Gall responses to drying habitats: Insights from the community of galling herbivores associated with the superhost Caryocar brasiliense Cambess. (Caryocaraceae).

Abstract

Galls are new plant organs formed in response to the stimuli of gall-inducing organisms, but may also be influenced by environmental conditions. This study evaluated the richness, abundance, and co-occurrence in the gall community associated with Caryocar brasiliense Cambess. (Caryocaraceae) areas with varying degrees of environmental stress due to the drying of palm swamps, called Veredas. Additionally, structural and metabolic attributes related to nutrition and protection were evaluated as possible stress markers. The research was conducted in two Cerrado areas with different water availability: the Parque Estadual Veredas do Peruaçu (lower water availability; more stressful) and the Área de Proteção Ambiental do Rio Pandeiros (higher water availability; less stressful). A total of 51,336 galls from five morphospecies were sampled: intralaminar globoid gall (IGG), extralaminar globoid gall (EGG), globoid petiolar gall (GPG), lenticular gall (LG) and clavate gall (CG). Gall richness was similar in both environments, but abundance was higher in the less stressful area, challenging the hypothesis that environmental stress increases gall formation. Random co-occurrence patterns suggested that gall inducers occupy distinct spatial niches to reduce competition. Structurally and metabolically, galls exhibited similarities, including nutritive tissues and nutritious substances in their internal compartments. However, in the more stressful environment, some galls had smaller internal and larger external compartments, with increased lignin and phenolic compounds in the outer tissue layers. Lignin deposition and phenolic accumulation are evidenced as stress markers which indicate that galls display phenotypic plasticity and adaptive strategies, enhancing protection and survival under the stressful conditions of drying environments.