The Importance of Sperm Limitation to the Evolution of Egg Size in Marine Invertebrates
The Importance of Sperm Limitation to the Evolution of Egg Size in Marine Invertebrates
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DOI：
10.1086/285489
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发表时间：
1993-04
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影响因子：
--
通讯作者：
D. Levitan
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文献类型：
--
作者：
D. Levitan
海洋无脊椎动物卵子大小的种间差异以前被解释为配子质量和数量之间的权衡：产生许多死亡率高的小卵或较少的发育迅速并经历浮游死亡率降低的大卵。这一理论假设卵子100%受精，并预测每一种策略在繁殖过程中投入的每单位能量都会产生类似数量的稳定后代。对这一理论的经验支持一直模棱两可。在这里，我提出了另一种假设：卵子越大，精子的目标就越大，因此受精率就越高。这一理论提出了一种权衡，即生产出许多受精概率较低的小卵子，还是生产出较少受精概率较高的大卵子。这一假设被用三种同类海胆--紫球海胆、法国海胆和海胆海胆--进行了验证，它们的卵体积相差五倍。卵子较大的物种受精率更高，如果假设资源分配均等，产生的受精卵至少与卵子较小、数量更多的物种一样多。这一替代假说可以解释不同物种间卵大小的持续变化，并提供了幼虫和成虫生活史之间的强烈联系。
Interspecific variation in egg size of marine invertebrates has been previously explained by a trade-off between gamete quality and quantity: the production of many small eggs with high mortality or fewer large eggs that develop quickly and experience reduced planktonic mortality. This theory assumes 100% fertilization of eggs and predicts that either strategy results in a similar number of settling offspring per unit of energy invested in reproduction. Empirical support for the theory has been equivocal. Here I offer an alternative hypothesis: larger eggs present a larger target for sperm and thus are fertilized at a higher rate. This theory suggests a trade-off between the production of many small eggs with a low probability of fertilization or fewer large eggs with a higher probability of fertilization. This hypothesis is tested with three congeneric sea urchins, Strongylocentrotus purpuratus, Strongylocentrotus franciscanus, and Strongylocentrotus droebachiensis, with a fivefold difference in egg volume. Species with larger eggs are fertilized at a higher rate and, if one assumes an equal allocation of resources, produce at least as many zygotes as species with smaller, more numerous eggs. This alternate hypothesis can explain continuous variation in egg size between species and provides a strong link between larval and adult life histories.