Biased geographical distribution of mitochondrial DNA that passed the species barrier from mountain hares to brown hares (genusLepus): an effect of genetic incompatibility and mating behaviour?

Abstract

Through interspeci®c hybridization and subsequent backcrossing, genes and genomes may be transferred over the species barrier. In Sweden, the introduced brown hare Lepus europaeus hybridizes with the native mountain hare L. timidus. To investigate the direction and the extent of transfer of mitochondrial DNA (mtDNA) between the species, the mtDNA haplotypes were screened in 522 brown hares and 149 mountain hares from areas of sympatry and allopatry. A total of 51 brown hares with mountain hare mtDNA, but no mountain hares with brown hare mtDNA were detected. Thus, mtDNA transfer over the species barrier is directed from mountain hares to brown hares. We argue that frequency-dependent hybridization and/or interspeci®c male competition mediates this directionality. Further, the percentage of brown hares with transmitted mountain hare mtDNA was lower in areas of former species sympatry (0.6%) compared to areas of current sympatry (15%). Thus, the transferred mtDNA may disappear from brown hare populations if there is no continuous input through hybridization. We suggest that specimens with an alien mtDNA experience a ®tness reduction as a result of a functional incompatibility between the cytoplasmic mitochondrial genomes and the cell nucleus.

Spatial patterns of genetic diversity across European subspecies of the mountain hare, Lepus timidus L.

“…Note that for L. t. hibernicus, where K ¼ 4, two clusters are almost equally likely for most samples except BBN, the most northeasterly sample in the subspecies (Figure 1). (Thulin, 2002;Alves et al, 2003;Melo-Ferreira et al, 2005). For this reason the diversity patterns observed across subspecies could result if introgression occurred from other species into some mountain hare subspecies, but not others.…”

Empirical study of hybrid zone movement

“…In a further 13 hybrid zones, patterns of introgression might be interpreted as evidence for movement: gulls Larus glaucescens and Larus occidentalis (Bell, 1996;Gay, 2006); pocket gophers Thomomys townsendii and Thomomys bottae (Patton, 1993;Patton and Smith, 1993); Thomomys bottae actuosus and Thomomys bottae ruidosae (Ruedi et al, 1997); fish Gambusia affinis and Gambusia holbrooki (Reznick, 1981;Scribner, 1993;Scribner and Avise, 1993;Scribner and Avise, 1994a, b); hares Lepus granatensis/Lepus europaeus and Lepus timidus (Thulin and Tegelströ m, 2002;Melo-Ferreira et al, 2005, 2007; salamander Chioglossa lusitanica North and South forms (Sequeira et al, 2005); mussels Mytilus galloprovincialis and Mytilus edulis (Gardner and Skibinski, 1988;Skibinski and Roderick, 1991;Willis and Skibinski, 1992;Gardner et al, 1993;Wilhelm and Hilbish, 1998;Bierne et al, 2003); beetles Carabus albrechti and Carabus lewisianus (Takami and Suzuki, 2005); lizard Sceloporus grammicus chromosomal races F5 and FM2 (Sites et al, 1996;Marshall and Sites, 2001) cottonwoods Populus angustifolia and Populus fremontii (Keim et al, 1989;Paige et al, 1991;Martinsen et al, 2001).…”

Nonreceding hare lines: genetic continuity since the Late Pleistocene in European mountain hares (Lepus timidus)

“…The brown hare is 567 common throughout western and central Europe whereas the mountain hare is found in 568 northern and north-eastern Europe, as well as in the Alps and British Isles (see Fig. 1 (Alves et al, 2008;Melo-Ferreira et al, 2005), results from northern Europe show that 581 acquired mountain hare mtDNA subsequently disappears from brown hare populations when 582 there is no continuous interspecific gene flow (Thulin & Tegelström, 2002 …”