Sex is your defence against parasites

Sex may have evolved in part as a defence against parasites, suggests a research article. Published in the journal American Naturalist, the article highlights the fact that when an a sexual creature reproduces, it makes clones — exact genetic copies of itself.
It further points out that each clone has the same genes, and, consequently, the same genetic vulnerabilities to parasites. The article states that if a parasite emerges that
can exploit those vulnerabilities, it can wipe out the whole population.

Sexual offspring, on the other hand, are genetically unique, often with different parasite vulnerabilities. That is why, a parasite that can destroy some can’t necessarily destroy all. In theory, that should help sexual populations maintain stability, while asexual populations face extinction at the hands of parasites. These propositions are based on several pieces of research on Potamopyrgus antipodarum, a snail common in fresh water lakes in New Zealand which has both sexual and asexual versions.

Jukka Jokela of the Swiss Federal Institute of Aquatic Science and Technology, Mark Dybdahl of the University of Washington and Curtis Lively of Indiana University, Bloomington, began observing several populations of these snails for ten years starting in 1994. The researchers monitored the number of sexuals, the number asexuals, and the rates of parasite infection for both.

They found that clones that were plentiful at the beginning of the study became more susceptible to parasites over time. However, sexual snail populations remained much more stable over time. This, the authors say, is exactly the pattern predicted by the parasite hypothesis.