Speciation Reversal in European Whitefish (Coregonus lavaretus (L.)) Caused by Competitor Invasion

Abstract

Invasion of exotic species has caused the loss of biodiversity and imparts evolutionary and ecological changes in the introduced systems. In northern Fennoscandia, European whitefish (Coregonus lavaretus (L.)) is a highly polymorphic species displaying adaptive radiations into partially reproductively isolated and thus genetically differentiated sympatric morphs utilizing the planktivorous and benthivorous food niche in many lakes. In 1993, Lake Skrukkebukta was invaded by vendace (Coregonus albula (L.)) which is a zooplanktivorous specialist. The vendace displaced the densely rakered whitefish from its preferred pelagic niche to the benthic habitat harbouring the large sparsely rakered whitefish. In this study, we investigate the potential influence of the vendace invasion on the breakdown of reproductive isolation between the two whitefish morphs. We inferred the genotypic and phenotypic differentiation between the two morphs collected at the arrival (1993) and 15 years after (2008) the vendace invasion using 16 microsatellite loci and gill raker numbers, the most distinctive adaptive phenotypic trait between them. The comparison of gill raker number distributions revealed two modes growing closer over 15 years following the invasion. Bayesian analyses of genotypes revealed that the two genetically distinct whitefish morphs that existed in 1993 had collapsed into a single population in 2008. The decline in association between the gill raker numbers and admixture values over 15 years corroborates the findings from the Bayesian analysis. Our study thus suggests an apparent decrease of reproductive isolation in a morph-pair of European whitefish within 15 years (≃ 3 generations) following the invasion of a superior trophic competitor (vendace) in a subarctic lake, reflecting a situation of “speciation in reverse”.

Managing cryptic biodiversity: Fine‐scale intralacustrine speciation along a benthic gradient in Alpine whitefish (Coregonusspp.)

“…This has resulted in hybridization between the invasive species and native whitefish in certain lakes (Kahilainen et al., 2011). In other lakes, competitive exclusion of native densely rakered whitefish species by the invasive has occurred, combined with massive introgression and the loss of phenotypic and genetic differentiation between the previously distinct densely rakered and large sparsely rakered whitefish species (Bhat et al., 2014). Alternatively, neutral models of coexistence (Leibold & McPeek, 2006), potentially followed by ecological character displacement or specialization within the shared niche, buttressed by the nonoverlap of spawning habitats between these species could allow the persistence of both species.…”

Post-glacial habitat release and incipient speciation in the genus Delphinus

“…Other Delphinus populations may be at a different stage in the process, in an environment where isolation is less strongly promoted, or even represent the collapse of a previous pattern of differentiation (for example, as seen for whitefish, Coregonus lavaretus; Bhat et al, 2014). Chance events associated with founder size and the extent of genetic drift, or differences associated with environmental conditions or local processes, may be relevant to the differential extent of isolation in different regions.…”

Allochrony as a potential driver for reproductive isolation in adaptive radiations of European whitefish ecomorphs

“…The whitefish from Stuorajávri were significantly more advanced in sexual maturity than the whitefish from Suohpatjávri. Hybrids between whitefish ecomorphs frequently occur in all northern Fennoscandian lakes, but genetic studies have only observed hybridisation between DR-LSR whitefish (Bhat et al, 2014) and between LSR-SSR whitefish (Praebel et al unpublished). We also found, in both lakes, that male and female DR and male LSR whitefish displayed a similar state of maturity, while the female LSR and male and female SSR whitefish were less mature.…”

“…Based on our own field observations, information from locals and the presence of hybrids between the ecomorphs (Bhat et al, 2014), it seems that all three ecomorphs mainly share the same spawning ground(s) in the littoral zone, and with the knowledge of whitefish ecomorphs' thermal niches, we hypothesised that differences in spawning time (allochrony) acts as the main driver of reproductive isolation. The challenge of revealing reproduction in these northern systems, compared with more southern lakes for example in Sweden, Denmark and the European Alps, is that the spawning takes place in late October to December, when the lake ice is too thin to work on, but too thick for boating.…”

“…Here, it has diverged from a monophyletic lineage into distinct ecological morphs through adaptive radiation Svärdson, 1979). However, the reproductive isolation among the ecomorphs is not complete, evidenced by the frequent occurrence of hybrids between the ecomorphs (Bhat et al, 2014). However, the reproductive isolation among the ecomorphs is not complete, evidenced by the frequent occurrence of hybrids between the ecomorphs (Bhat et al, 2014).…”