Apical Thickening of Epicarp is Responsible for Embryo Protection in Acorns of Quercus Variabilis

Abstract

The present study explored the evolutionary role of epicarp thickness ofQ. variabilisacorns as a defensive mechanism against weevil infestation. Our results, based on two years' study, suggested that length and fresh mass of insect-damaged acorns were not different from those of intact ones, but width did differ. About 2, 18, and 79% of oviposition sites are distributed at the apical end, middle part, and basal end of acorns, respectively. About 5, 49, and 55% of eggs or larvae are infested at the apical end, middle part, and basal end, respectively. Similarly, about 10, 43, and 45% of emergence holes are found at the apical end, middle part, and basal end. Epicarp thickness varied among the three parts of acorns and was significantly negatively correlated with the appearance percentage of oviposition sites, infestation sites, and emergence sites, respectively. However, secondary metabolites and nutrition reserve showed no close correlation with the appearance percentage of oviposition sites, infestation sites, and emergence sites. Acorns with emergence holes at the apical end exhibited significantly lower seedling emergence and survival rates. Therefore, variation in epicarp thickness in individual acorns may be responsible for the weevil's preference for oviposition, infestation, and emergence, and acts as an alternative and important strategy protecting acorn embryos from pre-dispersal larval damage.