Laidre Mark E
Department of Biological Sciences, Dartmouth College, Hanover, NH 03755, USA.
R Soc Open Sci. 2019 Jan 16;6(1):181760. doi: 10.1098/rsos.181760. eCollection 2019 Jan.
Evolution has generated enormous diversity in animal genitalia. However, the importance of private property in driving penis size evolution has rarely been explored. Here, I introduce a novel hypothesis, the 'private parts for private property' hypothesis, which posits that enlarged penises evolved to prevent the theft of property during sex. I tested this hypothesis in hermit crabs, which carry valuable portable property (a shell) and which must emerge from this shell during sex, risking social theft of their property by eavesdroppers. I measured relative penis size (penis-to-body ratio) for = 328 specimens spanning nine closely related species. Species carrying more valuable, more easily stolen property had significantly larger penis size than species carrying less valuable, less easily stolen property, which, in turn, had larger penis size than species carrying no property at all. These patterns in penis size remained even when phylogeny was controlled for, and the patterns were not explained by alternative hypotheses. Instead, the results suggest larger penises evolved as morphological adaptations to facilitate safe sex, in which individuals retain their valuable property by extending a long penis outside the shell to copulate. This hypothesis may likewise apply to other taxa, including those with valuable but non-portable property.
进化造就了动物生殖器的巨大多样性。然而，私有财产在推动阴茎大小进化方面的重要性却很少被探究。在此，我提出了一个新颖的假说，即“为私有财产而生的私密部位”假说，该假说认为增大的阴茎是为防止在交配过程中财产被盗而进化出来的。我在寄居蟹身上对这一假说进行了验证，寄居蟹拥有宝贵的可携带财产（一个外壳），并且在交配时必须从这个外壳中出来，从而冒着财产被偷听者社会性盗窃的风险。我测量了涵盖九个近缘物种的328个标本的相对阴茎大小（阴茎与身体的比例）。携带更有价值、更易被盗财产的物种，其阴茎尺寸显著大于携带价值较低、不易被盗财产的物种，而后者的阴茎尺寸又大于完全不携带财产的物种。即便对系统发育进行了控制，阴茎大小的这些模式依然存在，并且这些模式无法用其他假说解释。相反，结果表明较大的阴茎是作为一种形态学适应进化而来，以利于安全交配，即个体通过将长长的阴茎伸出外壳进行交配来保留其宝贵财产。这一假说同样可能适用于其他类群，包括那些拥有宝贵但不可携带财产的类群。
