SEXUAL POLYMORPHISM, GROWTH, AND REPRODUCTIVE EFFORT IN EGYPTIAN THYMELAEA-HIRSUTA (THYMELAEACEAE)

Gender phenotypes of Thymelaea hirsuta (L.) Endl. were surveyed in six major habitats in the western Mediterranean region of Egypt. Five gen der phenotypes were observed at all sites: subandroecious (male), subg ynoecious (female), protogynous, protandrous, and gender-labile indivi duals. Patterns of vegetative growth, reproductive effort, and sex-siz e relationships were also determined. Females and males were comparabl e in overall abundance (35.5% and 30.2%, respectively). However, the f requency of sex forms varied significantly among habitats. Plant size (canopy volume) was used as a measure of environmental quality for the species: the coastal dunes were by far the most favorable habitat, fo llowed by the nonsaline depressions, inland plateau, and inland silice ous deposits. The smallest plants were associated with the inland ridg es and saline depressions. Protandrous individuals, and female shrubs at the more favorable habitats (e.g., the coastal dunes and nonsaline depressions), had greater canopy volume than males. In contrast, males were larger than females at the less favorable habitats (e.g., the in land plateau and saline depressions). Advantageous growth conditions a t the coastal dunes are demonstrated by the greater rate of increase i n crown diameter and crown volume noted there, for each size class and sex form. The greatest rates of increase were present in smaller-size d individuals. Size differences between the sex forms were considered in terms of trade-offs between individual growth rate (GR) and reprodu ctive effort (RE); evidence of a trade-off was mixed. Indeed, in a com parison of GR and RE at two extremes of habitat (coastal dune vs. inla nd plateau), females had greater GR and greater RE at the relatively b enign coastal dunes, while at the more harsh, inland plateau site male s showed greater GR and RE than females. Peak reproductive effort vari ed significantly with gender phenotype and habitat type.