Data from: Polyandry, predation, and the evolution of frog reproductive modes

Frog reproductive modes are complex phenotypes that include egg/clutch characteristics, oviposition site, larval development, and sometimes, parental care. Two evident patterns in the evolution of these traits are the higher diversity of reproductive modes in the tropics and the apparent progression from aquatic to terrestrial reproduction, often attributed to higher fitness resulting from decreased predation on terrestrial eggs and tadpoles. Here, we propose that sexual selection—and not only natural selection due to predation—favors terrestrial breeding by reducing the loss of fitness due to polyandry. To examine this novel selective mechanism, we reconstructed the evolution of reproductive diversity in two frog families (Hylidae and Leptodactylidae) and tested for concerted evolution of egg and tadpole development sites with specific mating behaviors. We found that oviposition and tadpole development sites are evolving independently, do not show the same diversity and/or directionality in terms of terrestriality, and thus may be diversifying due to different selective mechanisms. In both families, terrestrial egg deposition is correlated with amplexus that is hidden from competing males, and in hylids, testes mass was significantly larger and more variable in males with exposed amplexus that are vulnerable to polyandry. Our results indicate that intrasexual selection has been an underappreciated mechanism promoting diversification of frog reproductive modes.蛙类繁殖模式是一类复杂的表型，涵盖卵/卵群特征、产卵位点、幼体发育过程，部分类群还涉及育幼行为。此类性状的演化存在两个显著模式：其一为热带区域的繁殖模式多样性更高；其二为繁殖策略从水生向陆生逐步演化的趋势，该趋势通常被归因于陆生卵与蝌蚪的被捕食压力降低，进而带来适合度提升。本研究提出，性选择——而非仅由捕食引发的自然选择——可通过降低一妻多夫制导致的适合度损失，促进陆生繁殖策略的演化。为验证这一全新的选择机制，我们重构了雨蛙科（Hylidae）与细趾蟾科（Leptodactylidae）两个蛙科的繁殖多样性演化历程，并检验了卵发育位点与蝌蚪发育位点是否与特定交配行为存在协同演化关系。研究结果显示，产卵位点与蝌蚪发育位点的演化彼此独立，二者在陆生适应性层面并未呈现一致的多样性与演化方向，因此其性状分化可能由不同的选择机制驱动。在两个科的类群中，陆生产卵均与可躲避其他雄性竞争的隐蔽抱对（amplexus）相关；而在雨蛙科中，抱对暴露于竞争雄性环境中、易受一妻多夫制影响的雄性，其睾丸质量显著更大且变异程度更高。本研究结果表明，种内性选择是一类长期被低估的、可推动蛙类繁殖模式多样化的演化机制。