Effective Population Sizes for Cytoplasmic and Nuclear Genes in a Gynodioecious Species: The Role of the Sex Determination System

Corresponding author: Valérie Laporte, Institute of Cell, Animal and Population Biology, University of Edinburgh, Ashworth Laboratory, King's Bldgs., W. Mains Rd., Edinburgh EH9 3JT, United Kingdom., valerie.laporte{at}ed.ac.uk (E-mail)

Communicating editor: M. SLATKIN

Equations are derived for the effective sizes of gynodioecious populations with respect to both nuclear and cytoplasmic genes (N_ec and N_en, respectively). Compared to hermaphroditism, gynodioecy generally reduces effective population sizes for both kinds of loci to an extent depending on the frequency of females, the sex determination system, and the selfing rate of hermaphrodites. This reduction is due to fitness differences between the sexes and is highly influenced by the mode of inheritance of this fitness. In absence of selfing, nuclear gynodioecy results in a reduction of N_ec that depends strongly on the dominance of male sterility alleles, while N_en remains equal to the census number (N). With cytonuclear gynodioecy, both cytoplasmic and nuclear effective sizes are reduced, and at the extreme, dioecy results 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 hermaphroditism with the same selfing rate of hermaphrodites. Unexpectedly, N_ec also varies with the selfing rate. Thus the genetic sex-determination system appears as a major factor for the nuclear and cytoplasmic genetic diversities of gynodioecious species.

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