Similar patterns of local barn owl adaptation in the Middle East and Europe with respect to melanic coloration

Abstract

The maintenance of phenotypic variation is a central question in evolutionary biology. A commonly suggested mechanism is that of local adaptation, whereby different phenotypes are adapted to alternative environmental conditions. A recent study in the European barn owl (Tyto alba) has shown that natural selection maintains a strong clinal variation in reddish pheomelanin‐based coloration. Studies in the region where phenotypic variation in this owl is the highest in Europe have further demonstrated that dark‐reddish and pale‐reddish owls exploit open and wooded habitats, predate voles and wood mice, and are long‐tailed and short‐tailed, respectively. However, it remains unclear as to whether these traits evolved as a consequence of allopatric evolution of dark colour in northern Europe and white colour in southern Europe, during which owls could have also evolved different morphologies and foraging behaviour. This scenario implies that covariation between coloration and foraging behaviour could be a specificity of the European continent, which is not found in other worldwide‐distributed populations. To investigate this issue, we studied a barn owl population in the Middle East. The results obtained show that, as in Central Europe, dark‐reddish female owls breed more often in the open landscape than their pale‐reddish female conspecifics, their offspring are fed with more voles than Muridae, and they are longer‐winged and longer‐tailed. These findings indicate that, in the barn owl, the association in females between pheomelanin‐based coloration and foraging behaviour and morphology is not restricted to the European continent but may well evolve in sympatry in many barn owl populations worldwide. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106, 447–454.

Sex‐linked inheritance, genetic correlations and sexual dimorphism in three melanin‐based colour traits in the barn owl

“…Spot size is associated, particularly in females, with numerous phenotypic attributes such as growth, appetite and resistance to various stressful factors including free radicals, pathogens and predators (Roulin & Ducrest, ; Van den Brink et al ., ). The number of spots is associated with thermoregulation and sibling competition (A. Roulin, unpublished) and pheomelanin‐based coloration is involved in foraging, with differently coloured individuals being adapted to different ecological conditions (Roulin, ; Charter et al ., ; Dreiss et al ., ). Extra‐pair paternity is rare in this species (Henry et al ., ).…”

Gloger's rule in North American Barn Owls

“…If cold ambient temperatures may indeed select darker reddish over lighter reddish Barn Owls ( Figure 4A), predator-prey interactions may also play a role. In both Switzerland and Israel, dark reddish owls are mainly found in fields, and white owls close to forests, something that could explain why dark and pale reddish Barn Owls have a different diet in these two countries (Roulin 2004b, Charter et al 2012, Dreiss et al 2012. Because Barn Owls in the USA consume more shrews and fewer rodents in regions where it rains more (Clark and Bunck 1991), it is possible that the association between reddish coloration and climate may be driven by predator-prey relationships.…”

Colour‐variable birds have broader ranges, wider niches and are less likely to be threatened

“…Highly colour‐variable species may be able to use broader niches and occupy a larger diversity of habitats if differently coloured individuals are better adapted to use different types of resources or (micro‐)habitats (Forsman et al ., ). Thus, variation in coloration may be indicative of individuals or populations adapted to local conditions, something that finds support in comparative (Galeotti et al ., ; Galeotti & Rubolini, ) and within‐species studies (Charter et al ., ; Dreiss et al ., ). For example, differently coloured individuals may be most cryptic against different backgrounds (Forsman et al ., ).…”