Data from: Phenotypic plasticity in genitalia: baculum shape responds to sperm competition risk in house mice

Males are known to adjust their expenditure on testes growth and sperm production in response to sperm competition risk. Genital morphology can also contribute to competitive fertilisation success but whether male genital morphology can respond plastically to the sperm competition environment has received little attention. Here, we exposed male house mice to two different sperm competition environments during their sexual development and quantified phenotypic plasticity in baculum morphology. The sperm competition environment generated plasticity in body growth. Males maturing under sperm competition risk were larger and heavier than males maturing under no sperm competition risk. We used a landmark-based geometric morphometric approach to measure baculum size and shape. Independent of variation in body size, males maintained under risk of sperm competition had a relatively thicker and more distally extended baculum bulb compared with males maintained under no sperm competition risk. Plasticity in baculum shape paralleled evolutionary responses to selection from sperm competition reported in previous studies of house mice. Our findings provide experimental evidence of socially mediated phenotypic plasticity in male genitalia.

已知雄性会根据精子竞争风险调整其在睾丸发育与精子生成上的资源投入。生殖器形态同样可提升竞争性受精成功率，但目前学界对雄性生殖器形态能否响应精子竞争环境产生表型可塑性的研究仍相对匮乏。本研究中，我们让雄性小家鼠在性发育阶段暴露于两种不同的精子竞争环境，并量化其阴茎骨（baculum）形态的表型可塑性。精子竞争环境对躯体发育产生了可塑性效应：处于精子竞争风险环境下发育成熟的雄性，其体型与体重均显著高于无精子竞争风险环境下发育的雄性个体。我们采用基于地标点的几何形态测量法，对阴茎骨的大小与形态进行量化分析。在控制躯体尺寸差异的前提下，相较于无精子竞争风险环境下的雄性，处于精子竞争风险环境中的雄性，其阴茎骨球相对更为粗壮且远端延伸程度更高。阴茎骨形态的表型可塑性，与既往小家鼠研究中报道的、由精子竞争选择所驱动的演化响应高度一致。本研究结果为雄性生殖器存在社会介导的表型可塑性提供了直接的实验证据。