Null model selection, compositional bias, character state bias, and the limits of phylogenetic information

Evolutionary trends and processes can distort phylogenetic information in sequences such that they do not reliably reflect the evolutionary processes that generate them. This fact of molecular evolution has a ubiquitous influence on the ability of researchers to adequately reconstruct genealogical relationships and histories of the processes of molecular evolution. This feature of phylogenetic inference can limit the capacity of researchers to adequately specify a relevant null hypothesis for testing hypothesis of relationships, data informativeness, and processes of molecular evolution. We show how this feature of historical inference also influences the exactness of the relative apparent synapomorphy analysis (RASA) test for phylogenetic signal and demonstrate how a permutation modification of the null hypothesis can improve the robustness of the underlying distributional assumption of the test. The RASA test (using either null model) was found not only to appropriately reject the combinability of independent lines of evidence for the relationships among the Physalaemus pustulosus frog species group, but also to be more appropriately sensitive to individual uninformative data sets than commonly used tree-based measures of signal, including the consistency index, the retention index, and the permutation tail probability test statistic

Isolation-by-Distance and Outbreeding Depression Are Sufficient to Drive Parapatric Speciation in the Absence of Environmental Influences

A commonly held view in evolutionary biology is that speciation (the emergence of genetically distinct and reproductively incompatible subpopulations) is driven by external environmental constraints, such as localized barriers to dispersal or habitat-based variation in selection pressures. We have developed a spatially explicit model of a biological population to study the emergence of spatial and temporal patterns of genetic diversity in the absence of predetermined subpopulation boundaries. We propose a 2-D cellular automata model showing that an initially homogeneous population might spontaneously subdivide into reproductively incompatible species through sheer isolation-by-distance when the viability of offspring decreases as the genomes of parental gametes become increasingly different. This simple implementation of the Dobzhansky-Muller model provides the basis for assessing the process and completion of speciation, which is deemed to occur when there is complete postzygotic isolation between two subpopulations. The model shows an inherent tendency toward spatial self-organization, as has been the case with other spatially explicit models of evolution. A well-mixed version of the model exhibits a relatively stable and unimodal distribution of genetic differences as has been shown with previous models. A much more interesting pattern of temporal waves, however, emerges when the dispersal of individuals is limited to short distances. Each wave represents a subset of comparisons between members of emergent subpopulations diverging from one another, and a subset of these divergences proceeds to the point of speciation. The long-term persistence of diverging subpopulations is the essence of speciation in biological populations, so the rhythmic diversity waves that we have observed suggest an inherent disposition for a population experiencing isolation-by-distance to generate new species

Cerebral arterial air embolism in a child after intraosseous infusion

Cerebral arterial air embolism (CAAE) has been reported as a rare complication of medical intervention. There has been one reported case of CAAE after the use of an intraosseous infusion (IO) system. We report on a case of CAAE after tibial IO infusion in a 7-month-old girl during resuscitation