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

2001年和2004年在实验室条件下研究了雄性对睾丸的投入、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。在这种合作的一妻多夫制鱼类中，很明显，一妻多夫制的两个雄性在睾丸大小上的投入远远超过了不存在精子竞争的一夫一妻制的雄性。而且，一妻多夫的雄性在实验开始一个月后就已经增加了睾丸的大小，这表明它们可以立即改变投入程度。这是第一个证明雄性个体可以根据精子竞争的强度动态改变睾丸投入程度的文献。利用指定的人工巢确定了雌性对父权分布的控制。在这种情况下，对合作繁殖实验鱼（三人组）的结果进行了比较。有领地配偶和小帮手的雌性比有配偶的雌性产卵范围更广。对卵的DNA分析表明：1)一妻多夫雌蜂的卵是由两个雄蜂共同孵出的；2)巢内的卵是由小帮手雄蜂孵出的；这一趋势表明，雌雄同体的雌性在更大范围内产卵，以使两个雄性的卵子受精。雌性对产卵地点的操纵可能为雌性控制两个雄性之间的父权分配提供了机会。当体型较小的雄性产下更多的卵时，它们往往会提供更多的父权照顾。这意味着雌性可以通过对父权的控制来获得更多的父权照顾，就像合作的多雄鸟dunnocks所表明的那样。这项研究将是第一个提供雌性控制鱼类父权的证据。本文通过对同属物种刺桐的交配制度的实地研究发现，刺桐具有多种交配制度，有单偶制、合作多夫制和多妻制。两性间较大的体型差异是导致这种差异的主要生态因素。我们对这一假设进行了验证，使用了同一实验水族箱中3只雄性和3只雌性的j . transcriptus。当所有鱼的大小相似时，单配偶制占优势。当一个雄性比其他雄性大得多时，在所有情况下都会形成一夫多妻制。当雌性占主导地位时，就形成了一妻多夫制。这些结果应该支持这一假设。布氏chalinochromis brichardi具有合作性的多雄交配系统，在这种交配系统中，雌性控制着共同的父权。作为控制，雌性应该得到一个楔形的巢穴，在那里小的贝塔雄可以从占统治地位的阿尔法雄那里寻求庇护。我们对没有这种避难所的楔形巢和宽巢两种巢的雌鸟选择的初步实验1表明，雌鸟选择楔形巢。研究结果表明，雌性控制可能是布里查德的情况，鸟类和哺乳动物中也有合作繁殖的记录。为了更好地理解繁殖系统，人们提出了许多生殖偏态模型。最近，我们的研究小组成员发现，在与不相关的帮助者合作繁殖中，1)帮助者（贝塔雄）分享父权，2)帮助者的数量是有限的，C.brichard有一个。这与生殖偏态模型的预测是一致的。然而，在这些模型中，两个或多个不相关的雄性之间的父权分担机制尚未明确。我们的实验研究表明，女性控制父权的重要性，应该得到更多的重视。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