Hybridization as a result of habitat alterations and/or species introductions frequently leads to difficulty in identifying species.  The problem is common in the ichthyofauna of lakes in the Western United States, driven in part by the stochastic and isolatory environment.  In Utah Lake, Utah, morphological ambiguities (presumably the result of hybridization) that create a continuum of intermediate forms between, and prevent positive identification of, the federally endangered, endemic June sucker, Chasmistes liorus (a zooplanktivorous lakesucker; limnetic), and the more widespread Utah sucker, Catostomus ardens (benthivorous; benthic/littoral), have become a conservation issue.  Here we investigate the morphological and genetic variation and the stable isotopic signatures in suckers in eutrophic Utah Lake.  We compare morphological variation with variation in amplified fragment length polymorphisms and microsatellites in Utah Lake suckers; additionally, we use stable isotopes (¹³C and ¹⁵N) to examine sucker diet along the morphological gradient.  Suckers were differentiated primarily using mouth characters associated with different feeding strategies.  We also compare Utah Lake findings with those of preliminary investigations of suckers in oligotrophic Jackson Lake, Wyoming where a similar morphological continuum of benthic to limnetic morphotypes exists.  Jackson Lake contains Utah sucker and suckers resembling the presumably extinct Snake River sucker, Chasmistes muriei.  

Results/Conclusions

            Although we found no genetic evidence for a deep divergence between June and Utah morphs in Utah Lake, slight, but significant, population structuring accompanied the substantial morphological variation. Bayesian model-based genetic clustering detected two sucker populations in Utah Lake, though these clusters were only weakly concordant with morphological groupings or between marker systems.  Stable isotopic signatures were congruent with presumed feeding strategies (e.g., morphology).  Only a single sucker population was detected using microsatellites in Jackson Lake, and stable isotopic signatures were less congruent with presumed feeding strategies.  The suckers in Jackson Lake warrant further investigation, especially given the current status of the Snake River sucker (extinct?) and the contrast between Jackson Lake and the other systems with extant lakesucker populations.  The suckers in Utah Lake present an interesting dilemma regarding conservation: should one conserve (breed and stock) a subset of the morphotypic variation in the sucker complex, focusing on the endangered June sucker morphotype, or should one conserve both benthic and limnetic morphotypes in this complex, possibly maximizing evolutionary potential?