Prezygotic Barriers to Hybridization in Marine Broadcast Spawners: Reproductive Timing and Mating System Variation
Prezygotic Barriers to Hybridization in Marine Broadcast Spawners: Reproductive Timing and Mating System Variation
复制标题
海洋广播产卵者的合子前杂交障碍：繁殖时间和交配系统变异
作者：
Carla A. Monteiro;E. Serrão;G. Pearson
具有不完全生殖屏障的同域同源组合为研究生态和非生态因素在生殖隔离中所起的作用提供了机会。虽然已知配子释放中的种间不同步和配子不亲和是杂交的前合子障碍，但在植物中，交配系统变异的作用已得到强调。研究了褐藻兄弟种Fucus spiralis， Fucus guiryi（自交雌雄同体）和Fucus vesiculosus（雌雄异株）之间的生殖隔离，因为它们在岩石潮间带形成异交杂交，在广泛的地理范围内保持物种完整性，并且具有不同的交配系统。我们比较了三个物种在不同时间尺度（年/季节、半月/潮汐和单潮时每小时）的生殖同步性（产卵重叠）。在季节（春季至初夏为单峰）和半月时间尺度上，种间放卵模式基本一致。现有资料的综合表明，产卵受半日潮汐和每日明暗线索的控制，而不是直接受半月周期的控制。重要的是，在单次潮汐期间，在小时尺度上检测到的种间时间变化与部分生态前合子杂交屏障一致。该物种的配子释放模式符合幂律分布，表明其生殖同行性较高，而雌雄同体在更宽的潮汐相位范围内产卵的观察结果支持了自交物种比异交物种对同行性的选择约束更弱的假设。同步释放配子对体外受精的成功至关重要，而高能潮间带环境可能只提供有限的繁殖机会窗口。然而，在这些时间窗口内，繁殖时间的微妙变化已经进化，有可能形成杂交的生态障碍。
Sympatric assemblages of congeners with incomplete reproductive barriers offer the opportunity to study the roles that ecological and non-ecological factors play in reproductive isolation. While interspecific asynchrony in gamete release and gametic incompatibility are known prezygotic barriers to hybridization, the role of mating system variation has been emphasized in plants. Reproductive isolation between the sibling brown algal species Fucus spiralis, Fucus guiryi (selfing hermaphrodite) and Fucus vesiculosus (dioecious) was studied because they form hybrids in parapatry in the rocky intertidal zone, maintain species integrity over a broad geographic range, and have contrasting mating systems. We compared reproductive synchrony (spawning overlap) between the three species at several temporal scales (yearly/seasonal, semilunar/tidal, and hourly during single tides). Interspecific patterns of egg release were coincident at seasonal (single peak in spring to early summer) to semilunar timescales. Synthesis of available data indicated that spawning is controlled by semidiurnal tidal and daily light-dark cues, and not directly by semilunar cycles. Importantly, interspecific shifts in timing detected at the hourly scale during single tides were consistent with a partial ecological prezygotic hybridization barrier. The species displayed patterns of gamete release consistent with a power law distribution, indicating a high degree of reproductive synchrony, while the hypothesis of weaker selective constraints for synchrony in selfing versus outcrossing species was supported by observed spawning in hermaphrodites over a broader range of tidal phase than in outcrossers. Synchronous gamete release is critical to the success of external fertilization, while high-energy intertidal environments may offer only limited windows of reproductive opportunity. Within these windows, however, subtle variations in reproductive timing have evolved with the potential to form ecological barriers to hybridization.