Genetic population structure of sympatric and allopatric populations of Baltic ciscoes (Coregonus albula complex, Teleostei, Coregonidae)

Abstract

BackgroundTeleost fishes of the Coregonidae are good model systems for studying postglacial evolution, adaptive radiation and ecological speciation. Of particular interest is whether the repeated occurrence of sympatric species pairs results from in-situ divergence from a single lineage or from multiple invasions of one or more different lineages. Here, we analysed the genetic structure of Baltic ciscoes (Coregonus albula complex), examining 271 individuals from 8 lakes in northern Germany using 1244 polymorphic AFLP loci. Six lakes had only one population of C. albula while the remaining two lakes had C. albula as well as a sympatric species (C. lucinensis or C. fontanae).ResultsAFLP demonstrated a significant population structure (Bayesian θB = 0.22). Lower differentiation between allopatric (θB = 0.028) than sympatric (0.063-0.083) populations contradicts the hypothesis of a sympatric origin of taxa, and there was little evidence for stocking or ongoing hybridization. Genome scans found only three loci that appeared to be under selection in both sympatric population pairs, suggesting a low probability of similar mechanisms of ecological segregation. However, removal of all non-neutral loci decreased the genetic distance between sympatric pairs, suggesting recent adaptive divergence at a few loci. Sympatric pairs in the two lakes were genetically distinct from the six other C. albula populations, suggesting introgression from another lineage may have influenced these two lakes. This was supported by an analysis of isolation-by-distance, where the drift-gene flow equilibrium observed among allopatric populations was disrupted when the sympatric pairs were included.ConclusionsWhile the population genetic data alone can not unambiguously uncover the mode of speciation, our data indicate that multiple lineages may be responsible for the complex patterns typically observed in Coregonus. Relative differences within and among lakes raises the possibility that multiple lineages may be present in northern Germany, thus understanding the postglacial evolution and speciation in the C. albula complex requires a large-scale phylogenetic analysis of several potential founder lineages.

Adaptive Phenotypic Diversification along a Temperature-Depth Gradient

“…The concordance in the ecological, physiological, and behavioral differentiation of the species with respect to temperature suggests thermal specialization as the main driver of their eco-evolutionary divergence. This divergence may have originated from two preexisting species through character displacement or from a single ancestral species through sympatric speciation, with the latter option being supported by genetic analyses (Schulz et al 2006;Mehner et al 2010b).…”

“…This temporal separation of reproduction, which hinders gene flow between the populations, might have evolved as a by-product of thermal specialization, owing to slower maturation and later spawning at lower temperatures. In fact, the majority of other European populations of the C. albula complex are autumn spawners (Kottelat and Freyhof 2007;Mehner et al 2010b) and generally show thermal preferences far above that of C. fontanae in Lake Stechlin (Ohl-berger et al 2008c). Another potential by-product of such a thermal adaptation is differentiation in body size, as observed for the coregonids in Lake Stechlin.…”

“…Their sympatric evolution has been suggested on the basis of mitochondrial DNA and microsatellite analyses (Schulz et al 2006). Recent amplified fragment length polymorphism analyses could neither confirm nor reject this hypothesis (Mehner et al 2010b). The species differ in their average population depths within the pelagic zone, with C. fontanae being found deeper in the water column than C. albula throughout the year.…”

Discrete thermal windows cause opposite response of sympatric cold-water fish species to annual temperature variability

“…The pelagic fish community is dominated by two sympatric Coregonus species, the common vendace (C. albula L.) for which Lake Stechlin represents their natural southern distribution range (Kottelat and Freyhof 2007), and the smaller, lake-endemic Fontane cisco (C. fontanae Schulz & Freyhof ) (Schulz and Freyhof 2003). The species are genetically closely related and may have emerged by post-glacial sympatric speciation in Lake Stechlin, although the exact evolutionary history is still unresolved (Mehner et al 2010b). Vendace is considered an autumnspawning species in Scandinavia, but peak spawning activity in Lake Stechlin which is at its southern distribution range is around 20 December.…”

Ecological commonalities among pelagic fishes: comparison of freshwater ciscoes and marine herring and sprat

“…Spring-spawning ciscoes were 136 genetically most closely related, but formed a separate 137 cluster together with their sympatric vendace populations 138 relative to other allopatric vendace populations. This pat-139 tern suggests the potential of parallel sympatric speciation 140 in both lakes, but the genetic signature modified by sec-141 ondary contacts and partial hybridization with other 142 Coregonus lineages (Mehner et al 2010b). Furthermore, 143 there was a significant isolation-by-distance pattern in the 144 genetic differentiation between German vendace popula-145 tions .…”