Eco-evolutionary spatial dynamics

Hanski, I. (2011) "Eco-evolutionary spatial dynamics in the Glanville fritillary butterfly." PNAS

This species of butterfly lives in a series of meadows on in the Åland Islands, the dynamics in this species were reviewed in the article. The butterflies constantly go extinct in individual meadows, which are then recolonized from others. It has been shown that after a series of extinctions, there is a burst of colonizations, leading to a fairly stable population size.

I found it very interesting that a variant of one gene, Pgi, has been shown to affect dispersal propensity. Individuals heterozygous at this locus carry one allele with an A and one with a C, these individuals are more likely to disperse than the AA homozygotes. Also, the CC homozygotes are very rare, the author indicates that this is probably because the C allele is linked to a recessive lethal mutation. Individuals with two copies of the C allele rarely survive through development. AA homozygotes primarily arise during inbreeding within a meadow, after it has been colonized, and have lower fitness. Therefore, the AC heterozygotes actually have higher fitness.

This is an example of heterozygote advantage (or overdominance), where individuals carrying two different alleles for a gene have higher fitness than individuals with two copies of the same allele. A primary example is sicle cell anemia in humans, a certain allele of one of the genes that makes hemoglobin. If you have two normal copies of the allele your blood cells are normal, but if you have two copies of the alternate allele your blood cells become sicle shaped and are very bad at delivering oxygen. But, if you have one copy of each gene you have a mix of cell shapes. Normally this is bad, but if someone with a mix lives in an area with a high rate of malaria infection they actually do better.