Enhancing Coral’s Resilience to Climate Change Through Selective Breeding

Unlocking the Genetic Basis of Coral Heat Tolerance

Marine heatwaves have become increasingly frequent, widespread, and severe, causing mass coral bleaching and mortality. While natural adaptation may not be sufficient to keep pace with the rate of climate change, the researchers set out to explore the potential of selective breeding to enhance the heat tolerance of corals.

The team focused on the reef-building coral Acropora digitifera, a species widely distributed throughout the western Indo-Pacific region. They first conducted heat stress experiments on wild-collected coral fragments to identify individuals with either low or high heat tolerance. These parent colonies were then selectively bred to produce offspring with different levels of heat tolerance.

Heritability: The Key to Selective Breeding Success

A critical factor in the success of selective breeding is the heritability of the trait being targeted. The researchers used a statistical approach called an “animal model” to estimate the narrow-sense heritability (h²) of heat tolerance in the Acropora digitifera population. They found that both short-term (h² = 0.29) and long-term (h² = 0.23) heat tolerance were substantially heritable, meaning that a significant portion of the observed variation in this trait was due to additive genetic effects.

These heritability estimates were corroborated using parent-offspring regressions, which showed that the heat tolerance of the offspring was closely related to the heat tolerance of their parents. This indicates that selective breeding could be an effective tool for enhancing the heat tolerance of coral populations.

Selective Breeding Boosts Offspring Heat Tolerance

The researchers then put this theory to the test by selectively breeding coral colonies with either low or high heat tolerance. When they exposed the resulting offspring to simulated marine heatwaves, they found that the offspring from high heat tolerance parents had significantly enhanced heat tolerance compared to the offspring from low heat tolerance parents. This demonstrated that a single generation of selective breeding can produce meaningful improvements in coral heat tolerance.

Notably, the researchers also found that selecting for short-term heat tolerance did not necessarily translate to improved long-term heat tolerance. This suggests that these two forms of heat tolerance may be under independent genetic control, highlighting the importance of understanding the specific genetic mechanisms underlying different aspects of stress response in corals.

Coral Resilience: A Race Against Time

The researchers’ findings indicate that selective breeding could be a valuable tool for enhancing the resilience of coral populations to the impacts of climate change. However, they also caution that the potential for such interventions to keep pace with the rapid rate of climate change may be limited.

The modest improvements in heat tolerance achieved through a single generation of selective breeding, while significant, may still fall short of the level of enhancement needed to ensure the long-term survival of coral reefs. As the researchers note, “Ultimately, accurate low-cost, rapid assays need to be developed to enable robust selection of required heat tolerance traits for assisted evolution to be implemented successfully.”

Moreover, the researchers emphasize that selective breeding and other assisted evolution approaches should be viewed as complementary to, not a substitute for, urgent global action to mitigate climate change. Without substantial reductions in greenhouse gas emissions and local-scale management of human impacts, the future of coral reefs will remain in jeopardy.

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