Study on social and ecological factors promoting cooperative polyandry in fish and on their reproductive tactics

2001-2004年，在实验室条件下，研究了雄性对睾丸的投资、雌性对领地雄性和辅助雄性之间父权分配的控制以及鱼体大小的影响。在这种合作多夫多妻制的情况下，两只雄性在一夫多妻制下对睾丸大小的投资显著高于在不存在精子竞争的一夫一妻制情况下的雄性。此外，一夫多妻的雄鱼在实验开始一个月后就已经增加了睾丸的大小，这表明他们可以立即改变投资的程度这是第一个文件，个体可以根据精子竞争的强度动态改变睾丸投资。在这种情况下，使用指定的人工巢证实了父权分布的女性控制，并将合作繁殖的实验鱼(TRIO)的结果与…的结果进行了比较更多的配对鱼。具有区域配对雄性和小辅助雄性的雌性比配对的雌性产卵范围更广。卵的DNA分析表明，1)多雄雌成虫的卵由两只雄鸟共同繁殖；2)巢内侧的卵由小帮手雄鸟繁殖，群外卵由大对雄鸟繁殖。这一趋势表明，性欲旺盛的雌性在更大的范围内产卵，以使两只雄性受精。雌性对产卵地点的操纵可能为雌性控制两种雄性之间的父权分配提供了机会。当体型较小的雄性交配出更多的卵子时，它们往往会提供更多的父性照顾。这意味着雌性能够通过其对父亲身份的控制获得更多的父性照顾，正如合作的一夫多妻制鸟类--矮人鸟所表明的那样。这项研究将首次提供雌性在鱼类中控制父权的证据。我们对与J.trascriptus同属的Ornateus的交配系统进行了野外研究，发现前者有多种交配系统，包括一夫一妻、合作一夫多妻和血缘一夫多妻制。这表明引起这种差异的主要生态因素是雌雄个体的大小差异较大。我们用3只雄性和3只雌性的J.trascriptus在同一个实验水族箱中检验了这一假设。当所有鱼的大小相近时，以单性生殖为主。当一个男性比其他男性大得多时，所有的案例都形成了一夫多妻制。当女性体型较大时，就会形成一夫多妻制。这些结果支持这一假说。小菜蛾具有合作性的多夫性交配系统，其中雌性控制着共同的父权。作为对照，雌性应该获得楔形巢穴，在那里小贝塔雄性可以寻求庇护，躲避占主导地位的阿尔法雄性。我们的初步实验一对没有这种避难所的楔形巢和宽巢两种巢的雌性选择进行了研究，结果表明雌性选择楔形巢。这一结果表明，雌性控制可能是布氏梭子蟹的情况。鸟类和哺乳动物中已有合作繁殖的记录。为了更好地理解繁育系统，人们提出了许多生殖偏斜模型。最近，我们研究小组的成员发现，在与无关帮手合作养殖鱼类时，1)帮手(贝塔雄性)分享父子关系，2)帮手数量受到限制，其中一个在C.brichard。这与生殖偏斜模型的预测是一致的。然而，在这些模型中，两个或多个无血缘关系的男性之间的父权分担机制还没有被明确。我们的实验研究表明，女性控制亲子关系的重要性应该得到更多的关注。较少

Male investment to testes, female control of paternity distribution between territorial males and helper males, and effect of fish body size in cooperatively breeding cichlid fish Julidochromis transcriptus were studied in laboratory conditions during 2001 and 2004.In this cooperatively polyandrous fish, it was cleared that both two males in polyandry invested in testes size significantly much more than males in monogamous situation where sperm competition should not exist. Moreover, the polyandrous males have already increased the testes size after one month of the start of experiment, suggesting they can immediately change the degree of investment This is the first document that individual males can dynamically change testes investment according with the intensity of sperm competition.Female control of paternity distribution was confirmed by using designated artificial nests In this case, results obtained from experimental fish of cooperative breeding (trio) were compared with those … More of paired fish. Female with territorial pair male and small helper males spawned egg masses in wider ranges than paired females. DNA analysis of eggs revealed that 1) eggs of polyandrous females were sired by both males, 2) eggs in inner side of nest were sired by small helper males and those in outside of the masses were sired by large pair males. This tendency suggests that potyandryous female spawned eggs in wider range to fertilize the egg by both males. The manipulation of egg depositing site by females may provide the chance of female control of paternity distribution between the two males. When small males sired more number of eggs, they tended to provide more paternal care. This implies that the female afford to obtain more paternal care through her control of paternity, as has been indicated in cooperative polyandrous bird, the dunnocks. This study will be the first that provide evidence of female control of paternity in fish.Our field studies on the mating system of J.ornateus, the congeneric species to J.trascriptus revealed that the former has a variety of mating systems, monogomay, cooperative polyandry and haremic polygamy. It is suggested that the main ecological factor inducing the variation is wide size variation in both sexes. We tested the hypothesis, using J.trascriptus of 3 males and 3 females in the same experimental aquaria. When size of all fish were similar monogomay was predominant. When one male was much larger than others, polygyny was formed in all cases. When a female was dominantly larger, polyandry was made. These results should support the hypothesis.Chalinochrormis brichardi has cooperative polyandrous mating system, in which female control of shared paternity has been suggested. For the control females should obtain wedge shaped nest where small beta males can seek refuge from dominant alpha males. Our preliminary experiment I on female choice of two nests of wedge-shape nest and wide nest which do not have such refuge indicated that the female choose wedge-shaped nests. The results implies that female control may be the case in C.brichard.Cooperative breedings have been documented in birds and mammals. A number of model of reproductive skew have been proposed for understanding of the breeding systems. Recently, members of our research team have revealed that in fish cooperative breeding with unrelated helpers, 1) helpers (beta males) share the paternity, and 2) helper numbers are restricted, one in C.brichard. These are consistent with the prediction from reproductive skew models. However, mechanism of paternity share between two or more unrelated males has not been cleared in these models. Our experimental studies suggest the importance of female control of paternity, which should be paid much more attention. Less