No association between candidate genes for colour determination and color phenotype in Hierophis viridiflavus, and characterization of a contact zone

Genetic and phenotypic differentiation in allopatric conditions can be explained eitherby neutral phenomena or adaptative processes driven by selection. In reptiles,coloration can affect aspects directly related to their survival, representing a classicalcharacter under selection. In this context, secondary contact areas are natural laboratoryto understand evolutionary processes underlying genetic permeability, especiallywhen populations differ in phenotypic traits such as coloration. The western whipsnake Hierophis viridiflavus presents two divergent mitochondrial clades, characterizedby the presence of one of two main color phenotypes, namely one with black andyellow stripes and a fully melanic one. Here, we investigated whether melanogenesislinkedgenes are determinant of the chromatic differences observed across the phenotypicvariation of the species. In addition, we used a multilocus dataset, including134 original ND4 sequences, to better define the overall genetic structure and toprovide a characterization of a contact zone identified in Central Italy by estimatingthe amount of nuclear gene exchange. While we found no evidence supporting adirect association between target genes and coloration, a non-synonymous substitutionpolymorphism, at high frequency, was detected in the ? melanocyte-stimulatinghormone whose possible function has been discussed. Concerning the genetic structure,both mtDNA and nuDNA were partly concordant indicating introgression eventsoccurring at the contact zone. When we measured the nuclear gene flow, we found asignificant amount of gene exchange, mainly guided from one clade to the other, thatis, asymmetric. These results might suggest the presence of ecological and/or behavioralprocesses driving the observed directional gene flow.