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Helpful Cichlids in the Gladiator’s Show

March 15, 2010

Image: The Daffodil Cichlid of Lake Tanganyika / Koen Eeckhoudt

ResearchBlogging.orgIn 1888 “Darwin’s Bulldog”, Thomas Henry Huxley, declared that nature was little more than a “gladiator’s show” whereby only “the strongest, the swiftest, and the cunningest live to fight another day.” Brutal competition was the only important factor in the natural world, in which a “Hobbesian war of each against all was the normal state of existence.” As such, we shouldn’t expect cooperation in nature because only strength and selfishness is rewarded by evolution.
But a paper by Dik Heg and colleagues, entitled Helpful Female Cichlids Are More Likely to Reproduce, in the open access journal PLoS One demonstrates a unique form of cooperation that represents the final bugle call for such a Hobbesian battlecry.
This study tops a long list of evidence demonstrating that cooperation and mutual aid are important factors in evolutionary history. Many species engage in cooperation through “kin selection” in which they help close relatives and, in effect, themselves through promoting their shared genes. Vampire bats will engage in “reciprocal altruism” with unrelated members of their group by sharing blood with their hungry neighbors in the anticipation that they will be shared with as well on nights when they go hungry. In more dramatic cases, rats will engage in “generalized reciprocity” and share with a complete stranger if another stranger had previously shared with them. Perhaps most remarkably, chimpanzees potentially demonstrate empathy in cases where they selflessly help others, even members of a different species, if they recognize that an individual needs assistance. (For more on these forms of cooperation see my post The Sacrifice of Admetus.)

In this case research has demonstrated another form of cooperation in the animal world, one based on a primitive form of economic exchange. In the present study Heg et al. were intrigued by the observation that some Daffodil Cichlids (Neolamprologus pulcher) would assist in raising the offspring of unrelated members of their species. This “alloparenting,” in which individuals other than the biological parents will take on the parental responsibilities of feeding and protecting the vulnerable offspring, was observed primarily when subordinate cichlids offered assistance to more dominant individuals. Interestingly, those who offered the assistance appeared to have more surviving offspring themselves compared to those subordinates who didn’t offer alloparental care.
To understand why the researchers conducted a series of trials on separate experimental groups (between 16 and 48 groups each) that included one pair of dominant cichlids in each test while manipulating the number and body size of subordinate females as a control. They found that unrelated subordinates who helped more dominant members ended up with greater reproductive success as a direct result of this assistance.

Subordinate females that performed more alloparental care were more likely to produce eggs themselves. This effect was independent of subordinate body size, which also influenced reproduction positively (Table 3).

Since alloparenting clearly resulted in direct fitness benefits, Heg and colleagues next wanted to determine whether this cooperative behavior by subordinates would be reciprocated (such as in the case of vampire bats) or alternatively, if the help was not paid back, whether the alloparenting could be seen as a form of payment for some other type of return benefit.
The relationship turned out to be a win-win for all involved, but in an unanticipated direction. Because of the alloparental care by subordinate females, dominant parents were able to spend less time raising their brood and could focus on additional reproduction. However, this alloparenting was not reciprocated. Dominant cichlids were happy to accept the parental assistance but didn’t seem to fulfill their end of the deal. Why? And why would the subordinates continue to cooperate with such free riders? As it turns out, the dominant cichlids were participating in a kind of market exchange. The subordinates would provide the daycare and the dominants would let them enjoy the protection and bounty of their territory. This agreement translated into significant benefits for both.

In conclusion, we did not find evidence of direct reciprocal ‘altruism’. However, we did find evidence of reciprocal benefits – help in exchange for opportunities to reproduce. . . The most likely mechanism is that by performing helping behaviour ensures that a subordinate has access to the breeding substrate, which she needs to lay eggs.

By laying their brood in the better conditions that the dominants had reserved for themselves, alloparental subordinates were able to have more offspring than those who were more individualistic. It seems that cooperation elicited a form of tolerance that inhibited the normal territoriality in this species and led to reproductive gains for both parties as a result. So much for Huxley’s “gladiator’s show.” In this match the strongest individuals put their aggression aside and saw cooperation as the best tactic for victory.
Huxley’s argument for a Hobbesian nature has now been discarded into the dustbin of history (and, notably, was largely refuted as early as 1890 by the Russian naturalist Peter Kropotkin, though his argument was dismissed at the time). However, what isn’t widely known is that a view of nature “red in tooth and claw” was originally challenged by none other than Darwin himself. In his 1879 Descent of Man the founder of natural selection argued the very point that Heg and colleagues have now demonstrated among the cooperative cichlids. Darwin hypothesized that:

Those communities, which included the greatest number of the most sympathetic members, would flourish best and rear the greatest number of offspring.

Darwin was writing about the evolution of cooperation in human societies, but it seems the origin of the social contract is considerably older than even he had anticipated.
Heg, D., Jutzeler, E., Mitchell, J., & Hamilton, I. (2009). Helpful Female Subordinate Cichlids Are More Likely to Reproduce PLoS ONE, 4 (5) DOI: 10.1371/journal.pone.0005458

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