Geographical Divergence and Environmental Drivers of the Symbiotic Bacterial Community Structure in a...

Symbiotic bacteria play a crucial role in the life history of insects. Aphids and their diverse symbiotic bacteria serve as an excellent model for studying the bacterial-insect symbiotic relationship. Our recent study revealed that the aphid Periphyllus koelreuteriae, an important ornamental pest specifically feeding on Koelreuteria plants and widely distributed in the temperate and subtropical regions of China, is actually a species complex that includes three species (P. koelreuteriae, P. blackmani, and P. guangxuei). To characterize the composition and abundance of the symbiotic bacterial communities within this species complex, we employed Illumina NovaSeq high-throughput sequencing to assess symbiotic bacterial diversity and further investigated the associations between symbiont community profiles and aphid species, geographic populations, and host plants. The results show that two dominant symbiotic bacteria were detected, namely Buchnera and Serratia. The mean relative abundance of Buchnera exhibited the trend: P. guangxuei (88.41%) < P. blackmani (95.36%) < P. koelreuteriae (98.51%), which are distributed in subtropical highland, subtropical humid, and temperate regions, respectively, whereas Serratia showed the opposite pattern. Redundancy analysis (RDA) revealed that latitude (LAT) and the minimum temperature of the coldest month (BIO6) are critical environmental factors affecting the composition of symbiotic bacteria in the P. koelreuteriae species complex. The relative abundance of Buchnera significantly decreased with decreasing latitude and increasing minimum temperature of the coldest month, whereas the relative abundance of Serratia exhibited the opposite. These results indicate that the composition and abundance of symbiotic bacteria in this species complex are influenced by both aphid species and geographic-climatic conditions, with latitude (LAT) and the minimum temperature of the coldest month (BIO6) identified as key environmental factors shaping the community structure. This study elucidates the distribution patterns of symbiotic bacteria across closely allied aphid species and along environmental gradients, providing a theoretical foundation for understanding the ecological adaptation mechanisms of this aphid species complex and laying a scientific basis for developing targeted integrated management strategies in the future.