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Environmentally Influenced Changes in Sex Expression in an Andromonoecious Plant
Author(s) -
Solomon Bruce Peary
Publication year - 1985
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1939185
Subject(s) - inflorescence , biology , pollen , pollination , perennial plant , sex ratio , germination , botany , herbaceous plant , sex allocation , pollinator , solanum , population , pregnancy , demography , genetics , sociology , offspring
Sexual expression and maternal investment were investigated in the herbaceous perennial Solanum carolinense (Solanaceae). Field censuses, pollen germination studies, and the results of hand—pollination experiments in a greenhouse revealed that there are three flower types. Morphological males (M) are found near the tip of the inflorescence and have short styles; these flowers did not set fruit when pollinated. All other flowers have long styles and are morphological hermaphrodites (H); among these, those near the base of an inflorescence set fruit when pollinated (fruiting hermaphrodites, FH) while those in intermediate positions did not (functional males, FM). No morphological differences were apparent between FH and FM flowers. Male function of M and H flowers was indistinguishable in terms of pollen germination and quantity and quality of seed produced. The proportions of FM flowers decreased with later inflorescences, but the proportion of FM flowers increased correspondingly. Thus, the morphological sex ratio, M/(M + H), decreased with plant size, while the functional sex ratio, (M + FM)/(M + FM + FH) did not vary. These data do not support evolutionary theories that predict increased allocation to female versus male function with increasing plant size. In addition, experimental manipulations were performed on greenhouse plants. Morphological sex ratio changed in response to various plant hormones, which suggests hormone involvement. Sex ratio increased in response to increased shade and water stress, which supports those evolutionary theories that predict a shift to maleness in response to stress. However, increasing levels of fertilizer also increased the morphological sex ratio Pollination did not influence the morphological sex of subsequent flowers; rather, regulation of fruit—set after pollination occurred via changes in the proportion of H flowers that did (FH) or did not (FM) set fruit. The results are discussed in terms of three stages at which maternal investment can be regulated: flower initiation, flower maturation, and fruit maturation.