ENVIRONMENTAL-STRESS AND THE MAINTENANCE OF SEX IN A FRESH-WATER SNAIL

Synergism among mutations can lead to an advantage to sexual reproduct ion, provided mutation rates are high enough (the mutational determini stic hypothesis). Here we tested the idea that competition for food ca n increase the advantage to sexual reproduction, perhaps by increasing the synergism among mutations in asexual individuals. We compared the survivorship of sexual and asexual snails (Potamopyrgus antipodarum) under two treatments: starved and fed. We predicted higher mortality f or asexual snails when starved, but found that sexual and asexual indi viduals survived at the same rate, independent of treatment. These res ults suggest that the distribution of sex in this snail may not be exp lained by variation in competition among populations.