Hybrid between Danio rerio female and Danio nigrofasciatus male produces aneuploid sperm with limited fertilization capacity

Abstract

In the Danio species, interspecific hybridization has been conducted in several combinations. Among them, only the hybrid between a zebrafish (D. rerio) female and a spotted danio (D. nigrofasciatus) male was reported to be fertile. However, beyond these investigations, by means of reproductive biology, gametes of the hybrid have also not been investigated genetically. For this study, we induced a hybrid of the D. rerio female and D. nigrofasciatus male in order to study its developmental capacity, reproductive performance and gametic characteristics. Its hybrid nature was genetically verified by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis of the rhodopsin gene. Almost all the hybrids (36/37) were males, and only one was female. Developing oocytes were observed in the hybrid female, but ovulated eggs have not been obtained thus far. Microscopic observation revealed various head sizes of sperm in the hybrid males. Flow cytometry showed that the hybrid males generated aneuploid sperm with various ploidy levels up to diploidy. In backcrosses between D. rerio females and hybrid males, fertilization rates were significantly lower than the control D. rerio, and most resultant progeny with abnormal appearance exhibited various kinds of aneuploidies ranging from haploidy to triploidy, but only one viable progeny, which survived more than four months, was triploid. This suggested the contribution of fertile diploid sperm of the hybrid male to successful fertilization and development.

Genome elimination from the germline cells in diploid and triploid male water frogs Pelophylax esculentus

“…Histological observations confirmed degeneration of some spermatozoa, which suggest that not all aneuploid gametes will survive until mating and fertilization. In fish hybrid males evolving from crosses of different Danio species ploidy disorders were also recorded from below 1C to 2C DNA content an in rare cases diploid sperms gave rise to triploid progeny (Endoh et al, 2020). For such a phenomenon as the production of several types of sperm by one male, Vinogradov et al (1991) proposed the term "hybrid amphispermy".…”

Asymmetric viability in reciprocal crosses of zebrafish Danio rerio and pearl danio Danio albolineatus

“…There are previous reports of hybridizations involving Danio spp. (Endoh et al, 2020;Umezawa et al, 2020) and specifically of hybridizing D. rerio and D. albolineatus. Hart and Cook (1977) were unsuccessful in obtaining hybrids by spawning and therefore utilized in vitro fertilization.…”

Who is the best surrogate for germ stem cell transplantation in fish?

“…Similarly, Wong and Saito (2011) also did not record any hybrid chimeric females after ovarian cell transplantation. In overall, low incidence of hybrid females in danio species was recently reported in cross of zebrafish and spotted danio ( Danio nigrofasciatus ) (Endoh et al, 2020). It is evident that female hybrids are likely to experience more severe gametogenesis alteration than males.…”