Author: Isabella Reeves
Reeves, Isabella, 2025 Evolutionary ecology of Australasian killer whales (Orcinus orca), Flinders University, College of Science and Engineering
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Killer whales (Orcinus orca) are top predators with remarkable ecological, morphological, and genetic diversity. While populations in high-latitude regions have been extensively studied, those in low-latitude areas remain largely undocumented despite potentially having the highest diversity in behaviour, diet, and ancestry. This thesis investigates the ecological and evolutionary processes shaping Australasian killer whale populations using a multidisciplinary approach. I first explore the historical population once present in Eden, New South Wales, known for its cooperative hunting with whalers. Through genomic analysis of “Old Tom,” a museum specimen, and collaboration with Indigenous custodians, I find these whales are genetically distinct and likely locally extinct, with closest ties to New Zealand killer whales and no strong match to modern populations. Next, I assess the genomic ancestry of contemporary Australasian killer whales. Whole genome comparisons reveal evidence of recent admixture—within the last 2–4 generations—between lineages with Antarctic-like ancestry in southwestern Australia. This admixture has reduced homozygosity, maintained effective population size, and introduced potentially adaptive genetic variants, supporting the role of natural genetic rescue in promoting long-term population viability. Additionally, I analysed a white shark carcass stranded in southeastern Australia with signs of killer whale attack. DNA metabarcoding of wound swabs confirmed killer whale DNA in the major bite areas, while other wounds showed evidence of scavengers. Notably, the liver and internal organs had been removed, aligning with reports of selective tissue predation by killer whales on specific organs. Finally, I examine tissue selection by killer whales of specific prey tissues such as blubber, liver, and tongue. Through a global review and biochemical analyses of 800+ prey tissues, I find killer whales consistently select tissues high in lipids and low in protein and discard tissues lower in these nutrients, providing the first evidence that wild carnivores can nutrient balance. These selective feeding events also act as nutrient pulses, comparable to ecological phenomena like salmon spawning. Together, these findings reveal the unique evolutionary history, genomic resilience, and ecological impact of Australasian killer whales, offering new insight into their conservation and role in marine ecosystems.
Keywords: cetaceans, population genomics, evolutionary genomics, nutritional ecology, trophic ecology, aDNA, eDNA, whole genomes, selective foragaing, indigenous knowledge
Subject: Science, Technology and Enterprise thesis
Thesis type: Doctor of Philosophy
Completed: 2025
School: College of Science and Engineering
Supervisor: Lauren Meyer