Potential Ecological Constraints on the Evolution of Gynodioecy inMimulus guttatus: Relative Fecundity and Pollinator Behavior in a Mixed-Sex Population

Abstract

Although plant breeding systems are evolutionarily labile, a shift from one system to another can involve formidable ecological obstacles. In order for gynodioecy to evolve from hermaphroditism, the carriers of a male-sterility mutation (i.e., females) must overcome two major hurdles: females must attract pollinators without offering pollen as a reward, and they must produce enough seeds to compensate for the loss of reproduction through the paternal route. We investigated the relative performance of female and hermaphroditic plants in a greenhouse study of Mimulus guttatus originating from a largely hermaphroditic population. Females had larger floral displays than did hermaphrodites, with 5% wider corollas and 34% more flowers open at one time. They also produced 22% more flowers over a lifetime and 25% more ovules per ovary than hermaphrodites, giving females 1.53 times more maternal reproductive potential. In a related experiment, bumblebees visited female plants just as frequently as hermaphroditic p...