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

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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.