Evolution of Dioecy in Buchloe dactyloides (Gramineae): Tests for Sex-Specific Vegetative Characters, Ecological Differences, and Sexual Niche-Partitioning

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.Buchloe dactyloides is a perennial dioecious grass in which male and female inflorescences are so strikingly dimorphic that they were originally assigned to different genera. The objective of this paper is to present the results of tests for sex-specific vegetative characters, ecological differences, and sexual niche-partitioning, combining them with prior information on the reproductive biology of Buchloe for an evaluation of the key factors leading to the evolution of dioecy and sexual dimorphism. Field and greenhouse data were collected from Oklahoma and Kansas populations on vegetative characters, allocation to reproduction, and relative growth and competitive success along resource gradients. Except for greater susceptibility to leaf rust by males, there were no significant differences between males and females in vegetative characters, total biomass, or reproductive effort. Field studies of spatial distributions of males and females failed to show any relation to soil, topography, or soil moisture. In a 45-month greenhouse experiment starting at the seedling stage, the relative growth and competitive success ofrandomly paired individuals showed no evidence for differential competitive success or for niche-partitioning of males and females. The "outcrossing advantage" and subsequent sexual specialization of the female inflorescence appear to be the major factors underlying this dimorphic system.

Sex expression, sex‐specific traits, and the effects of salinity on growth and reproduction of Amaranthus cannabinus (Amaranthaceae), a dioecious annual

“…Males, however, were significantly taller than females in the field at the salt marsh and in the greenhouse. Other investigators have reported taller males in dioecious plants (Lloyd and Webb, 1977;Quinn, 1991;Quinn et al, 1994). Many investigators (e.g., Lloyd and Webb, 1977;Freeman et al, 1997, and references therein;Dawson and Geber, 1999) have suggested that increased height in males may aid in pollen dispersal in wind-pollinated species.…”

Predicting the pathway to wind pollination: heritabilities and genetic correlations of inflorescence traits associated with wind pollination in Schiedea salicaria (Caryophyllaceae)

“…Among wind-pollinated species that have been investigated, flowers in the female inflorescence of Ateleia herbertsmithii, a dioecious legume, are more tightly clustered than in male inflorescences (Janzen, 1989). Striking inflorescence dimorphism in the grass Buchloe dactyloides may be related to wind pollination, because reproductive culms of male plants are taller and have more flowers than female inflorescences (Quinn, 1991), although selection on dispersal may also have been important in evolution of inflorescence dimorphism in B. dactyloides (Quinn, 1987). Significant sexual dimorphism of inflorescence structure in the Restionaceae (Kircher, 1986) is probably related to wind pollination.…”

“…In sexually dimorphic species, the effectiveness of wind pollination might be increased by differences in secondary sex traits (Freeman et al, 1997;Lloyd & Webb, 1977). For example, in several abiotically pollinated species, the increased height of male relative to female plants, or production of more male than female flowers, may result in greater pollen dispersal by males (Lloyd & Webb, 1977;Lemen, 1980;Quinn, 1991;Bram & Quinn, 2000). Sexual dimorphism in secondary sex traits including flower size, nectar production, and inflorescence traits are also known (e.g.…”

Female Salix viminalis are more severely infected by Melampsora spp. but neither sex experiences associational effects

“…The sex ratios of neighboring plants in stands of dioecious species can be expected to have consequences for ecological interactions such as fungal pathogen infections, because genetic variation can influence infection and sex is mostly genetically determined. Furthermore, sex-biased fungal infections are common (e.g., Alexander 1989;Quinn 1991). Currently, there is no established explanation of the mechanisms driving plant sex-biases in fungal pathogen infections.…”