Parallel metatranscriptome analysis reveals degradation of plant secondary metabolites by beetles and their gut symbionts.

Switching to a new host plant is a driving force for divergence and speciation in herbivorous insects. This process of incorporating a novel host plant into the diet may require a number of adaptations in the insect herbivores that allow them to consume host plant tissue that may contain toxic secondary chemicals. As a result, herbivorous insects are predicted to have evolved efficient ways to detoxify major plant defences and increase fitness by either relying on their own genomes or by recruiting other organisms such as microbial gut symbionts. In the present study we used parallel metatranscriptomic analyses of Altica flea beetles and their gut symbionts to explore the contributions of beetle detoxification mechanisms versus detoxification by their gut consortium. We compared the gut meta-transcriptomes of two sympatric Altica species that feed exclusively on different host plant species as well as their F1 hybrids that were fed one of the two host plant species. These comparisons revealed that gene expression patterns of Altica are dependent on both beetle species identity and diet. The community structure of gut symbionts was also dependent on the identity of the beetle species, and the gene expression patterns of the gut symbionts were significantly correlated with beetle species and plant diet. Some of the enriched genes identified in the beetles and gut symbionts are involved in the degradation of secondary metabolites produced by plants, suggesting that Altica flea beetles may use their gut microbiota to help them feed on and adapt to their host plants.

Two Apriona Species Sharing a Host Niche Have Different Gut Microbiome Diversity.

The adaptability of herbivorous insects to toxic plant defense compounds is partly related to the structure of the gut microbiome. To overcome plant resistance, the insect gut microbiome should respond to a wide range of allelochemicals derived from dietary niches. Nevertheless, for sibling herbivorous insect species, whether the gut microbiome contributes to success in food niche competition is unclear. Based on 16S rDNA high-throughput sequencing, the gut microbiomes of two Apriona species that share the same food niche were investigated in this study to determine whether the gut microbiome contributes to insect success in food-niche competition. Our observations indicated that the gut microbiome tended to play a part in host niche competition between the two Apriona species. The gut microbiome of Apriona swainsoni had many enriched pathways that can help degrade plant toxic secondary compounds, including xenobiotic biodegradation and metabolism, terpenoid and polyketide metabolism, and secondary metabolite biosynthesis. Meanwhile, A. swainsoni hosted a much greater variety of microorganisms and had more viable bacteria than A. germari. We conclude that gut microbes may influence the coevolution of herbivores and host plants. Gut bacteria may not only serve to boost nutritional relationships, but may also play an important role in insect food niche competition.

The complete mitochondrial genomes of two sibling species of camellia weevils (Coleoptera: Curculionidae) and patterns of Curculionini speciation.

Complete mitochondrial genomes contain large and diverse datasets for species delineation. To better understand the divergence of the two morphologically indistinguishable weevil species in Curculionini, we first sequenced and compared their complete mitochondrial genomes. The complete mitochondrial genomes of Curculio chinensis and Curculio sp. were 19,713 bp with an A + T content of 76.61% and 19,216 bp with an A + T content of 76.85%, respectively. All 37 of the typical mitochondrial genes were determined in both species. The 13 protein sequences of the two species shared high homology (about 90%) except for ATP8 (73.08%). The differences in secondary structure of ATP8 were the number of possible proteins and nucleic acid binding sites. There were 22 and 15 mismatched base-pairs in the tRNA secondary structures from C. chinensis and Curculio sp., respectively. Maximum Likelihood and Bayesian analyses indicated that Curculio sp. is a novel species closely related to C. chinensis. The divergence time estimation suggests that Cryptorhynchinae and Curculionini lines diverged in the Cenozoic Period, while C. chinensis and Curculio sp. diverged at 6.7079 (95% CI 5-13) Mya. This study demonstrates the utility of using complete mitochondrial gene sets for phylogenetic analysis and enhances our understanding of the genetic basis for the evolution of the Curculionini.