Sedentary broadcast‐spawning marine invertebrates, which release both eggs and sperm into the water for fertilization, are of special interest for sexual selection studies. They provide unique insight into the early stages of the evolutionary succession leading to the often‐intense operation of both pre‐ and post‐mating sexual selection in mobile gonochorists. Since they are sessile or only weakly mobile, adults can interact only to a limited extent with other adults and with their own fertilized offspring. They are consequently subject mainly to selection on gamete production and gamete success, and so high gonad expenditure is expected in both sexes. We review literature on gonadosomatic index (GSI; the proportion of body tissue devoted to gamete production) of gonochoristic broadcast spawners, which we use as a proxy for gonad expenditure. We show that such taxa most often have a high GSI that is approximately equal in both sexes. When GSI is asymmetric, female GSI usually exceeds male GSI, at least in echinoderms (the majority of species recorded). Intriguingly, though, higher male GSI also occurs in some species and appears more common than female‐biased GSI in certain orders of gastropod molluscs. Our limited data also suggest that higher male GSI may be the prevalent pattern in sperm casters (where only males release gametes).

中文翻译：

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雄性和雌性广播产卵无脊椎动物的性腺支出和性腺体指数（GSI）的演变

久坐的广播产卵海洋无脊椎动物将卵子和精子释放到水中进行受精，对性选择研究特别感兴趣。它们提供了对进化演替的早期阶段的独特见解，导致移动性生殖器中交配前和交配后的性选择经常激烈运作。由于它们是无柄的或只有微弱的移动性，成年人只能在有限的范围内与其他成年人和他们自己的受精后代互动。因此，它们主要受配子产生和配子成功的选择的影响，因此预计两性的性腺支出都很高。我们回顾了关于生殖腺繁殖体的性腺体指数（GSI；用于配子产生的身体组织的比例）的文献，我们将其用作性腺支出的代理。我们表明，此类分类群通常具有较高的 GSI，在两性中大致相等。当 GSI 不对称时，雌性 GSI 通常超过雄性 GSI，至少在棘皮动物（记录的大多数物种）中是如此。然而，有趣的是，较高的雄性 GSI 也发生在某些物种中，并且在某些腹足类软体动物目中似乎比偏向雌性的 GSI 更常见。我们有限的数据还表明，较高的雄性 GSI 可能是精子铸工（只有雄性释放配子）的普遍模式。较高的雄性 GSI 也发生在某些物种中，并且在某些腹足类软体动物目中似乎比偏向雌性的 GSI 更常见。我们有限的数据还表明，较高的雄性 GSI 可能是精子铸工（只有雄性释放配子）的普遍模式。较高的雄性 GSI 也发生在某些物种中，并且在某些腹足类软体动物目中似乎比偏向雌性的 GSI 更常见。我们有限的数据还表明，较高的雄性 GSI 可能是精子铸工（只有雄性释放配子）的普遍模式。