Evidence of gynodioecy in Kallstroemia grandiflora (Zygophyllaceae): Microsporogenesis in hermaphrodite and female plants and lack of reproductive compensation

Abstract

Understanding mechanisms involved in the maintenance of gynodioecy in natural populations requires evidence concerning the phenotypic expression and reproductive consequences of male sterility. We have recently discovered male sterility in populations of Kallstroemia grandiflora from northwestern Mexico. Here we describe the development of anther and pollen grains in hermaphrodite and female plants and explore whether females experience any compensatory advantage over hermaphrodites. The major difference in anther development between morphs was the early disintegration of tapetal cells in anthers of pistillate flowers. Abnormalities in developing pollen grains in pistillate flowers were seen in the microspore mother cells, microspore tetrads, and young and mature pollen grains. Biomass allocation to flowers, petals, and stamens were larger in hermaphrodites, while both sexes had the same number of ovules per flower. Hermaphrodite flowers were self-compatible. Pollination experiments revealed evidence of pollinator limitation for female plants but not for hermaphrodites. No evidence of reproductive compensation was detected, as flower and fruit production were similar for both sexes in two populations of K. grandiflora. We suggest alternative mechanisms that could maintain male sterility in natural populations of K. grandiflora.