Why Do Male Myrmarachne Ant-mimic Jumping Spiders Have Elongated Chelicerae

The world which our lives in is mystery.Nature endowed with various biological form,especially in the animal world,each animal has a feature specific.Sexual dimorphism is widespread in nature,which is a common phenomenon,especially in invertebrates,this phenomenon is more prominent.Usually the animal which have sexual dimorphism trait,males and females also have a bigger difference on the genital form.In those animals,males have very obvious ornaments or weapons,but females do not have the obvious exaggerated trait.There are many relevant sexually dimorphic research at home and abroad.However,few studies have quantified sexual dimorphism in chelicerae size in Myrmarachne.Myrmarachne is the largest of genus in salticidae,more than 200 species are known worldwide.Existing research shows that jumping spiders in invertebrates have very colourful body color and significant sexual dimorphism.In a lot of jumping spiders,the male spiders have exaggerated extended chelicerae while the female jumping spiders are normal.Myrmarachne also exists this phenomenon.However,there are no articles to quantify the characteristics and report the causes and functions of the feature.Therefore,the origin of this feature in the different species of Myrmarachne and its evolutionary trend to is necessary to be studied.In this study,we investigated the existence of chelicerae sexual dimorphism phenomena and their extent by morphological investigation,study on the function of male chelicerae by means of animal behavior,the evolutionary trend of chelicerae length was studied by molecular chemistry.This article selected three species from Hainan and Guizhou provinces,have sex selection test,body measurement,DNA sequence alignment.The study found,there was a significant difference in the absolute length of the male and female chelicerae length and the relative width of the carapace.It indicating that there is a sexual dimorphism trait in chelicerae length.However,there is a difference in the degree of the two species of chelicerae.It is shown that the existence of chelicerae is a process of change.This article set up female-mate choice and male-male competition in the sexual selection test,it is used to verify the function of male chelicerae.In the female-mate choice,we found that the preferred males and non-preferred males in the chelicerae length were significantlydifferent.Indicating that the two species of male and female more preferred with a long chelicerae length of the male as a mating object.In the male-male competition,there were significant differences in the chelicerae length between the winners and the losers,it indicating that Myrmarachne chelicerae in the competition with the role of weapons.Finally,we used molecular biology methods,whole genomic DNA amplification of the Myrmarachne was carried out using 28 S,CO1,Histone3 and ND1,after sequencing,the phylogenetic tree was constructed.And the data of the spider morphology were matched to the phylogenetic tree constructed to explore the evolution trend of the chelicerae length.The study found,the chelicerae length of male and female was fluctuating with the degree of evolution.From what has been discussed above,the male and female spider does have sexual characteristics on the chelicerae length,and the causes of sexual dimorphism are related to male competition and female selection.The length of the chelicerae has an evolutionary state of evolution,may be because too long chelicerae in the survival will have too much consumption in turn to contain the length of the development of chelicerae.This study not only further elucidates the mechanism of animal sexual selection,but also provides a new research direction for systematic evolution of animal sexual selection.