Microbiomes are vast communities of microbes and viruses that populate all natural ecosystems. Viruses have been considered the most variable component of microbiomes, as supported by virome surveys and examples of high genomic mosaicism. However, recent evidence suggests that the human gut virome is remarkably stable compared to other environments. Here we investigate the origin, evolution, and epidemiology of crAssphage, a widespread human gut virus. Through a global collaboratory, we obtained DNA sequences of crAssphage from over one-third of the world's countries, and showed that its phylogeography is locally clustered within countries, cities, and individuals. We also found colinear crAssphage-like genomes in both Old-World and New-World primates, challenging genomic mosaicism and suggesting that the association of crAssphage with primates may be millions of years old. We conclude that crAssphage is a benign globetrotter virus that may have co-evolved with the human lineage and an integral part of the normal human gut virome.

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Discoveries of how social behavior can influence the plasticity of gonadotropin-releasing hormone (GnRH) have revolutionized the field of behavioral neuroendocrinology by providing new insights into the neural mechanisms controlling behavior. In 2000, the neuropeptide gonadotropin inhibitory hormone (GnIH) was discovered and is changing the way we view how the brain mediates reproduction and associated behaviors. GnIH acts as a reproductive 'pause button', momentarily inhibiting the activity of the reproductive system. However, how GnIH fluctuates naturally in response to social environment is unknown. We examine how the outcome of competition for limited resources needed for reproduction is associated with GnIH. We experimentally manipulated nesting opportunities for pairs of European starlings (Sturnus vulgaris) and examined brain GnIH mRNA and peptide content, as well as GnRH content and plasma testosterone and corticosterone. By limiting the number of nest boxes per enclosure and thus the number of social pairing and nesting opportunities, we observed that birds which outcompeted others for nest boxes ('winners') had significantly fewer numbers of GnIH peptide-producing cells than those without nest boxes ('losers') and this relationship changed with breeding stage. GnRH content, testosterone and corticosterone did not vary with nest box ownership. Thus, while birds appeared reproductively capable across treatments, our data indicate that GnIH may serve as a modulator of reproductive behaviors in response to social environment. Additionally, we provide some evidence of the adaptive value of this mechanism. . For all vertebrates studied, the gonadotropin-releasing hormone (GnRH) family of peptides is a key regulator of the reproductive, or hypothalamic-pituitary-gonadal (HPG), axis. Gonadotropinreleasing hormone released from the hypothalamus signals the anterior pituitary gland to release the gonadotropic hormones luteinizing hormone (LH) and follicle-stimulating hormone (FSH) into the bloodstream. Luteinizing hormone and FSH then promote testicular spermatogenesis, follicular growth and estradiol and testosterone release which feedback to and modulate all levels of the HPG axis. Several studies on how social behavior can influence the plasticity of the GnRH system have revolutionized the field of behavioral and reproductive neuroendocrinology by expanding our understanding of how social interactions can influence neural mechanisms associated with reproduction (Burmeister 2005;Fox et al. 1997;Francis et al. 1993). The discovery of the novel neurohormone gonadotropin inhibitory hormone (GnIH; Tsutsui et al.) in 2000 is changing the way we view how reproduction and sexual behavior are regulated by the brain.Found in the area of the brain responsible for reproduction, the hypothalamus, GnIH inhibits reproduction and sexual behavior. Gonadotropin inhibitory hormone decreases the activity of GnRH neurons in addition to reducing synthesis and release of the gonadotropins LH and, in some cases, FSH from the pituita...