Adaptations to Climate-Mediated Selective Pressures in Humans

Humans inhabit a remarkably diverse range of environments, and adaptation through natural selection has likely played a central role in the capacity to survive and thrive in extreme climates. Unlike numerous studies that used only population genetic data to search for evidence of selection, here we scan the human genome for selection signals by identifying the SNPs with the strongest correlations between allele frequencies and climate across 61 worldwide populations. We find a striking enrichment of genic and nonsynonymous SNPs relative to non-genic SNPs among those that are strongly correlated with these climate variables. Among the most extreme signals, several overlap with those from GWAS, including SNPs associated with pigmentation and autoimmune diseases. Further, we find an enrichment of strong signals in gene sets related to UV radiation, infection and immunity, and cancer. Our results imply that adaptations to climate shaped the spatial distribution of variation in humans

Agricultural contracts, adverse selection, and multiple inputs

A significant and growing share of US agricultural output is produced under a production or marketing contract. An important controversy regarding agricultural production contracts is the control of non-labor inputs. Over time, contracts have tended to place more inputs under the buyer’s control and fewer under the farmer’s. This analysis examines the welfare effects of this trend. In the framework considered here, returns are reduced for some farmers and left unaffected for others. Returns to the buyer increase. The net effect on total surplus has two components. Output is higher when the buyer controls the input, due to lower information rents accruing to more productive farmers. However, this reduction distorts input use away from the production cost-minimizing level, which is costly. The net effect on total surplus depends primarily on the elasticity of substitution between inputs. Given the limited substitutability between labor and non-labor inputs in many agricultural activities, the analysis suggests that greater control of non-labor inputs by the buyer increases total surplus. The increase in returns to the buyer is consistent with the growing share of output produced under vertical coordination and the tendency to specify a greater number of production activities rather than allowing farmers to make their own decisions. The reduction in the returns obtained by some farmers is consistent with farmers’ opposition to such requirements

Amphibian phylogeography: a model for understanding historical aspects of species distributions

Phylogeographic analysis has become a major tool for investigating historical aspects of biogeography and population genetic structure. Anuran amphibians are particularly informative subjects for phylogeographic research on account of their global distribution, high degree of population genetic structure and ease of sampling. Studies on all the world's inhabited continents have demonstrated the nature and locations of refugia, including the Gulf Coast in North America and the Mediterranean peninsulas in Europe during the Pleistocene glaciations; the importance of vicariance events such as the uplift of the Andes in shaping modern distributions; and colonization routes in temperate zones during postglacial climatic amelioration. Features identified as important to amphibian biogeography, notably mountain ranges, large rivers such as the Amazon and climatic fluctuations, are common to many other taxa. New analytical methods based on coalescent, Bayesian and likelihood approaches permit more rigorous hypothesis testing than has hitherto been possible and offer the prospect of even more detailed insights into species and population history in future work

Tuber size variation and organ preformation constrain growth responses of a spring geophyte

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Multiple Single-Cell Genomes Provide Insight into Functions of Uncultured Deltaproteobacteria in the Human Oral Cavity

Campbell AG, Campbell JH, Schwientek P, et al. Multiple Single-Cell Genomes Provide Insight into Functions of Uncultured Deltaproteobacteria in the Human Oral Cavity. PLoS ONE. 2013;8(3): e59361.Despite a long history of investigation, many bacteria associated with the human oral cavity have yet to be cultured. Studies that correlate the presence or abundance of uncultured species with oral health or disease highlight the importance of these community members. Thus, we sequenced several single-cell genomic amplicons from Desulfobulbus and Desulfovibrio (class Deltaproteobacteria) to better understand their function within the human oral community and their association with periodontitis, as well as other systemic diseases. Genomic data from oral Desulfobulbus and Desulfovibrio species were compared to other available deltaproteobacterial genomes, including from a subset of host-associated species. While both groups share a large number of genes with other environmental Deltaproteobacteria genomes, they encode a wide array of unique genes that appear to function in survival in a host environment. Many of these genes are similar to virulence and host adaptation factors of known human pathogens, suggesting that the oral Deltaproteobacteria have the potential to play a role in the etiology of periodontal disease