Experimental insight into the proximate causes of male persistence variation among two strains of the androdioecious Caenorhabditis elegans (Nematoda)

We determined the kinetics of the loss of males over time for multiple population sizes and wild isolates and found significant differences. We performed systematic inter- and intra-strain crosses with N2 and CB4856 and show that the males and the hermaphrodites contribute to the difference in male maintenance between these two strains. In particular, CB4856 males obtained a higher number of successful copulations than N2 males and sired correspondingly more cross-progeny. On the other hand, N2 hermaphrodites produced a higher number of self-progeny, both when singly mated and when not mated.These two differences have the potential to explain the observed variation in male persistence, since they should lead to a predominance of self-progeny (and thus hermaphrodites) in N2 and, at the same time, a high proportion of cross-progeny (and thus the presence of males as well as hermaphrodites) in CB4856.The nematode Caenorhabditis elegans is a facultative hermaphrodite that reproduces either by virtue of self-fertilization or cross-breeding with a male (androdioecious reproductive system). The hermaphrodites are somatically female but produce a limited number of sperm during their late larval development before switching to the production of eggs. The sperm is stored in the spermatheca and can be used to fertilize the newly formed eggs. Except for a very few males (around 0.2% in the standard laboratory strain N2) that arise spontaneously as the result of X chromosome non-disjunction, the entire self-progeny is hermaphroditic. Males can mate with hermaphrodites and give rise to 50% males in the cross-progeny. Cross-fertilization is not possible among hermaphrodites [1,2]. Male derived sperm is also stored in the spermatheca where it competes with the hermaphrodite's own sperm for the fertilization of the oocytes. Male sperm is usually larger and therefore has a competitive advantage over the hermaphrodite's sperm [3,4].If hermaphrodites can reproduce by self-fertilization