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PNAS Papers on Bee Gut Bugs, Selection in Mycobacterium tuberculosis Complex, Primate Evolution

A University of Texas team investigates gut microbial community diversification in honey bees and bumble bees, focusing on symbiotic Gilliamella and Snodgrassella bacteria that appear to have evolved in concert with these social bees over tens of millions of years. Using genome sequences from more than 100 Gilliamella isolates and 57 isolates of Snodgrassella, the researchers documented microbial population diversification despite minimal gene flow, with adaptations related to everything from the host species to microbe location in the bee body — results they explored further with spatial analyses conducted with engineered fluorescent Gilliamella lineages. "Our findings show that bee gut bacteria can diversify due to isolation in different host species and also due to the spatial niche partitioning within individual hosts, leading to barriers to gene flow."

Investigators in Spain outline findings from an evolutionary analysis of Mycobacterium tuberculosis complex (MTBC) strains, which tend to have very low levels of genetic diversity. The team analyzed some 5,000 whole-genome sequences representing MTBC strains from around the world to search for signs of selection across individual genes and within the context of the MTBC phylogenetic tree. "Genetic differences between different [MTBC] strains determine their ability to transmit within different host populations, their latency times, and their drug resistance profiles," the authors write, adding that their analyses uncovered "regions that have evolved under changing types of selection since the time of the MTBC common ancestor."

A team from the University of Utah and the University of Oregon present a nucleotide site pattern-based analysis of bonobo (Pan paniscus) and chimpanzee (P. troglodytes) evolutionary history, searching past demographic clues and ancestral admixture events similar to those found between humans and archaic hominins. Based on nucleotide site pattern analyses using whole-genome sequences for 71 bonobo or chimp representatives, the researchers saw signs of admixture in the bonobo and chimp, including genetic introgression between chimp groups and sex-biased movement or breeding. Together, the authors note, these and other findings "offer insight into bonobo and chimpanzee evolutionary history and suggest considerable differences between current and historic chimpanzee biogeography.

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