A melanin‐based trait is more strongly related to body size in the tropics than in temperate regions in the globally distributed barn owl family

Hirzel

et al. 2019

Global Ecol Biogeogr

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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.

Section: Museum Skins Collectionmentioning

confidence: 93%

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

Hirzel

et al. 2019

Global Ecol Biogeogr

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“…This is the case both among and within populations (Romano et al., 2019; Roulin, 2003). In addition, populations show a variable sexual dimorphism in colour traits, with females being darker and showing more and bigger spots than males (Roulin, 2003; Roulin et al., 2018). The degree of reddish colouration is associated with foraging behaviour (San‐Jose et al., 2019), climatic conditions (Romano et al., 2019) and dispersal propensity (Van der Brink et al., 2012).…”

Section: Methodsmentioning

confidence: 99%

“…For each individual, we also measured the diameter of one representative average black spot on the breast and one on the belly to the nearest 0.1 mm using a calliper. This measure has been proven to be highly repeatable (Roulin et al., 2018). We then averaged these values to have a single value of spot size per individual.…”

Section: Methodsmentioning

confidence: 99%

Evolution of wing length and melanin‐based coloration in insular populations of a cosmopolitan raptor

Journal of Biogeography

Roulin

2021

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Aim Insular populations face different conditions than those living on continents, thus, resulting in the evolution of typical insular phenotypes, like smaller body sizes or reduced colourations. However, the generality of the so‐called “island rule” has been questioned, and intraspecific analyses on the effects of insularity on cosmopolitan species are lacking. Here, we tested the predictions of the island rule in the cosmopolitan common barn owl group. Location World. Taxon Barn owl species complex. Methods We compared wing and bill length, as well as melanin‐based plumage traits, between thousands of insular and continental barn owls living in the Afro‐Palearctic region (Tyto alba), in the Americas (Tyto furcata) and in Australasia (Tyto javanica). We also tested whether the difference between insular and continental populations in these phenotypic traits varies among islands/archipelagos of different size and isolation. Results In all the regions, we found differences between insular and continental owls in all the traits but bill length, with insular populations convergently evolving shorter wings and paler colourations. In addition, the difference in wing size between insular and continental populations is particularly marked on small and remote island systems, while melanin‐based traits are less expressed especially on large islands. Main conclusions We thus provide unprecedented evidence that insular conditions drive predictable phenotypic variations, even at the intraspecific level in different biogeographic regions, possibly promoting speciation events. In addition, our results also indicate that selective advantages of a given colouration can arise as the by‐product of positive selection on individuals displaying phenotypic traits which can favour island colonization and are genetically linked to melanization.

“…This categorization was used in several previous studies (e.g. Romano et al, 2021aRomano et al, , 2021bRomano, Séchaud, et al, 2019;Roulin et al, 2018) and has been shown to be highly correlated with reflectance in the visible light when compared to spectrophotometric measures (Dreiss & Roulin, 2010). Moreover, this categorization is correlated with pheomelanin, but not eumelanin (Roulin et al, 2008), thus indicating that it is a good proxy of pheomelanin content.…”

Section: Museum Skin Collection and Their Insular Originmentioning

confidence: 99%

“…In addition, the barn owl shows a large geographical variation in the colouration of the ventral body part, with populations being dark brownish‐reddish and other displaying white and immaculate plumage (see e.g. Romano, Séchaud, et al, 2019; Roulin et al, 2018). The colour of ventral plumage is mainly due to pheomelanin (Roulin et al, 2008; San‐Jose et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Island volcanism predicts pheomelanin‐based plumage colouration in a cosmopolitan raptor

Journal of Biogeography

Montanarella

et al. 2023

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AimPheomelanin is a pigment responsible for yellowish‐to‐reddish colours of vertebrate teguments. Its biosynthesis is favoured under high concentration of intracellular thiols, which, in turn, can depend on the environmental exposure to sulphur. Thus, pheomelanin production should be more intense and frequent in environments characterized by high level of sulphur, such as volcanic regions. In this study, we aimed at addressing this hypothesis by investigating variation in plumage colour of insular populations of the cosmopolitan barn owl (Tyto alba species complex) according to the presence of soils of volcanic origin (i.e. andosols) and recent volcanic activity.LocationWorld.TaxonBarn owl species complex.MethodsWe measured plumage colouration of more than 2000 museum specimens from 50 islands and archipelagos worldwide. We then compared plumage colouration between populations living on volcanic (i.e. where andosols and/or recent volcanic activity are present) and non‐volcanic islands/archipelagos.ResultsConsistently with the prediction, plumage colouration is significantly darker (i.e. pheomelanic) on islands/archipelagos where andosols and/or recent volcanic activity are present than absent, although this environmental factor explains a small fraction of plumage colour variability across islands (<10%). Similar results were obtained when specimens' sex and climatic predictors were included in the analyses.Main ConclusionsBecause excessive intracellular levels of thiols can be toxic, pheomelanin synthesis may function as a mechanism keeping these compounds below the toxicity threshold and limiting their detrimental effects on physiology. Darker plumage may also be favoured because it promotes background matching against the dark environment typical of volcanic islands (dense vegetation cover and/or dark soil). Our results add to the little evidence that the environmental exposure of compounds that are involved in melanin biosynthesis can affect animal pigmentation and suggest that soil composition may be a factor that affects melanogenesis, possibly contributing to generate spatial variation in pheomelanin‐based traits in animals.