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性双型的特征通常被认为产生于种内争夺交配优先权的斗争。例如,现生和化石的雄性长鼻类动物具有较大的体型和较粗壮的上门齿。本研究阐释了如下现象:化石象型类动物(Elephantiformes,长鼻类的主要类群)一些性双型特征与其进化历史具有相关性,而与性别竞争并非直接相关。在中新世的葛氏铲齿象(Platybelodon grangeri)和狭齿嵌齿象(Gomphotherium angustidens)中,雄性比雌性倾向于具有进化中更进步的特征,如同雄性在进化中领先雌性一步。这种现象可能与雌性偏好的机制相耦合。在象型类动物进化的早期(繁荣期),性别选择压促使雄性比雌性产生更加显著的进步特征;然而,在它们进化的晚期(衰退期),性别选择压似乎减弱,性别的异时进化也减少。这种新的发现或许在大型有蹄类的演化过程中有一定的普遍意义,因为那些繁荣的类群中通常性双型显著,如鹿科和牛科;而衰落的类群中通常性双型不显著。
Sexual bimodal traits are generally thought to arise from the fight over mate priority. For example, living and fossilized male proboscis animals have larger body sizes and thicker upper teeth. This study illustrates the following phenomena: Elephantiformes (major group of proboscis) Some bi-type features are related to their evolutionary history, but are not directly related to gender competition. In the Miocene Platybelodon grangeri and Gomphotherium angustidens, males tend to have more evolved features than females, as males evolve one step ahead of their females. This phenomenon may be coupled with the female preference mechanism. In the early (prosperous) period of the evolution of the leptotype, the pressure of gender selection led to more pronounced advances in males than females; however, in the late stages of their evolution (recession), the gender selection pressure appears to be diminishing, and heterochronous evolution of sex Also reduce. This new discovery may have some general significance in the evolution of large ungulates, as those that flourish generally have significant billabongs, such as deer and bovine families, whereas the usually bisexual ones in the declining group are insignificant .