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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
March 2014
ABSTRACT:
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.