THE GENETICS OF GENDER AND THE EFFECTS OF GENDER ON FLORAL CHARACTERS IN GYNODIOECIOUS PHACELIA LINEARIS (HYDROPHYLLACEAE)

The evolution of gynodioecy depends in part on the location (nucleus or cytoplasm) of gender-determining genes. Characters genetically correlated with gender also can be important in the evolution of this sexual system. For example, gender differences in the costs of flowers affect the potential for resource compensation by females for the loss of male function. This paper reports the genetics of gender and the nature of secondary sex characters of flowers in Phacelia linearis (Hydrophyllaceae), a gynodioecious annual in which females exhibit substantial compensation. A single nuclear gene has a major effect on gender, recessive homozygotes being male-sterile, but not all the data can be explained by this or other simple inheritance models. In nature, hermaphrodites have wider corollas than females and begin to flower slightly later than females. In a common environment, gender effects on corolla size are modified by genetic background and/or maternal effects. Hermaphrodite flowers have 15% greater dry biomass than female flowers, but similar ovule number and nectar sugar production. Hermaphrodite and female flowers differ in the linear dimensions and biomass allocation of several floral organs. In particular, the androecia and corollas of female flowers are smaller than those of hermaphrodite flowers, both in absolute terms and relative to the size of the rest of the flower. Corolla size reduction could be an important source of resources for compensation by females.