Relative risks of fungal rot for temperate ericaceous fruits: effects of seasonal variation on selection for chemical defense

Abstract

To quantify factors influencing the risk of fungal rot for vertebrate-dispersed fruits and to refine predictions concerning antifungal defense patterns, we examined physical, chemical, and phenological characteristics of ericaceous plants in New Jersey. In the field, three summer-ripening species had shorter persistence in the ripe state, shorter total retention times, and lower fungal resistance than three fall-ripening species. Summer fruits also had higher pulp carbohydrate content, lower fiber content, and (or) lower seed/pulp ratios. Whereas fungal colonization rates were somewhat lower during the ripening periods of summer species, fungal growth rates were higher owing to higher summer temperatures. In vitro fungal growth tests indicated only small effects of pulp nutrient content on fungal growth. We suggest that seasonal and chemical nutrient factors influencing risk of fungal rot for our study species are of minor significance relative to the degree to which these factors affect fruit removal by dispersers. We predict that owing to selection for high palatability, summer species should exhibit antifungal defenses with little or no antifrugivore effects (microbe-specific defenses). We also predict that because of consistently high removal rates (lower apparency), summer fruits should exhibit antifungal defenses less effective than those of fall species. Key words: antifungal defense, coadaptation, fruit rot, fruit nutrients, secondary chemistry, seed dispersal.