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

Within an area spanning approximately 1 km², individuals belonging to a population of andromonoecious Euphorbia xanti range in their sex expression from all-staminate to all-cosexual. In this study I attempt to evaluate this variation using measures of non-directional asymmetry as potential indicators 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 relationship between asymmetry and 'femaleness' (i.e. the per-plant proportion of cosexual cyathia). Unexpectedly, per-plant mean asymmetry peaked at intermediate sexuality (femaleness of approx. 0.5). At the same time, intermediate sexuality was qualitatively associated with relatively low probabilities of cosexual cyathia developing fruit. I discuss two hypothetical explanations for these observations.