The ecological and life history drivers of the diversification of reproductive modes in early vertebrates are not fully understood. Sharks, rays and chimaeras (group Chondrichthyes) have an unusually diverse variety of reproductive modes and are thus an ideal group to test the factors driving the evolution of reproductive complexity. Here, using 960 species representing all major Chondrichthyes taxa, we reconstruct the evolution of their reproduction modes and investigate the ecological and life history predictors of reproduction. We show that the ancestral Chondrichthyes state was egg-laying and find multiple independent transitions between egg-laying and live-bearing via an intermediate state of yolk-only live-bearing. Using phylogenetically informed analysis, we also show that live-bearing species have larger body size and larger offspring than egg-laying species. In addition, live-bearing species are distributed over shallow to intermediate depths, while egg-layers are typically found in deeper waters. This suggests that live-bearing is more closely associated with pelagic, rather than demersal habitats. Taken together, using a basal vertebrate group as a model, we demonstrat how reproductive mode co-evolves with environmental conditions and life-history traits.

中文翻译：

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鲨鱼和鳐鱼生殖模式的进化。

早期脊椎动物生殖模式多样化的生态和生活史驱动因素尚不完全清楚。鲨鱼、鳐鱼和银鲛（软骨鱼类）具有异常多样化的生殖模式，因此是测试驱动生殖复杂性进化因素的理想群体。在这里，我们利用代表所有主要软骨鱼类群的 960 个物种，重建了它们繁殖模式的进化，并研究了繁殖的生态和生活史预测因子。我们表明，祖先软骨鱼类的状态是产卵，并通过仅卵黄生育的中间状态发现产卵和生育之间的多个独立转变。通过系统发育分析，我们还表明，与卵生物种相比，活体物种具有更大的体型和更大的后代。此外，活体物种分布在浅层到中层深度，而卵层通常出现在较深的水域。这表明活生生的动物与浮游栖息地的关系比与底层栖息地的关系更为密切。综上所述，我们使用基础脊椎动物群作为模型，展示了生殖模式如何与环境条件和生活史特征共同进化。