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New(t)s and views from hybridizing MHC genes: introgression rather than trans-species polymorphism may shape allelic repertoires

Authors

  • K. MATHIAS WEGNER,

    1. Leibniz Institute for Marine Sciences (IFM-Geomar), Evolutionary Ecology of Marine Fishes, Düsternbroker Weg 20, 24105 Kiel, Germany
    2. Alfred Wegener Institute for Polar and Marine Research, Wadden Sea station Sylt, Hafenstrasse 43, 25992 List/Sylt, Germany
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  • CHRISTOPHE EIZAGUIRRE

    1. Leibniz Institute for Marine Sciences (IFM-Geomar), Evolutionary Ecology of Marine Fishes, Düsternbroker Weg 20, 24105 Kiel, Germany
    2. Max Planck Institute for Evolutionary Biology, Evolutionary Ecology, August Thienemannstrasse 2, 24306, Ploen, Germany
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K. Mathias Wegner, Fax: +49 4651 956200; E-mail: mwegner@ifm-geomar.de

Abstract

One of the key features of major histocompatibility complex (MHC) genes is the frequent occurrence of trans-species polymorphism, that is ‘the passage of allelic lineages from ancestral to descendant species’ (Klein et al. 2007). Selectively maintained ancestral polymorphism may, however, be hard to distinguish from introgression of MHC alleles between hybridizing species (Fig. 1). In this issue of Molecular Ecology, Nadachowska-Brzyska et al. (2012) present data that suggest that the latter can be observed in two closely related species of newts, Lissotriton vulgaris (Lv) and L. montandoni (Lm) from south-east Europe. Strikingly, allelic MHC variation displayed more structure between geographically separated populations of L. vulgaris than across species in the hybrid zone. This suggests that high MHC variation in L. montadoni may result from mainly unidirectional gene flow between species, while differentiation between northern and southern populations of L. vulgaris might reflect local adaptation.

Figure 1.

Figure 1.

 Potential mechanisms generating shared repertoires of major histocompatibility complex alleles between southeast European newt species: Trans-species polymorphism (left side) maintaining ancestral polymorphism across speciation events and introgression (right side) where alleles arising in one species after speciation introgress into the other by hybridization. The study Nadachowska-Brzyska et al. 2012 suggests that the latter can be observed in two closely related newt species. Photos by Benny Trapp and Magdalena Herdegen.

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