This is the main finding of new research led by the ICM-CSIC, which shows that, in sea bass, exposure to heat in grandparents and parents triggers a new compensatory response in their offspring, helping to balance the sex ratio.
A new study led by the Institut de Ciències del Mar (ICM-CSIC) has revealed that the European sea bass fish can compensate for the effects of climate-driven imbalances in sex ratios. The research published in the journal Global Change Biology, demonstrates that successive generations of European Seabass (Dicentrarchus labrax) respond to rising temperatures through transgenerational plasticity, which can mitigate the risk of extreme population imbalances, offering a new perspective on how these species might avoid demographic collapse in a warming ocean.
An unexpected compensatory mechanism
It is well-documented that direct exposure to heat during early development skews fish populations toward males. However, this new work uncovers a parental effect that acts as a corrective force. In this sense, researchers found that the direction of this effect depends on what is called the "sex tendency", i.e., the tendency of individuals of a given family to produce more or fewer females in the offspring.
"We observed that families naturally predisposed to producing more males actually produced overall more females when their ancestors had been exposed to heat," explain Gabriel Ecker-Eckhofen and Silvia Beato, first and second authors of the study, respectively. "This suggests that the thermal history of previous generations can prime the offspring to resist runaway masculinization. This finding is of relevance because such a mechanism could act as a potential buffer against the impacts of climate change".
A decade of research and three generations of fish
The study, carried out in collaboration with the IFREMER experimental station in Palavas-les-Flots in France, and the Institute of Biosciences from São Paulo State University, Brazil, involved more than 3000 fish and lasted more than a decade. The team reared three successive generations (F0, F1, and F2) under controlled conditions, involving 8 combinations of exposures to warmer waters in both the grandparents, parents, and offspring. This allowed to disentangle the effects of ancestral heat from direct exposure. By analysing roughly 1,500 juveniles from the third generation (F2), they proved that the influence of the environment experienced by the grandfather or the father could be just as significant as the water temperature experienced by their offspring during the thermosensitive period, located when fish are larvae.
The study also considered the physiological costs of these thermal shifts. Thus, female development remained largely unaffected, but heat-exposed males showed a significant delay in spermatogenesis at one year of age, suggesting that surviving a heatwave may come with a temporary reproductive trade-off.
Also, for the first time, the work reported effects of sex and heat on the chemical composition of fish gonads. This was made possible by combining scanning electron microscopy with energy dispersive spectroscopy, an analysis that was carried out at ICM’s Electron and Optical Microscopy Service.
Implications for climate resilience and conservation
These findings challenge current models that suggest the possibility of total collapse of temperature-sensitive species. Instead of a simple cumulative decline, the research highlights a frequency-dependent adjustment that pushes populations back toward a 1:1 sex ratio —the biological equilibrium known as Fisher's principle.
"This study shows that at least some species may have an intrinsic capacity to adjust their biology across generations," highlights Francesc Piferrer (ICM-CSIC), the principal investigator of the study.
"However, we also saw that not all families respond the same way, which means that while some are resilient, others may still fall into demographic problems. Therefore, to truly protect marine biodiversity, we must incorporate this multigenerational perspective into our conservation strategies and to determine whether this compensatory mechanism is also observed in other species".
Finally, the results also emphasize that the chemical composition and growth of these fish are primarily driven by their sex rather than temperature alone, reinforcing the idea that targeted regulatory mechanisms —likely epigenetic— are at work to maintain balance without disrupting overall health.