Data from: More than bindin divergence: reproductive isolation between sympatric subspecies of a sea urchin by asynchronous spawning

The evolution of reproductive barriers is crucial to the process of speciation. In the Echinoidea, studies have focused on divergence in the gamete recognition protein, bindin, as the primary isolating mechanism among species. As such, the capacity of alternate mechanisms to be effective reproductive barriers and the phylogenetic context in which they arise is unclear. Here, we examine the evolutionary histories and factors limiting gene exchange between two subspecies of Heliocidaris erythrogramma that occur sympatrically in Western Australia. We found low, but significant differentiation between the subspecies in two mitochondrial genes. Further, coalescent analyses suggest that they diverged in isolation on the east and west coasts of Australia, with a subsequent range expansion of H. e. erythrogramma into Western Australia. Differentiation in bindin was minimal, indicating gamete incompatibility is an unlikely reproductive barrier. We did, however, detect strong asynchrony in spawning seasons; H. e. erythrogramma spawned over summer while H. e. armigera spawned in autumn. Taken together, we provide compelling evidence for a recent divergence of these subspecies and their reproductive isolation without gamete incompatibility. Western Australian H. erythrogramma may therefore present an intriguing case of incipient speciation, which depends on long-term persistence of the factors underlying this spawning asynchrony.

生殖隔离机制的演化对于物种形成过程至关重要。在海胆纲（Echinoidea）类群中，现有研究多将配子识别蛋白结合素（bindin）的分化视为物种间首要的生殖隔离机制。然而，其他替代机制作为有效生殖隔离的能力，以及其演化出现的系统发育背景，目前仍尚不明确。本研究针对西澳大利亚同域分布的两个红海胆（Heliocidaris erythrogramma）亚种，探讨了二者间基因交流受限的演化历史与影响因素。研究结果显示，两个亚种的两个线粒体基因仅存在微弱但显著的遗传分化。进一步的溯祖分析表明，二者最初在澳大利亚东西海岸隔离分化，随后红海胆指名亚种（H. e. erythrogramma）的分布范围扩张至西澳大利亚。结合素基因的分化程度极低，提示配子不相容并非有效的生殖隔离机制。但本研究检测到二者的产卵期存在显著异步性：红海胆指名亚种于夏季产卵，而红海胆武装亚种（H. e. armigera）则于秋季产卵。综上，本研究为这两个亚种的近期分化以及非配子不相容型生殖隔离提供了强有力的证据。西澳大利亚的红海胆种群或代表一个极具研究价值的初期物种形成案例，该物种形成过程依赖于产卵异步性相关调控因子的长期维持。