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Natural hybridization between endangered and introduced species of Pseudorasbora, with their genetic relationships and characteristics inferred from allozyme analyses

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From 25 populations of Pseudorasbora in Japan, polymorphism at 22 allozyme loci indicated that the level of genetic differentiation between Pseudorasbora parva and Pseudorasbora pumila (D = 0·421–0·517) was greater than that between the two subspecies of P. pumila, P. pumila pumila and P. pumila subsp. (D = 0·164), consistent with morphological differences. While P. parva displayed genetic variation (H = 0·003–0·100) similar to other freshwater fishes, P. pumila pumila and P. pumila subsp. populations showed no genetic variation. In five of the 15 populations collected from the contact zone between P. parva and P. pumila pumila, hybrids were detected by allozyme analyses. All hybrids were presumed to represent the F1 generation, because they were heterozygous at all 12 loci diagnostic between P. parva and P. pumila pumila. Although four populations were characterized by high frequencies of F1 hybrids (c. 40%), only one of the parental species was observed in each case. The results indicated that the two species have hybridized easily under natural conditions, but cannot coexist in the long-term. It is suggested that continued invasion of P. parva would hasten the extinction of P. pumila pumila.

Keywords: Pseudorasbora; allozyme; endangered species; hybridization; introductions; species replacement

Document Type: Regular Paper


Affiliations: 1: Graduate School of Science and Technology, Shinshu University, 3-1-1 Asahi, Matsumoto, Nagano 390-8621, Japan and 2: Department of Fisheries, Faculty of Agriculture, Kinki University, Nakamachi, Nara 631-8505, Japan

Publication date: 2003-07-01

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