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Diet and host phylogeny drive the taxonomic and functional contents of the gut microbiome in mammals, yet it is unknown whether these patterns hold across all vertebrate lineages. Here, we assessed gut microbiomes from ∼900 vertebrate species, including 315 mammals and 491 birds, assessing contributions of diet, phylogeny, and physiology to structuring gut microbiomes. In most nonflying mammals, strong correlations exist between microbial community similarity, host diet, and host phylogenetic distance up to the host order level. In birds, by contrast, gut microbiomes are only very weakly correlated to diet or host phylogeny. Furthermore, while most microbes resident in mammalian guts are present in only a restricted taxonomic range of hosts, most microbes recovered from birds show little evidence of host specificity. Notably, among the mammals, bats host especially bird-like gut microbiomes, with little evidence for correlation to host diet or phylogeny. This suggests that host-gut microbiome phylosymbiosis depends on factors convergently absent in birds and bats, potentially associated with physiological adaptations to flight. Our findings expose major variations in the behavior of these important symbioses in endothermic vertebrates and may signal fundamental evolutionary shifts in the cost/benefit framework of the gut microbiome.IMPORTANCE In this comprehensive survey of microbiomes of >900 species, including 315 mammals and 491 birds, we find a striking convergence of the microbiomes of birds and animals that fly. In nonflying mammals, diet and short-term evolutionary relatedness drive the microbiome, and many microbial species are specific to a particular kind of mammal, but flying mammals and birds break this pattern with many microbes shared across different species, with little correlation either with diet or with relatedness of the hosts. This finding suggests that adaptation to flight breaks long-held relationships between hosts and their microbes.

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Breath‐hold diving presents air‐breathing vertebrates with the challenge of maintaining aerobic respiration while exercising underwater. Adaptive increases in the oxygen (O2) storage capacity in the lungs, blood, or muscle tissues can enhance these reserves and greatly extend aerobic foraging time underwater. Here, we report blood‐ and muscle‐O2 storage parameters (blood hemoglobin concentration ([Hb]), hematocrit, and myoglobin concentration ([Mb]) in the pectoralis and gastrocnemius) for 16 species of diving and dabbling ducks found in North America, and investigate which parameters are correlated with the diving behaviors reported in both the sea ducks (Mergini) and the pochards (Aythini). Both [Hb] in the blood and [Mb] in the gastrocnemius, a major leg muscle used in propulsion for these predominantly leg‐propelled divers, were significantly higher in the sea ducks compared to the dabblers (Anatini). The pochards also showed a significant increase in [Hb] and were intermediate between the sea ducks and the dabblers in hematocrit and [Mb] in the gastrocnemius. Among these four variables and total body mass, [Mb] in the gastrocnemius was the most significant predictor of mean species dive time, and these two variables were correlated across the phylogeny. Our results indicate that the observed changes in O2 storage capacity in the blood and muscles are positively correlated with diving behavior in two clades of ducks, such that larger increases are correlated with longer dive times. [ABSTRACT FROM AUTHOR]

Geographic variation in body size has been studied in the context of Bergmann's and Allen's ecogeographic rules, which relate changes in body and appendage sizes to temperature fluctuations associated with latitude and altitude. Moreover, organisms adapted to high-altitude exhibit blunted hematological responses, promoting survival in hypoxic environments. We collected 117 adult Slate-colored Coots (Fulica ardesiaca), representing both color morphs (68 chestnut-fronted and 49 pale-fronted) and sexes (49 males and 68 females), and sampled at three latitudinal (north, central, and south) and two altitudinal (low and high altitude) levels in the Peruvian Andes. Given the absence of geographic variation in morphometric and hematological traits across color morphs and sexes, we grouped these data together. We then used linear mixed models to assess latitudinal and altitudinal variations in body size (body mass and skull length) and appendage size (relative wing chord, tarsal and culmen lengths adjusted for both body mass and skull length). The same models were applied to analyze altitudinal variation in hematological traits (hemoglobin concentration, hematocrit, and mean corpuscular hemoglobin concentration). Our findings corroborated Bergmann's and Allen's rules, showing variation in body and culmen size across elevational and latitudinal gradients. No significant differences (P < 0.05) were observed in the three hematological traits, suggesting that polycythemia is not a necessary response to hypoxia in this species. Depending on when these coots first inhabited high altitudes, our results might support the hypothesis of duration of high-altitude ancestry, suggesting that species residing at high altitudes for longer evolutionary periods might be better adapted. [ABSTRACT FROM AUTHOR]

Asian-origin avian influenza (AI) viruses are spread in part by migratory birds. In Alaska, diverse avian hosts from Asia and the Americas overlap in a region of intercontinental avifaunal mixing. [...]

Population genetic variation in Mallards (Arias platyrhynchos; n = 152) from Western Russia, North Asia, the Aleutian Islands, and mainland Alaska was investigated using 667 base pairs of the 5'-end of the mitochondrial DNA (mtDNA) control region. DNA sequencing revealed two clades that correspond to Avise et al.'s (1990) group A and B mtDNA haplotypes. Group A haplotypes (80.3%) were widespread in all localities from Western Russia to Alaska. Group B haplotypes (19.7%), by contrast, were found primarily in mainland Alaska, where they occurred at high frequency (77.4%), but they also occurred at low frequencies (declining east to west) in the Aleutian Islands (11.8%) and the Primorye region of North Asia (4.4%). Group B haplotypes were not observed in Western Russia or elsewhere in North Asia outside Primorye. Consequently, Mallards exhibited substantial genetic structure between Old World and New World ([[PHI].sub.ST] = 0.4112-0.4956) but possessed little genetic structure within the Old World continental area ([[PHI].sub.ST] = 0.0018). Nonetheless, when only group A haplotypes were included in the analysis, Mallards from the Aleutian Islands differed (albeit with low levels of divergence) from each of the other three sampled regions in the Old World and New World ([[PHI].sub.ST] = 0.0728-0.1461, P < 0.05). Mallards inhabit the Aleutian Islands year-round, so these insular populations may be isolated from Asian and North American populations that occur in the Aleutian Islands only during migration. Overall weak phylogeographic structure and low genetic differentiation within Asia, and between Asia and North America when only group A haplotypes were evaluated, is probably explained by large long-term population sizes and significant intra-continental dispersal. The coexistence and nonrandom distribution of two divergent mtDNA haplotype lineages in Alaska, the Aleutian Islands, and the Primorye region of North Asia, but not in Western Russia or elsewhere in North Asia, is consistent with historical and contemporary hybridization and incomplete sorting of A and B mtDNA haplotype lineages in Mallards and closely related species inhabiting the Old World and New World. Key words: Anas platyrhynchos, hybridization, incomplete lineage sorting, Mallard, paraphyly.