TY - JOUR
T1 - Frequency-dependent pollinator discrimination acts against female plants in the gynodioecious Geranium maculatum
AU - Van Etten, Megan L.
AU - Chang, Shu Mei
N1 - Funding Information:
We thank D. York, A. Paul, E. Millard and G. Van Etten for help collecting data, the Georgia State Botanical Gardens for access to field locations and the staff at the University of Georgia Plant Biology greenhouses for maintaining plants before and after the study. This work was supported by a research grant from the Plant Biology Department, University of Georgia, to M.V.E., a faculty research grant to S.-M.C. from the University of Georgia Research Foundation and National Science Foundation grant DEB 0640881 to S.-M.C.
Publisher Copyright:
© 2014 The Author.
PY - 2014/12/1
Y1 - 2014/12/1
N2 - Background and Aims Gynodioecy, the co-occurrence of female and hermaphroditic individuals, is thought to be an intermediate step between hermaphroditism and separate sexes, a major transition in flowering plants. Because retaining females in a population requires that they have increased seed fitness (to compensate for the lack of pollen fitness), factors that affect seed fitness are of great importance to the evolution of this mating system and have often been studied. However, factors negatively affecting female fitness are equally important and have been largely neglected. One such factor stems from female flowers being less attractive to insects than hermaphrodite flowers, thereby decreasing their relative fitness. Methods To test the severity and consequences of this type of pollinator discrimination in Geranium maculatum, experimental populations with the range of sex ratios observed in nature were created, ranging from 13 % to 42 % females. Pollinators were observed in order to measure the strength of discrimination, and pollen deposition and seed production of both sexes were measured to determine the fitness consequences of this discrimination. Additionally a comparison was made across the sex ratios to determine whether discrimination was frequency-dependent. Key Results It was found that female flowers, on average, were visited at half of the rate of hermaphrodite flowers, which decreased their pollen receipt and seed production. Additionally, females were most discriminated against when rare, due to both changes in the pollinators' behaviour and a shift in pollinator composition. Conclusions The results suggest that pollinator discrimination negatively affects females' relative fitness when they are rare. Thus, the initial spread of females in a population, the first step in the evolution of gynodioecy, may be made more difficult due to pollinator discrimination.
AB - Background and Aims Gynodioecy, the co-occurrence of female and hermaphroditic individuals, is thought to be an intermediate step between hermaphroditism and separate sexes, a major transition in flowering plants. Because retaining females in a population requires that they have increased seed fitness (to compensate for the lack of pollen fitness), factors that affect seed fitness are of great importance to the evolution of this mating system and have often been studied. However, factors negatively affecting female fitness are equally important and have been largely neglected. One such factor stems from female flowers being less attractive to insects than hermaphrodite flowers, thereby decreasing their relative fitness. Methods To test the severity and consequences of this type of pollinator discrimination in Geranium maculatum, experimental populations with the range of sex ratios observed in nature were created, ranging from 13 % to 42 % females. Pollinators were observed in order to measure the strength of discrimination, and pollen deposition and seed production of both sexes were measured to determine the fitness consequences of this discrimination. Additionally a comparison was made across the sex ratios to determine whether discrimination was frequency-dependent. Key Results It was found that female flowers, on average, were visited at half of the rate of hermaphrodite flowers, which decreased their pollen receipt and seed production. Additionally, females were most discriminated against when rare, due to both changes in the pollinators' behaviour and a shift in pollinator composition. Conclusions The results suggest that pollinator discrimination negatively affects females' relative fitness when they are rare. Thus, the initial spread of females in a population, the first step in the evolution of gynodioecy, may be made more difficult due to pollinator discrimination.
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U2 - 10.1093/aob/mcu204
DO - 10.1093/aob/mcu204
M3 - Article
C2 - 25326647
AN - SCOPUS:84922551569
VL - 114
SP - 1769
EP - 1778
JO - Annals of Botany
JF - Annals of Botany
SN - 0305-7364
IS - 8
ER -