Contrasting patterns of mitochondrial DNA and microsatellite introgressivehybridization between lineages of lake whitefish (Coregonus clupeaformis);relevance for speciation

Citation
G. Lu et al., Contrasting patterns of mitochondrial DNA and microsatellite introgressivehybridization between lineages of lake whitefish (Coregonus clupeaformis);relevance for speciation, MOL ECOL, 10(4), 2001, pp. 965-985
Citations number
75
Categorie Soggetti
Environment/Ecology,"Molecular Biology & Genetics
Journal title
MOLECULAR ECOLOGY
ISSN journal
09621083 → ACNP
Volume
10
Issue
4
Year of publication
2001
Pages
965 - 985
Database
ISI
SICI code
0962-1083(200104)10:4<965:CPOMDA>2.0.ZU;2-G
Abstract
We performed a combined analysis of mitochondrial DNA (mtDNA) and microsate llite loci among lake whitefish (Coregonus clupeaformis) populations in ord er to assess the levels of congruence between both types of markers in defi ning patterns of genetic structuring, introgressive hybridization and infer ring population origins in the hybrid zone of the St. John River basin. a s econd objective was to test the hypothesis that secondary contact between g lacial lineages always resulted in the occurrence of sympatric dwarf and no rmal whitefish ecotypes. Fish were sampled from 35 populations and polymorp hism was screened at mtDNA and sir microsatellite loci for a total of 688 a nd 763 whitefish, respectively. Four lakes harbouring a single whitefish po pulation of normal ecotype admired with mtDNA haplotypes of different linea ges were found. This confirmed that secondary contact between whitefish evo lutionary lineages did not always result in the persistence of reproductive ly isolated ecotypes. Microsatellites further supported the definition of d istinct glacial lineages by identifying lineage-specific allelic size group s. They also further supported the hypothesis that ecotypes originated from either a single founding lineage (sympatric divergence) or following secon dary contacts between lineages (allopatric divergence), depending on the la ke. In general, however, the pattern of population differentiation and intr ogressive hybridization observed at microsatellites was in sharp contrast w ith that depicted by mtDNA variation. Both factorial correspondence analysi s and analysis of admixture proportion revealed a much more pronounced patt ern of introgressive hybridization than depicted by mtDNA analyses. Variabl e levels of introgression indicated that environmental differences may be a s important as the historical contingency of secondary contact in explainin g the persistence of sympatric ecotypes and the differential pattern of int rogressive hybridization among lakes. Whitefish populations from the St. Jo hn River basin hybrid zone represent a rare illustration of a continuum of both morphological and genetic differentiation within a given taxon, spanni ng from complete introgression to possibly complete reproductive isolation, depending on lakes. Thus, each lake may be viewed as a different temporal snapshot taken throughout the gradual process of speciation.