Nancy A. Moran

“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.”

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

“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.”

“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.”