| Budget Amount *help |
¥4,680,000 (Direct Cost: ¥3,600,000、Indirect Cost: ¥1,080,000)
Fiscal Year 2012: ¥1,430,000 (Direct Cost: ¥1,100,000、Indirect Cost: ¥330,000)
Fiscal Year 2011: ¥3,250,000 (Direct Cost: ¥2,500,000、Indirect Cost: ¥750,000)
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| Research Abstract |
Cichlids in Lake Tanganyika are endemic and show diversified reproductive behavior. Seminal plasma protein 120 (SPP120) is predicted to immobilize and aggregate sperm. Cichlids show unique spawning behavior, “oral fertilization” . Sequence of oral fertilization behavior is as follows; 1) male sends sperm to female mouth, 2) female spawns eggs and picks up to female mouth, 3) fertilization occurs. SPP120 may facilitate to send sperm to female mouth, and immobilize until spawning eggs. On the other hand, many cichlids in Lake Tanganyika do not show oral fertilization. In these species, quick sperm motility activation and diffusion of semen contribute fertilization success. Thus, SPP120 may not contribute fertilization success in these “non-oral fertilization species”. In other words, molecular evolution of SPP120 is related to diversification of spawning behavior, but relationship is still not obscure. In this project, I focused on following topics; 1) description of spawning behavior by underwater observation, 2) molecular analyses of SPP120 by cDNA cloning and test of rete of molecular evolution (ω: rate of non-synonymous mutation/synonymous mutation). In underwater observation, cichlids that build spawning site by sand called “bower” did not send their sperm directly to female mouth but release sperm to the bower. Female spawned eggs at the bower, and fertilization is supposed to occur by pre-released sperm. In the bower-builders, semen should diffuse thus functional modification of SPP120 is predicted to be favored. To support this prediction, the rates of molecular evolution (ω) in several bower-builders are accelerated in these species. These results suggested that diversification of spawning behavior affect molecular evolution of SPP120.
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