Host-associated differentiation of species of Sternorrhyncha in pecan and water hickory and its correspondence with bacterial diversity

Background/Question/Methods

Host Associated Differentiation (HAD) is the formation of genetically distinct host associated populations. HAD has been invoked to explain the enormous diversity of phytophagous insects. Individual case studies of HAD are interesting but by themselves they are unable to provide clues on the mechanisms that might promote it. Thus, we are studying HAD on several species associated with the same host-plant species pair: Pecan and water hickory (both in the genus Carya). To date we have recorded 29 insect species shared by these two host-plants. It has been suggested that bacteria in insect herbivores may play a role in HAD by allowing their insect hosts to use different plant species. The objectives of this study were: 1) to assess HAD in 6 species (3 exophytic and 3 endophytic Sternorrhyncha) associated with pecan and water hickory and 2) to document if HAD in these Sternorrhyncha corresponded with differences in the composition of their associated bacteria. We sampled these species on pecan and water hickory. We then obtained AFLPs and analyzed them using Bayesian clustering methods to assess HAD. We then characterized the bacteria associated with these insects when on pecan and water hickory, through metagenomic analyses using 454 sequencing.

Results/Conclusions

For each insect species, we obtained between 72 and 353 AFLP loci. We found that HAD was present in 4 out of 6 species tested. Species showing HAD were: yellow pecan aphid, black margined aphid, pecan leaf phylloxera, and pecan stem phylloxera. HAD was not present in black pecan aphid and southern pecan leaf Phylloxera. Differences in bacterial diversity were found between pecan leaf Phylloxera populations associated with pecan and water hickory. The bacteria, Pantoea agglomerans and Serratia marcescens were absent in the Phylloxera water hickory population whereas both species accounted for more than 69.72% of bacterial abundance in the pecan population. Future studies will assess if the same phenomena occurs in other Sternorrhyncha species. We stress the importance of the Carya system as a parthenogen rich contrast to the already well characterized Solidago system for the study of HAD.