TOXICITY IN FLESHY FRUITS - A NONADAPTIVE TRAIT

We compared characteristics of species with toxic vs non-toxic fleshy fruits in a nemoral-boreal area in order to examine five hypotheses proposed by C. M. Herrera in 1982. The hypotheses predict that toxicity in fleshy fruits should be associated with (1) herbaceous growth form, (2) suboptimal fruiting phenology, (3) low abundance and low fecundity, (4) high seed number, and (5) low nutrient content, as compared to non-toxic fruits. Only one of the hypotheses was supported in this study: toxic fruits were significantly over-represented among herbs. The tested hypotheses are based on the assumption that fruit toxicity is a mechanism against fruit destroying pests and insects. A literature survey of distribution of toxins in plant tissues indicated, however, that toxic fruit pulp occurs in species which are generally ''toxic''. Furthermore. concentration of toxins in fruit pulp tend to be lower than in other plant tissue. Toxic fruits may consequently be an incidental ''non-adaptive'' effect of plants evolving anti-herbivory mechanisms, in combination with an inability to exclude toxins from fruit pulp.