The occurrence of hypertetraploid and other unusual polyploid loaches Misgurnus anguillicaudatus among market specimens in Japan

Abstract

Exotic animals may cause a genetic contamination of indigenous species if they escape and reproduce in wild populations. Loach Misgurnus anguillicaudatus and its related species have been imported to Japan for commercial uses. We collected live loach specimens from central wholesale market in Tokyo. Among 451 specimens, ploidy status was examined by DNA content flow cytometry and polyploid loaches with triploid, tetraploid and other higher DNA content ranges were detected. Hyper-triploid and hyper-tetraploid individuals could be easily detected by flow cytometry using a standard eudiploid, eutriploid and eutetraploid controls and then reproductive capacity of these hyper-polyploid males was examined. Sperm of hyper-triploid males did not exhibit active progressive motility and major populations of spermatozoa or spermatozoon-like cells were detected in triploid and hexaploid ranges. Motile haploid spermatozoa were very few in sperm from hyper-triploid males. Therefore, hyper-triploid males were sterile, whereas hyper-tetraploid males produced fertile hyper-diploid spermatozoa with active progressive motility after contact with ambient water. Viable progeny occurred in the cross between normal wild-type diploid female and hyper-tetraploid males, but androgenotes induced by fertilization of UV-irradiated eggs with sperm of hyper-tetraploid males were inviable hyper-diploid. Cytogenetic analyses in such androgenotes indicated that hyper-tetraploid males should produce hyper-diploid spermatozoa with 2n=54, i.e. presence of four supernumerary micro-chromosomes.

Development of nuclear DNA markers to characterize genetically diverse groups of Misgurnus anguillicaudatus and its closely related species

“…Other anguillicaudatus loaches with B-2 nucleus and B-2 mtDNA, which may be genetically close to Continental strains [11], to the indigenous populations of the group B-1 loaches. Carassius auratus, 15: negative control, 16: molecular marker with 100 bp ladder.…”

“…Triploids frequently appear by incorporation of sperm nucleus of diploid wild-type [25]. Resultant males are sterile, while resultant triploid females produce fertile haploid eggs only with the group-A specific nucleus by the atypical reproductive system, meiotic hybridogenesis [11,26]. In contrast, clonal lineages in Ishikawa Prefecture were being unstably maintained and frequencies were lower than those in eastern area of Hokkaido Prefecture.…”

Comparison of spermatozoa parameters, fine structures, and energy‐related factors among tetraploid, hyper‐tetraploid, and hyper‐triploid loaches (Misgurnus anguillicaudatus)

“…No differences in characteristics between diploid and hyper‐diploid spermatozoa were observed in the present study. Cytogenetic observation of artificially induced androgenotes, produced by fertilizing UV‐irradiated loach eggs with spermatozoa of hyper‐tetraploid males, indicated that hyper‐diploid spermatozoon had 54 chromosomes, comprising regular diploid members of chromosomes (2n = 50) and four additional supernumerary micro‐chromosomes (Zhao et al, ). Therefore, these facts suggest that the presence of supernumerary micro‐chromosomes does not have an influence on meiotic and spermatogenetic processes.…”

“…Clonal diploid males were induced from a progeny of clonal females by the administration of 17‐α methyltestosterone during sex differentiation (Yoshikawa et al, , ), while neo‐tetraploids were produced by a cross between wild‐type diploid females (1n eggs) and natural tetraploid males (2n sperm) obtained from the market sample, followed by the inhibition of release of the second polar body (1n) (Arai et al, ; Zhang and Arai, ; Fujimoto et al, ). Tetraploid and hyper‐tetraploid individuals sorted from market specimens produced fertile diploid and hyper‐diploid spermatozoa, while hyper‐triploid individuals generated unusual spermatozoa in which hexaploid‐range cells were dominant (Zhao et al, ).…”

“…In China, a diploid–tetraploid complex exists in wild M. anguillicaudatus populations; bisexually reproducing diploids (2n = 50) and tetraploids (4n = 100) are sympatrically distributed along with a few triploids (3n = 75) (Li et al, , , , , ). Tetraploid and aneuploid (hyper‐triploid and hyper‐tetraploid) individuals were recently detected using DNA content flow cytometry in specimens obtained from the Central Wholesale Market in Tokyo (Zhao et al, ). Thus, their spermatozoa were considered to be good material to evaluate the influence of polyploidy and aneuploidy on spermatogenesis.…”