Effective population sizes for cytoplasmic and nuclear genes in a gynodioecious species: The role of the sex determination system

Equations are derived for the effective sizes of gynodioecious populations with respect to both nuclear and cytoplasmic genes (N-ec and N-en, respecti vely), Compared to hermaphroditism, gynodioecy generally reduces effective population sizes for both kinds of loci to an extent depending on the frequ ency of females, the sex determination system, and the selfing rate of herm aphrodites. This reduction is due to fitness differences between the sexes and is highly influenced by the mode of inheritance of this fitness, In abs ence of selfing, nuclear gynodioecy results in a reduction of N-ec that dep ends strongly on the dominance of male sterility alleles, while N-en remain s equal to the census number (N). With cytonuclear gynodioecy, both cytopla smic and nuclear effective sizes are reduced, and at the extreme, dioecy re sults in the minimum N-ec values and either minimum or maximum N-en values (for low or high frequency of females, respectively). When selfing occurs, gynodioecy either increases or decreases N-en as compared to hermaphroditis m with the same selfing rate of hermaphrodites. Unexpectedly, N-ec also var ies with the selfing rate. Thus the genetic sex-determination system appear s as a major factor for the nuclear and cytoplasmic genetic diversities of gynodioecious species.