The ins and outs of sex change in medaka fish

The ins and outs of sex change in medaka fish
The teleost fish medaka (Oryzias latices) used in this study. Left: male (XY). Right: female (XX). Female turns into male after starvation during a very early stage of larva. Credit: TANAKA

Larval nutrition plays a role in determining the sexual characteristics of Japanese rice fish, also called medaka (Oryzias latipes), report a team of researchers led by Nagoya University. The findings, published in the journal Biology Open, could further understanding of a rare condition in humans and other vertebrates, where they genetically belong to one sex but also have characteristics of the other.

Decades ago, scientists found that fish often undergo sex reversal in the wild. This involves genetically female larvae (meaning they have two X chromosomes) going on to develop male characteristics, or vice versa. This has made medaka fish a for studying environmental sex development and other biological processes they have in common with vertebrates.

Now, Nagoya University reproductive biologist Minoru Tanaka and colleagues in Japan have gained further insight into the factors that affect medaka sex reversal, potentially providing direction for future research into similar conditions in other species.

Scientists had already discovered that environmental factors, such as temperature changes in the brackish and where medaka fish live, are likely involved in their sex reversal. Tanaka and his team wanted to know if nutrition also played a role.

They starved medaka larvae for five days. This was enough time to affect their metabolism without killing them. Three to four months later, the team examined the fish and found that 20% of the genetically female medaka had developed testes and characteristically male fins. The same did not occur in larvae that were not starved.

Further tests showed that sex reversal in the fish was associated with reduced fatty acid synthesis and lipid levels. Specifically, starvation suppressed a that synthesizes an enzyme called CoA, and disrupted a gene called fasn. These disruptions led to reductions in fatty acid synthesis. The scientists also found that a male gene, called dmrt1, was involved in the female-to-male reversal.

"Overall, our findings showed that the sex of medaka is affected by both the and internal metabolism," Tanaka says. "We believe lipids may represent a novel sex regulation system that responds to nutritional conditions."

The team next plans on identifying other internal factors involved in medaka . Future research should try to find the tissues or organs that sense changes in the internal environment and then produce key metabolites to regulate sex differentiation.


Explore further

Inherent feminizing effect of germ cells—new insights into sex determination

More information: Yuta Sakae et al. Starvation causes female-to-male sex reversal through lipid metabolism in the teleost fish, medaka (Olyzias latipes), Biology Open (2020). DOI: 10.1242/bio.050054
Provided by Nagoya University
Citation: The ins and outs of sex change in medaka fish (2020, May 21) retrieved 27 May 2020 from https://phys.org/news/2020-05-ins-outs-sex-medaka-fish.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
5 shares

Feedback to editors

User comments