02
Mar
10

Speciation?

No, not like this; like this.

In sticking with a recent spat of “environmental effects on gene expression” themed posts, I began writing this about two weeks ago, but completely forgot about it; I have finally finished.

In all animals, the environment can elicit distinct responses via genetic regulatory pathways. Some bacteria produce lactase only when lactose is present, others can switch between harmless and pathogenic forms. In this particular paper, by Ryan A. Martin and David Pfennig, the size of the mother frog is shown to influence the likelihood of the offspring developing into the carnivore-morph forms. This form is easily distinguished by having heads larger than those of the normal omnivore morph. (Look at the image, if you don’t believe me!)

The hypothesis was that the size of the mother played a role in the size (and thus, ability to ingest more shrimp earlier-which influences development into carnivore morphs) of the offspring. An interesting idea which this paper illustrates quite well is that a single species can inhabit different niches. An omnivore morph, for example, will compete with other omnivore morphs while the carnivore morph will compete mostly with other carnivore morphs. Additionally, different two species of Spea co-occur in many locations. Where these two species are found together, one produces a superior carnivore which out-competes the carnivore morph of the other type, resulting in selection against the carnivore morph in the second species. Interestingly, morph types seem to be developmentally canalized; i.e. the adults from a population of the species producing omnivore morphs is more likely to produce mostly omnivore morphs when reared separated from the other–this implies the traits are influenced by maternal factors.

This raises interesting questions for speciation. Since maternal influences can favor specific resource-use polymorphisms, such maternal-mediated divergence could be a mechanism of evolution (specifically, something called “genetic accommodation*”).

*Genetic accommodation is selection towards traits which are more responsive to environmental triggers (the development into the carnivore morph may be an example of this)

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