Smithsonian Tropical Research Institute, Apartado Postal 0843-03092, Balboa, Ancon, Republic of Panama.
Integr Comp Biol. 2013 Oct;53(4):723-35. doi: 10.1093/icb/ict076. Epub 2013 Jun 19.
Molluscs show a wide diversity of sexual systems and strategies. There are both gastropod and bivalve families that are each primarily dioecious, simultaneous hermaphrodites, or sequential hermaphrodites, and other families in which almost every sexual strategy occurs. The multiple evolutionary transitions of sexual systems within molluscs would allow comparative analyses of the associated ecological factors, but data on all but a few groups are too sparse to draw many solid conclusions. The phylogenetic distribution of sexual systems in the Mollusca shows that gastropods and bivalves demonstrate different patterns, possibly associated with the presence/absence of copulation. The distribution of change of sex suggests that, in gastropods, sequential hermaphrodites do not evolve from simultaneous hermaphrodites, and that sex reversal (flip-flopping) occurs in free-spawners but not in copulators. Three well-studied protandrous gastropod groups (calyptraeids, coralliophilids, and patellogastropods) show similar responses to environmental conditions and associations with conspecifics. They all have the following attributes: (1) they are sedentary, (2) they live in groups, patches, or aggregates, and (3) size at sex change varies among sites and among aggregates. In addition the available experimental evidence suggests that (4) the presence of females or large individuals represses growth and sex change of males, and (5) behavior seems to mediate the repressive influence of large females. Available data from other species tend to support these patterns. Finally, the repression of growth of males by females in protandry likely facilitates the evolution of dwarf males.
软体动物表现出广泛的性系统和策略多样性。既有主要为雌雄异体的腹足纲和双壳纲家族，也有同时具有雌雄同体的家族，还有其他家族中几乎每种性策略都存在。软体动物中性系统的多次进化转变可以允许对相关生态因素进行比较分析，但除了少数几个群体之外，几乎所有群体的数据都过于稀疏，无法得出许多确凿的结论。软体动物中性系统的系统发育分布表明，腹足纲和双壳纲表现出不同的模式，这可能与交配的存在/缺失有关。性别的变化分布表明，在腹足纲中，连续雌雄同体不是从同时雌雄同体进化而来的，并且性反转（翻转）发生在自由交配者中，但不在交配者中发生。三个研究充分的先雄腹足纲群体（钙质藻、珊瑚恋物癖和盘足腹足纲）对环境条件表现出相似的反应，并与同种个体相关联。它们都具有以下属性：（1）它们是固着的，（2）它们生活在群体、斑块或聚集体中，（3）性转变时的大小在不同地点和聚集体之间有所不同。此外，现有的实验证据表明，（4）雌性或大个体的存在会抑制雄性的生长和性转变，（5）行为似乎介导了大雌性的抑制影响。其他物种的现有数据往往支持这些模式。最后，雌性对先雄雄性的生长抑制可能促进了矮雄性的进化。
