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Tuesday, November 1, 2016

Aphids in Red

I've found myself very busy lately. The little free time I've had after work and on the weekends has been consumed with the process of repairing some windows in my old house as well as sundry other necessary tasks. The main consequence for this blog has been that I haven't found myself able to sit down in front of my computer for long enough to write a post.

I have no plans to end this blog, but I do expect that life will occasionally get in the way like it has lately. To get myself back into the swing of things, I'm probably going to have a few light posts while I work on some more intensive ones.

Earlier in the summer, my wife and I went camping with some friends. Early one of the mornings, I was wandering around looking for photographic subjects when I noticed a bright red color along the stems of some plants. On closer examination, I realized the red color was a mass of aphids.

Aphids may be the bane of many a gardener, but they illustrate some really interesting biology. Aphids have a very complicated life cycle. During most of the year they're all females and don't have sex. Instead they multiply through parthenogenesis. They're so efficient at this that new baby aphids are born (not hatched) already pregnant. Most of the new babies don't waste energy growing wings, instead every calorie is dedicated to growing the swarm. When food starts to run out or the aphids get too crowded some babies will grow wings and fly off to other plants and continue their parthenogenic ways. When the weather starts turning colder in fall, winged male babies are produced. The males then mate with females to produce eggs which can survive more extreme winters than the adults.

Aphids come in a whole range of colors, from pale white to yellow, green, red, or even black. These red ones are really interesting because their color is due to high levels of carotenoid pigments (lycopene and related compounds) that are normally only synthesized by plants and fungi. Since the plants the aphids feed on don't have high levels of these compounds, it was at first confusing as to where they would get them. I turned out that the aphids have the genes needed to produce carotenoids and they seem to have acquired them from a fungus via horizontal gene transfer.

The really bizarre thing about these aphids is that they seem to be using the carotenoids to harvest energy from light. It isn't exactly photosynthesis the way plants do it since they're not incorporating CO2 to build sugars, but they do seem to produce more ATP when they're in sunlight compared to when they're not. This ability might help them survive tough times when other tiny insects would perish, but it really isn't at all clear.