Ring distributions leading to species formation: a global topographic analysis of geographic barriers associated with ring species

<p>Abstract</p> <p>Background</p> <p>In the mid 20^thcentury, Ernst Mayr and Theodosius Dobzhansky championed the significance of circular overlaps or ring species as the perfect demonstration of speciation, yet in the over 50 years since, only a handful of such taxa are known. We developed a topographic model to evaluate whether the geographic barriers that favor processes leading to ring species are common or rare, and to predict where other candidate ring barriers might be found.</p> <p>Results</p> <p>Of the 952,147 geographic barriers identified on the planet, only about 1% are topographically similar to barriers associated with known ring taxa, with most of the likely candidates occurring in under-studied parts of the world (for example, marine environments, tropical latitudes). Predicted barriers separate into two distinct categories: (i) single cohesive barriers (< 50,000 km²), associated with taxa that differentiate at smaller spatial scales (salamander: <it>Ensatina eschscholtzii</it>; tree: <it>Acacia karroo</it>); and (ii) composite barriers - formed by groups of barriers (each 184,000 to 1.7 million km²) in close geographic proximity (totaling 1.9 to 2.3 million km²) - associated with taxa that differentiate at larger spatial scales (birds: <it>Phylloscopus trochiloide</it>s and <it>Larus </it>(sp. <it>argentatus </it>and <it>fuscus</it>)). When evaluated globally, we find a large number of cohesive barriers that are topographically similar to those associated with known ring taxa. Yet, compared to cohesive barriers, an order of magnitude fewer composite barriers are similar to those that favor ring divergence in species with higher dispersal.</p> <p>Conclusions</p> <p>While these findings confirm that the topographic conditions that favor evolutionary processes leading to ring speciation are, in fact, rare, they also suggest that many understudied natural systems could provide valuable demonstrations of continuous divergence towards the formation of new species. Distinct advantages of the model are that it (i) requires no <it>a priori </it>information on the relative importance of features that define barriers, (ii) can be replicated using any kind of continuously distributed environmental variable, and (iii) generates spatially explicit hypotheses of geographic species formation. The methods developed here - combined with study of the geographical ecology and genetics of taxa in their environments - should enable recognition of ring species phenomena throughout the world.</p

Biomechanical spinal growth modulation and progressive adolescent scoliosis – a test of the 'vicious cycle' pathogenetic hypothesis: Summary of an electronic focus group debate of the IBSE

There is no generally accepted scientific theory for the causes of adolescent idiopathic scoliosis (AIS). As part of its mission to widen understanding of scoliosis etiology, the International Federated Body on Scoliosis Etiology (IBSE) introduced the electronic focus group (EFG) as a means of increasing debate on knowledge of important topics. This has been designated as an on-line Delphi discussion. The text for this debate was written by Dr Ian A Stokes. It evaluates the hypothesis that in progressive scoliosis vertebral body wedging during adolescent growth results from asymmetric muscular loading in a "vicious cycle" (vicious cycle hypothesis of pathogenesis) by affecting vertebral body growth plates (endplate physes). A frontal plane mathematical simulation tested whether the calculated loading asymmetry created by muscles in a scoliotic spine could explain the observed rate of scoliosis increase by measuring the vertebral growth modulation by altered compression. The model deals only with vertebral (not disc) wedging. It assumes that a pre-existing scoliosis curve initiates the mechanically-modulated alteration of vertebral body growth that in turn causes worsening of the scoliosis, while everything else is anatomically and physiologically 'normal' The results provide quantitative data consistent with the vicious cycle hypothesis. Dr Stokes' biomechanical research engenders controversy. A new speculative concept is proposed of vertebral symphyseal dysplasia with implications for Dr Stokes' research and the etiology of AIS. What is not controversial is the need to test this hypothesis using additional factors in his current model and in three-dimensional quantitative models that incorporate intervertebral discs and simulate thoracic as well as lumbar scoliosis. The growth modulation process in the vertebral body can be viewed as one type of the biologic phenomenon of mechanotransduction. In certain connective tissues this involves the effects of mechanical strain on chondrocytic metabolism a possible target for novel therapeutic intervention

Non-technical Skills in Healthcare

AbstractNon-technical Skills (NTS) are a set of generic cognitive and social skills, exhibited by individuals and teams, that support technical skills when performing complex tasks. Typical NTS training topics include performance shaping factors, planning and preparation for complex tasks, situation awareness, perception of risk, decision-making, communication, teamwork and leadership. This chapter provides a framework for understanding these skills in theory and practice, how they interact, and how they have been applied in healthcare, as well as avenues for future research

Natural Course and Classification of Idiopathic Scoliosis

Scoliosis is an elusive pathology in which a therapeutic decision must depend on an accurate prognostic stratification. It is defined as a three-dimensional deformity of the vertebral column which manifests itself in different forms, affecting the cervical, dorsal and lumbar regions. In more than 80% of scoliosis cases, a specific cause is actually not known (Idiopathic Scoliosis, IS)

Olanzapine versus lithium in the maintenance treatment of bipolar disorder: a 12-month, randomized, double-blind, controlled clinical trial.

OBJECTIVE: The authors compared the efficacy of olanzapine and lithium in the prevention of mood episode relapse/recurrence. METHOD: Patients with a diagnosis of bipolar disorder (manic/mixed), a history of two or more manic or mixed episodes within 6 years, and a Young Mania Rating Scale total score > or =20 entered the study and received open-label co-treatment with olanzapine and lithium for 6-12 weeks. Those meeting symptomatic remission criteria (Young Mania Rating Scale score < or =12; 21-item Hamilton depression scale score < or =8) were randomly assigned to 52 weeks of double-blind monotherapy with olanzapine, 5-20 mg/day (N=217), or lithium (target blood level: 0.6-1.2 meq/liter) (N=214). RESULTS: Symptomatic relapse/recurrence (score > or =15 on either the Young Mania Rating Scale or Hamilton depression scale) occurred in 30.0% of olanzapine-treated and 38.8% of lithium-treated patients. The noninferiority of olanzapine relative to lithium (primary objective) in preventing relapse/recurrence was met, since the lower limit of the 95% confidence interval on the 8.8% risk difference (-0.1% to 17.8%) exceeded the predefined noninferiority margin (-7.3%). Secondary results showed that compared with lithium, olanzapine had significantly lower risks of manic episode and mixed episode relapse/recurrence. Depression relapse/recurrence occurred in 15.7% of olanzapine-treated and 10.7% of lithium-treated patients. Mean weight gain during open-label co-treatment was 2.7 kg; during double-blind monotherapy, weight gain was significantly greater with olanzapine (1.8 kg) than with lithium (-1.4 kg). CONCLUSIONS: These results suggest that olanzapine was significantly more effective than lithium in preventing manic and mixed episode relapse/recurrence in patients acutely stabilized with olanzapine and lithium co-treatment. Both agents were comparable in preventing depression relapse/recurrence