A Cryptic Clonal Line of the Loach Misgurnus anguillicaudatus (Teleostei: Cobitidae) Evidenced by Induced Gynogenesis, Interspecific Hybridization, Microsatellite Genotyping and Multilocus DNA Fingerprinting

Abstract

-In Memanbetsu town, Hokkaido island, Japan, a high frequency of natural triploid loaches Misgurnus anguillicaudatus (7.4% on average) was detected by flow cytometry for relative DNA content. Among sympatric diploid females (n=6) from a single population, we found two unique females that laid unreduced diploid eggs. They gave normal diploid progeny even after induction of gynogenesis with genetically inert UV-irradiated sperm. When fertilized with normal loach sperm, some unreduced eggs developed into triploids, but the rest into diploids. Hybridization using goldfish Carassius auratus sperm gave both normal diploid loaches and inviable allotriploid hybrids possessing the diploid loach genome and the haploid goldfish genome. Microsatellite genotyping and DNA fingerprinting demonstrated that the diploid progeny developing from the unreduced eggs were genetically identical to the mother, while the triploids had some of the paternal DNA. These results indicate that the diploid eggs reproduced unisexually as a diploid clone and in other cases developed into triploids after accidental incorporation of sperm nucleus. The presence of at least one clonal line in this area was shown by the identical DNA fingerprint detected in five out of 17 diploid loaches examined.

Simultaneous Mendelian and clonal genome transmission in a sexually reproducing, all-triploid vertebrate

“…In the present paper, we performed sibship analyses with 15 co-dominant microsatellite loci to evaluate genome-wide clonal (males absent), restricted to reptiles [7,8]; Sperm-dependent parthenogenesis (i.e. gynogenesis): clonal, embryogenesis requires trigger from allospecific sperm that is not incorporated (rare 'paternal leakage' might incorporate subgenomic amounts of paternal DNA), occurs in teleost fishes and urodelan amphibians [9]; Kleptogenesis: females acquire full or partial genomes from their mates by a not fully understood mechanism, allowing them to purge genomes from deleterious alleles (here BB); described from urodelan amphibians [10]; Unnamed form of hybridogenesis: clonal diploid eggs are fertilized by sperm from a recombining sexual species that can be diploid or triploid (as in meiotic hybridogenesis); occurs in anuran amphibians and teleost fishes [11][12][13]; Meiotic hybridogenesis: may occur in triploid males and/or females; found in teleost fishes and anuran amphibians [14,15]; ploidy elevation of the diploid offspring, which might produce diploid hybrid gametes, can occur in the next generation (becoming then e.g. ABB 0 ) to restore triploidy (similar to preceding form of hybridogenesis); Pre-equalizing hybrid meiosis: occurring in Batura toads: Both sexes are triploid and exhibit Mendelian segregation and recombination in the B genomes (equivalent to NORþ; this paper), while the A genome (i.e.…”

Chromosome banding and FISH with rDNA probe in the diploid and tetraploid loach Misgurnus anguillicaudatus

“…In wild populations of Japan, most individuals are bisexually reproducing diploid with 2n = 50 chromosomes, but a small number of gynogenetically reproducing clonal diploid individuals have been detected in a few localities by experimental reproduction and molecular genetic analyses (Morishima et al 2002(Morishima et al , 2008. The occurrence of natural triploid and diploid-triploid mosaic individuals has also been recorded at low frequencies in a few localities in Japan (Zhang and Arai 1999;Arai 2003;Morishima et al 2004;Yoshikawa et al 2007).…”

Meiotic hybridogenesis in triploid Misgurnus loach derived from a clonal lineage

“…In the latter case, diploid females (2n ¼ 50) spawn genetically identical, unreduced diploid eggs, most of which develop gynogenetically. However, some eggs produce triploid (3n ¼ 75) progeny following the accidental incorporation of a haploid sperm nucleus after fertilization (Morishima et al, 2002;Itono et al, 2006Itono et al, , 2007. The relationship between atypical reproduction and hybridization is uncertain in the loach because Japanese M. anguillicaudatus has been taxonomically identified as a single species entity (Saitoh, 1989).…”