Altruism and Conflict in the Social Insects - An Introduction to Behavioural Ecology

Biology Reference

In-Depth Information

Summary

In the social insects there are sterile workers that never have offspring but instead help

to rear younger siblings. This appears at first sight to go against the idea of natural

selection favouring maximum efficiency at passing on genes. However, the fact that

sterile workers help rear close relatives provides the explanation for this altruism.

Much debate has focused on whether haplodiploid genetics predisposes individuals to

become sterile workers. However, despite much enthusiasm for this idea, it appears to

have largely been a red herring. Instead, what appears to have been key from a genetic

perspective is the need for strict lifetime monogamy. Monogamy leads to the relatedness

to siblings being equal to that to offspring ( r

0.5), in which case only a small efficiency

benefit to cooperation ( B / C > 1) is required to start a species down the route to eusociality

as long as it persists over many generations.

The ecological factors which appear to have been most important in favouring

eusociality are life insurance and fortress defence. The life insurance (or assured fitness

returns) benefits of allowing helpers to complete parental care after the death of the

mother are likely to have been important in ants, bees, and wasps. The fortress defence

benefits of remaining to help use or defend a food source, when opportunities for

successful migration are low, are likely to have been important in aphids, beetles, lower

termites, thrips and shrimps.

In the Hymenoptera, haplodiploid genetics leads to conflicts over the sex ratio of

reproductives (queens and drones) and who should produce males. Queens and workers

disagree over the sex ratio. Whilst there is much data showing how workers win this

conflict, they do not win all the time, and there are cases where the queens win. Workers

can disagree over who should produce males, leading to the scenario that some workers

lay male eggs, but these eggs are destroyed by other workers when most of them are not

full sisters. This policing can help enforce altruistic sterility within colonies.

Kin selection is central to explaining both cooperation and conflict in the social

insects. It is perhaps ironic that some of the clearest quantitative support for kin

selection theory comes from its ability to explain and predict conflicts over the sex ratio

and who produces males. The reason is that, in these situations, clear predictions can be

made on the basis of relatedness ( r ) alone, and that we don't have to worry so much

about the details of the harder to measure costs ( C ) and benefits ( B ).

A comparison of cooperation in insects and vertebrates shows both similarities (e.g.

subsocial route, nest defence, provisioning of young, and promiscuity matters) and

differences (e.g. strict lifetime monogamy, life insurance and fortress defence are all less

important in vertebrates).

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