Is the older the better? Host plant ontogeny and resource availability drives gall-inducing insect diversity and network topology

Abstract

Plant ontogeny modifies resource availability to herbivore communities, with drastic effects on gall-inducing insects preference during the host's development. In this study, we investigated the effects of plant ontogeny on the richness, abundance and interaction networks of gall communities. We used saplings, juveniles and mature individuals of the host plant Bauhinia brevipes Vogel (Fabaceae) and their associated galls as study models. Our results showed that gall-inducing insect richness was highest in mature plants, while abundance was higher in both sapling and mature plants. Moreover, gall community composition differed among the three developmental stages. These diversity parameters were positively associated with the number of leaves of the plants. The prevalence of gall-inducing insects on mature plants was also reflected in the network topology: galls were more linked, and significantly specialized, nested, and presented modules in mature plants. The interaction strength of one gall-inducing species increased in mature plants, while three gall-inducing insects increased with the number of leaves independently of the ontogenetic stage of plants, therefore refuting an ontogenetic succession in the system. We suggest that resource quantity and quality variation of host ontogeny act together to drive gall diversity and the network topology. Our study is one of the few to investigate the diversity of gall-inducing insect communities on host ontogeny, and pioneer to evaluate this effect on interaction networks. Overall, this study advances in the understanding of plant ontogeny in the interaction of gall-host systems, which may contribute to ecological aspects, including conservative efforts of gall-inducing insects.