A small population of dolphins in Shark Bay, Australia, has been observed employing a remarkable technique: they utilise marine sponges to cover their snouts while searching for fish hidden beneath the sand. This method not only safeguards their mouths from the harshness of the sand but also enhances their foraging efficiency by allowing them to cover a larger area and probe deeper into the ocean floor.
Humans have recognised this innovative behaviour for over 25 years, highlighting dolphins as tool users. Research has documented that dolphins in Shark Bay also employ shells to capture and consume fish, a behaviour termed “shelling,” which, according to studies from 2020, they learn from their peers. Conversely, the sponging technique is transmitted from mothers to their calves and presents challenges due to its interference with echolocation, yet it is sufficiently beneficial for dolphins to pass it down through generations.
New research reveals that these dolphins exhibit not only distinct behaviours but also subtle differences in their epigenomes—the chemical modifications affecting gene expression without altering the DNA sequence. This suggests that cultural practices may leave a biological imprint.
The research team, consisting of evolutionary biologist Michael Krützen from the University of Zurich, indicates that exploring the relationship between culture and epigenetics has been largely overlooked outside human studies. The implications could extend to understanding human evolution by linking cultural practices to biological foundations.
Among Shark Bay’s Indo-Pacific bottlenose dolphins, primarily females practice sponging, which, while energetically demanding, appears to confer specific advantages. These dolphins forage for longer durations, engage less in rest, and often hunt alone. They also target different prey and maintain unique social networks, potentially enhancing their resilience to environmental changes such as marine heatwaves.
To investigate further, researchers analysed skin samples from 96 dolphins over two decades, identifying 23 confirmed spongers and 73 non-spongers. They examined nearly 30,000 genomic sites for DNA methylation—an epigenetic modification akin to a dimmer switch that adjusts gene activity without altering the genetic code.
The study found moderate success in using methylation patterns to differentiate between spongers and non-spongers, indicating that no single genetic marker predominated; rather, multiple small differences played a role. This aligns with current understanding of complex behaviours, which typically emerge from a range of genetic interactions.
However, the study raises questions about causality. While cultural behaviours like sponging might influence an individual’s lifestyle and associated epigenetic changes, it remains uncertain whether these changes are inherited or if they arise from pre-existing genetic factors. The ethical considerations of using skin samples, the only feasible method for studying wild dolphins, may not fully capture the complexities of brain or organ-level changes linked to behaviour.
This research exemplifies the potential for gaining insights into the intersection of culture and biology. Evolutionary biologists recognise that culture can shape genetics over generations. This study suggests that epigenetics may offer a more immediate means for organisms to convey survival strategies through biological mechanisms. Further explorations are anticipated to clarify these phenomena and their implications.
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