Evolutionäre Mechanismen: MHC (major histocompatibility complex) und sein Beitrag zu sozialer Interaktion und Populationsaufspaltung während Speziationsprozessen

Description

In preliminary investigations I have shown that Eurasian perch (<it>Perca fluviatilis</it> L.) of Lake Constance that form local aggregations with kin can olfactory discriminate between kin and non-kin, and additionally between the own and a foreign population that lives in sympatry within the same lake. Specific allelic compositions at MHC (major histocompatibility complex) genes have been shown to play a major role in kin recognition and to influence mate choice decisions in a variety of vertebrate species, including freshwater fishes, by affecting the individual body odour. In this project I want to investigate the role of MHC genes for kin- and population recognition. First, I will test if perch differentiate individuals by "family specific" MHC alleles learned by phenotype matching and use this information for kin recognition. Secondly I develop and test a new hypothesis that kin recognition could be the basal mechanism from which olfactory based population recognition may have derived. There I would show that in species using chemical communication for social interactions like e.g. kin recognition, MHC genes that determine specific odours could be under strong disruptive selection during the speciation process. This could lead to "population specific" MHC genes that can be used to olfactory discriminate between populations and drive reproductive isolation. Molecular genetic investigations about differences in the individual composition of specific MHC alleles within and between the coexisting perch populations of Lake Constance will be combined with behavioural experiments for MHC-mediated kin- and population recognition and mate choice strategies.

Institutions
  • FB Biologie
Publications
    Behrmann-Godel, Jasminca; Gerlach, Gabriele; Eckmann, Reiner(2006): Kin and population recognition in sympatric Lake Constance perch (Perca fluviatilis L.) : can assortative shoaling drive population divergence? Behavioral Ecology and Sociobiology ; 59 (2006), 4. - S. 461-468. - ISSN 0340-5443. - eISSN 1432-0762

Kin and population recognition in sympatric Lake Constance perch (Perca fluviatilis L.) : can assortative shoaling drive population divergence?

×
Prior studies have shown that perch (Perca fluviatilis L.) of Lake Constance belong to two genetically different but sympatric populations and that local aggregations of juveniles and adults contain closely related kin. In this study, we analysed the genetic structure of pelagic perch larvae to investigate if kin-structured shoals already exist during early ontogenetic development or might be the result of homing to natal sites. Analysis of the gene frequencies at five microsatellite loci revealed that three out of five pelagic aggregations of larvae showed significant accumulation of kin. To investigate possible mechanisms of shoal formation, we tested if perch use olfactory cues to<br />recognize their kin. Choice tests in a fluviarium showed preference for odours of unfamiliar kin vs unfamiliar non-kin. Additionally, we showed that perch could differentiate between the odours of the two sympatric populations and<br />significantly preferred unfamiliar and unrelated conspecifics of their own over the foreign population. Our results present a behavioural mechanism that can lead to the observed formation of kin-structured shoals in perch. We further discuss if the ability to discriminate between their own and a foreign population can result in assortative mating within populations and thus form the basis of socially mediated speciation in perch.

Origin (projects)

    Behrmann-Godel, Jasminca; Gerlach, Gabriele; Eckmann, Reiner(2004): Postglacial colonization shows evidence for sympatric population splitting of Eurasian perch (Perca fluviatilis L.) in Lake Constance Molecular Ecology ; 13 (2004), 2. - S. 491-497. - eISSN 1365-294X

Postglacial colonization shows evidence for sympatric population splitting of Eurasian perch (Perca fluviatilis L.) in Lake Constance

×
Previous microsatellite analysis showed that two subpopulations of perch (Perca fluviatilis L.) exist in Lake Constance. This raises questions of whether (i) Lake Constance was colonized by two populations that diverged in allopatry, or (ii) the two subpopulations diverged in sympatry. Sequence analysis of a 365 bp mtDNA fragment (5-end of the D-loop) of perch from Lake Constance and adjacent waters revealed 10 haplotypes. We suggest colonization via the Danube river, based on the frequency and dispersion of haplotypes, and knowledge of the lake s palaeohydrological development. Pairwise FST-values using mitochondrial DNA sequences showed no significant population subdivision. Our study provides strong evidence that subpopulations of perch in Lake Constance have diverged in sympatry.

Origin (projects)

  Behrmann-Godel, Jasminca(2004): Evolutionary mechanisms of population divergence in Eurasian perch (Perca fluviatilis L.)

Evolutionary mechanisms of population divergence in Eurasian perch (Perca fluviatilis L.)

×
The central issue of this thesis is the understanding of evolutionary mechanisms, that maintain and drive the divergence of populations and can lead to sympatric speciation. A former study showed that two populations of perch (Perca fluviatilis L.) co-exist in Lake Constance. For the first time I provide empirical evidence, that socially mediated divergence (kin- and population preference) in combination with ecological factors (difference in spawning times) could explain the origin and persistence of the perch subpopulations. Divergence between perch populations could be reinforced by reduced hybrid fitness.<br />My results support that both populations originated from a single source population because analysis of the variability of mitochondrial DNA (mtDNA D-loop sequencing) showed no difference in haplotype frequencies between the eastern and western subpopulations of perch in Lake Constance. Moreover, perch originated most likely from the Danube River because Danube and Lake Constance perch share the same distinct haplotype, whereas perch from the Rhine (the second possible refuge) lack this special haplotype. This is consistent with the geological history of Lake Constance with a known connection between the lake and the Danube during lake formation in the Pleistocene (app. 15 000 years ago). Subsequent upstream colonization from the Rhine is unlikely because there has always been a impassable waterfall.<br />A microsatellite analysis on the genetic structure of larval perch in the pelagic zone of Lake Constance showed that perch form shoals of closely related conspecifics. To test if this behaviour is due to a preference for members of their own subpopulation, including kin, I investigated active choice for olfactory cues in laboratory reared perch. Juvenile perch were tested in a two-channel flume for preference of odours from different conspecifics of known relatedness. Three different choice experiments were conducted: holding water from kin (three different sibling groups were tested: full-sibs, maternal half sibs or paternal half sibs) was always tested vs. holding water of non-kin belonging to the same subpopulation. Perch significantly preferred kin over non kin, there was no difference between the different kinship tests. In a second experiment population recognition was tested. Juvenile perch significantly preferred unrelated members of their own versus members of the foreign population. From these experiments I conclude that kin and population coherence can be an active choice based on olfactory preference, which could easily lead to assortative mating.<br />An important constraint on disruptive population divergence is selection against hybrids. Therefore I measured the fertilization and hatching success of F1 hybrids of the two populations compared to those within each parental population. Two different F1 hybrids (mother eastern population, father western population and vice versa) were produced by artificial fertilization. Compared to the eastern and western populations, fitness was significantly lower for both hybrids. These laboratory measures of hybrid fitness suggest that some genetic incompatibility has already accumulated in the parental populations. Therefore, genetic divergence between the two perch populations in Lake Constance seems to be underway and is reinforced by reduced hybrid fitness.<br />Differences in lake basin morphology could lead to ecological separation of the two subpopulations based on asynchrony in spawning time/location. In a preliminary morphological analysis slight but significant differences could be found between the two subpopulations. Differences in morphological traits did not affect characters, that are commonly driven by ecological speciation but reflect an accumulation of neutral genetic differences between reproductively isolated subpopulations.<br />To conclude, I provide empirical evidence for a socially mediated divergence, that may drive sympatric speciation of perch: asynchrony in spawning time and location cause ecological separation of perch into subpopulations. The resulting disruptive population divergence is enhanced by olfactory preference for kin and conspecifics of the same population, and is reinforced by selection against hybrids.

Origin (projects)

Funding sources
NameProject no.DescriptionPeriod
Deutsche Forschungsgemeinschaft622/06no information
Further information
Period: 01.04.2006 – 31.03.2010