Observations on the behaviour and ecology of a threatened and poorly known dwarf antelope: the beira (<Emphasis Type="Italic">Dorcatragus megalotis</Emphasis>)

Observations on the behaviour and ecology of the beira (Dorcatragus megalotis) were made during spring 2004 in a wild population discovered in 1993 in a low mountain range in the South of the Republic of Djibouti. Spring was found to be both a birthing and a mating season. Beiras fed in the first and last daylight hours, mainly on dicotyledons and in patches supporting trees and/or bushes. They spent the warmest hours of the day in the shade of trees, or in rock shelters when the temperature became too hot. Observed groups (n = 56) ranged in size from one to five individuals (mean ± SD = 2.70 ± 1.49). Most of these groups included a single adult male (62.5%) or no adult male at all (33.9%). The only encounter observed between two adult males resulted in the chasing of one by the other. Furthermore, the mixed-sex groups including a single adult male seemed rather stable, and their members used collective urination–defecation sites. From a behavioural point of view, the beira thus appears not very far from the dik-diks (Madoqua spp.), but differs from them by a greater sociability between adult females and its type of habitat.     

Efficient shared memory and RDMA based collectives on multi-rail QsNetII SMP clusters

Clusters of Symmetric Multiprocessors (SMP) are more commonplace than ever in achieving high-performance. Scientific applications running on clusters employ collective communications extensively. Shared memory communication and Remote Direct Memory Access (RDMA) over multi-rail networks are promising approaches in addressing the increasing demand on intra-node and inter-node communications, and thereby in boosting the performance of collectives in emerging multi-core SMP clusters. In this regard, this paper designs and evaluates two classes of collective communication algorithms directly at the Elan user-level over multi-rail Quadrics QsNet^II with message striping: 1) RDMA-based traditional multi-port algorithms for gather, all-gather, and all-to-all collectives for medium to large messages, and 2) RDMA-based and SMP-aware multi-port all-gather algorithms for small to medium size messages. The multi-port RDMA-based Direct algorithm for gather and all-to-all collectives gain an improvement of up to 2.15 for 4 KB messages over elan_gather(), and up to 2.26 for 2 KB messages over elan_alltoall(), respectively. For the all-gather, our SMP-aware Bruck algorithm outperforms all other all-gather algorithms including elan_gather() for 512 B to 8 KB messages, with a 1.96 improvement factor for 4 KB messages. Our multi-port Direct all-gather is the best algorithm for 16 KB to 1 MB, and outperforms elan_gather() by a factor of 1.49 for 32 KB messages. Experimentation with real applications has shown up to 1.47 communication speedup can be achieved using the proposed all-gather algorithms.

Dynamic imaging of cancer growth and invasion: a modified skin-fold chamber model

The metastatic invasion of cancer cells from the primary lesion into the adjacent stroma is a key step in cancer progression, and is associated with poor outcome. The principles of cancer invasion have been experimentally addressed in various in vitro models; however, key steps and mechanisms in vivo remain unclear. Here, we establish a modified skin-fold chamber model for orthotopic implantation, growth and invasion of human HT-1080 fibrosarcoma cells, dynamically reconstructed by epifluorescence and multiphoton microscopy. This strategy allows repeated imaging of tumor growth, tumor-induced angiogenesis and invasion, as either individual cells, or collective strands and cell masses that move along collagen-rich extracellular matrix and coopt host tissue including striated muscle strands and lymph vessels. This modified window model will be suited to address mechanisms of cancer invasion and metastasis, and related experimental therapy.     

Coarse analysis of collective motion with different communication mechanisms

We study the effects of a signalling constraint on an individual-based model of self-organizing group formation using a coarse analysis framework. This involves using an automated data-driven technique which defines a diffusion process on the graph of a sample dataset formed from a representative stationary simulation. The eigenvectors of the graph Laplacian are used to construct 'diffusion-map' coordinates which provide a geometrically meaningful low-dimensional representation of the dataset. We show that, for the parameter regime studied, the second principal eigenvector provides a sufficient representation of the dataset and use it as a coarse observable. This allows the computation of coarse bifurcation diagrams, which are used to compare the effects of the signalling constraint on the population-level behavior of the model.     

Nutritional ecology beyond the individual: a conceptual framework for integrating nutrition and social interactions

Over recent years, modelling approaches from nutritional ecology (known as Nutritional Geometry) have been increasingly used to describe how animals and some other organisms select foods and eat them in appropriate amounts in order to maintain a balanced nutritional state maximising fitness. These nutritional strategies profoundly affect the physiology, behaviour and performance of individuals, which in turn impact their social interactions within groups and societies. Here, we present a conceptual framework to study the role of nutrition as a major ecological factor influencing the development and maintenance of social life. We first illustrate some of the mechanisms by which nutritional differences among individuals mediate social interactions in a broad range of species and ecological contexts. We then explain how studying individual‐ and collective‐level nutrition in a common conceptual framework derived from Nutritional Geometry can bring new fundamental insights into the mechanisms and evolution of social interactions, using a combination of simulation models and manipulative experiments.     

Three-dimensional collective cell motions in an acinus-like lumen

Collective cell migration is an essential process in embryo development, wound healing, inflammatory response, and cancer invasion. Although cell motions in two-dimensional (2D) monolayers have been studied previously, three-dimensional (3D) collective cell migration, which constantly occurs during embryogenesis such as the establishment of ducts and acini in vivo, remains elusive. In this paper, we develop a cell-based model incorporating cell mechanics and cell motility to address coherent cell motions in a spherical acinus-like lumen with different cell populations. It is found that the interplays between cell persistence, random fluctuation, and geometrical confinement may engender rich and novel migratory modes. In a 3D spherical lumen, two cells may undergo stripe-like or cross-circular coherent rotations, whereas multiple cells can form dynamic twisting or circulating bands, leaving sparse cells at the center or even a hollow cavity in the cell aggregate. The cell density is found to profoundly influence the collective cell migration modes. Our model can reproduce the fundamental features observed in experiments and highlight the role of mechanics in steering 3D collective cell dynamics during mammary acinar morphogenesis.     

Viscoelasticity of multicellular surfaces

Various modeling approaches have been applied to describe viscoelasticity of multicellular surfaces. The viscoelasticity is considered within three time regimes: (1) short time regime for milliseconds to seconds time scale which corresponds to sub-cellular level; (2) middle time regime for several tens of seconds to several minutes time scale which corresponds to cellular level; and (3) long time regime for several tens of minutes to several hours time scale which corresponds to supra-cellular level. Short and middle time regimes have been successfully elaborated in the literature, whereas long time viscoelasticity remains unclear. Long time regime accounts for collective cell migration. Collective cell migration could induce uncorrelated motility which has an impact to energy storage and dissipation during cell surface rearrangement. Uncorrelated motility influences: (1) volume fraction of migrating cells, (2) distribution of migrating cells, (3) shapes of migrating cell groups. These parameters influence mechanical coupling between migrating and resting subpopulations and consequently the constitutive model for long time regime.This modeling consideration indicates that additional experimental work is needed to confirm the feasibility of constitutive models which have been applied in literature for long time regime as: (1) relaxation of stress and strain, (2) storage and loss moduli as the function of time, (3) distribution of migrating cells.     

Planar Cell Polarity Signaling in Collective Cell Movements During Morphogenesis and Disease

Collective and directed cell movements are crucial for diverse developmental processes in the animal kingdom, but they are also involved in wound repair and disease. During these processes groups of cells are oriented within the tissue plane, which is referred to as planar cell polarity (PCP). This requires a tight regulation that is in part conducted by the PCP pathway. Although this pathway was initially characterized in flies, subsequent studies in vertebrates revealed a set of conserved core factors but also effector molecules and signal modulators, which build the fundamental PCP machinery. The PCP pathway in Drosophila regulates several developmental processes involving collective cell movements such as border cell migration during oogenesis, ommatidial rotation during eye development, and embryonic dorsal closure. During vertebrate embryogenesis, PCP signaling also controls collective and directed cell movements including convergent extension during gastrulation, neural tube closure, neural crest cell migration, or heart morphogenesis. Similarly, PCP signaling is linked to processes such as wound repair, and cancer invasion and metastasis in adults. As a consequence, disruption of PCP signaling leads to pathological conditions. In this review, we will summarize recent findings about the role of PCP signaling in collective cell movements in flies and vertebrates. In addition, we will focus on how studies in Drosophila have been relevant to our understanding of the PCP molecular machinery and will describe several developmental defects and human disorders in which PCP signaling is compromised. Therefore, new discoveries about the contribution of this pathway to collective cell movements could provide new potential diagnostic and therapeutic targets for these disorders.     

Moving together: Incidental leaders and naïve followers

Elucidating whether common general mechanisms govern collective movements in a wide range of species is a central issue in the study of social behaviour. In this paper, we describe a new experimental paradigm for studying the dynamic of collective movements. Some sheep (Ovis aries) were first trained to move towards a coloured panel, in response to a sound cue. We present data comparing the behaviour of test groups composed of one of the trained sheep and 3 naïve sheep, and control groups composed of 4 naïve sheep. In the tests, for both test and control groups, sheep were observed for 20 min before the sound cue was delivered and the panel made visible. Before the sound, trained and naïve sheep were similar in terms of activity budgets, spatial distribution, social behaviour and spontaneous movement initiation. After the sound, trained sheep moved toward the panel and systematically triggered a collective movement in all test groups. The results suggest that any individual moving away from the group can elicit a collective movement. Our experimental protocol provides an opportunity to quantify mechanisms involved in group movements, and to investigate differences between species and the effect of social context on collective decision-making.     

The hidden variables of leadership

The dynamics of a collective move can be untangled into three components: initiation, following and cancellation. Varying the response function parameters attached to one individual can switch the collective phenomenology from an absence of well identified leader (“distributed leadership”) to the emergence of a “despotic regime”, i.e. this individual leading more often the collective moves. I show that not all parameters have the same impact but rather that only a large increase of the initiation rate can empower an obvious leader, up to the “despotic” regime. Being more readily followed, or cancelling less often can enhance the leader's prominence only up to a limited level. To overtake this limit would then further require to affect also the parameters attached to the others (e.g. to lower their eagerness to initiate group motion as well as their probability to be followed when they do).