Climate Change and Animal Sex Reversal

GS-III | Environment and Ecology | Biodiversity | Climate Change | Conservation

Why in News?

•   A research article published in Science Advances (September 3) assessed how climate-related sex reversal is affecting the population stability of agile frogs in Hungary.
•  Researchers discovered that the male-to-female sex-reversed mice were less successful at reproducing, and the offspring produced by them were more likely to die from heat stress or infectious disease.

Learning About Sex Reversal

• Meaning: Sex reversal is the process of an organism developing physically or reproductively as the opposite of what their genes would indicate.
• Occurrence: Documented across the animal world, from invertebrates to amphibians and birds.
• Sex Determination via Chromosomes: Agile Frogs have two X-chromosomes to genetically create females, while one X-chromosome and one Y-chromosome genetically creates males.
• The Role of Temperature: High temperatures while a tadpole is developing will cause the genetic sex determination system to fail, resulting in some tadpoles that are genetically female becoming fully functional and reproductive males.

Climate Change and Its Effects on Sex Reversal

• Rising Temperatures: An increase in global temperature will cause an increase in the number of times that sex reversal occurs in those species that are sensitive to changes in temperature.
• Sex Ratio Disparity: A decrease in the number of female individuals in comparison to the number of male individuals results in a reduced opportunity for individuals to find breeding partners.
• Reduced Reproductive Success: The mating success of male sex-reversed fish may be decreased compared to other male fish, in a wild environment.
• Susceptibility to Disease: High temperature and exposure to infectious disease may lead to increased mortality rates for offspring.
• Population Decline: The effect of the other two pressures (habitat destruction/fragmentation) can lead to a reduction in population growth, genetic diversity, and potential for long-term survival.

Principal Results of the Agile Frog Study

• Lower Paternity: Although sex reversed males made up about 20% of the natural population, they were only responsible for approximately 4% of the eggs produced.
• Higher Percentage of Sex Reversal in Offspring: Approximately 61 percent of offspring from sex reversed males developed sex reversal, while only about 17 percent of offspring from sex concordant males developed sex reversal.
• Greater Disease Susceptibility: Under hot temperatures, tadpoles from sex reversed male frogs had greater viral loads after being exposed to ranavirus.
• Threat to Small Populations: The loss of as little as several breeding females can seriously reduce the ability for a small population to produce offspring.
• Extinction Probability: The results of the computer simulations showed that a number of populations may cease to exist in approximately 60 to 70 years due to the effects of increased temperature on sex reversal resulting in a greater percentage of males.
• Ranavirus Related Mortality: The addition of ranavirus-related mortality to the model resulted in an earlier start for population declines (by approximately ten years) and an even earlier extinction date (by approximately nine and one half years).

Impact on Species Diversity

• Threat to Amphibians: Around 40% of amphibian species face the risk of extinction, making them the most threatened vertebrates on earth.
• Population Viability: An unequal sex ratio will limit potential mating opportunities, and may hinder a population’s ability to rebound.
• Genetic Diversity: A loss of reproductive success can reduce the amount of genetic variation within a species, which makes them less able to adapt to changing environments.
• Extinction Risk:  The combination of climate-induced changes in sex ratios and the spread of infectious disease may increase the rate at which populations are lost to extinction.
• Conservation Challenges: There are potential conservation problems as a result of underestimating sex-reversed animals. These underestimations could lead to inaccurate assessments of species and poor conservation management decisions.

Way Forward

• Scientific Research: Understand how different factors in the environment influence when an organism will undergo sex reversal, and what are the effects on its ability to survive over time.
• Population Assessment: Consider how the existence of sex reversed animals will affect the interpretation of population trends, and the evaluation of reproductive performance.
• Climate Change Mitigation: Take steps to lower the temperature in order to minimize the effects of climate change on at-risk wildlife.
• Disease Management: Assess the synergistic effects of heat stress and infectious disease in wildlife population dynamics.
• Conservation Strategies: Revise conservation interpretations and management strategies based on new scientific findings.
• Protection of small populations :Pay special attention to those populations where the death of a few breeding females can negatively impact their ability to reproduce.

Conclusion

The way in which increasing temperatures will impact both the physical environment as well as the reproduction capabilities of organisms through climate induced sex reversal is one of the many ways in which we are currently witnessing the effects of climate change. When combined with reduced mating success and the proliferation of infectious disease, climate induced sex reversal can result in a more rapid decline in organism populations. In order to effectively protect and manage biological diversity during a time of global warming it is necessary to understand how these factors interact with each other.

UPSC Mains Practice Question

Q. Climate Change affects biodiversity through both direct loss of habitat and indirect changes to species reproduction biology. Please provide a discussion of how climate-driven sex reversals would impact population viability and wild animal conservation.

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