Abstract
Domestication begins with the selection of animals showing less fear of humans. In most domesticates, selection signals for tameness have been superimposed by intensive breeding for economical or other desirable traits. Old World camels, conversely, have maintained high genetic variation and lack secondary bottlenecks associated with breed development. By re-sequencing multiple genomes from dromedaries, Bactrian camels, and their endangered wild relatives, here we show that positive selection for candidate genes underlying traits collectively referred to as ‘domestication syndrome’ is consistent with neural crest deficiencies and altered thyroid hormone-based signaling. Comparing our results with other domestic species, we postulate that the core set of domestication genes is considerably smaller than the pan-domestication set – and overlapping genes are likely a result of chance and redundancy. These results, along with the extensive genomic resources provided, are an important contribution to understanding the evolutionary history of camels and the genomic features of their domestication.
Highlights
Domestication begins with the selection of animals showing less fear of humans
The second hypothesis proposed by Wilkins et al.[3] predicts that domestication syndrome’ (DS) is a consequence of mild deficits in neural crest cells during embryonic development; a product of artificial selection for behavior on standing genetic variation
Our collection included representatives of all three extant species (Fig. 1a), C. dromedarius (n = 9), C. bactrianus (n = 7), and C. ferus (n = 9). In both domesticated varieties (C. dromedarius and C. bactrianus), we sampled across geographical regions in an attempt to minimize effects of genetic drift[8]
Summary
Domestication begins with the selection of animals showing less fear of humans. In most domesticates, selection signals for tameness have been superimposed by intensive breeding for economical or other desirable traits. By resequencing multiple genomes from dromedaries, Bactrian camels, and their endangered wild relatives, here we show that positive selection for candidate genes underlying traits collectively referred to as ‘domestication syndrome’ is consistent with neural crest deficiencies and altered thyroid hormone-based signaling. The domestication of animals has led to a suite of morphological, physiological, and behavioral changes common to many species These shared traits—including tameness, changes in coat color, modified reproductive cycles, altered hormone and neurotransmitter levels, and features of neotenization—are collectively referred to as the ‘domestication syndrome’ (DS)[3]. Comparisons between genomes of village dogs and wolves highlighted the role of neural crest cell migration, differentiation, and development in dog domestication[9] Evidence for both hypotheses exists, they are not necessarily mutually exclusive, and the relative contribution of each may vary along a continuum[5].
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