Macroscopic anisotropic bone material properties in children with severe osteogenesis imperfecta

Children with severe osteogenesis imperfecta (OI) typically experience numerous fractures and progressive skeletal deformities over their lifetime. Recent studies proposed finite element models to assess fracture risk and guide clinicians in determining appropriate intervention in children with OI, but lack of appropriate material property inputs remains a challenge. This study aimed to characterize macroscopic anisotropic cortical bone material properties and investigate relationships with bone density measures in children with severe OI. Specimens were obtained from tibial or femoral shafts of nine children with severe OI and five controls. The specimens were cut into beams, characterized in bending, and imaged by synchrotron radiation X-ray micro-computed tomography. Longitudinal modulus of elasticity, yield strength, and bending strength were 32–65% lower in the OI group (p < 0.001). Yield strain did not differ between groups (p ≥ 0.197). In both groups, modulus and strength were lower in the transverse direction (p ≤ 0.009), but anisotropy was less pronounced in the OI group. Intracortical vascular porosity was almost six times higher in the OI group (p < 0.001), but no differences were observed in osteocyte lacunar porosity between the groups (p = 0.086). Volumetric bone mineral density was lower in the OI group (p < 0.001), but volumetric tissue mineral density was not (p = 0.770). Longitudinal OI bone modulus and strength were correlated with volumetric bone mineral density (p ≤ 0.024) but not volumetric tissue mineral density (p ≥ 0.099). Results indicate that cortical bone in children with severe OI yields at the same strain as normal bone, and that their decreased bone material strength is associated with reduced volumetric bone mineral density. These results will enable the advancement of fracture risk assessment capability in children with severe OI.     

Evolutionary biogeography of Manihot (Euphorbiaceae), a rapidly radiating Neotropical genus restricted to dry environments

Aim The aims of this study were to reconstruct the phylogeny of Manihot, a Neotropical genus restricted to seasonally dry areas, to yield insight into its biogeographic history, and to identify the closest wild relatives of a widely grown, yet poorly known, crop: cassava (Manihot esculenta). Location Dry and seasonally dry regions of Meso‐ and South America. Methods We collected 101 samples of Manihot, representing 52 species, mostly from herbaria, and two outgroups (Jatropha gossypiifolia and Cnidoscolus urens). More than half of the currently accepted Manihot species were included in our study; our sampling covered the whole native range of the genus, and most of its phenotypic and ecological variation. We reconstructed phylogenetic relationships among Manihot species using sequences for two nuclear genes and a non‐coding chloroplast region. We then reconstructed the history of traits related to growth form, dispersal ecology and regeneration ability. Results Manihot species from Mesoamerica form a grade basal to South American species. The latter species show a strong biogeographic clustering: species from the cerrado form well defined clades, species from the caatinga of north‐eastern Brazil form another, and so do species restricted to forest gaps along the rim of the Amazon basin. Vine and tree growth habits evolved repeatedly in the genus, as did fruit indehiscence and loss of ant‐mediated seed dispersal. Main conclusions The genus Manihot probably originated in Mesoamerica, where it diversified prior to colonizing South America. Within South America, several groups then radiated southwards and eastwards within all kinds of seasonally dry lowland habitats. Some species also adapted to more humid environments, such as forest gaps, around the rim of the Amazon basin. Given the limited dispersal abilities of Manihot species, we propose that this radiation is most likely to have occurred only after, or shortly before, the completion of the Isthmus of Panama, around 3.5 Ma. Our results are in agreement with the past existence of a corridor of dry vegetation through Amazonia or along the eastern South American coast. In addition, our phylogeny allows identification of cassava’s closest wild relatives.     

Pharyngeal biting mechanics in centrarchild and cichlid fishes: insights into a key evolutionary innovation

This study compares the pharyngeal biting mechanism of the Cichlidae, a family of perciform fishes that is characterized by many anatomical specializations, with that of the Centrarchidae, a family that possesses the generalized perciform anatomy. Our objective was to trace the key structural and functional changes in the pharyngeal jaw apparatus that have arisen in the evolution from the generalized to derived (cichlid) perciform condition. We propose a mechanical model of pharyngeal biting in the Centrarchidae and compare this with an already existing model for pharyngeal biting in the family Cichlidae. Central to our centrarchid model is a structural coupling between the upper and lower pharyngeal jaws. This coupling severely limits independent movement of the pharyngeal jaws, in contrast to the situation in the speciose Cichlidae, in which the upper and lower pharyngeal jaw movements are to a large extent independent. We tested both models by electrically stimulating nine muscles of the branchial and hyoid apparatuses in three centrarchild and three cichlid species. The results confirmed the coupled movement of the upper and lower pharyngeal jaws in the Centrarchidae and the independence of these movements in the Cichlidae. We suggest that the key structural innovation in the development of the functionally versatile cichlid (labroid) pharyngeal jaw apparatus was the decoupling of epibranchials 4 from the upper pharyngeal jaws. This structural decoupling implies the decoupling of the movements of the upper and lower pharyngeal jaws and leads to a cichlid (labroid) type of pharyngeal bite. The initial decoupling facilitated a cascade of changes, each leading to improved biting effectiveness and/or to increased mobility and mechanical flexibility of the pharyngeal jaws. The shift of insertion of the m. levator externus 4 which has been considered the primary innovation in the transformation probably arose secondarily. The transformation of the pharyngeal biting mechanism in the perciforms is an excellent example of decoupling of structures associated with diversification of form and function and with increased speciation rates.     

Understanding processes at the origin of species flocks with a focus on the marine Antarctic fauna

Species flocks (SFs) fascinate evolutionary biologists who wonder whether such striking diversification can be driven by normal evolutionary processes. Multiple definitions of SFs have hindered the study of their origins. Previous studies identified a monophyletic taxon as a SF if it displays high speciosity in an area in which it is endemic (criterion 1), high ecological diversity among species (criterion 2), and if it dominates the habitat in terms of biomass (criterion 3); we used these criteria in our analyses. Our starting hypothesis is that normal evolutionary processes may provide a sufficient explanation for most SFs. We thus clearly separate each criterion and identify which biological (intrinsic) and environmental (extrinsic) traits are most favourable to their realization. The first part focuses on evolutionary processes. We highlight that some popular putative causes of SFs, such as key innovations or ecological speciation, are neither necessary nor sufficient to fulfill some or all of the three criteria. Initial differentiation mechanisms are diverse and difficult to identify a posteriori because a primary differentiation of one type (genetic, ecological or geographical) often promotes other types of differentiation. Furthermore, the criteria are not independent: positive feedbacks between speciosity and ecological diversity among species are expected whatever the initial cause of differentiation, and ecological diversity should enhance habitat dominance at the clade level. We then identify intrinsic and extrinsic factors that favour each criterion. Low dispersal emerges as a convincing driver of speciosity. Except for a genomic architecture favouring ecological speciation, for which assessment is difficult, high effective population sizes are the single intrinsic factor that directly enhances speciosity, ecological diversity and habitat dominance. No extrinsic factor appeared to enhance all criteria simultaneously but a combination of factors (insularity, fragmentation and environmental stability) may favour the three criteria, although the effect is indirect for habitat dominance. We then apply this analytical framework to Antarctic marine environments by analysing data from 18 speciose clades belonging to echinoderms (five unrelated clades), notothenioid fishes (five clades) and peracarid crustaceans (eight clades). Antarctic shelf environments and history appear favourable to endemicity and speciosity, but not to ecological specialization. Two main patterns are distinguished among taxa. (i) In echinoderms, many brooding, species‐rich and endemic clades are reported, but without remarkable ecological diversity or habitat dominance. In these taxa, loss of the larval stage is probably a consequence of past Antarctic environmental factors, and brooding is suggested to be responsible for enhanced allopatric speciation (via dispersal limitation). (ii) In notothenioids and peracarids, many clades fulfill all three SF criteria. This could result from unusual features in fish and crustaceans: chromosome instability and key innovations (antifreeze proteins) in notothenioids, ecological opportunity in peracarids, and a genomic architecture favouring ecological speciation in both groups. Therefore, the data do not support our starting point that normal evolutionary factors or processes drive SFs because in these two groups uncommon intrinsic features or ecological opportunity provide the best explanation. The utility of the three‐criterion SF concept is therefore questioned and guidelines are given for future studies.     

UV-B radiation reduces biocontrol ability of Clonostachys rosea against Botrytis cinerea

There is a lack of information comparing UV-B radiation conidial sensitivity of the biocontrol agent Clonostachys rosea (Cr) and its target pathogen, Botrytis cinerea (Bc). We investigated the interactions in vitro and on strawberry leaf discs between previously selected Cr and Bc strains tolerant to UV-B radiation. Strawberry leaf discs inoculated with Bc, Cr, or combinations of both fungi were exposed to UV-B doses (2.9, 5.9, and 8.9?kJ?m^?2). Incidence and sporulation of both fungi were evaluated, and the Area Under Incidence Progress Curve (AUIPC) and Area Under Sporulation Progress Curve (AUSPC) were calculated. AUIPC and AUSPC of Cr on leaf discs were negatively correlated to increased UV-B. When inoculated alone on leaf discs, Bc was not affected by UV-B, but when inoculated with Cr the incidence and sporulation of Bc were positively correlated to UV-B radiation dose. In the absence of UV-B, Cr reduced incidence and sporulation of Bc. However, the ability of Cr to control Bc was reduced by 20% to 50% with increasing UV-B radiation. Increasing the applied concentration of Cr conidia 10-fold partially overcame the deleterious effects of UV-B on the ability of the biocontrol agent to reduce Bc sporulation in strawberry leaves. The selection of antagonists must fulfil many requirements; besides being active against the specific targeted plant pathogens, they must be cost-effective and have ecological characteristics suitable for the desired use conditions. We suggest that UV-B exposure must be taken into account during the development of bio-fungicides based on Cr.     

Impact of landscape predictors on climate change modelling of species distributions: a case study with Eucalyptus fastigata in southern New South Wales,Australia

Aim We consider three questions. (1) How different are the predicted distribution maps when climate‐only and climate‐plus‐terrain models are developed from high‐resolution data? (2) What are the implications of differences between the models when predicting future distributions under climate change scenarios, particularly for climate‐only models at coarse resolution? (3) Does the use of high‐resolution data and climate‐plus‐terrain models predict an increase in the number of local refugia? Location South‐eastern New South Wales, Australia. Methods We developed two species distribution models for Eucalyptus fastigata under current climate conditions using generalized additive modelling. One used only climate variables as predictors (mean annual temperature, mean annual rainfall, mean summer rainfall); the other used both climate and landscape (June daily radiation, topographic position, lithology, nutrients) variables as predictors. Predictions of the distribution under current climate and climate change were then made for both models at a pixel resolution of 100 m. Results The model using climate and landscape variables as predictors explained a significantly greater proportion of the deviance than the climate‐only model. Inclusion of landscape variables resulted in the prediction of much larger areas of existing optimal habitat. An overlay of predicted future climate on the current climate space indicated that extrapolation of the statistical models was not occurring and models were therefore more robust. Under climate change, landscape‐defined refugia persisted in areas where the climate‐only model predicted major declines. In areas where expansion was predicted, the increase in optimal habitat was always greater with landscape predictors. Recognition of extensive optimal habitat conditions and potential refugia was dependent on the use of high‐resolution landscape data. Main conclusions Using only climate variables as predictors for assessing species responses to climate change ignores the accepted conceptual model of plant species distribution. Explicit statements justifying the selection of predictors based on ecological principles are needed. Models using only climate variables overestimate range reduction under climate change and fail to predict potential refugia. Fine‐scale‐resolution data are required to capture important climate/landscape interactions. Extrapolation of statistical models to regions in climate space outside the region where they were fitted is risky.     

ADAPTIVE RADIATION OF DAY-GECKOS (PHELSUMA) IN THE SEYCHELLES ARCHIPELAGO: A PHYLOGENETIC ANALYSIS

A phylogenetic analysis using characters derived from mitochondrial DNA was used to show that the species of Phelsuma in the Seychelles Islands represent a single, monophyletic lineage that has diversified as a result of both historical and ecological factors. In the distant past, the Seychelles archipelago was physically invaded by a single species of Phesluma. Separate eustatic sea level changes likely led first to allopatric speciation and then to the secondary contact of these sister species. Differences in the relative timing of the secondary contact between island groups resulted in P. sundbergi evolving an intermediate body size in the group of islands associated with Mahé and a large body size, while sympatric with P. astriata, in the group of islands associated with Praslin. Ecological information was used to support the conclusion that the actual evolutionary mechanism for the body size shift was a response to frequency dependent natural selection of P. sundbergi in single-species and two-species competitive regimes.     

DISPARITY: MORPHOLOGICAL PATTERN AND DEVELOPMENTAL CONTEXT

Abstract:  The distribution of organic forms is clumpy at any scale from populations to the highest taxonomic categories, and whether considered within clades or within ecosystems. The fossil record provides little support for expectations that the morphological gaps between species or groups of species have increased through time as it might if the gaps were created by extinction of a more homogeneous distribution of morphologies. As the quantitative assessments of morphology have replaced counts of higher taxa as a metric of morphological disparity, numerous studies have demonstrated the rapid construction of morphospace early in evolutionary radiations, and have emphasized the difference between taxonomic measures of morphological diversity and quantitative assessments of disparity. Other studies have evaluated changing patterns of disparity across mass extinctions, ecomorphological patterns and the patterns of convergence within ecological communities, while the development of theoretical morphology has greatly aided efforts to understand why some forms do not occur. A parallel, and until recently, largely separate research effort in evolutionary developmental biology has established that the developmental toolkit underlying the remarkable breadth of metazoan form is largely identical among Bilateria, and many components are shared among all metazoa. Underlying this concern with disparity is a question about temporal variation in the production of morphological innovations, a debate over the relative significance of the generation of new morphologies vs. differential probabilities of their successful introduction, and the relative importance of constraint, convergence and contingency in the evolution of form.