Developmental instability and within-population variation in sex expression by andromonoecious Euphorbia xanti

Within an area spanning approximately 1 km(2), individuals belonging to a p opulation of andromonoecious Euphorbia xanti range in their sex expression from all-staminate to all-cosexual. In this study I attempt to evaluate thi s variation using measures of non-directional asymmetry as potential indica tors of developmental instability. Assuming that developmental homeostasis and sex allocation are sensitive to the same, or correlated, stress factors , I expected an adaptive explanation to be manifested in a monotonic relati onship between asymmetry and 'femaleness' (i.e. the per-plant proportion of cosexual cyathia). Unexpectedly, per-plant mean asymmetry peaked at interm ediate sexuality (femaleness of approx. 0.5). At the same time, intermediat e sexuality was qualitatively associated with relatively low probabilities of cosexual cyathia developing fruit. I discuss two hypothetical explanatio ns for these observations.