EVOLUTION OF SEX RATIOS IN THE ISOPOD,
EVOLUTION OF SEX RATIOS IN THE ISOPOD,
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等足类动物性别比例的演变，
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通讯作者：
Clifford Johnson
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Venezillo Evergladensis;Clifford Johnson
本文报道了兄弟姐妹个体和成年种群的性别比例，近亲繁殖的影响以及这些特征对等足类动物（Venezillo evergladensis）适合度的可能相互作用。陆地等足类动物的性别决定已被证明是难以解释的。染色体的数量多而尺寸小（在犰狳中为2N = 54）阻碍了对特定性染色体的识别（Teichmann, 1962）。一些工作者认为雌性是异型配子，还有一些人认为雄性是异型配子，尽管所有的论点都是基于间接证据。Bacci（1965）回顾了许多证据。等足类动物的文献中确认了三种雌性类型，雌雄同体产生1:1性别比例的幼崽，单生型和单生型分别产生较高比例的雌性和雄性幼崽。单性生殖这个术语仅仅表示后两种女性类型中的任何一种的存在。不同雌性后代中单基因的原因可能很好地为两性和单基因雌性之间的相对适合度提供了一种见解。第一次认真尝试确定致病机制可以追溯到Vandel（1938）。Vandel（1938, 1939）从法国对毛虫属（Trichoniscus）和犰狳属（Armadillidium）的一系列育种研究中，解释了单系是对雌性传播的细胞质因子的反应。这个因素的存在可能会超越性别决定的核心作用。Howard（1940, 1942, 1958）继续对普通犰狳进行育种研究。他获得了雌雄同体和雌雄同体的系，并发现了母系影响的证据，尽管不能排除父系对女儿类型的影响。他还发现，不同类型的女性之间的兄弟姐妹数量并没有显著的差异，也无法通过得分前的死亡率差异来解释性别差异。最近，Juchault和Legrand（1970,1972）以及Legrand和Juchault（1972）提供了令人信服的证据，证明细胞质因子具有自我复制的感染性，可以改变性别比例。这些研究人员通过实验将雌性从两性交配转化为雌性交配，这种情况类似于影响果蝇性别比例的螺旋体样颗粒（Poulson和Sakaguchi， 1961）。雌雄同体的雌性没有这些微粒。目前尚不清楚是致癌性和非致癌性反映了不同的粒子，还是对同一粒子的遗传不同反应。实验室育种数据显示单基因雌性的频率很高，因此间接证明这种雌性在提供繁殖种群的种群中频率很高。evergladensis的这类数据如下。直接从自然界中采集的雌性样本很少会根据其后代的性别比例进行评分。Vandel（1938, 1939）在88只滴虫（Trichoniscus provisorius）雌性样本中发现41种非遗传性和32种非遗传性，在15只普通犰狳（Armadillidium vulgare）雌性样本中发现这两种类型各有4种。我在佛罗里达州盖恩斯维尔（Gainesville）收集的后一种的30只怀孕雌性中，有9只产生了后代，每窝超过68只，偏离了1:1的比例。05概率水平，4和5分别有较大的女性和男性人数。因此，单性发生的频率能够在……中发挥重要作用
This paper reports sex ratios in individual sibships and in adult populations, the effects of inbreeding and the likely interaction of these features on fitness in the isopod, Venezillo evergladensis. Sex determination in terrestrial isopods has proved difficult to explain. The large number and small size of the chromosomes (2N = 54 in Armadillidium nasatum) have prevented recognition of specific sex chromosomes (Teichmann, 1962). Some workers have argued for heterogametic females, still others for heterogametic males though all arguments have been based on indirect evidence. Much of the evidence is reviewed by Bacci (1965). The isopod literature recognizes three female types, amphogenics producing broods with 1: 1 sex ratios, thelygenics, and arrhenogenics producing broods with higher proportions of females and males respectively. The term, monogeny, simply denotes the presence of either of the latter two female types. The cause of monogeny in the progenies of different females may well provide an insight to the relative fitness between amphogenic and monogenic females. The first serious attempt to identify the causative mechanism dates back to Vandel (1938). Judging from a series of breeding studies in France on the genera Trichoniscus and Armadillidium, Vandel (1938, 1939) explained monogeny as a response to a cytoplasmic factor transmitted by females. The factor's presence could presumably override the nuclear role of sex determination. Howard (1940, 1942, 1958) continued inquiries by breeding studies using Armadillidium vulgare. He obtained lines breeding true for amphogeny and thelygeny and found evidence for a maternal influence, though a paternal effect on the daughter's type could not be excluded. He also found sibship size between female types did not vary in a meaningful way and was unable to explain the absence of one sex by differential mortality prior to scoring. More recently, Juchault and Legrand (1970, 1972) and Legrand and Juchault (1972) provided convincing evidence for cytoplasmic factors having self reproducing, infective properties that act to modify the sex ratios. These investigators experimentally converted females from amphogeny to thelygeny, and the case is similar to the spirochete-like particle affecting sex ratios in Drosophila willistoni (Poulson and Sakaguchi, 1961). Amphogenic females are free of the particles. It is not clear whether thelygenics and arrhenogenics reflect different particles or a genetically different response to the same particle. Laboratory breeding data reveal high frequencies of monogenic females and thus indirectly attest to high frequencies of such females in the populations providing the breeding stocks. Such data for V. evergladensis are given below. Samples of females taken directly from nature have infrequently been scored by the sex ratios of their offspring. Vandel (1938, 1939) found 41 arrhenogenics and 32 thelygenics in a sample of 88 females of Trichoniscus provisorius, and four each of these two types in 15 females of Armadillidium vulgare. Nine of 30 gravid females of the latter species I collected in Gainesville, Florida, produced broods, exceeding 68 young per brood, departing from 1: 1 ratios at the .05 probability level, 4 and 5 having greater female and male numbers respectively. Thus, monogeny occurs in a frequency capable of playing a significant role in