Article

Placentation patterns and seed number in fruits of South American Solanum subgen. Leptostemonum (Solanaceae) species

Darwiniana : Revista del Instituto de Botanica Darwinion 01/2007;
Source: DOAJ

ABSTRACT Thirty-seven South American species representing seven sections of Solanum subgen. Leptostemonum were analyzed. Andromonoecious as well as hermaphrodite species were considered. The length and width of their fruits was measured, and the number of seeds per fruit was counted. Medial cross sections of fresh, ripe fruits were observed with a stereoscopic microscope and illustrated. Six placentation patterns and three types of seeds were described. A relationship among seed number, fruit size, fruit color and sexual system was detected by means of statistical analysis. These results suggest that andromonoecy affects fruit size and placentation patterns, in order to contain a higher number of seeds per fruit.

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  • American Journal of Botany - AMER J BOT. 01/1993; 80(8).
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    ABSTRACT: We examined the influence of secondary metabolites (glycoalkaloids) of Solanum fruits on fruit consumption by seed dispersers and seed predators. Our goal was to determine the degree to which secondary metabolites might explain fruit-frugivore in- teractions that heretofore have not been explained by other fruit-related variables (e.g., color, nutrient content, seediness, etc.). Using feeding trails with real fruits and artificial fruit pulp media, we tested two sets of hypotheses, one relating to the specificity of sec- ondary metabolites and the other to intra- and interspecific variation in secondary metabolite content. First, the Directed Toxicity Hypothesis was tested against its alternative, the General Toxicity Hypothesis. The Directed Toxicity Hypothesis posits that fruit pulp secondary metabolites are directed primarily toward organisms that destroy seeds following fruit consumption, remaining nontoxic to organisms that disperse seeds. The General Toxicity Hypothesis states that these secondary metabolites are general in their effects. Second, the Removal Rate Hypothesis was tested against its alternative, the Nutrient-Toxin Titration Hypothesis. The Removal Rate Hypothesis posits that profitable fruits, with high natural rates of removal, contain only low levels of secondary metabolites as defenses against seed predators and pathogens. In contrast, the Nutrient-Toxin Titration Hypothesis states that profitable fruits are better able to afford protection by high levels of secondary metabolites because high nutrient levels compensate for deterrent effects of secondary metabolites. We compared Solanum carolinense, with high levels of secondary metabolites (gly- coalkaloids) in ripe fruit, and S. americanum, with negligible levels, conducting four sets of feeding trials: (1) Real Fruit trials to determine the preferences of our study animals for real fruit of each plant species; (2) Fruit Mimic trials using artificial fruit pulp media to determine the relative effects of nutrient and glycoalkaloid content on fruit preferences; (3) Interaction trials using artificial fruit pulp media to examine relative and interactive effects of the two main glycoalkaloids in our fruits (a-solasonine and a-solamargine); and (4) Nutrient-Toxin Titration trials using artificial fruit pulp media to determine how much nutrient content might compensate for deterrent effects. Both seed predators and seed dispersers preferred the low-glycoalkaloid S. americanum fruits and were deterred by glycoalkaloid levels typical of ripe S. carolinensefruits. Because of the generality of the deterrent effects, we rejected the Directed Toxicity Hypothesis. Additionally, we found no evidence for differences between the two glycoalkaloids in their deterrent effects, and no evidence of synergism between them. Nutrient effects were gen- erally small; we found no evidence that nutrient variation could compensate for the deter- rence produced by levels of glycoalkaloids found in ripe S. carolinense fruits. Ripe fruits of the presumably more profitable, preferred S. americanum contain much lower levels of glycoalkaloid. Taken together, our results support the Removal Rate Hypothesis. Secondary metabolites of ripe fleshy fruits are an important determinant of fruit use by frugivores. We suggest that a primary function of these metabolites is defense against pests and patho- gens. Thus, these organisms should be considered an important influence on fruit-seed disperser interactions.
    Ecology. 01/1997; 78(3):782-798.
  • American Journal of Botany - AMER J BOT. 01/1991; 78(3).

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