¹Laboratory of Aquaculture Genetics and Genomics, Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Japan

Correspondence: H Yoshikawa, Laboratory of Aquaculture Genetics and Genomics, Graduate School of Fisheries Sciences, Hokkaido University, 3-1-1, Minato, Hakodate city 041-8611, Japan. E-mail: yosikawa@fish.hokudai.ac.jp

²Current address: Fisheries Laboratory, Kinki University, 3153 Shirahama, Wakayama 649-2211, Japan.

Received 9 September 2007; Revised 19 February 2008; Accepted 26 February 2008; Published online 2 April 2008.

Abstract

Triploid loaches Misgurnus anguillicaudatus are derived from unreduced diploid gametes produced by an asexual clonal lineage that normally undergoes gynogenetic reproduction. Here, we have investigated the reproductive system of two types of triploids: the first type carried maternally inherited clonal diploid genomes and a paternally inherited haploid genome from the same population; the second type had the same clonal diploid genomes but a haploid genome from another, genetically divergent population. The germinal vesicles of oocytes from triploid females (3n=75) contained only 25 bivalents, that is, 50 chromosomes. Flow cytometry revealed that the majority of the progeny resulting from fertilization of eggs from triploid females with normal haploid sperm were diploid. This indicates that triploid females mainly produced haploid eggs. Microsatellite analyses of the diploid progeny of triploid females showed that one allele of the clonal genotype was not transmitted to haploid eggs. Moreover, the identity of the eliminated allele differed between the two types of triploids. Our results demonstrate that there is preferential pairing of homologous chromosomes as well as the elimination of unmatched chromosomes in the course of haploid egg formation, that is, meiotic hybridogenesis. Two distinct genomes in the clone suggest its hybrid origin.