Researchers analyzed skin samples from 96 Indo-Pacific bottlenose dolphins in Shark Bay and found that the 23 individuals that use sponges while foraging show distinct DNA methylation patterns across nearly 30,000 genomic sites. Using machine learning, the team separated spongers from non-spongers with moderate accuracy. While the results link a cultural foraging tactic to epigenetic differences, the study cannot yet determine whether behavior causes methylation changes or vice versa.
Dolphins That Use Sponges Show Distinct Epigenetic Marks, Study Suggests
Photo Credit: University of Bristol
Researchers studying Indo-Pacific bottlenose dolphins in Shark Bay, Australia, report that individuals using marine sponges as foraging tools show distinct epigenomic patterns compared with non-spongers. The work links a learned cultural behavior to differences in DNA methylation, though causality remains unresolved.
What Is Sponging? Sponging is a rare, tool-assisted foraging technique in which some dolphins — mostly females — place a sea sponge over their rostrum and probe sandy seafloors for hidden prey. The sponge appears to protect the snout from abrasion and allows the dolphins to forage in deeper or rougher substrates.
The Study A team led by Michael Krützen of the University of Zurich analyzed skin samples collected over more than 20 years from 96 wild dolphins (23 confirmed spongers and 73 non-spongers). They examined nearly 30,000 genomic sites for DNA methylation, a common epigenetic mark that can influence gene activity without changing the DNA sequence.
The researchers used machine-learning methods to search for methylation patterns that distinguished spongers from non-spongers and were able to separate the two groups with moderate accuracy. The findings imply that cultural behaviors might be associated with physiological as well as behavioral differences.
Implications and Caveats
These results raise the possibility that animal culture could be linked to epigenetic states that affect biology on shorter timescales than genetic evolution. That could matter ecologically: sponging dolphins spend more time foraging, rest less, and often hunt alone, but they also target different prey and might be better equipped to cope when environmental conditions — such as marine heat waves — alter food availability.
Important Limitations The study relies on skin biopsies (the only tissue that can be safely collected from wild dolphins) and cannot yet determine directionality. It remains unclear whether adopting sponging causes methylation changes, whether preexisting epigenetic differences make some dolphins more likely to adopt the behavior, or whether external factors (diet, stress, social networks, or habitat) influence both behavior and methylation.
"The data suggest an intriguing link between learned behaviour and epigenetic state, but more work is needed to establish mechanism and causality," the authors note.
Next Steps Future research could track individuals longitudinally, combine methylation data with diet and social network information, and investigate functional consequences of the methylation differences to better understand how culture and biology interact in wild populations.
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