An analysis of population genetic differentiation and genotype–phenotype association across the hybrid zone of carrion and hooded crows using microsatellites andMC1R

Abstract

The all black carrion crow (Corvus corone corone) and the grey and black hooded crow (Corvus corone cornix) meet in a narrow hybrid zone across Europe. To evaluate the degree of genetic differentiation over the hybrid zone, we genotyped crows from the centre and edges of the zone, and from allopatric populations in northern (Scotland-Denmark-Sweden) and southern Europe (western-central northern Italy), at 18 microsatellites and at a plumage candidate gene, the MC1R gene. Allopatric and edge populations were significantly differentiated on microsatellites, and populations were isolated by distance over the hybrid zone in Italy. Single-locus analyses showed that one locus, CmeH9, differentiated populations on different sides of the zone at the same time as showing only weak separation of populations on the same side of the zone. Within the hybrid zone there was no differentiation of phenotypes at CmeH9 or at the set of microsatellites, no excess of heterozygotes among hybrids and low levels of linkage disequilibrium between markers. We did not detect any association between phenotypes and nucleotide variation at MC1R, and the two most common haplotypes occurred in very similar frequencies in carrion and hooded crows. That we found a similar degree of genetic differentiation between allopatric and edge populations irrespectively of their location in relation to the hybrid zone, no differentiation between phenotypes within the hybrid zone, and neither heterozygote excess nor consistent linkage disequilibrium in the hybrid zone, is striking considering that carrion and hooded crows are phenotypically distinct and sometimes recognised as separate species.

Restricted gene flow and fine-scale population structuring in tool using New Caledonian crows

“…'Introduction' section). Previous genetic studies of other corvids have largely attributed finescale structuring to short dispersal distances, strong philopatry and use of patchy habitats (common ravens, F ST 0 0.032, Fleischer et al 2007; Florida scrub jays Aphelocoma coerulescens, F ST 00.074, Coulon et al 2008; see also Haas et al 2009;Tarr and Fleischer 1999). Cooperative breeding, in which young delay dispersal and assist their parents to raise subsequent broods, is one possible mechanism by which genetic differences could accumulate over small geographic scales (McDonald et al 1999).…”

The dark side of birds: melanism—facts and fiction

“…As variation in MC1R encoded by the extension gene has been demonstrated to be associated with dark and pale plumages, Haas et al (2009) tested whether this also applied to the colour differences between Carrion Crow Corvus corone corone, Hooded Crow C. c. cornix and their hybrids. However, they found neither any evidence of variation in MC1R related to the degree of melanism nor any significant genetic variation in the extension gene between the black and the grey crows.…”

“…The popular hypothesis to explain the differences between them are that they diverged from a common ancestor and, during an extended period of geographical separation, these populations underwent genetic differentiation before meeting again. Genetic studies, however, reveal no significant molecular differentiation (Haring et al 2007, Haas et al 2009, suggesting that the forms have either not been separated, or at least not for long. Another possible scenario, however, is that at some point a colour aberration occurred, probably the melanistic form, and that, due to different behaviour and physiology related to melanism, this form finally evolved into a distinct taxon.…”

An extensive candidate gene approach to speciation: diversity, divergence and linkage disequilibrium in candidate pigmentation genes across the European crow hybrid zone

“…Genetic evidence for the regulation of melanin-based plumage colouration in wild populations is, to date, mostly restricted to one gene, the melanocortin 1 receptor (Mc1r) (for example, Mundy et al, 2004). However, rich resources in vertebrate model species such as mice should allow identification of other genes in species systems for which there is no evidence of an involvement of Mc1r (such as in crows, Haas et al, 2009). Research in laboratory mice has uncovered the identity of many genes in the melanin pigmentation pathway (Bennett and Lamoreux, 2003;Hoekstra, 2006), many of which have the potential to alter pigmentation phenotypes.…”