Emergence of large-scale cell morphology and movement from local actin filament growth dynamics

Variations in cell migration and morphology are consequences of changes in underlying cytoskeletal organization and dynamics. We investigated how these large-scale cellular events emerge as direct consequences of small-scale cytoskeletal molecular activities. Because the properties of the actin cytoskeleton can be modulated by actin-remodeling proteins, we quantitatively examined how one such family of proteins, enabled/vasodilator-stimulated phosphoprotein (Ena/VASP), affects the migration and morphology of epithelial fish keratocytes. Keratocytes generally migrate persistently while exhibiting a characteristic smooth-edged “canoe” shape, but may also exhibit less regular morphologies and less persistent movement. When we observed that the smooth-edged canoe keratocyte morphology correlated with enrichment of Ena/VASP at the leading edge, we mislocalized and overexpressed Ena/VASP proteins and found that this led to changes in the morphology and movement persistence of cells within a population. Thus, local changes in actin filament dynamics due to Ena/VASP activity directly caused changes in cell morphology, which is coupled to the motile behavior of keratocytes. We also characterized the range of natural cell-to-cell variation within a population by using measurable morphological and behavioral features—cell shape, leading-edge shape, filamentous actin (F-actin) distribution, cell speed, and directional persistence—that we have found to correlate with each other to describe a spectrum of coordinated phenotypes based on Ena/VASP enrichment at the leading edge. This spectrum stretched from smooth-edged, canoe-shaped keratocytes—which had VASP highly enriched at their leading edges and migrated fast with straight trajectories—to more irregular, rounder cells migrating slower with less directional persistence and low levels of VASP at their leading edges. We developed a mathematical model that accounts for these coordinated cell-shape and behavior phenotypes as large-scale consequences of kinetic contributions of VASP to actin filament growth and protection from capping at the leading edge. This work shows that the local effects of actin-remodeling proteins on cytoskeletal dynamics and organization can manifest as global modifications of the shape and behavior of migrating cells and that mathematical modeling can elucidate these large-scale cell behaviors from knowledge of detailed multiscale protein interactions.     

Climate and plant distribution at global and local scales

This paper investigates, with predictive models, the utility of ecophysiological responses to climate as predictors of plant distribution. At the global scale responses to extreme minimum temperatures and to the hydrological budget effectively predict the distribution limits of the major vegetation types of the World. A minimum temperature of -15°C, for example, appears critical in controlling the poleward spread of vegetation that is dominated by evergreen broadleaved species; however, the presence or absence of more frost resistant species, such as those that are deciduous broadleaved, is not obviously explained in terms of extremes of climate. In such cases, predicting the competitive relationships between species is necessary and dependent on the climatic sensitivity of population dynamics.We are grateful to Hans de Kroon for discussions on the application of matrices to ecology.     

Seasonal distribution of a migratory bird: effects of local and regional resource tracking

Aim We studied how local and regional abundance of a migratory passerine (the blackcap Sylvia atricapilla) track resource availability in breeding and wintering grounds, in an attempt to understand the processes underlying the distribution and regulation of migratory bird populations in summer and in winter. Location Our study was conducted in Spain. In summer, we sampled five localities representing the diversity of environmental conditions met by breeding Spanish blackcaps. In winter, we sampled eight localities in the wintering range of the species including different habitat types (forests and shrublands). Methods Our approach was based on the matching rule, a model that predicts that any local variation in resource abundance between two adjacent habitat patches should be tracked by animals through a similar variation in population abundance. Eventually, this local process should conform to abundance distributions at regional scales. We sampled two habitat patches in each locality, each one including three to five line transects, 500‐m long and 50‐m wide, where we counted blackcaps and measured vegetation structure and fruit abundance. Results During the breeding season, the abundance of blackcaps was strongly correlated with the ground cover of brambles (Rubus spp.), a bush which grows in moist sectors in Mediterranean forests and is the commonest nesting substrate of Spanish blackcaps. Both local and regional changes in bramble cover were tracked by variations in blackcap abundance. However, the rate of increase in blackcap abundance with increasing bramble cover along the Spanish gradient was lower than the one predicted under resource matching. In winter, abundance of fruiting shrubs was the best predictor of blackcap abundance, although local abundance of blackcaps not always fitted local abundance of fruits. Notwithstanding this effect, the regional pattern of abundance tracked changes in fruit availability according to the matching rule. Main conclusions Our results support the strong effect of habitat quality on the abundance distribution of blackcaps and the tracking of different key resources along the year. Together with the different degrees of resource tracking by blackcaps at local and regional scales, these results also support the view that both breeding and wintering processes have to be studied, and studies have to be conducted at the appropriate spatial scales, if we are to understand the processes underlying the abundance distribution of migratory birds.     

Protein-protein interactions: from global to local analyses

For the increasing number of species with complete genome sequences, the task of elucidating their complete proteomes and interactomes has attracted much recent interest. Although the proteome describes the complete repertoire of proteins expressed, the interactome comprises the pairwise protein-protein interactions that occur, or could occur, within an organism, and forms a large-scale sparse network. Here we discuss the challenges provided by present data, and outline a route from global analysis to more detailed and focused studies of protein-protein interactions. Carefully using protein-interaction data allows us to explore its potential fully alongside the evaluation of mechanistic hypotheses about biological systems.     

Alien plant species with a wider global distribution are better able to capitalize on increased resource availability

? A high ability of alien plant species to capitalize on increases in resource availability has been suggested as an explanation for being globally successful. Here, we tested this hypothesis meta-analytically using existing data from experiments manipulating plant resources (light, water and nutrients). ? From these studies we extracted the response to resource increase of biomass, as an indicator of plant performance, and the responses of two traits related to resource capture: root : shoot ratio and specific leaf area (SLA). For 211 species recorded in the Global Compendium of Weeds, we assessed the relationship between effect sizes from such studies and the number of global regions where a species was established. ? We found that globally widespread species exhibited greater biomass responses to increases in resources overall, compared to less widespread species. Root : shoot ratio and SLA responses to increased resource availability were not related to species global distribution. ? In general, globally widespread alien plant species were better able to capitalize on increased availability of resources, through achieving increased growth and biomass accumulation, while greater plasticity of key resource-capture traits per se did not appear to be related to greater success.     

Limitations of a morphological criterion of adaptive inference in the fossil record

Experimental analyses directly inform how an anatomical feature or complex functions during an organism's lifetime, which serves to increase the efficacy of comparative studies of living and fossil taxa. In the mammalian skull, food material properties and feeding behaviour have a pronounced influence on the development of the masticatory apparatus. Diet‐related variation in loading magnitude and frequency induce a cascade of changes at the gross, tissue, cellular, protein and genetic levels, with such modelling and remodelling maintaining the integrity of oral structures vis‐à‐vis routine masticatory stresses. Ongoing integrative research using rabbit and rat models of long‐term masticatory plasticity offers unique insight into the limitations of functional interpretations of fossilised remains. Given the general restriction of the palaeontological record to bony elements, we argue that failure to account for the disparity in the hierarchical network of responses of hard versus soft tissues may overestimate the magnitude of the adaptive divergence that is inferred from phenotypic differences. Second, we note that the developmental onset and duration of a loading stimulus associated with a given feeding behaviour can impart large effects on patterns of intraspecific variation that can mirror differences observed among taxa. Indeed, plasticity data are relevant to understanding evolutionary transformations because rabbits raised on different diets exhibit levels of morphological disparity comparable to those found between closely related primate species that vary in diet. Lastly, pronounced variation in joint form, and even joint function, can also characterise adult conspecifics that differ solely in age. In sum, our analyses emphasise the importance of a multi‐site and hierarchical approach to understanding determinants of morphological variation, one which incorporates critical data on performance.     

The functional response predicts the effect of resource distribution on the optimal movement rate of consumers

Understanding how often individuals should move when foraging over patchy habitats is a central question in ecology. By combining optimality and functional response theories, we show analytically how the optimal movement rate varies with the average resource level (enrichment) and resource distribution (patch heterogeneity). We find that the type of functional response predicts the effect of enrichment in homogeneous habitats: enrichment should decrease movement for decelerating functional responses, but increase movement for accelerating responses. An intermediate resource level thus maximises movement for type‐III responses. Counterintuitively, greater movement costs favour an increase in movement. In heterogeneous habitats predictions further depend on how enrichment alters the variance of resource distribution. Greater patch variance always increases the optimal rate of movement, except for type‐IV functional responses. While the functional response is well established as a fundamental determinant of consumer–resource dynamics, our results indicate its importance extends to the understanding of individual movement strategies.     

Hubbell's local abundance distribution: insights from a simple colonization rule

A simple colonization rule yields Hubbell's local abundance distribution with less math, more intuition, and weaker assumptions.     

A strategy of movement and resource utilization

A set of age-specific rates of birth and death implies expected numbers of kin. An individual girl or woman chosen at random out of a population whose birth and death rates are specified can be expected to have a certain number of older sisters, younger sisters, nieces, cousins; expressions for these values are provided for both total kin and kin who are still living. Included also are the probabilities of living mother, grandmother, and great grandmother for girls and women of various ages. The methods are applicable to the size of the nuclear and the extended family. All formulas have been programmed and specimen numerical values are given.     

Emergence of non-random structure in local food webs generated from randomly structured regional webs

Previous studies have shown that high-resolution, empirical food webs possess a non-random network structure, typically characterized by uniform or exponential degree distributions. However, the empirical food webs that have been investigated for their structural properties represent local communities that are only a subset of a larger pool of regionally coexisting species. Here, we use a simple model to investigate the effects of regional food web structure on local food webs that are assembled by two simple processes: random immigration of species from a source web (regional food web), and random extinction of species within the local web. The model shows that local webs with non-random degree distributions can arise from randomly structured source webs. A comparison of local webs assembled from randomly structured source webs with local webs assembled from source webs generated by the niche model shows that the former have higher species richness at equilibrium, but have a nonlinear response to changing extinction rates. These results imply that the network structure of regional food webs can play a significant role in the assembly and dynamics of local webs in natural ecosystems. With natural landscapes becoming increasingly fragmented, understanding such structure may be a necessary key to understanding the maintenance and stability of local species diversity.     

Comparison between subjective and ultrasound assessments of fetal movement.

Forty pregnant women participated in a study to compare subjective with ultrasound assessments of fetal movements. A real-time ultrasound scanner was used. Movements were recorded for 45 minutes in all cases. There was a significant positive correlation between the number of movements recorded by the two methods, but the 95% confidence limits were wide and no correlation was found in those patients who recorded fewer than 20 movements in the study period. Thus "false-positive" information may be obtained from purely subjective data, and in patients reporting low "kick counts" fetal activity should be assessed from real-time ultrasound recordings.