Climate‐driven convergent evolution of plumage colour in a cosmopolitan bird

Abstract

Aim The investigation of phenotypic diversity across geographical gradients is pivotal to understanding the evolution and adaptive functions of alternative phenotypes. The aim of the present study was to investigate whether the polymorphism in ventral plumage colouration observed in the cosmopolitan common barn owl group is determined by climatic factors, such as temperature and rainfall, consistent with Gloger’s and Bogert’s biogeographical rules. Location World. Time period 1809–2017. Major taxa studied Tyto alba species complex. Methods We analysed the variation in heritable melanin‐based plumage colour according to annual temperature and rainfall in 9,110 individuals of the cosmopolitan barn owl, with three distinct evolutionary lineages representing its entire distribution range: the Afro‐European Tyto alba, occurring between Scandinavia and South Africa, the American Tyto furcata, found from southern Canada to Patagonia, and the Australasian Tyto javanica, living between the Himalayan Plateau and Tasmania. Results Although the geographical distribution of colour morphs is heterogeneous among the lineages, in all of them plumage colour becomes darker with increasing annual rainfall, indicating a convergent selection of darker morphs in humid habitats possibly to improve camouflage against the dark environment and/or to repel water more efficiently. Moreover, in T. alba and T. furcata, melanization increases at decreasing temperature, suggesting its possible role in thermoregulation. Discussion These findings provide convincing evidence of repeated evolution of similar body colouration patterns at a worldwide scale compatible with the main biogeographical rules, while emphasizing the possible role of melanin‐based traits in animal adaptation to climate change.

Geographical variation in bill size provides evidence for Allen’s rule in a cosmopolitan raptor

“…Although the taxonomy of the common barn owl species complex has not yet been determined fully (Uva et al, ), all the phylogenetic analyses (Aliabadian, Alaei‐Kakhki, Mirshamsi, Nijman, & Roulin, ; Uva et al, ; Wink, El‐Sayed, Sauer‐Gürth, & Gonzalez, ) agreed that this group is split into three genetically distinct evolutionary lineages. Irrespective of their taxonomic level, from an evolutionary perspective these lineages can be considered as adaptive radiations occurring simultaneously in geographically separated regions: (a) the Western barn owl ( T. alba ), occurring in Africa, the Arabian Peninsula, the Middle East and Europe up to Southern Scandinavia; (b) the American barn owl ( T. furcata ), living from Southern Canada to Patagonia, including throughout the Caribbean, Galapagos and Hawaiian islands; and (c) the Eastern barn owl ( T. javanica ), inhabiting the part of Asia south of the Himalayan plateau and Australasia, including Tasmania and all the archipelagos in the Pacific Ocean (for further details, see Romano et al, ).…”

“…To this end, we used > 7,600 specimens of the three distinct evolutionary lineages of this species complex, representing their entire range of distribution. Although their taxonomic status has yet to be elucidated fully (see Section 2.1), they can be considered as adaptive radiations occurring in different geographical regions and producing a large variety of local adaptations (see details described by Romano, Séchaud, Hirzel, & Roulin, ; Uva, Päckert, Cibois, Fumagalli, & Roulin, ): the Western (or Afro‐European) barn owl, T. alba , the American barn owl, Tyto furcata , and the Eastern (or Australasian) barn owl, Tyto javanica . The investigation of this model system therefore provides the unique opportunity to compare traits among populations exposed to very different climatic and ecological conditions, and to disclose whether the same abiotic factors promoted the evolution of convergent traits in geographically separated regions.…”

The dark side of coloration: Ecogeographical evidence supports Gloger's rule in American marsupials

“…2018a; Romano et al. 2019). Constantin Gloger (1833), a pioneer of this type of research, observed that coloration in birds varied with local climatic conditions (Delhey 2019).…”

Differential fitness effects of moonlight on plumage colour morphs in barn owls

“…A white plumage might compromise camouflage during the daytime, particularly against harassing competitors, such as carrion crows, Corvus corone . There may also be added benefits of displaying a redder plumage, particularly in harsh conditions when a higher melanin feather content may increase protection against feather abrasion, humidity, and/or cold temperatures 59 . Thus, the hunting-related benefits of a white plumage may trade off against survival to some extent.…”