Demonstration of viability and fertility and development of a molecular tool to identify YY supermales in a fish with both genotypic and environmental sex determination

Abstract

The pejerrey possesses a genotypic sex determination system driven by the amhy gene and yet shows marked temperature‐dependent sex determination. Sex‐reversed XY females have been found in a naturally breeding population established in Lake Kasumigaura, Japan. These females could mate with normal XY males and generate YY “supermale” individuals that, if viable and fertile, would sire only genotypic male offspring. This study was conducted to verify the viability, gender, and fertility of YY pejerrey and to develop a molecular method for their identification. Production of YY fish was attempted by crossing a thermally sex‐reversed XY female and an XY male, and rearing the progeny until sexual maturation. To identify the presumable YY individuals, we first conducted a PCR analysis using amhy‐specific primers to screen only amhy‐positive (XY and YY) fish. This screening showed that 60.6% of the progeny was amhy‐positive, which suggested the presence of YY fish. We then conducted a second screening by qPCR in order to identify the individuals with two amhy copies in their genome. This screening revealed 13 individuals, all males, with values twice higher than the other 30 amhy‐positive fishes, suggesting they have a YY complement. This assumption as well as the viability, fertility, and “supermale” nature of these individuals was confirmed in progeny tests with XX females that yielded 100% amhy‐positive offspring. These results demonstrate that qPCR can obviate progeny test as a means to identify the genotypic sex and therefore may be useful for the survey of all three possible genotypes in wild populations.

The Duplicated Y-specific amhy Gene Is Conserved and Linked to Maleness in Silversides of the Genus Odontesthes

“…A comparative analysis between species that takes the type of habitat into consideration points to a trend of higher sex reversal rates in inland waters as compared to marine or estuarine environments. Sex reversal occurred in both directions in O. humensis and O. mirinensis , with XY/YY females (feminization) and XX males (masculinization), similarly to the reported in O. bonariensis [11,17], which also inhabits shallow lakes. It is still unknown if such sex-reversed animals are formed naturally as part of the species reproductive strategy or if they are the consequence of changes in natural environments, such as global climate change.…”

“…The silversides (Atheriniformes) stand out among the group of teleosts with temperature-dependent sex determination, because of the high sensitiveness of their gonads to both high (masculinizing) and low (feminizing) temperatures during early life [22,23]. The discovery of the testis-determining gene amhy in some of these species has provided a valuable tool in the research on interactions between sex determination mechanisms in this group of fishes [11,12,17]. The presence of amhy orthologue was investigated in South American silversides in order to increase the usefulness of silversides on sex determination research and to try to trace back the evolution of amhy .…”

“…For example, amhy could be used to detect phenotypic/genotypic sex mismatches such as (sex-reversed) XX males or XY females and study their association with unusual environment conditions and/or chemical pollutants with endocrine-disrupting properties. In addition, in O. bonariensis , the amhy gene can be used to detect YY genotypes, which are expected from mating between sex-reversed XY females and XY males, and that are both viable and fertile in this species [17].…”

Mismatches between the genetic and phenotypic sex in the wild Kou population of Nile tilapia Oreochromis niloticus

“…In several fish species such as guppy Poecilia reticulata , medaka O. latipes , pejerrey Odontesthes bonariensis , goldfish Carassius auratus , rainbow trout Oncorhynchus mykiss , and Nile tilapia Oreochromis niloticus , gene content is so similar between the X and Y chromosomes that it allows the YY male to be viable and fertile (Devlin & Nagahama, 2002). Furthermore, the process of sex determination and sex differentiation in fish is extremely flexible leading to discordance between the sexual phenotype and the sexual genotype (Baroiller & D’Cotta, 2001; Devlin & Nagahama, 2002; Baroiller et al, 2009; Heule, Salzburger & Böhne, 2014; Baroiller & D’Cotta, 2016; Hattori et al, 2018).…”

Spatiotemporal Correlations between<b><i> amh</i></b> and <b><i>cyp19a1a</i></b> Transcript Expression and Apoptosis during Gonadal Sex Differentiation of Pejerrey, <b><i>Odontesthes bonariensis</i></b>

“…On the other hand, monosex or highly sex-skewed populations can be easily obtained at low feminizing and high masculinizing temperatures during the critical period of sex determination [Strüssmann et al, 1996a[Strüssmann et al, , 1997Zhang et al, 2018]. Moreover, sex reversal can be monitored at the individual level by comparison of the phenotypic (gonadal) sex with the genotypic background (presence or absence of amhy ) [Yamamoto et al, 2014;Hattori et al, 2018]. With these characteristics, the pejerrey seems to be an excellent model for the study of the molecular processes involved in the interactions between ESD and GSD and to examine the ecological implications of TSD in wild populations .…”