Parallel evolution and speciation by hybridization in the European whitefish complex of northern Germany.

Phelps, Luke (2013) Parallel evolution and speciation by hybridization in the European whitefish complex of northern Germany. (Master thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 58 pp.

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Abstract

Like many northern hemisphere fish species, the European whitefish (Coregonus /avaretus (L.)) was able to colonize new habitats as the glaciers retreated. Being able to occupy new niches, these fish show signs of recent genetic and phenotypic divergence both between the different lakes and rivers and also sympatrically within those habitat types. This evolutionary process has resulted in many different ecotypes causing taxonomic confusion and the formation of the European whitefish complex. Interestingly, this genetic divergence may also be an initiation of the development of reproductive isolation, leading ultimately to complete speciation. This could simply be the result of neutral evolutionary processes or may possibly be as a result of divergent ecologically based selection. The situation in Germany has an additional element of complexity in that two endangered ecotypes have been stocked, as a conservation measure, into different systems for the last 20 years without true knowledge of the genetic authenticity of the parent stocks. In an attempt to clarify the biogeography of the European whitefish specifically in Germany we first used two different mitochondrial markers to establish the colonization and demographic history of the different fish types. Results suggest that there were two major colonization events likely from the same ancestral population. We also found that the three different ecotypes currently recognized in Germany were already genetically divergent historically. Furthermore, using 16 bi-parentally inherited microsatellite loci we ascertained that most individual populations have recently diverged in parallel whilst at the same time hybridization between historical ecotypes is present and widespread in certain populations. In order to assess whether this ongoing genetic divergence perhaps has its source in ecologically based divergent selection, we then used the two ecologically relevant traits of gill raker number which is highly heritable and body morphology which is highly plastic to test for differences at both the historical ecotype and current population levels. We found highly significant differences for both traits at the ecotype level and mixed results at the population level. Many modern populations were significantly different for both traits in concordance with the ongoing genetic differentiation found in our genetic analyses. However, areas with significant admixture seemed to take on the characteristics of their predominant allele contributor giving evidence for the considerable effect hybridization can have on phenotypic variability. Lastly, we checked for the effect of hybridization on salinity preference a trait used for differentiating one ecotype, the North Sea houting, from other whitefish. We found that three areas with substantial admixture of North Sea houting and Baltic houting (another ecotype) have extremely high variation along the salinity tolerance gradient and what seem to be three different stages of niche separation in the three different populations. This differentiation was also reflected in genetic distances between the intra-population salinity groupings. Combined, our results suggest that genetic and ecological divergence is occurring in the European whitefish complex within Germany and could possibly be linked by the process of ecological speciation in progress. We also found that hybridization is having a substantial effect on ecologically relevant traits and is adding phenotypic variation to some populations which could possibly be facilitating niche separation and ultimately speciation. In order to truly infer divergent ecological selection we must identify the trait being selected for, the selection pressure and the genetic basis of it. We suggest that experimental designs to test our hypotheses are the next step to shed more light on the situation.

Document Type: Thesis (Master thesis)
Thesis Advisor: Eizaguirre, Christophe and Reusch, Thorsten B. H.
Subjects: Course of study: MSc Biological Oceanography
Research affiliation: OceanRep > GEOMAR > FB3 Marine Ecology > FB3-EV Marine Evolutionary Ecology
Date Deposited: 24 Jul 2013 08:51
Last Modified: 10 Jan 2022 10:57
URI: https://oceanrep.geomar.de/id/eprint/21850

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