Thursday, April 17, 2008

Haplodiploidy in social insects

The haplodiploid reproductive system in hymenoptera, such as bees and wasps, leads to some very interesting genetics. For example the drones produce sperm cells that contain their entire genome and so each fertilized egg will get the same genetic information from the father. Thus, if a queen bee mates with only one drone, any two of her daughters will share, on average, 3/4 of their genes (identical copies from the father, 50% chance of sharing genes from mother).

In some species female workers can lay unfertilized eggs that become males. However due to the haplodiploid system the female workers are actually more closely related to their sister workers than they are to their offspring. They share 75% of their genes with sisters and only 50% with offspring. This is the root of an explanation for why some individuals devote all their energy to caring for sisters and the evolution of sociality.

Much of the original work was done by Bill Hamilton in the 1960's but this 1976 paper by Trivers and Hare 1976 - Haplodiploidy and the evolution of the social insects - is a classic that is well worth reading.

On a slightly different note parasitic wasps lay their eggs in, or on, host insects and some of them are able to select for each host whether to lay a fertilized egg - which becomes a female offspring, or an unfertilized egg which becomes a male offspring. If the host insects come in a variety of sizes which ones (large or small) do you think get the female offspring and which ones get the male offspring? If you want to explore this further Eric Charnov's 'Theory of sex allocation' book is the way to go for the theory or Charles Godfray's 'Parasitoids' book is a fascinating overview of parasitoids including their behavior, ecology and evolution.

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