Do males facilitate the spread of novel phenotypes within populations of the androdioecious nematode <I>Caenorhabditis elegans</I> ?

Abstract

In the androdioecious nematode Caenorhabditis elegans, self-fertilization is the predominant mode of reproduction. Nevertheless, males do occur, and it is still unclear if these represent a selective advantage or merely an evolutionary relict. In this study, we first tested the hypothesis that the production of males might benefit invaders to resident populations. We added single, GFP-marked worms to established laboratory populations and followed GFP frequencies over time. Mated hermaphrodites and also males were more successful in invading resident populations if compared to single, unmated hermaphrodites. The observed higher frequencies should increase the likelihood that any of the associated invading alleles persist. Second, we tested the hypothesis that males and, thus, higher outcrossing rates, are specifically favored under changing environmental conditions. After an outbred population was subjected to changing stress or to control laboratory conditions, we measured the male maintenance of the resulting populations. Interestingly all populations, experimental and control alike, showed high male maintenance, suggesting that persistence of males is also favored under standard laboratory conditions.