How Climate Change Affects Fish Births and Hormones

Jim Crocker
25th March, 2024

How Climate Change Affects Fish Births and Hormones

New research on fish like the medaka (Oryzias latipes) reveals that a population's reproductive survival in warming waters is determined by the unique heat sensitivity of its internal hormone pathways, a key trait that dictates its ability to adapt to climate change.

Photo adapted from: Junichi Mandai / CC BY (Source)

Key Findings

  • Study from California Polytechnic State University shows how heat affects fish reproduction
  • Fish hormone pathways vary in heat sensitivity, impacting their reproductive success
  • Some fish may adapt to warmer temperatures through changes in hormone pathways
Reproduction is a fundamental process for the survival of species, and in the world of fishes, it's particularly sensitive to environmental cues, notably temperature. As the Earth's climate changes, with more frequent and intense heat waves, understanding how fish reproduction is affected is critical. Researchers from California Polytechnic State University have delved into this issue, examining the role of hormone pathways in fish reproduction and how they respond to elevated temperatures[1]. The study's central concern is the thermal sensitivity of endocrine pathways, which are like the body's hormone highways, regulating crucial reproductive functions such as sex determination, the creation of eggs and sperm (gametogenesis), and the timing of spawning. These pathways are not uniform across fish species; they vary and evolve, shaping how different fish populations react to temperature changes. Earlier research has shown that temperature can drastically influence the sex determination process in some fish species. For instance, in the pejerrey fish, high and low temperatures can induce the development of testicular or ovarian tissues, respectively, during a critical period when sex is being determined[2]. Similarly, other studies have noted that genes in the TGF-β signaling pathway often emerge as master regulators of sex in fish, with temperature having the power to sway sex determination even in species with sex chromosomes[3]. Adding to this, there's evidence that thyroid hormones, which are involved in metabolism and growth, may also play a role in temperature-induced sex reversal. In the medaka fish, for example, thyroid hormones were found to be active in males during gonadal development, and exposure to high temperatures upregulated genes related to both thyroid and stress axes, leading to increased levels of the thyroid hormone T3[4]. The current study by California Polytechnic State University builds on these findings by exploring how different fish species' hormone pathways might reach a temperature maximum for reproductive success. This threshold is the highest temperature at which a fish can reproduce effectively, and it's shaped by the sensitivity of the hormone pathways to temperature. The study suggests that for fish populations that can't migrate to cooler waters, surviving in a warming world may depend on the adaptability of these hormone pathways. The research team highlights that the variability in thermal sensitivity among species and populations is key. Some fish may have hormone pathways that are more resistant to temperature changes, while others are more vulnerable. This variability can determine which fish are most at risk of reproductive failure as global temperatures rise. Moreover, the study considers the potential for fish populations to adapt to these changes through shifts in the temperature responsiveness of their hormone pathways. This adaptation could occur over time through natural selection, favoring individuals with hormone pathways that can withstand higher temperatures. Alternatively, transgenerational plasticity, where traits are passed on from parents to offspring that help them cope with environmental stresses, could also play a role. The findings from California Polytechnic State University underscore the complexity of fish reproduction in the face of climate change. They show that understanding the temperature sensitivity of hormone pathways is crucial for predicting which fish populations are most at risk. This knowledge can guide conservation efforts and inform strategies for managing fish stocks in a warming world. In conclusion, the study advances our understanding of the intricate relationship between temperature and fish reproduction. It integrates previous research on the role of stress-related genes, sex-determination mechanisms, and thyroid hormones in sex reversal[2][3][4], providing a broader context for interpreting how fish reproductive processes might fare in an increasingly hot environment. As temperatures continue to climb, the adaptability of these hormone pathways will be a decisive factor in the reproductive resilience of fish populations worldwide.

EcologyMarine BiologyEvolution

References

Main Study

1) Fish reproduction in a warming world: vulnerable points in hormone regulation from sex determination to spawning.

Published 25th March, 2024

https://doi.org/10.1098/rstb.2022.0516

Related Studies

2) Temperature- and genotype-dependent stress response and activation of the hypothalamus-pituitary-interrenal axis during temperature-induced sex reversal in pejerrey Odontesthes bonariensis, a species with genotypic and environmental sex determination.

https://doi.org/10.1016/j.mce.2023.112114

3) Diversity and Convergence of Sex-Determination Mechanisms in Teleost Fish.

https://doi.org/10.1146/annurev-animal-021122-113935

4) Thyroid axis participates in high-temperature-induced male sex reversal through its activation by the stress response.

https://doi.org/10.1007/s00018-023-04913-6


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