The influence of demography and local mating environment on sex ratios in a wind-pollinated dioecious plant Journal Article

Author(s): Pickup, Melinda; Barrett, Spencer C
Article Title: The influence of demography and local mating environment on sex ratios in a wind-pollinated dioecious plant
Affiliation IST Austria
Abstract: Negative frequency-dependent selection should result in equal sex ratios in large populations of dioecious flowering plants, but deviations from equality are commonly reported. A variety of ecological and genetic factors can explain biased sex ratios, although the mechanisms involved are not well understood. Most dioecious species are long-lived and/or clonal complicating efforts to identify stages during the life cycle when biases develop. We investigated the demographic correlates of sex-ratio variation in two chromosome races of Rumex hastatulus, an annual, wind-pollinated colonizer of open habitats from the southern USA. We examined sex ratios in 46 populations and evaluated the hypothesis that the proximity of males in the local mating environment, through its influence on gametophytic selection, is the primary cause of female-biased sex ratios. Female-biased sex ratios characterized most populations of R. hastatulus (mean sex ratio = 0.62), with significant female bias in 89% of populations. Large, high-density populations had the highest proportion of females, whereas smaller, low-density populations had sex ratios closer to equality. Progeny sex ratios were more female biased when males were in closer proximity to females, a result consistent with the gametophytic selection hypothesis. Our results suggest that interactions between demographic and genetic factors are probably the main cause of female-biased sex ratios in R. hastatulus. The annual life cycle of this species may limit the scope for selection against males and may account for the weaker degree of bias in comparison with perennial Rumex species.
Keywords: dioecy; female-biased sex ratios; gametophytic competition; local mating environment; plant density; sex ratios; wind pollination
Journal Title: Ecology and Evolution
Volume: 3
Issue 3
ISSN: 2045-7758
Publisher: Wiley-Blackwell  
Date Published: 2013-03-01
Start Page: 629
End Page: 639
Copyright Statement: CC-BY
Sponsor: Funded by Natural Sciences and Engineering Research Council of Canada; Canada Research Chair's Program
DOI: 10.1002/ece3.465
Notes: We thank Caroli de Waal for assistance with the field survey of sex ratios and Allison Kwok for help with the glasshouse experiment.
Open access: yes (OA journal)