|Budget Amount *help
¥3,000,000 (Direct Cost: ¥3,000,000)
Fiscal Year 2003: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 2002: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 2001: ¥1,600,000 (Direct Cost: ¥1,600,000)
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
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