Tool Use in Dolphins has Shaped Their Genetic Make Up

Simon Allen

Dolphins often demonstrate imitative behaviour both in the wild and captivity, and have the ability to learn social behaviours exhibited by others. But recent studies have demonstrated that ecological explanations are inadequate to solely explain the presence of certain behaviours and that genetics play a big part. 

A group of researchers at the University of New South Wales have been investigating a particular foraging behaviour called "sponging" in wild bottlenose dolphins in Western Australia. This is where the animal breaks off a marine sponge and wears it over its rostrum (nose) in order to probe for fish, possibly for some protective purpose. Previous research has demonstrated that sponging is a sex-biased activity, occurring almost exclusively in females. Intriguingly, behavioural observations of both male and female offspring from "spongers" have shown that despite both spending time with their mother as they mature, only the female will take up sponging. To add to the complexity, both males and non-sponging females have been observed in the same area as sponging females. This demonstrates that sponging cannot be explained solely by ecological differences and imitation behaviours. 

In a study published in the journal Proceedings of the Royal Society B, lead author Dr Anna Kopps and her colleagues investigated foraging behaviour of bottlenose dolphins in Western Australia's Shark Bay, which lies about 850 kilometres north of Perth. They also took samples for genetic analysis. Interestingly, dolphins living in areas where sponges do not grow fell into a different genetic group than dolphins living in areas where sponges are present. The former dolphins were identified as haplotype H, whereas the latter were either E or F. A haplotype is a combination of specific genes found next to each other on the same chromosome that are inherited together. Dr Kopps says that "This striking geographic distribution of a genetic sequence cannot be explained by chance. Our research shows that social learning should be considered as a possible factor that shapes the genetic structure of a wild animal population."

This research backs up previous findings which investigated mitochondrial DNA (mDNA) of spongers and non-spongers; mDNA is found in structures within our cells called mitochondria, and is inherited solely from the mother. They found that sponging showed almost exclusive mother-to-calf transmission within a single mother line (matriline), and that current spongers probably arose from a single recent sponger, a "Sponging Eve". 

This phenomenon is known as "cultural hitchhiking" and also occurs in humans; it is responsible for our lactose tolerance. Although it has long been known that culture can shape genetics in humans, this is one of the first examples of such a process occurring in non-human animals. 

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