| Sexual dimorphism has always been a biological question of great concern,and its driving mechanism is one of the indispensable parts to understand the adaptive evolution of creatures.Chiroptera(bat)as the only taxon of mammals that can really fly,its female-biased sexual dimorphism is more attractive than others.However,there are few systematic studies on the driving mechanism of sexual dimorphism in bat which lacked of comparative research on specific taxa.Therefore,in this study,three tube-nosed bats(Murininae)were selected as the research object,and we tried to explore their driving mechanism of sexual dimorphism from interdisciplinary and multi-perspective.Since 2012,our team has been conducting field surveys on forest-type chiroptera resources in south China.45 Harpiocephalus harpia(female: 22;male: 23),47 Murina harrisoni(female: 19;male: 28)and 29 Murina cyclotis(female: 13;male: 16)were collected from Guangdong,Guangxi,Jiangxi,Hunan,Hainan,Guizhou,Hubei,Zhejiang and Yunan province,China.Based on the existing phylogenetic results,H.harpia is located in the basal branch,which means it's an ancient group,while M.harrisoni and M.cyclotis as the representative species of ‘cyclotisgroup',they are not sister groups although their morphology is similar.These three tube-nosed bats both have sexual dimorphism,but their specific characteristics are still indistinct,and their potential driving mechanism and comparative studies haven't reported yet.Therefore,we try to integrate the traditional morphology(external,skull and wing elements),geometric morphology(shape variation of wing),multivariate statistics,phylogeography and ecology(stable isotope analysis)to quantify the sexual size dimorphism and reveal the intersexual differences of ecological adaptation and dispersal.Finally,in order to explore the potential driving mechanism and evolutionary rule of the three tube-nosed bats,we identify the degree of agreement between our results and the three traditional sexual dimorphism driving hypotheses.The main consequences of this study are as follows:(1)Result of phylogeography in H.harpia indicated that mitochondrial COI gene had more complex and obvious population genetic structure than nuclear RAG2 gene.And the results of genetic diversity,genetic distance and population historical dynamics in these two genes also were different.These findings were broadly supported by microsatellite analyses,which indicated that females had a higher degree of genetic differentiation than males,moreover in the analysis of genetic relationship,females were more likely to be related in the same region,while males were mostly in the exotic region,which further suggested that females consistent with strong philopatry,while males tend to dispersal outward.The results were also consistent with the sequences data.We predicted that sex-biased dispersal not only decreased the possibility of inbreeding,but also reduced the intersexual competition in resource utilization,so indirectly supporting the sexual dimorphism hypothesis of ‘Resource utilization stagger';On the other hand,the results of multivariate statistical analysis showed that females were larger than males,and there was specific differentiation between males and females in some indexes related to masticatory force and tooth characteristics,while no significant difference in wing elements and areas,which further supported that there were differences in resource utilization between males and females.The results of geometric morphological analysis showed that the wing shape of females were wider and shorter,which was suitable for increasing flight load,while males were longer and narrower,which was suitable for fast and long distance flight.The pattern of wing shape was consistent with the results of phylogeography and the breeding habits of bats,which supported male-baised dispersal.However,due to the lack of sample size,the results of stable isotope analysis are complicated.Comprehensive the above results,we believed that the driving mechanism of sexual dimorphism in H.harpia was more consistent with the hypothesis of ‘Resource utilization stagger' rather than ‘Big mother' hypothesis.Besides,although the hypothesis of ‘resource competition' among females was consistent with females staying in their birthplaces potentially lead to increased competition,more evidences(such as behavior,genomics etc)were needed to confirm it.(2)Results of phylogeography and geometric morphology in M.harrisoni and M.cyclotis were basically similar to H.harpia,both showing the dispersal pattern with females consistent with strong philopatry and males tending to dispersal outward.However,the results of traditional morphological analysis were different from H.harpia: it was not only had specific intersexual differentiation in skull,but also had absolute and relative differences in wing elements and areas.And females showed a trend of overall amplification.Since females always needed to take care of their cub,the overall amplification of wing morphology was beneficial to improve their reproductive fitness,which was consistent with the ‘Big mother' hypothesis.As for the phenotypic differences of these three tube-nosed bats,the differences in body size might be the part of explanation.Because of the selection pressure on smaller species to reproduction,care and flight carrying of cub were more pronounced than those on larger species,M.harrisoni and M.cyclotis showed more obvious trend of differentiation than H.harpia.There were also some differences in stable isotope composition between male and female.In summary,the sexual dimorphism in M.harrisoni and M.cyclotis was accorded with both the hypothesis of ‘Resource utilization stagger' and ‘Big mother' hypothesis.(3)Sexual dimorphism and its driving mechanism in three tube-nosed bats had interspecific differences,and coupled with their phylogenetic relationships,we thought that sex-biased dispersal behavior caused by reduced intersexual resource competition and/or decreased inbreeding was the common driving factor of sexual dimorphism.And the differences in microhabitats further drived the allometry of bones associated with teeth and occlusal force resulting in resource utilization differences.Lager size of females might be due to the fact that females competed with each other,which was consistent with the hypothesis of ‘resource competition'.As for the derived species(M.harrisoni and M.cyclotis),in addition to according above hypotheses,the more obvious(more indexes had significant differences in external,skull and wing morphology)sexual dimorphism further implied that the differentiation of females in body size,wing morphology and locally relative areas to obtain more reproductive advantages might be the subsequent driving mechanism of sexual dimorphism,leading to more obvious sexual dimorphism. |
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