Abstract
As climate change accelerates, rising temperatures pose a significant risk to biodiversity, particularly for small and inbred fish populations. Elevated water temperatures have been associated with sex ratio imbalances, primarily the masculinization of fish populations. A study on zebrafish (Danio rerio) demonstrates the effects of increased water temperatures during embryogenesis on the sex ratio and gene expression associated with sex determination (SD) and color patterning (CP). The insights from this study not only shed light on the risks faced by such species but also advance our understanding of the genetic mechanisms of sexual plasticity.
In a groundbreaking study published in BMC Genomics, researchers have revealed how elevated water temperatures during embryogenesis can lead to masculinization in zebrafish, resulting in male-biased sex ratios that could contribute to population declines under natural conditions. This investigation is pivotal as it blends ecological concerns with molecular biology to emphasize the risks of small and inbred fish populations approaching extinction due to climate change.
Genetic Mechanisms of Sexual Plasticity
The study led by Shahrbanou S. Hosseini and her team at the University of Goettingen explored the effects of temperature on gonadal development and sex-biased gene expression profiles in zebrafish, an ideal model due to their sexual plasticity. The research unraveled the complex interplay of genes involved in SD and CP, finding that male SD genes such as dmrt1, amh, cyp11c1, and sept8b were significantly upregulated, while female SD genes like zp2.1, vtg1, cyp19a1a, and bmp15 were downregulated in male gonads compared to females.
Moreover, the study unexpectedly identified differential expression of CP genes in the gonads but not in the caudal fin, which determines external coloration. This finding points to the possibility of neofunctionalisation of genes, as they may have novel roles in reproduction that deviate from their original function in color patterning.
Results indicated a striking 25.5% increase in males among zebrafish raised in high-temperature conditions. It emphasized the role of temperature as an environmental cue influencing SD in zebrafish and underscored the support for a polygenic SD system (PSD), which could mean that several genes contribute to sex determination rather than it being dictated by a single genetic factor.
Ecological and Evolutionary Consequences of Sex Ratio Shifts
The shift towards a male-dominated population has severe ecological implications, including the potential decrease in genetic diversity as mating becomes more competitive among males and fewer females are available for reproduction. In turn, this can result in reduced resilience to environmental changes and increased vulnerability to extinction. These consequences are not just theoretical but align with empirical observations from previous studies indicating that rising temperatures can induce similar sex ratios shifts in other species.
Implications of Research on Conservation Strategies
Considering the evidence of high-temperature conditions leading to unnatural sex ratio configurations, conservationists must assess the resilience of various species to temperature fluctuations attributed to climate change. Proactive measures such as assisted migration, genetic augmentation, or habitat restoration to adjust temperature exposures could be necessary to preserve at-risk populations.
Future Directions and Research Recommendations
The study underscores the need for further research into how these genetic expressions shift under different environmental conditions. There is also a pressing need to examine how these changes affect long-term population dynamics and viability. Other species with different forms of sexual plasticity should also be studied to assess whether similar temperature-dependent sex ratio biases occur.
Conclusion
The research by Hosseini et al. illuminates the complex genetic underpinnings of how environmental factors like temperature can dictate sex determination in zebrafish, potentially reflecting a broader issue among ectothermic species. As climate conditions continue to change at an unprecedented rate, understanding and mitigating the effects on sensitive populations must be a priority in preserving biodiversity.
DOI and References
DOI: 10.1186/s12864-019-5722-1
References
1. Ribas L, et al. Heat-induced masculinization in domesticated zebrafish is family-specific and yields a set of different gonadal transcriptomes. Proc Natl Acad Sci USA. 2017.
2. Liew WC, Orbán L. Zebrafish sex: a complicated affair. Brief Funct Genomics. 2014.
3. Kobayashi Y, et al. Diversity and plasticity of sex determination and differentiation in fishes. Sex Dev. 2013.
4. Webster KA, et al. Dmrt1 is necessary for male sexual development in zebrafish. Dev Biol. 2017.
5. Baroiller JF, et al. Environmental effects on fish sex determination and differentiation. Sex Dev. 2009.
Keywords
1. Zebrafish Sex Determination
2. Effects of Climate Change on Fish
3. Sex Ratio Imbalance
4. Elevated Water Temperature
5. Sexual Plasticity in Fish
