Host specificity of herbivorous insects promotes negative species–genetic diversity relationship

Although genetic diversity and species diversity in a community often covary, the direction and strength of the covariation vary. However, this variation in the relationship of these two diversities is poorly understood. Here we investigated the role of host-specific herbivores in generating species–genetic diversity relationship in plant communities. We quantified host specificity for Fagaceae plants–acorn weevil bipartite networks in a subtropical forest and modeled the effect of weevil herbivory on the relationship. The results showed a consistently negative relationship between Fagaceae species diversity and the genetic diversity of the dominant species, Lithocarpus glaber. Our analysis showed this negative relationship arose from a positive effect of weevil host-specificity on Fagaceae plant richness on the one hand and the negative effect of weevil host-specificity on the genetic diversity of L. glaber on the other hand. This latter negative effect was possibly due to differentiated selection of weevils on different genotypes of L. glaber. Our study highlights the importance of considering trophic interactions and herbivore host-specificity in explaining the species–genetic diversity relationship.

Methods
Leaves of L. glaber trees were sampled in November 2013 and March 2015. The genomic DNA was extracted from dried leaves of L. glaber after grinding via RIO 101 (FR120A-230 Thermo). DNA was extracted using the Plant Genomic DNA Kit (Tiangen, Beijing, China). Polymerase chain reaction (PCR) was carried out using 7 pairs of polymorphic SSR primers for L. glaber DNA. These highly-specific variable sites were selected from 13 pairs of polymorphic sites (Zhang et al. 2014). All PCR products resolved clearly on 8% polyacrylamide denaturing gels were scanned on an ABI 3130 automated sequencer (Applied Biosystems, Foster City, California, USA). Allele binning and calling were performed in GeneMAPPER version 4.0 (Applied Biosystems). Genotyping was performed according to Selkoe and Toonen's (2006) standard.