Abstract
Neural crest cell genes control the migration of neural crest cells to multiple parts of developing vertebrate embryos. A recent hypothesis posits that the “domestication syndrome” characteristic of domesticated animals is driven by selection for tameness acting on neural crest cell genes, particularly those affecting cell migration. This is posited to explain why this syndrome involves many disparate phenotypic effects. These effects can be connected to deficits in neural crest cell migration. This hypothesis predicts that patterns of selection on these neural crest cell genes will differ between domesticated species and related wild species. Specifically, it predicts higher levels of positive selection on these genes in domesticated species, relative to closely related wild species. Here we test this prediction in a comparative framework. We obtained DNA sequences from a public database (NCBI) for eleven key neural crest cell genes from a set of thirty domesticated vertebrates and matched close relatives that remain wild. We used the program Contrast-FEL in the software suite HyPhy to compare the number of sites under positive selection (as measured by non-synonymous to synonymous nucleotide substitution rates across codons) between these two types of taxa in a phylogenetic framework. We found that domesticated lineages showed a consistently higher level of positive selection on these key genes, relative to their closely related wild counterparts. In addition, we found support for relaxation of selection and purifying selection. We argue that this result is consistent with an important role for these genes in the domestication syndrome.
Highlights
The “domestication syndrome” refers to an apparently disconnected set of phenotypic traits that appear to characterize domesticated species, in comparison with their wild relatives
Our results indicated that the signals of positive selection we found are specific to neural crest genes, and are not found in most of the control genes we used for comparison
We have tested a major prediction of the neural crest cell gene hypothesis for the evolution of the domestication syndrome, as proposed by Wilkins et al [2]
Summary
The “domestication syndrome” refers to an apparently disconnected set of phenotypic traits that appear to characterize domesticated species, in comparison with their wild relatives. In addition to tameness (reduced reactive aggression), these traits include other elements of behavior (such as prolongation of juvenile behavior), and aspects of morphology (brain and tooth size, ear and tail size and shape, craniofacial structure), and physiology (levels of andrenocorticotropic hormones and neurotransmitters, frequency of estrus cycles). The association between domestication and a seemingly unconnected suite of characters was noted and investigated by [1], but continues to be a topic of scientific debate to the present [2–4]. Wilkins et al [2] have proposed a novel theory that purports to explain why all of these seemingly disparate features are connected. They take as their starting point the assumption.
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