Nancy A. Moran

“The guts of honey bee workers contain a distinctive community of bacterial species. They are microaerophilic or anaerobic, and were not clearly deliniated by earlier studies relying on laboratory culture of isolates under atmospheric oxygen levels. Recently, a more complete picture of the potential metabolism and functions of these bacteria have been possible, using genomic approaches based on metagenomic samples, as well as cultured isolates. Of these, most are host-restricted and are generally absent outside adult guts.”

“The genomes of long-term obligate symbionts often undergo irreversible gene loss and deterioration even as hosts evolve dependence on them. In some cases, animal genomes may have acquired genes from symbionts, mirroring the gene uptake from mitochondrial and plastid genomes. Multiple symbionts often coexist in the same host, resulting in coadaptation among several phylogenetically distant genomes.”

“Buchnera only have 600 genes, compared to about 4,000 or 5,000 for E. coli ... This is a recurring pattern in the genomes of both bacterial symbionts and pathogens, but why do they get so small? ... while part of the reduction is due to adaptation, a lot of it just reflects genetic drift ... It's just a consequence of long-term evolution in a restricted environment with small population sizes.”

“Symbioses are central in the evolution of complexity; have evolved many times and are critical to the lifestyles of many animals and plants and also to whole ecosystems, in which symbiotic organisms are key players. The primary reason that symbiosis research is suddenly active, after decades at the margins of mainstream biology, is that DNA technology and genomics give us enormous new ability to discover symbiont diversity, and more significantly, to reveal how microbial metabolic capabilities contribute to the functioning of hosts and biological communities.”

“Life cycles that incorporate discrete, morphologically distnct phases predominate among animals.”

“The aphid Pemphigus betae typically shows a complex life cycle, with annual alternation between cottonwood trees, where it forms leaf galls, and herbaceous plants, where it lives on roots. Distinct phenotypes are associated with each phase. In a population in Utah, aphid clones vary in their tendencies to undergo the cottonwood phase of the life cycle, with certain clones rarely producing the winged migrants that initiate the cottonwood phase.”

“Heteroecy appears to be a consequence of the seasonal polymorphism of aphids, which causes some morphs (the fundatrices) to be more evolutionarily constrained than others (the summer females) in their abilities to acquire hosts. Some aphid lineages have escaped this constraint by replacing the ancestral fundatrix morph and remaining all year on former secondary hosts, thus becoming secondarily autoecious. Most of the large and species-rich groups of Aphidinae on herbaceous angiosperms probably are derived from ancestors showing such life-cycle reduction.”