Bacteria modulate the degree of amphimix of their symbiotic entomopathogenic nematodes (Heterohabditis spp) in response to nutritional stress

Facultatively sexual entomopathogenic nematodes are a promising model for t he experimental study of the adaptive values of sex. Our experiments in the laboratory showed that entomopathogenic nematodes display at least two dif ferent strategies in regulating the degree of amphimix as a response to nut ritional stress. One strategy promotes the production of mates, amphimix an d the genetic variability of the offspring, improving the chances for a suc cessful new adaptation. Another strategy increases the production of hermap hrodites at the expense of males, increasing the total number of reproducti ve individuals and thus the total number of offspring produced. Surprisingl y, the strategy used depends upon the strain of symbiotic bacteria the nema todes are growing. The relevance of the results, in helping to discriminate between rival theories for the evolutionary maintenance of sex, is discuss ed.