Evolutionary diversification of TTX-resistant sodium channels in a predator-prey interaction

Understanding the molecular genetic basis of adaptations provides incomparable insight into the genetic mechanisms by which evolutionary diversification takes place. Whether the evolution of common traits in different lineages proceeds by similar or unique mutations, and the degree to which phenotypic evolution is controlled by changes in gene regulation as opposed to gene function, are fundamental questions in evolutionary biology that require such an understanding of genetic mechanisms. Here we identify novel changes in the molecular structure of a sodium channel expressed in snake skeletal muscle, tsNa(V)1.4, that are responsible for differences in tetrodotoxin (TTX) resistance among garter snake populations coevolving with toxic newts. By the functional expression of tsNa(V)1.4, we show how differences in the amino-acid sequence of the channel affect TTX binding and impart different levels of resistance in four snake populations. These results indicate that the evolution of a physiological trait has occurred through a series of unique functional changes in a gene that is otherwise highly conserved among vertebrates.     

Parasites and climate synchronize red grouse populations

There is circumstantial evidence that correlated climatic conditions can drive animal populations into synchronous fluctuations in abundance. However, it is unclear whether climate directly affects the survival and fecundity of individuals, or indirectly, by influencing food and natural enemies. Here we propose that climate affects trophic interactions and could be an important mechanism for synchronizing spatially distributed populations. We show that in specific years the size of red grouse populations in northern England either increases or decreases in synchrony. In these years, widespread and correlated climatic conditions during May and July affect populations regionally and influence the density-dependent transmission of the gastrointestinal nematode Trichostrongylus tenuis, a parasite that reduces grouse fecundity. This in turn forces grouse populations into synchrony. We conclude that specific climatic events may lead to outbreaks of infectious diseases or pests that may cause dramatic, synchronized changes in the abundance of their hosts.     

Adaptive evolution of non-coding DNA in Drosophila

A large fraction of eukaryotic genomes consists of DNA that is not translated into protein sequence, and little is known about its functional significance. Here I show that several classes of non-coding DNA in Drosophila are evolving considerably slower than synonymous sites, and yet show an excess of between-species divergence relative to polymorphism when compared with synonymous sites. The former is a hallmark of selective constraint, but the latter is a signature of adaptive evolution, resembling general patterns of protein evolution in Drosophila. I estimate that about 40-70% of nucleotides in intergenic regions, untranslated portions of mature mRNAs (UTRs) and most intronic DNA are evolutionarily constrained relative to synonymous sites. However, I also use an extension to the McDonald-Kreitman test to show that a substantial fraction of the nucleotide divergence in these regions was driven to fixation by positive selection (about 20% for most intronic and intergenic DNA, and 60% for UTRs). On the basis of these observations, I suggest that a large fraction of the non-translated genome is functionally important and subject to both purifying selection and adaptive evolution. These results imply that, although positive selection is clearly an important facet of protein evolution, adaptive changes to non-coding DNA might have been considerably more common in the evolution of D. melanogaster.     

The Emergent Properties of SSM in Use: A Symposium by Reflective Practitioners

Two careers, in industry and in university teaching at postgraduate level, have led to the development of Soft Systems Methodology (SSM) in a 30-year program of action research. The most cogent comments on SSM come from reflective practitioners, and in this symposium I have asked eight such users of SSM to reflect on their experience and to address the question of what it is that happens when the approach is used in real-world problem situations. Their responses reflect their different backgrounds, experience, and ways of working, but a broad general picture emerges. This suggests that SSM (whose process does not necessarily have to be made explicit to participants in a study) can engender a process of on-going (cyclic) coherent structured learning which feels natural, and which can surface previously unexamined assumptions, thus creating an arena in which accommodations can emerge which enable and motivate "action to improve" to be taken.     

Structural change and the combination of forecasts

Forecasters are generally concerned about the properties of model-based predictions in the presence of structural change. In this paper, it is argued that forecast errors can under those conditions be greatly reduced through systematic combination of forecasts. We propose various extensions of the standard regression-based theory of forecast combination. Rolling weighted least squares and time-varying parameter techniques are shown to be useful generalizations of the basic framework. Numerical examples, based on various types of structural change in the constituent forecasts, indicate that the potential reduction in forecast error variance through these methods is very significant. The adaptive nature of these updating procedures greatly enhances the effect of risk-spreading embodied in standard combination techniques.     

Dissociation between compensatory renal growth and induction of (Na++K+-ATPase in rat kidney after uninefrectomy

Zusammenfassung Nach Uninephrektomie und bilateraler Adrenalektomie entsteht eine Dissoziation zwischen der Nierenvergrösserung und der (Na⁺+K⁺)-ATPase Aktivität. Es besteht wahrscheinlich kein Zusammenhang zwischen der Nierenvergrösserung und der Induktion von (Na⁺+K⁺)-ATPase. Auch in der vergrösserten Niere sind die Nebennierenhormone notwendig, um die (Na⁺+K⁺)-ATPase zu erhalten.

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The work was supported by a grant from P. Carl Petersen's Fund. Mrs.Birthe Bagge Hansen provided excellent technical assistance.