Dolphins teach daughters because daughters teach granddaughters: The evolutionary ecology of sex-biased social learning

Background/Question/Methods

The success of many social animals depends on their learning foraging behavior from conspecifics. Often learning occurs through local enhancement or imitation. But in some species, such as whales and dolphins, there is evidence that foraging techniques may be taught – that is the model pays a cost to help the learner adopt the behavior. In two dolphin populations in Shark Bay, Australia, some individuals (~5%) forage for bottom-dwelling fish using sponges. Dolphins have uniparental care and there is strong evidence that "sponging" is socially transmitted from mothers to their offspring. However, there is debate about whether it is taught or simply imitated. Curiously, female spongers transmit the technique to almost all (~90%) of their daughters but to a much smaller fraction (~30%) of their sons. Other foraging behaviors show a similar sex-biased pattern. The most accepted hypotheses for this discrepancy are that (1) daughters have more need for fish because of pregnancy or (2) male dolphins have large social networks that take them away from prime foraging areas. However, I show that this pattern is a likely consequence of social transmission being constrained to uniparental teaching.

Results/Conclusions

I use a simple numerical simulation to show that preferentially teaching daughters is a likely outcome if females are uniparental teachers. This is because teaching one's daughter potentially confers a reproductive advantage over multiple generations, because one's daughter might teach her daughters. However, the reproductive advantage from teaching a son lasts for, at most, one generation. My model also explains how uniparental teaching creates an equilibrium for teaching males at relatively low frequency. Males who sponge have a reproductive benefit from sponging, but do not pay a cost for teaching the next generation. This gives sponging males a “rare type advantage” and sponging will increase in the male population until its reproductive benefit is balanced by the reproductive cost mothers pay in teaching it. My model explains the sex-biased distribution of foraging behavior in dolphins and strongly suggests foraging is taught instead of imitated. This finding implies that similar sex-biased distributions of socially-learned traits may point to evidence of teaching in other species.