Study On The Evolution Of Antler Shape And Its Association With Bone Morphogenesis Protein 4 Gene

Antlers are osseous and deciduous cranial appendiages of male deer used as either the weapons for fighting against predators and defensing territory and mates from conspecific males,or the ornamental tools during lekking to females.The evolution of the shape and size of antlers are associated with the evolution of body structure and behavior modes,while the laters are associated with strateggy for habitat adaptation.Therefore,the study of antlers evolution is of essential significance to breakthrough the mystery of deer evolution.However,traditional studies of deer antlers have been constricted with the lack of quantitative description tools of antler shapes.This study proposed such a description tool containing 17 indices that are quantifiable in binary mode.Data were collected on antler specimen of 13 cervid species,based on which clustering analysis was performed using X2 Distance and four clustering algorithms namely the Average Linkage Method,Single Linkage Method,Complete Linkage Method and Ward's Minimum Variance Method.Results showed that,despite of different clutering algorithms,the shapes of antlers were clustered into two major clades,the simple form clade mainly represented by Muntiacini species,and the complex form clade mainly represented by species of Cervini,Alceini and Odocoileini,with a trend transitting from simple form to complex form.Such clustering structure voilated the already established molecular phylogeny of cervids,but fit the facts of morphological variation demonstrating a trustable trend of antler diversification.This set of indices are simple and straight forward to quantify and effective for studying the shapes of antlers.Bone morphogenesis protein 4(BMP 4)plays an important role in facial morphogenesis and evolution of the viscerocranium.Antlers are appendiges of frontal bone.BMP4 was detected actively experssed in growing antlers,suggesting that BMP4 is involved in morphogenesis of antlers.However,it has not been studied if antler shape evolution is associated with BMP4 evolution.In order to test the presence or absence of the association,the phylogenetic relationship of Exon 4,the most variable region of BMP4 gene was studied in 15 cervid species,and compared it to phylogenetic relations of antler morphology and cervid phylogeny.Results showed that phylogenetic trees of antler morphology violated species phylogeny and BMP4 phylogeny,while BMP4 phylogeny also violated species phylogeny.Of the 207 codons of the exon,29 codons revealed significant positive selection with mean probability of 0.891.All results above suggest that morphological variation of antler is results of secondary and individualized adaptive evolution of deer species after speciation.BMP4 is an actively evolving gene driven by positive selection.The selective pressure might be primarily from other morpholigical traits of deers and constrained by functional attributes of antlers for fighting,ornamentation and habitat adaptation.