The Benefits And Costs Of Male Elongated Chelicerae In Ant-like Jumping Spiders

Most animals in nature exhibit sexual dimorphism,especially in invertebrates.In animals with sexual dimorphism,males generally have very exaggerated ornaments or weapons,while females do not.Currently,extensive studies have been focused on documenting sexual dimorphism across animal kingdom,but few studies have investigated the benefits and costs of ornaments or weapons,including elongated chelicerae in ant-like jumping spiders.In many jumping spiders(family Salticidae),males have elongated chelicerae,but females do not.The ant-like salticid spiders of the genus Myrmarachne are the most diverse genus in Salticidae,and Myrmarachne contains 188 known over the world.All Myrmarachne species show extremely sexual dimorphism in cheliceral size,where males but not females have elongated chaelicerae.However,the benefits and costs of male elongated chelicerae in Myrmarachne remain largely understudied.In this thesis,I explored the benefits and costs of male elongated chelicerae in Myrmarachne using two species,M.gisti and M.robusta,from Hubei and Yunnan Provinces,China,respectively.I first confirmed whether Myrmarachne species exhibited sexual dimorphism in cheliceral length.I then determined functional benefits of male elongated chelicerae in male-male competition and female mate-choice using behavoural experiments.Furthermore,I examined the costs of male elongated chelicerae by comparing the prey-capture efficacy between Myrmarachne males and females using both winged and wingless prey.Finally,I explored the developmental costs of the elongated chelicerae by examining the correlations between cheliceral length with neighbouring body parts such as eye size,palp length,foreleg length and abdomen length.I found that there were significant differences in the length of the chelicerae between males and females in both the two species,suggesting that two species of Myrmarachne used exhibit sexually dimorphism in cheliceral length.However,the degree of sexually dimorphism in cheliceral length betweendifferent species was different,indicating that sexually dimorphism in cheliceral length of the genus Myrmarachne varies with species.Moreover,I found that there were significant differences in the length of chelicerae between preferred or non-preferred males,suggesting that females preferred males with longer chelicerae than males with shorter chelicerae.Furthermore,the chelicerae of the winners were significantly longer than those of the losers,suggesting that male chelicerae play a role in male-male competition.However,I found no significant differences in prey-capture efficacy in terms of the success rate of prey-capture and the time taken to capture the prey between males and females regardless of whether a prey was winged or wingless.I also found that in contrast to my prediction,there were positive or no correlations between cheliceral length and other body parts in both males and females.Taken together,I concluded that Myrmarachne species show sexual dimorphism in cheliceral length,and the cheliceral length might be sexually selected through female mate-choice or male-male competition.However,the elongated chelicerae of males may not impair their predation efficiency as well as the growth of other neighbouring body structures.The specific costs of the male elongated chelicerae remain further research.