Population genomics and local adaptation in wild isolates of a model microbial eukaryote.

Elucidating the connection between genotype, phenotype, and adaptation in wild populations is fundamental to the study of evolutionary biology, yet it remains an elusive goal, particularly for microscopic taxa, which comprise the majority of life. Even for microbes that can be reliably found in the wild, defining the boundaries of their populations and discovering ecologically relevant phenotypes has proved extremely difficult. Here, we have circumvented these issues in the microbial eukaryote Neurospora crassa by using a "reverse-ecology" population genomic approach that is free of a priori assumptions about candidate adaptive alleles. We performed Illumina whole-transcriptome sequencing of 48 individuals to identify single nucleotide polymorphisms. From these data, we discovered two cryptic and recently diverged populations, one in the tropical Caribbean basin and the other endemic to subtropical Louisiana. We conducted high-resolution scans for chromosomal regions of extreme divergence between these populations and found two such genomic "islands." Through growth-rate assays, we found that the subtropical Louisiana population has a higher fitness at low temperature (10 °C) and that several of the genes within these distinct regions have functions related to the response to cold temperature. These results suggest the divergence islands may be the result of local adaptation to the 9 °C difference in average yearly minimum temperature between these two populations. Remarkably, another of the genes identified using this unbiased, whole-genome approach is the well-known circadian oscillator frequency, suggesting that the 2.4°-10.6° difference in latitude between the populations may be another important environmental parameter.

Mortality associated with multiple organ system failure and sepsis in pediatric intensive care unit.

Seven hundred twenty-six patients from five pediatric intensive care units were studied to determine the association of multiple organ system failure (MOSF) with mortality and to test the hypothesis that MOSF associated with sepsis has a higher mortality rate than MOSF without sepsis. There were 177 (24%) patients with MOSF and 83 (11%) nonsurvivors of MOSF. The mortality rates for two, three, or four or more failed organ systems were 26%, 62%, and 88%, respectively (P less than 0.001). Eighty-four (47%) patients with MOSF had associated sepsis. Sepsis (both bacteremia and clinical sepsis syndrome) did not significantly increase mortality rates in the groups with organ system failure. Mortality rates for patients with sepsis before or within 24 hours of development of MOSF (early sepsis) did not differ from mortality rates for those patients with onset of sepsis more than 24 hours after developing MOSF (late sepsis, 53% vs 33%, P = NS). We conclude that underlying pathophysiologic mechanisms of MOSF other than sepsis are as important as sepsis in critically ill pediatric patients.