To speciate,or not to speciate? Resource heterogeneity,the subjectivity of similarity,and the macroevolutionary consequences of niche‐width shifts in plant‐feeding insects

Coevolutionary studies on plants and plant‐feeding insects have significantly improved our understanding of the role of niche shifts in the generation of new species. Evolving plant lineages essentially constitute moving islands and archipelagoes in resource space, and host shifts by insects are usually preceded by colonizations of novel resources. Critical to hypotheses concerning ecological speciation is what happens immediately before and after colonization attempts: if an available plant is too similar to the current host(s), it simply will be incorporated into the existing diet, but if it is too different, it will not be colonized in the first place. It thus seems that the probability of speciation is maximized when alternative hosts are at an ‘intermediate’ distance in resource space. In this review, I wish to highlight the possibility that resource similarity and, thus, the definition of ‘intermediate’, are subjective concepts that depend on the herbivore lineage's tolerance to dietary variation. This subjectivity of similarity means that changes in tolerance can either decrease or increase speciation probabilities depending on the distribution of plants in resource space: insect lineages with narrow tolerances are likely to speciate by ‘island‐hopping’ on young, species‐rich plant groups, whereas more generalized lineages could speciate by shifting among resource archipelagoes formed by higher plant taxa. Repeated and convergent origins of traits known to broaden or to restrict host‐plant use in multiple different insect groups provide opportunities for studying how tolerance and resource heterogeneity may interact to determine speciation rates.     

Pripper: prediction of caspase cleavage sites from whole proteomes

Background  

Caspases are a family of proteases that have central functions in programmed cell death (apoptosis) and inflammation. Caspases mediate their effects through aspartate-specific cleavage of their target proteins, and at present almost 400 caspase substrates are known. There are several methods developed to predict caspase cleavage sites from individual proteins, but currently none of them can be used to predict caspase cleavage sites from multiple proteins or entire proteomes, or to use several classifiers in combination. The possibility to create a database from predicted caspase cleavage products for the whole genome could significantly aid in identifying novel caspase targets from tandem mass spectrometry based proteomic experiments.     

Fragile X mental retardation syndrome: structure of the KH1-KH2 domains of fragile X mental retardation protein

Fragile X syndrome is the most common form of inherited mental retardation in humans, with an estimated prevalence of about 1 in 4000 males. Although several observations indicate that the absence of functional Fragile X Mental Retardation Protein (FMRP) is the underlying basis of Fragile X syndrome, the structure and function of FMRP are currently unknown. Here, we present an X-ray crystal structure of the tandem KH domains of human FMRP, which reveals the relative orientation of the KH1 and KH2 domains and the location of residue Ile304, whose mutation to Asn is associated with a particularly severe incidence of Fragile X syndrome. We show that the Ile304Asn mutation both perturbs the structure and destabilizes the protein.     

Quantitative measures of femoral fracture repair in rats derived by micro-computed tomography

Although fracture healing is frequently studied in pre-clinical models of long bone fractures using rodents, there is a dearth of objective quantitative techniques to assess successful healing. Biomechanical testing is possibly the most quantitative and relevant to a successful clinical outcome, but it is a destructive technique providing little insight into the cellular mechanisms associated with healing. The advent of X-ray computed tomography (CT) has provided the opportunity to quantitatively and non-destructively assess bone structure and density, but it is unknown how measurements derived using this technology relate to successful healing. To examine possible relationships, we used a pre-clinical model to test for statistically significant correlations between quantitative characteristics of the callus by micro-CT (μCT) and the bending strength, stiffness, and energy-to-failure of the callus as assessed by three-point bending of excised bones. A closed, transverse fracture was generated in the mid-shaft of rat femurs by impact loading. Shortly thereafter, the rats received a one-time, local injection of either the vehicle or one of four doses of lovastatin. Following sacrifice after 4 weeks of healing, fractured femurs were extracted for μCT analysis and then three-point bending. Setting the region of interest to be 3.2 mm above and below the fracture line, we acquired standard and new μCT-derived measurements. The mineralized callus volume and the mineral density of the callus correlated positively with callus strength (r_xy=?0.315, p=0.016 and r_xy=0.444, p<0.0005, respectively) and stiffness (r_xy=?0.271, p=0.040 and r_xy=0.325, p=0.013, respectively), but the fraction of the callus that mineralized and the moment of inertia of the callus did not. This fraction did correlate with energy-to-failure (r_xy=?0.343, p=0.0085). Of the μCT-derived measurements, quantifying defects within the outer bridging cortices of the callus produced the strongest correlation with both callus strength (r_xy=0.557, p<0.0001) and stiffness (r_xy=0.468, p=0.0002). By both reducing structural defects and increasing mineralization, lovastatin appears to increase the callus strength.     

The structure of the PP2A regulatory subunit B56 gamma: the remaining piece of the PP2A jigsaw puzzle

The PP2A serine/threonine phosphatase regulates a plethora of cellular processes. In the cell the predominant form of the enzyme is a heterotrimer, formed by a core dimer composed of a catalytic and a scaffolding subunit, which assemble together with one of a range of different regulatory B subunits. Here, we present the first structure of a free non-complexed B subunit, B56 gamma. Comparison with the recent structures of a heterotrimeric complex and the core dimer reveals several significant conformational changes in the interface region between the B56 gamma and the core dimer. These allow for an assembly scheme of the PP2A holoenzyme to be put forth where B56 gamma first complexes with the scaffolding subunit and subsequently binds to the catalytic subunit and this induces the formation of a binding site for the invariant C-terminus of the catalytic subunit that locks in the complex as a last step of assembly.     

A Bayesian analysis of multivariate doubly-interval-censored dental data

A Bayesian survival analysis is presented to examine the effect of fluoride-intake on the time to caries development of the permanent first molars in children between 7 and 12 years of age using a longitudinal study conducted in Flanders. Three problems needed to be addressed. Firstly, since the emergence time of a tooth and the time it experiences caries were recorded yearly, the time to caries is doubly interval censored. Secondly, due to the setup of the study, many emergence times were left-censored. Thirdly, events on teeth of the same child are dependent. Our Bayesian analysis is a modified version of the intensity model of Harkanen et al. (2000, Scandinavian Journal of Statistics 27, 577-588). To tackle the problem of the large number of left-censored observations a similar Finnish data set was introduced. Our analysis shows no convincing effect of fluoride-intake on caries development.     

Increasing frequency of low summer precipitation synchronizes dynamics and compromises metapopulation stability in the Glanville fritillary butterfly

Climate change is known to shift species'' geographical ranges, phenologies and abundances, but less is known about other population dynamic consequences. Here, we analyse spatio-temporal dynamics of the Glanville fritillary butterfly (Melitaea cinxia) in a network of 4000 dry meadows during 21 years. The results demonstrate two strong, related patterns: the amplitude of year-to-year fluctuations in the size of the metapopulation as a whole has increased, though there is no long-term trend in average abundance; and there is a highly significant increase in the level of spatial synchrony in population dynamics. The increased synchrony cannot be explained by increasing within-year spatial correlation in precipitation, the key environmental driver of population change, or in per capita growth rate. On the other hand, the frequency of drought during a critical life-history stage (early larval instars) has increased over the years, which is sufficient to explain the increasing amplitude and the expanding spatial synchrony in metapopulation dynamics. Increased spatial synchrony has the general effect of reducing long-term metapopulation viability even if there is no change in average metapopulation size. This study demonstrates how temporal changes in weather conditions can lead to striking changes in spatio-temporal population dynamics.     

Adaptations to fasting in the American mink (Mustela vison): carbohydrate and lipid metabolism

The aim of this study was to investigate whether the actively wintering American mink Mustela vison is strictly dependent on continuous food availability or if it has evolved physiological adaptations to tolerate nutritional scarcity. Fifty farm-bred male minks were divided into a fed control group and four experimental groups fasted for 2, 3, 5 or 7 days. The rate of weight loss was several-fold higher (1.5-3.2% day(-1)) in the mink than recorded previously in larger carnivores utilizing passive wintering strategies. The minks remained normoglycaemic, although their liver glycogen stores and glucose-6-phosphatase activities decreased during fasting. Adipose tissue constituted approximately 36% of their body mass after 7 days of food deprivation. Intra-abdominal fat, especially retroperitoneal but also mesenteric adipose tissue, were the most important fat depots to be hydrolyzed, but the ability of the mink to utilize its body lipids during fasting may be limited. The increased liver size, hepatic triacylglycerol accumulation and increases in the activities of plasma aminotransferases indicated liver dysfunction. Food deprivation also affected the red blood cell indices, and the blood monocyte and lymphocyte counts decreased suggesting immunosuppression during fasting. The results of the present study suggest that the mink has not evolved sophisticated adaptations to wintertime fasting.