Water warming: lessons from tilapia’s adaptation

Informations

Funding country

France

Acronym

CLIMSEX

URL

-

Start date

10/1/2015

End date

-

Budget

402,212 EUR

Fundings

Abstract

Water warming due to climate change will have effects on fish reproduction and sex-differentiation. Changes in sex-ratios can strongly impact the effective genetic population size of wild populations, and then the patterns of growth and persistence. In many fish species, high temperatures may induce sex reversal (TISR) in controlled conditions. Within the framework of changes in global and local temperatures, the study of TISR and the consequences of associated fitness at a population level become very relevant in fish. Modelling studies report that besides the short term effects of TISR (or other environmental sex-reversal) on the population sex-ratio, long-term effects can also be expected such as a decrease in male or female genotype frequency. In addition, induced skewed sex-ratios could facilitate the emergence of new sex chromosomes or a shift between a male heterogametic (XX/XY) and a male homogametic (ZZ/ZW) system. For these transitions to occur the heterogametic sex chromosome (the Y or W) cannot be too degenerated. Hence, recombination between the X and Y, usually suppressed in classic XY males, becomes possible in sex-reversed individuals. Such a recombination, followed by natural and sexual selection could prevent the evolutionary decay of the Y chromosome and therefore, TISR could be a ‘fountain of youth’ for sex chromosomes. Thus, TISR could play a role in shaping the genetics, ecology and evolution of sex determination in some populations. A better characterization of TISR effects and the consequences of associated fitness could help in understanding unstable sex-determining systems and sex-determining genes in fish but also allow the protection of vulnerable populations. Lessons can be learnt from the Nile tilapia, a species for which some wild populations have already adapted to extreme temperatures, e.g. hot springs at 36°C. In tilapia, sex is predominantly genetic (genetic sex determination = GSD) with a XX/XY system but temperature can induce sex reversal with high temperatures masculinising some offspring. We have demonstrated that this thermosensitivity exists at different levels in all the wild populations analysed including one adapted to warm temperatures in hydrothermal springs. Moreover, our studies strongly suggested the existence of naturally sex-reversed fish in at least two wild populations. Through progeny testing (a long and tedious approach) on some wild breeders, we identified putative XX males that sired all-female progenies in different wild populations suggesting a significant prevalence of temperature or environmental sex-reversal. However the consequences of TISD and associated fitness on fish are scarce, notably for wild tilapia populations. CLIMSEX will combine the use of wild and domestic populations of interest, important genetic and genomic resources including its genome sequence, and complementary tilapia expertise of the CLIMSEX partners covering population genetics, evolutionary genetics & genomics, genetics & genomics of sex determination/differentiation, thermal biology and reproductive physiology. The project aims to characterize why and how GSD and TISR coexist, and what are the associated benefits/risks for the populations. We will analyse temperature-dependent growth trajectories, thermal preferendum and some reproductive traits of genetic versus temperature-induced males. These studies are important to understand how climate change could impact biodiversity through TISR and its potential demographic consequences on wild populations and how they may respond. Finally, tilapia is a major aquaculture species for feeding the World. High temperature treatment is a possible alternative for the farmers instead of the present sex reversal treatments used to produce male monosex populations. CLIMSEX will give information on possible long term effects of such temperature treatments on the evolution of the sex determination system of the strain.