We report the reproductive strategy of the nematode Mesorhabditis belari. This species produces only 9% males, whose sperm is necessary to fertilize and activate the eggs. However, most of the fertilized eggs develop without using the sperm DNA and produce female individuals. Only in 9% of eggs is the male DNA utilized, producing sons. We found that mixing of parental genomes only gives rise to males because the Y-bearing sperm of males are much more competent than the X-bearing sperm for penetrating the eggs. In this previously unrecognized strategy, asexual females produce few sexual males whose genes never reenter the female pool. Here, production of males is of interest only if sons are more likely to mate with their sisters. Using game theory, we show that in this context, the production of 9% males by M. belari females is an evolutionary stable strategy.

The mechanism of biological silicification in plants remains to be elucidated. There are strong arguments supporting a role for the plant extracellular matrix and the -1-3-glucan, callose, has been identified as a possible template for silica deposition in the common horsetail, Equisetum arvense. The model plant Arabidopsis thaliana, which is not known as a silica accumulator, can be engineered to produce mutants in which, following a pathogenassociated molecular pattern challenge, callose production in leaves is either induced