Environmentally Influenced Changes in Sex Expression in an Andromonoecious Plant

Abstract

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.

The effect of sheltered load on reproduction in Solanum carolinense, a species with variable self-incompatibility

“…The majority of the flowers are perfect and functionally hermaphroditic. However, some of the flowers, usually located at the tip of the raceme, exhibit reduced non-functional pistils and are considered functionally staminate (Solomon 1985).…”

Floral phenology in relation to pollination and reproductive output in Commelina caroliniana (Commelinaceae)

“…The last two are particularly rare (Yampolsky and Yampolsky 1922;Charlesworth 1984) and, therefore, least understood. Only in recent years has there been awareness of these systems (Symon 1979(Symon , 1981Primack and Lloyd 1980;Solomon 1985;Whalen and Costich 1986;Anderson and Symon 1989;Emms 1993Emms , 1996Narbona et al 2002).…”

“…The proportions of each kinds of flowers vary among different individuals and populations of andromonoecious species (Stephenson 1979;Primack and Lloyd 1980;May and Spears 1988;Anderson 1990;Diggle 1991Diggle , 1993Diggle , 1994Narbona et al 2002). This variation stems from ecological factors (Solomon 1985) and resource availability (Stephenson 1979;Diggle 1991;Narbona et al 2002).…”

Floral trait variation in Spergularia marina (Caryophyllaceae): ontogenetic, maternal family, and population effects

“…sequence on characters such as flower size, gender expression, or gamete production (Bawa & Webb, 1983;Holtsford, 1985;Solomon, 1985;Thomson, 1985Pellmyr, 1987;Lee, 1988;Nybom, 1989;Thompson & Pellmyr, 1989;Kang & Primack, 1991;Thomson & Barrett, 1991;Ashman & Baker, 1992;Emms, 1993). Very few studies, however, provide measures of both ontogenetic and genetic sources of variation in floral traits (Young & Stanton, 1990;Armbruster, 1991;Diggle, 1993).…”