The Way I See It: Male or female? It depends on whether you’re infected

BY EFFIE RAHMAN
Special to Rice News

Beneath the beautiful, protective dome of oak trees on the Rice campus lies a hidden world of roots and leaf litter. Scrape away the top layer of leaves beneath the hedges, and take a close look: Ants and cockroaches quickly scurry away, and the occasional centipede or worm wriggles into the soil. Wait a few seconds, and what at first glance appeared to be a clump of soil springs to life — uncurling itself as its legs appear to shuffle it away.

	Armadillidium vulgare

I remember playing with these “roly-polies,” properly known as Armadillidium vulgare, during my elementary school days in Oklahoma. I was fascinated with these creatures, amused at their instinct to roll into a tight ball at the smallest signal of alarm. But what I didn’t know then was how easy it was to tell female pill bugs from males by flipping them on their backs and peering at them under a light microscope. In Scott Solomon’s EBIO 213 class, we discovered that here on campus, most of the pill bugs are females. Or at least appear to be.

Dr. Solomon explained in class that many of what appear to be female A. vulgare may actually be males that are infected with a bacteria called Wolbachia. These bacteria are notorious for causing males to develop into females. Since the only way for Wolbachia to spread is from females to their offspring, the bacteria do whatever they can to make females more common in the population. Wolbachia can even go to extreme measures in some species and inhibit males from reproducing — or simply kill them.

In EBIO 213, students have been monitoring the Rice campus A. vulgare for the past two years by calculating sex ratios and tracking how they change over time. Identifying more females than males is evidence that Wolbachia may be tinkering with these tiny crustaceans and manipulating them to advance their own reproductive interests. But until this summer, Dr. Solomon and his students had no way of knowing for sure whether these roly-polies were actually infected.

This summer, a grant from the Brown Foundation allowed Dr. Solomon and me to investigate whether our pill bugs are actually infected with Wolbachia. I used PCR (polymerase chain reaction) to amplify small sections of DNA that are unique to Wolbachia; if any of these gene segments were detected after gel electrophoresis analysis, it would confirm a Wolbachia infection. Our results were quite interesting: Out of 36 A. vulgare samples (22 females, 14 males), six of them (five females, one male) tested positive for Wolbachia — an infection rate of 17 percent overall and 23 percent among females. And so it appears that the little pill bugs I played with as a child had more secrets than I could have imagined.

Dr. Solomon’s EBIO 213 class will continue investigating Wolbachia infection rates in A. vulgare this semester and in the seasons to come. We invite all of you to take a closer peak at the ground below your feet – you’d be amazed at what you might find!

–Effie Rahman is a Wiess College senior studying psychology, biochemistry and cell biology.