Diversification of reproductive behavior and evolution of seminal plasma protein in Tangnyikan cichlids

坦噶尼喀湖的慈鱼是特有的，表现出多样化的繁殖行为。精浆蛋白120(SPP120)被预测可以固定和聚集精子。慈鱼表现出独特的产卵行为，即“口头受精”。口交行为的先后顺序为：1)雄性向雌性口送精，2)雌性产卵，取卵至雌性口，3)受精。SPP120可能有助于将精子送到雌性口中，并在产卵前不动。另一方面，坦噶尼喀湖的许多慈鱼并不表现出口腔受精。在这些物种中，精子的快速运动激活和精液的扩散有助于受精成功。因此，SPP120可能对这些“非受精物种”的受精成功没有贡献。也就是说，SPP120的分子进化与产卵行为的多样化有关，但两者之间的关系还不是很清楚。在本项目中，我主要研究了以下几个方面的内容：1)通过水下观察来描述其产卵行为；2)通过基因克隆对SPP120进行分子分析，并对分子进化速率(ω：非同义突变率/同义突变率)进行检验。在水下观察中，在沙子上建立产卵场所的慈鱼并不是直接将精子送到雌性嘴里，而是把精子释放到房间里。雌性在凉亭产卵，受精应该通过预先释放的精子进行。在造房者中，精液应该扩散，因此SPP120的功能修饰被预测为更受欢迎。为了支持这一预测，在这些物种中，几个弓形虫的分子进化(ω)速度加快。这些结果表明，产卵行为的多样化影响了SPP120的分子进化。

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.