Caballes Ciemon Frank, Pratchett Morgan S
ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Queensland, Australia.
PLoS One. 2017 Mar 29;12(3):e0173964. doi: 10.1371/journal.pone.0173964. eCollection 2017.
Sporadic outbreaks of the coral-eating crown-of-thorns starfish are likely to be due, at least in part, to spatial and temporal variation in reproductive and settlement success. For gonochoric and broadcast spawning species such as crown-of-thorns starfish, spawning synchrony is fundamental for achieving high rates of fertilization. Highly synchronized gamete release within and among distinct populations is typically the result of the entrainment of neurohormonal endogenous rhythms by cues from the environment. In this study, we conducted multiple spawning assays to test the effects of temperature change, reduced salinity and nutrient enrichment of seawater, phytoplankton, gametes (sperm and eggs), and the combined effect of sperm and phytoplankton on the likelihood of spawning in male and female crown-of-thorns starfish. We also investigated sex-specific responses to each of these potential spawning cues. We found that (1) abrupt temperature change (an increase of 4°C) induced spawning in males, but less so in females; (2) males often spawned in response to the presence of phytoplankton, but none of the females spawned in response to these cues; (3) the presence of sperm in the water column induced males and females to spawn, although additive and synergistic effects of sperm and phytoplankton were not significant; and (4) males are more sensitive to the spawning cues tested and most likely spawn prior to females. We propose that environmental cues act as spawning 'inducers' by causing the release of hormones (gonad stimulating substance) in sensitive males, while biological cues (pheromones) from released sperm, in turn, act as spawning 'synchronizers' by triggering a hormonal cascade resulting in gamete shedding by conspecifics. Given the immediate temporal linkage between the timing of spawning and fertilization events, variability in the extent and synchronicity of gamete release will significantly influence reproductive success and may account for fluctuations in the abundance of crown-of-thorns starfish.
食珊瑚的棘冠海星的零星爆发至少部分可能归因于繁殖和定居成功率的时空变化。对于像棘冠海星这样的雌雄异体且体外受精的物种，产卵同步性是实现高受精率的基础。在不同种群内部和之间高度同步的配子释放通常是环境线索使神经激素内源性节律同步的结果。在本研究中，我们进行了多次产卵试验，以测试温度变化、海水盐度降低、海水营养富集、浮游植物、配子（精子和卵子）以及精子和浮游植物的联合作用对雌雄棘冠海星产卵可能性的影响。我们还研究了对每种潜在产卵线索的性别特异性反应。我们发现：（1）温度突然变化（升高4°C）会诱导雄性产卵，但对雌性的诱导作用较小；（2）雄性常常对浮游植物的存在做出产卵反应，但没有雌性对这些线索做出产卵反应；（3）水柱中精子的存在会诱导雄性和雌性产卵，尽管精子和浮游植物的相加和协同作用不显著；（4）雄性对所测试的产卵线索更敏感，并且很可能比雌性先产卵。我们提出，环境线索通过促使敏感雄性释放激素（促性腺物质）而充当产卵“诱导物”，而来自已释放精子的生物线索（信息素）反过来通过触发激素级联反应导致同种个体释放配子，从而充当产卵“同步器”。鉴于产卵时间与受精事件之间存在直接的时间联系，配子释放程度和同步性的变化将显著影响繁殖成功率，并可能解释棘冠海星数量的波动。
