Baeza J Antonio
Department of Biology, The University of Louisiana at Lafayette, Lafayette, Louisiana 70504-2451, USA.
Evolution. 2006 Sep;60(9):1840-50.
Protandric simultaneous hermaphroditism, as reported for shrimps in the genus Lysmata, is a sexual system in which individuals invariably reproduce as males first and later in life as simultaneous hermaphrodites. I tested three models (i.e., sex-dependent energetic costs, sex-dependent mortality rates and sex-dependent time commitments) in an attempt to explain the adaptive value of protandric simultaneous hermaphroditism in the shrimp L. wurdemanni. Specific assumptions and predictions of each model were evaluated using manipulative experiments. In the laboratory, males grew faster than simultaneous hermaphrodites of the same size and age, an indication that the female function incurs higher energetic costs of reproduction than the male function. Also, large SHPs were more successful in monopolizing food than small males. The sex-dependent growth rate and size-dependent resource holding power agree with predictions of the sex-dependent energetic cost model. The time that simultaneous hermaphrodites required for replenishing their sperm reservoirs after mating as males was much shorter (2 days) than the time required to brood one clutch of embryos (11 days). Also, small simultaneous hermaphrodites experienced heavier mortality due to predatory fishes than large ones. The sex-dependent reproductive time commitment and size-dependent mortality agree with predictions of the sex-dependent time commitment model. Conversely, I found no evidence that the sex-dependent mortality model explains protandric simultaneous hermaphroditism in the studied species. In contrast to model predictions, mortality due to predatory fishes suffered by simultaneous hermaphrodites was not greater than that suffered by males of the same body size. In L. wurdemanni, the relationship between sex-specific investment and reproductive success seems to change during ontogeny in a way that is consistent with an adaptive adjustment of sex allocation to improve age-specific reproductive success.
如对鞭藻虾属虾类的报道，雄性先熟的同步雌雄同体现象是一种性系统，即个体总是先作为雄性进行繁殖，而后在生命后期作为同步雌雄同体进行繁殖。我测试了三种模型（即性别依赖的能量成本、性别依赖的死亡率和性别依赖的时间投入），试图解释雄性先熟的同步雌雄同体现象在伍氏鞭藻虾中的适应性价值。通过操纵性实验评估了每个模型的具体假设和预测。在实验室中，相同大小和年龄的雄性比同步雌雄同体生长得更快，这表明雌性功能比雄性功能产生更高的繁殖能量成本。此外，大型同步雌雄同体在独占食物方面比小型雄性更成功。性别依赖的生长速率和大小依赖的资源占有能力与性别依赖的能量成本模型的预测一致。同步雌雄同体在作为雄性交配后补充精子库所需的时间（2天）比孵化一窝胚胎所需的时间（11天）短得多。此外，小型同步雌雄同体因掠食性鱼类而经历的死亡率比大型同步雌雄同体更高。性别依赖的繁殖时间投入和大小依赖的死亡率与性别依赖的时间投入模型的预测一致。相反，我没有发现证据表明性别依赖的死亡率模型可以解释所研究物种中的雄性先熟的同步雌雄同体现象。与模型预测相反，同步雌雄同体因掠食性鱼类而遭受的死亡率并不高于相同体型雄性所遭受的死亡率。在伍氏鞭藻虾中，特定性别的投资与繁殖成功之间的关系似乎在个体发育过程中发生变化，这种变化方式与性别分配的适应性调整一致，以提高特定年龄的繁殖成功率。
