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SYMPATRIC SPECIATION AND PATTERNS OF MORPHOLOGICAL AND GENETIC DIVERSITY AMONG CISCOES IN DEEPWATER LAKES
1Aquatic Research and Monitoring Section, Ontario Ministry of Natural Resources, Peterborough, Ontario, Canada
2Département de biologie, Université Laval, Quebec City, Quebec, Canada
3Great Lakes Laboratory for Fisheries and Aquatic Sciences, Fisheries and Oceans Canada, Sault Ste. Marie, Ontario, Canada
North American coregonines exhibit great morphological and life history diversity with multiple sympatric morphotypes occurring across their range. The Great Lakes once supported seven putative cisco species with each lake possessing several taxa that displayed differences in trophic position, spawning season and habitat depth. However, much of this diversity had been lost. Development of conservation and re-establishment plans for deepwater ciscoes has been hindered by uncertainty regarding the taxonomy of different morphs, and the historical and contemporary processes responsible for phenotypic diversity. We used morphological and genetic data to: 1) describe variation within and among four Great Lakes and 16 inland lakes; 2) test predictions generated from the Sympatric Origin Hypothesis; and, 3) assess the role of adaptive divergence in the diversification of Great Lakes ciscoes. Cisco and Shortjaw Cisco were phenotypically distinct (largely reflective of differences in gill raker number and jaw morphology) within lakes but highly variable across lakes. In some lakes, Shortjaw Cisco is only recognizable when compared to its sympatric Cisco form. Analysis of AFLP data revealed two genetic clusters that conformed to differences in geography (eastern and western groups), not hypothesized taxonomic boundaries. Genetic variation strongly suggests that each of these unique pairs of
morphotypes recently originated, in parallel, locally from the ancestral Cisco. Divergent selection could have played a role within lakes where morphotypes are genetically distinct, but evidence is tempered by the very high phenotypic variance among lakes for each morphotype. There was no support for the presence of genetically distinct morphotypes in Lake Superior or Lake Huron. Similar to inland lakes, genetic variation is best explained by geography, not species identifications based on morphology. Results do not support the current application of species-level taxonomy (based on morphology alone) within and outside the Great Lakes. Based on these results, it has been recommended that status assessments and recovery planning for ciscoes in Canadian waters be lake specific and, apply a species-flock approach where more than one morphotype is present.