CCMAR-CIMAR, University of Algarve, Gambelas, Faro, Portugal.
PLoS One. 2012;7(4):e35978. doi: 10.1371/journal.pone.0035978. Epub 2012 Apr 26.
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.
同域共存的近缘种具有不完全生殖隔离屏障，为研究生态和非生态因素在生殖隔离中的作用提供了机会。虽然配子释放的种间不同步和配子不相容性是杂交的已知的合子前生殖隔离屏障，但植物中交配系统的变异作用已得到强调。研究了亲缘关系密切的棕色海藻物种 Fucus spiralis、Fucus guiryi（自交雌雄同体）和 Fucus vesiculosus（雌雄异株）之间的生殖隔离，因为它们在潮间带形成近缘杂种，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几个时间尺度（年/季节、半月/潮汐和单个潮汐期间的每小时）之间的生殖同步性（产卵重叠）。在半月时间尺度上，种间的卵子释放模式是一致的。有数据表明，产卵受半昼夜潮汐和每日光暗线索的控制，而不是直接受半月周期的控制。重要的是，在单个潮汐的每小时尺度上检测到的种间时间变化与部分生态合子前杂交障碍一致。物种的配子释放模式与幂律分布一致，表明生殖同步性程度较高，而自交种与异交种的同步性选择性约束较弱的假设得到了观察到的雌雄同体在更广泛的潮汐相位范围内产卵的支持。同步配子释放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，在这些窗口内，生殖时间的细微变化已经进化，有可能形成杂交的生态障碍。
