Infanticide and Cannibalism in Sociobiology

This is a little quote from E. O. Wilson’s Sociobiology that I deleted from the previous post for being a little tangential, but it is still interesting

Guppies (Lebistes reticulatus) are well known for the stabilization of their populations in aquaria by the consumption of their excess young.

So that’s what happened to my pet fish! I always wondered why they seemed to appear and disappear at random. It wasn’t a big enough bowl to logically be losing them in.

Um. Poor guppies.

“Cannibalism is commonplace in the social insects, where it serves as a means of conserving nutrients as well as a precise mechanism for regulating colony size. The colonies of all termite species so far investigated promptly eat their own dead and injured. Cannibalism is in fact so pervasive in termites that it can be said to be a way of life in these insects. …

The eating of immature stages is common in the social Hymenoptera.

Hymenoptera is an order of insects with over 150,000 species, including ants and bees. (Termites, despite also being social, are not members of hymenoptera, and are more closely related to cockroaches.)

Quoting Wikipedia:

Among most or all hymenopterans, sex is determined by the number of chromosomes an individual possesses.[17] Fertilized eggs get two sets of chromosomes (one from each parent’s respective gametes) and develop into diploid females, while unfertilized eggs only contain one set (from the mother) and develop into haploid males. The act of fertilization is under the voluntary control of the egg-laying female, giving her control of the sex of her offspring.[15] This phenomenon is called haplodiploidy.

However, the actual genetic mechanisms of haplodiploid sex determination may be more complex than simple chromosome number. In many Hymenoptera, sex is actually determined by a single gene locus with many alleles.[17] In these species, haploids are male and diploids heterozygous at the sex locus are female, but occasionally a diploid will be homozygous at the sex locus and develop as a male, instead. This is especially likely to occur in an individual whose parents were siblings or other close relatives. Diploid males are known to be produced by inbreeding in many ant, bee, and wasp species. Diploid biparental males are usually sterile but a few species that have fertile diploid males are known.[18]

One consequence of haplodiploidy is that females on average actually have more genes in common with their sisters than they do with their own daughters. Because of this, cooperation among kindred females may be unusually advantageous, and has been hypothesized to contribute to the multiple origins of eusociality within this order.[15][19] In many colonies of bees, ants, and wasps, worker females will remove eggs laid by other workers due to increased relatedness to direct siblings, a phenomenon known as worker policing.[20]

Another consequence is that hymenopterans may be more resistant to the deleterious effects of inbreeding. As males are haploid, any recessive genes will automatically be expressed, exposing them to natural selection. Thus, the genetic load of deleterious genes is purged relatively quickly.[21]

Back to Wilson:

In ant colonies, all injured eggs, larvae, and pupae are quickly consumed. When colonies are starved, workers begin attacking healthy brood as well. In fact, there exists a direct relation between colony hunger and the amount of brood cannibalism that is precise enough to warrant the suggestion that the brood functions normally as a last-ditch food supply to keep the queen and workers alive. In the army ants of the genus Eciton, cannibalism has apparently been further adapted to the purposes of caste determination. According to Schneirla (1971), most of the female larvae in the sexual generation (the generation destined to transform into males and queens) are consumed by workers. The protein is converted into hundred or thousands of males and several of the very large virgin queens. It seems to follow, but is far from proved, that female larvae are determined as queens by this special protein-rich diet. Other groups of ants, bees, and wasps show equally intricate patterns of specialized cannibalism…

E. O. Wilson once said of Marxism, “Wonderful theory, wrong species.”

Nomadic male lions of the Serengeti plains frequently invade the territories of prids and drive away or kill the resident males. The cubs are also sometimes killed and eaten during territorial disputes. … Infant mortality is much higher as a result of the disturbances [in the social order of langurs.] In the case of P. entellus, [a langur species,] the young are actually murdered by the usurper…

 

 

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2 thoughts on “Infanticide and Cannibalism in Sociobiology

  1. One consequence of haplodiploidy is that females on average actually have more genes in common with their sisters than they do with their own daughters.

    Thinking about this, I think this is based on the idea that a male’s daughters receive his entire genome without recombination (since the male is haploid), plus half the genome of the diploid mother (recombined normally).

    Thus:

    – A father shares 100% of his genes with his daughter.

    – A mother shares 50% of her genes with her daughter.

    – A daughter shares 50% of her genes with her mother…

    – …and the other 50% with her father. The father/daughter relationship is asymmetric.

    – A grandfather and grandson will in expectation share 50% of their genes with each other, symmetrically.

    – Two sisters share 100% of their paternal genes, and an expected 50% of their maternal genes, for an expected coefficient of relatedness of 75%.

    Like

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