populations. Currently, the only species used for reintroductions is C. cognatus. Research started in 2005 at the University of Minnesota examined overall ancestry, changes in genetic diversity, and fitness in reintroduced C. cognatus populations up to two generations after stocking. New introductions were conducted to examine the initial dynamics in survival and reproduction and how they affect genetic diversity. Two streams were stocked in the fall of 2007 with an equal mix of individuals from two source strains. Fin clip samples were taken from all individuals stocked into each stream, and samples from their offspring were collected the following fall. Parentage analysis requires highly polymorphic genetic markers, and microsatellite loci developed for other Cottus species were insufficient for the needs of this study. To fulfill this need, thirteen polymorphic microsatellite loci were developed from C. cognatus libraries enriched for tri- and tetranucleotide repeats. These loci had 2 to 22 alleles and observed heterozygosities ranged from 0.36 to 0.86 in a sample of 47 individuals from one population. All parents and offspring from the two reintroduction sites were genotyped at 12 microsatellite loci, 6 from those described above and 6 from an existing set. Parentage analysis revealed small founder numbers, differential strain success, and skewed contributions by individuals. One family in each reintroduction stream was responsible for 21-28% of the offspring genotyped, and there was evidence for polygamy in both streams. Allelic diversity in the offspring was reduced by 35-49%. These findings indicate that the effective population size in reintroduced sculpin populations is likely low, and a large number of fish would have to be stocked to maintain genetic diversity in new populations.
University of Minnesota M.S. thesis. June 2010. Major: Conservation Biology. Advisor: Loren M. Miller. 1 computer file (PDF); vii, 65 pages.
Fujishin, Lorissa M..
Lessons from two sculpin species in southeastern Minnesota: Species interactions in native populations and reproduction dynamics in reintroduced populations..
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