Abstract
The process of domestication has long fascinated evolutionary biologists, yielding insights into the rapidity with which selection can alter behaviour and morphology. Previous studies on dogs, cattle and pigeons have demonstrated that domesticated forms show greater magnitudes of morphological variation than their wild ancestors. Here, we quantify variation in skull morphology, modularity and integration in chickens and compare those to the wild fowl using three-dimensional geometric morphometrics and multivariate statistics. Similar to other domesticated species, chickens exhibit a greater magnitude of variation in shape compared with their ancestors. The most variable part of the chicken skull is the cranial vault, being formed by dermal and neural crest-derived bones, its form possibly related to brain shape variation in chickens, especially in crested breeds. Neural crest-derived portions of the skull exhibit a higher amount of variation. Further, we find that the chicken skull is strongly integrated, confirming previous studies in birds, in contrast to the presence of modularity and decreased integration in mammals.
Highlights
The diversity of domesticated fowl (Gallus gallus) sparked the interest of Charles Darwin, leading him to dedicate an entire chapter to them in The variation of animals and plants under domestication [1]
The most variable part of the chicken skull is the cranial vault, being formed by dermal and neural crest-derived bones, its form possibly related to brain shape variation in chickens, especially in crested breeds
We found that the skull of the domesticated fowl, i.e. chickens, shows greater morphological variation than that of the wild fowl, a result that is consistent with those of many other studies that quantified shape variation of ancestral and domesticated breeds, like horses, pigs or pigeons
Summary
The diversity of domesticated fowl (Gallus gallus) sparked the interest of Charles Darwin, leading him to dedicate an entire chapter to them in The variation of animals and plants under domestication [1]. Chickens have been used as a model organism for the study of vertebrate development [6], but their morphological variability has never been quantified and the skull anatomy of breeds in comparison to fowl has never been described. We explored skull shape of wild and domesticated fowl. The association of traits into modules (=modularity) and low magnitudes of trait intercorrelation (=integration) have together been hypothesized to generate morphological variation [10]. Whether the same pattern is true for domesticated animals, considered by some as a case of rapid evolution [13], has barely been tested
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