拟髭蟾属角质刺性二态的形成及进化的分子机制

Sexual dimorphism, which refers to any phenotypic difference between sexes of one species, plays important roles in species’ survival and reproduction. It is one of the hotspot issues in the fields of Ecology and Evolutionary Biology. Many amphibians are known to develop sexual dimorphic traits during breeding season, yet it has seldom been studied on the molecular mechanisms for the development and evolution of these traits. Some species of Leptobrachium genus possess male-specific keratinized spines with seasonal development, whereas other species of this genus do not show this trait. Thus, Leptobrachium species provide an ideal taxon for studying the developmental and evolutionary mechanism of sexual dimorphism. We have found that spines’ size was significantly correlated with body size, and hormone pathways related genes showed significantly different expressions between breeding and post-breeding periods. These results indicate the important roles of hormone pathways in developing spines. Therefore, we hypothesize that the development of sexually dimorphic spines is correlated with hormone pathways and this trait has experienced rapid evolution. To test this hypothesis, we will combine the phenotypic analyses, physiological detection and comparative genomic methods to 1) investigate the phenotypic differences of spines among Leptobrachium species, 2) test the correlation between spines’ development and hormone pathways, 3) detect differences of genomic structure between sexually dimorphic and sexually monomorphic species. Based on these analyses, we aim to test the hypothesis of shaping sexually dimorphic spines and to further reveal the molecular mechanism of spines evolution.

性二态是指同一物种的不同性别具有不同表型的现象，它对物种的生存和繁殖至关重要，是生态学和进化生物学领域关注的热点问题。许多两栖动物在繁殖期具有性二态特征，但很少有关于其形成及进化分子机制的研究。拟髭蟾属的部分物种具有雄性特有的角质刺结构，且呈现季节性的“生长-脱落”变化，而部分物种不具有这种结构，是研究性二态形成与进化的理想类群。我们前期研究发现，角质刺大小与身体大小显著正相关，且激素通路基因在生长与脱落阶段的表达水平差异显著，暗示激素通路在角质刺形成过程中的重要作用。因此，我们提出假设：拟髭蟾属角质刺的形成与激素通路有关，该性状在属内经历了快速进化。为了检验这一假设，本项目拟用表型分析、生理检测和比较基因组学方法，研究拟髭蟾属：1)不同物种角质刺的表型差异；2)角质刺的形成与激素通路的关系；3)性二态与性单态物种的基因组结构差异，进而验证角质刺形成的理论假设，揭示角质刺进化的分子机制。

为了研究拟髭蟾属特有的角质刺性二态形成及进化的分子机制，我们利用野外表型观测、比较基因组分析以及转录组基因表达分析相结合的方法，研究了角质刺表型的进化规律、角质刺表型变异相关的基因组差异以及角质刺形成的分子调控通路。研究发现，角质刺起源于原髭蟾与其他髭蟾的共同祖先，并在腾冲拟髭蟾和华深拟髭蟾的进化过程中发生了二次丢失。在拟髭蟾属物种的进化过程中，编码角蛋白的中间丝蛋白家族发生了多次扩张，而调控细胞凋亡的基因家族也在不同物种发生了特异性扩张。进一步的研究发现，串联复制形成的毛发角蛋白基因、神经配体受体互作通路、性类固醇生物合成通路以及Wnt通路在角质刺形成过程中具有重要的调控作用。因此，本研究支持了角质刺性二态的激素调控假说，鉴定了一系列与角质刺形成相关的基因及通路，系统性地揭示了拟髭蟾属角质刺形成及进化的分子机制。