鞭藻虾性分配研究

Although protandric hermaphroditism has been reported in some decapod crurtaceans, protandric simultaneous hermaphroditism (PSH), a distinguished and rare reproductive system even in animal kingdom, is only reported in the closely related genera of Lysmata and Exhippolysmata. The caridean shrimp first matures as male, then may change to simultaneous hermaphrodite. The euhermaphrodite-phase (EP) shrimp has female external morphology, but with both male and female reproductive capacity. Empirical evidence indicates that timing of sex change varies among the species and populations, and some individuals may delay change sex or not change sex. So far, almost all the studies have focused on single model species. A recent study in a family of protandrous gastropods indicates that study on sex change of closely related species would provide more complete understanding of conditions that favor sex change and of the timing/size of sex change. For the EP, although sex allocation in one of the species has been studied, the method is questionable. The study used ovary and spermatophore weights to represent male and female fitnesses. Fitness is defined as the expected number of offspring produced by an individual. However, it is confused in empirical study. Ovary and testis weight, fertilization rate, hatching rate are often used to mean fitness in the previous studies. It is a challenge to compare the conclusions of sex allocation with the different indicators. In consideration of quality, post-larvae number produced by an individual is the best one to mean fitness. Although an individual has ovary, it may not produce any offspring due to low egg quality. Apparently, using postlarve number to mean fitness would result in more accurate sex allocation. Therefore, the sex allocation in Lysmata shrimp should be re-investigated using post-larvae number to mean fitness, and more species need to be examined to better understand the adaptive significance of PSH, and to provide a base to develop a theory to explain completely PSH. The proposed study will investigate sex allocation (specifically, sex change timing/size and resource allocation in EP) in 5 most common species of Lysmata. Sex change patterns between species within a social system and between the social systems; the role of sex pheromones in controlling sex change will be examined; male fitness between male phase and euhermaphrodite will be compared; and resource allocation in euhermaphrodite between populations will be examined. Specifically, four hypotheses, size-advantage hypothesis, age-dependent euhermaphrodite fitness hypothesis, sex-dependent male fitness hypothesis, and pheromone-induced sex change hypothesis, will be tested.

鞭藻虾类（Lysmata）具有动物界少有的性系统―先雄后常雌雄同体。该属虾类的共同特点是雄性功能先发育成熟，雌性功能后成熟（即性转变），后期同时具有雌雄两种功能（常雌雄同体期）。目前对鞭藻虾的先雄后常雌雄同体性系统的进化意义仍然知之甚少，对这一混合型雌雄同体现象的理论研究相当滞后。科学地解释其性分配不仅可丰富我们对雌雄同体现象的认识，也对探讨生物的性选择和进化过程会有很大的帮助。本项目将研究5种常见鞭藻虾的性分配。研究内容包括：运用性分配理论（Sex Allocation Theory）研究不同密度和不同性比条件下个体性分配；不同生态类型种性转变类型差异；性外激素在性转变中的作用;比较雄虾和常雌雄同体虾的雄性繁殖力差异。本研究将用幼体变态率代表生殖力研究性分配，改变过去性分配研究中生殖力参数使用混乱的状况，为更准确研究性分配提供示范。本研究是首次系统地研究先雄后常雌雄同体的进化意义。

鞭藻虾类（Lysmata）具有动物界少有的性系统―先雄后常雌雄同体。该属虾类的共同特点是雄性功能先发育成熟，雌性功能后成熟（即性转变），后期同时具有雌雄两种功能（常雌雄同体期）。目前对鞭藻虾的先雄后常雌雄同体性系统的进化意义仍然知之甚少。科学地解释其性分配不仅可丰富我们对雌雄同体现象的认识，也对探讨生物的性选择和进化过程会有很大的帮助。本项目研究了5种常见鞭藻虾的性分配。研究内容包括：运用性分配理论（Sex Allocation Theory）研究不同密度和不同性比条件下个体性分配；不同生态类型种性转变类型差异；性外激素在性转变中的作用;比较雄虾和常雌雄同体虾的雄性繁殖力差异。同时，本项目还初步研究了鞭藻虾的性别控制机制，以为今后彻底搞清楚性别控制和性分配机制的关系奠定基础。. 结果表明，鞭藻虾的性变不仅和种群密度有关，而且和其长期野外生活社会环境有关。低密度生活种和高密度生活种在较低密度环境下性变相对快，同等时间内变性率相对高，即L. pederseni ≥ L. ankeri > L. wurdemanni ≥ L. boggessi。和薄荷虾类的四个种比，L. amboinensis的性变相对容易。这应该是一种提高种群繁殖成功率的适应行为。种群补充新个体可有效地促进老种群的性变，其性转变率显著高于未补充新个体的种群。性外激素是鞭藻虾判定群体结构的社会信号（social cue）之一，从而控制性转变。鞭藻虾的的怀卵量和体长呈正线性关系，但高龄虾的孵化率、幼体变态率会下降。雄性期和常雌雄同体期虾的雄性功能差异不显著。. 本研究从生态学角度，并初步从生理学角度揭示了鞭藻虾的性分配机制，为进一步从分子角度揭示高等甲壳类的性别控制根本机制奠定了良好基础。