Randy Rotifers: Environmental Variation Prompts More Sex

By Katherine Harmon

rotifers engage in more sex in varried environments MORE SEX IN THE (ROTIFER) CITY: A heterogeneous environment seems to be all it takes to get rotifers to have more sex. The sexual females in this group are carrying dark eggs. Image: KUIPER/BECKS

Sex can be a costly endeavor—biologically, that is. Combining genetic material can of course bring beneficial new combinations, but even for tiny organisms that are barely visible to the naked eye, mating is fraught with all kinds of hazards, such as a long wait for offspring, sexually transmitted diseases, and the risk of getting eaten during or after sex. So why, if many of these bitty beasts can produce asexually, do some of them do it anyway?
Evolutionary theory has suggested that the nature of the environment might have something to do with the mode of reproduction. And a rare experiment has demonstrated that the idea holds true in a lab setting.

A team of researchers found that they could make one breed of rotifers (Brachionus calyciflorus)—microscopic or near-microscopic "pseudocoelomate" animals that can reproduce both sexually and asexually—more prone to sexual reproduction just by culturing the organisms in environments with different levels of food quality. The results are published in the October 14 issue of Nature. (Scientific American is part of Nature Publishing Group.)

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