Evolution of Sex Determination in the Conchostracan Shrimp Eulimnadia texana
Evolution of Sex Determination in the Conchostracan Shrimp Eulimnadia texana
复制标题
壳足虾性别决定的进化
DOI：
10.1086/285476
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发表时间：
1993
期刊：
影响因子：
--
通讯作者：
M. Feldman
中科院分区：
文献类型：
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作者：
S. Otto;C. Sassaman;M. Feldman
Sassaman和Weeks（1993）描述了蛤虾Eulimnadia texana（Packard）的不寻常的混合交配系统，其中自交和异交都发生。系统中有三种交配类型：SS雄性、SS雌雄同体和SS雌雄同体，其中S和S因子作为替代遗传元件遗传，在决定性别方面，S对S隐性。这两种类型的雌雄同体都能够与雄性自交和异交，但都不能使其他雌雄同体的卵受精。因此，雌雄同体只在异交时起雌性的作用。在没有雄性的情况下，SS雌雄同体（两性）可以通过自交产生所有三种类型的后代（大约比例为1/4 SS：1/2 SS：1/4 SS），包括雄性后代，而SS雌雄同体（单基因）繁殖真实。这样的系统类似于隐性雄二分体，雌雄同体不能相互受精（Ross and Weir 1976; Gregorius et al. 1983）。在这篇文章中，我们开发了一个群体遗传学模型，这个育种系统。我们推导出递归方程来描述在交配位点下的性比选择，性别特异性的生存力选择，和近交衰退的动态。在这个模型中，只有两个平衡是可能的：固定在纯合子雌雄同体（异交缺席）和多态性包含所有三个交配类型。因此，多态性稳定的条件决定了我们期望在种群中找到雄性的条件。会有异交的代价（通常被称为性的代价）由这样一个人口产生男性以及雌雄同体所引起的（威廉姆斯1975;梅纳德史密斯1978），这必须通过一些自交的代价来平衡，如近交衰退（Charlesworth 1980; Uyenoyama nd Waller 1991 a，1991 b，1991 c），以解释雄性的持续存在。因此，该系统提供了一个框架，在其中研究的相对成本异交和自交。
Sassaman and Weeks (1993) describe the unusual mixed mating system of the clam shrimp Eulimnadia texana (Packard), in which both selfing and outcrossing occurs. There are three mating types in the system: ss males, Ss hermaphrodites, and SS hermaphrodites, in which the s and S factors are inherited as alternative genetic elements, with s recessive to S in determining sex. Both types of hermaphrodites are capable of selfing and outcrossing with males, but neither are able to fertilize the eggs of other hermaphrodites. Thus, the hermaphrodites only function as females when outcrossing. In the absence of males, Ss hermaphrodites (amphigenics) can, through selfing, produce all three types of offspring (in the approximate ratios of 1/4 ss: 1/2 Ss: 1/4 SS) including male offspring, whereas the SS hermaphrodites (monogenics) breed true. Such a system is analogous to recessive androdioecy with hermaphrodites unable to fertilize one another (Ross and Weir 1976; Gregorius et al. 1983). In this note we develop a population-genetics model of this breeding system. We derive recursive quations to describe the dynamics at the mating locus under sex-ratio selection, sex-specific viability selection, and inbreeding depression. In this model, only two equilibria re possible: fixation on homozygous hermaphrodites (outcrossing absent) and a polymorphism containing all three mating types. The conditions under which the polymorphism is stable therefore determine the conditions under which we expect to find males in the population. There will be a cost of outcrossing (generally known as the cost of sex) incurred by such a population that produces males as well as hermaphrodites (Williams 1975; Maynard Smith 1978), which must be balanced by some cost of selfing, such as inbreeding depression (Charlesworth 1980; Uyenoyama nd Waller 1991a, 1991b, 1991c), in order to account for the continued presence of males. Thus, this system provides a framework in which to study the relative costs of outcrossing and of selfing.