Ecological and genetic study on conservation of endangered Pseudorasbora pumila pumila from the extinction by invasion of P.parva

本研究的目的是评估濒危鲤科鱼类Pusorasbora puila puila入侵对其遗传和生态的影响，并提出有效的保护重点。通过生态学和遗传学的研究，获得了以下有价值的结果：1)在1950年S之前仅有南美白对虾分布的北海道和东北地区的一些湖泊和池塘中，发生了物种向小白杨转移或两种共存的现象。2)在两个物种的三个共域种群中，遗传型的个体频率组成(小白对虾、小白对虾、F_1杂种和子代杂交种)存在显著差异：仅庆州公园的小对虾和小对虾两种。3)交配实验表明，体型较大的雄鱼在两个物种中都获得了较高的繁殖成功率，并发生了较强的选配交配。4)雌雄竞争产卵资源的实验室实验表明，体型较大的雄鱼在每个物种获得产卵底物的成功率较高，并且不同物种在放置产卵底物的位置上的成功率不同。5)根据这些结果，有理由认为，通过失去大量雌配子的物种之间的杂交，小青杨应该被小黑杨取代。在可利用的产卵底物差、物理环境变化性低的条件下。这反过来表明，在相反的条件下，这两个物种能够通过各自的强烈换算交配在湖泊和池塘中共存。

The objectives of the present study were to estimate the genetic and ecological effects on an endangered cyprinid species, Pseudorasbora pumila pumila, by invasion of a closely related P.parva, and then to present effective conservation priorities of P.pumila populations. Through both ecological and genetic studies, following valuable results were obtained.1)In some lakes and ponds of Hokkaido and Tohoku District where P.pumila was solely distributed before 1950's, it was found that species displacement into P.parva or coexisting of both species occurred.2)In three sympatric populations of two species, the individual frequency composition of genetic types (P.pumila, P.parva, F_1 hybrid and later filial generation hybrid) were significantly different from each other : only P.pumila and P.parva in the Keijo Park, both species, F_1 hybrid and later filial generation hybrid in the Lake Konuma and Junsai.3)Mate choice experiments indicated that larger males acquired higher reproductive success in both species and that strong assortative mating occurred in both species.4)Laboratory experiments on male-male competition for spawning resources revealed that larger males had higher success in acquisition of spawning substrate in each species, and that the success ratio was different between species in the location of spawning substrate placed in an aquarium.5)Based on these results, it is reasonable to consider that P.pumila should be replaced by P.parva, through hybridization between the species by which much female gamates of the former are lost, under the conditions with poor available spawning substrate and low variable physical environment. This suggests, in turn, that under the opposite conditions the two species are able to coexist in lakes and ponds through strong assotative mating in each species.