Evolution in the Pantry

3 inches of snow on the ground, temps haven't been above freezing in 2 weeks, this isn't the sort of weather I'd expect to photograph moths in. And yet:

Indian Meal Moth (Plodia interpunctella), Lake Co, IL 2/5/2014

This little guy is an Indian Meal Moth (Plodia interpunctella). As the name suggests, the caterpillars feed mostly on stored grain products, which explains how this one is still active in mid-winter: we caught it indoors.

Given this guy's diet, it's not at all surprising that it is the subject of a lot of research -- a quick search on GoogleScholar turned up 100 pages of hits just since 2010! (Many of those were mentioned in papers about other critters, of course.) A similar search on the genus Schreckensteinia yielded 2 pages, and only one paper with the genus as a focus.

Many of those articles dealt with reproductive biology, and quite a few others with ways to control infestations, of course, but the one I found particularly interesting used them as a test platform for examining the effects of selective pressures that differ between males and females. In this species, selection favors larger body size and faster development in females, and smaller bodies and slower development in males. Since the genetic bases for these traits are the same for males and females, the selection on males is directly opposing the selection on females. They found that while some sexual dimorphism has managed to evolve, the intralocus sexual conflict (to use the technical term) is preventing either sex from reaching the phenotypic optimum -- the point at which selection starts acting to stabilize rather than change the trait. This is a constraint upon natural selection that I had never really considered, but it's neat work. (1)

It's rather impressive how much of our work on basic biology uses critters that in other contexts are considered pests - white mice, lab rats, fruit flies. (Even E. coli can be a pest when it picks up the wrong genes.) To a large degree, this is a matter of convenience: organisms that are commensal with people tend to be easy to find, lack much in the way of legal protection, and are typically comfortable living in captivity. But in this paper, the authors gave an explicit reason why they used a commensal species. They pointed out that the conditions that their test subjects were raised in were basically the same that "wild" Indian Meal Moths grow up in, which removes one concern about extrapolating their results out of the lab.

Just another example of how we can find Nature everywhere, even a pantry in a lab!

Lewis, Z., Wedell, N., & Hunt, J. (2011). Evidence for strong intralocus sexual conflict in the Indian meal moth, Plodia interpunctella. Evolution, 65(7), 2085-2097.