An international team of marine biologists have published research in Molecular Ecology that shows the benefits of gene flow between geographically distant and genetically different killer whale populations.
The study highlights that about 20% of the genetic makeup of southwestern Australian killer whales can be traced back to Antarctic ancestors, with gene flow occurring both historically and recently in the past century.
This influx of genetic material helps reduce the risk of inbreeding and boosts the population's genetic health, perhaps increasing their ability to adapt to shifting environmental conditions.
"Despite their low densities, killer whale populations in low-latitude oceans maintain exceptionally high genetic diversity, driven by sporadic gene flow from distinct lineages – and this is evident in Australasian killer whales" says lead author Isabella Reeves, PhD Candidate at Flinders University, and part of the Cetacean Research Centre, and the Southern Shark Ecology Group based at Flinders.
"We even identified the presence of great-grandparents from Antarctica in the southwestern Australian killer whales. This sporadic mixing with other populations acts as a mechanism to maintain long-term genetic health and survival. It reduces the effects of inbreeding, promotes a rare natural genetic rescue effect, and increases the population's ability to adapt."
Such natural genetic mechanisms are crucial in an era of rapid environmental change.
"This genetic mixing is supporting the long-term viability of these populations, helping safeguard these whales, hopefully in the future of environmental change, but future research will tell," says Reeves.
The study provides rare evidence of mechanisms in wild populations that promote population health and resilience. It also illustrates how natural genetic rescue protects the genetic integrity of the population, and may enhance their capacity to evolve and thrive in the face of environmental challenges.
This genetic evidence of population health aligns with nearly 15 years of ecological research led by John Totterdell from the Cetacean Research Centre.
"Southwestern Australian killer whales thrive in a nutrient-rich environment, feeding on a diverse range of prey and forming one of the largest aggregations in the Southern Hemisphere," says Mr Totterdell.
"They calve regularly and maintain consistent body condition, painting a picture of a robust and healthy population.
"Evolutionary history-based studies such as this provide valuable insights into the processes that have shaped modern populations.
"By understanding the genetic past of these killer whale populations, we gain a clearer picture of their present-day resilience and the factors contributing to their continued survival and adaptability."
The research – "Admixture Increases Genetic Diversity and Adaptive Potential in Australasian Killer Whales", by Isabella Reeves, John Totterdell, Jonathan Sandoval-Castillo, Emma Betty, Karen Stockin, Ramari Stewart, Muriel Johnstone and Andrew Foote – has been published in Molecular Ecology. https://doi.org/10.1111/mec.17689
The study underscores the critical role of gene flow in enhancing genetic diversity and increasing the adaptive potential of populations.
It also highlights that populations have the capacity to naturally evolve mechanisms to maintain their health, a crucial trait for survival in the face of environmental change.
