Social context modulates scale-free movements in a social insect.

Most animals move intermittently, pausing or slowing down for short moments and short moves, and darting away towards a new location where to hover again. This pattern occurs at a range of spatial and temporal scales (thence, resembling 'scale-free'), from the quick inspection of local areas to the sum of all movements performed from birth to death. While this pattern has been extensively described, its proximate drivers remain open to debate. A current hypothesis states that underlying proximate generative mechanisms of intermittent movement of animals are linked to external stimuli, e.g., interactions with the abiotic environment, resources, and other individuals. Here we investigated a prediction from this hypothesis, using termites as a biological model. We verified whether the social background in which a termite is inserted will modify the parameters of its intermittent scale-free spatial displacement. This relates to the hypothesis because it inspects how do external stimuli coming from intraspecifics can affect this type of movement. We tracked the trajectories of a focal termite confined along its nestmates in experimental clueless arenas, every 0.5 s along about six hours. Arenas varied in group size and comprised 22 distinct caste compositions, yielding 75 trackings (> 400 h) and more than two million Cartesian coordinates. Most of these trajectories (96% or 72/75) were classified as intermittent scale free (Lévy-like), indicating prevalence of this type of movement over non-Lévy-like ones (P=1.62×10-15). Moreover, intermittent scale-free movements performed by the focal termite (i) did arise outside the foraging-searching framework, and (ii) were modified by the social context while remaining within the limits of Lévy-walk realms. That is, some limits seem to exist along with the necessary plasticity to provide room for natural selection. Moreover, by arising outside the foraging framework, Lévy-like movements are shown to have broader relevance. Studies on processes that depend on social context and movement (e.g., collective behaviour, the spread of diseases) may, hence, profit from such concepts.

Scale-free movement patterns in termites emerge from social interactions and preferential attachments.

As the number or density of interacting individuals in a social group increases, a transition can develop from uncorrelated and disordered behavior of the individuals to a collective coherent pattern. We expand this observation by exploring the fine details of termite movement patterns to demonstrate that the value of the scaling exponent µ of a power law describing the Lévy walk of an individual is modified collectively as the density of animals in the group changes. This effect is absent when termites interact with inert obstacles. We also show that the network of encounters and interactions among specific individuals is selective, resembling a preferential attachment mechanism that is important for social networking. Our data strongly suggest that preferential attachments, a phenomenon not reported previously, and favorite interactions with a limited number of acquaintances are responsible for the generation of Lévy movement patterns in these social insects.

Multiscale model for the effects of adaptive immunity suppression on the viral therapy of cancer.

Oncolytic virotherapy-the use of viruses that specifically kill tumor cells-is an innovative and highly promising route for treating cancer. However, its therapeutic outcomes are mainly impaired by the host immune response to the viral infection. In this paper, we propose a multiscale mathematical model to study how the immune response interferes with the viral oncolytic activity. The model assumes that cytotoxic T cells can induce apoptosis in infected cancer cells and that free viruses can be inactivated by neutralizing antibodies or cleared at a constant rate by the innate immune response. Our simulations suggest that reprogramming the immune microenvironment in tumors could substantially enhance the oncolytic virotherapy in immune-competent hosts. Viable routes to such reprogramming are either in situ virus-mediated impairing of CD8(+) T cells motility or blockade of B and T lymphocytes recruitment. Our theoretical results can shed light on the design of viral vectors or new protocols with neat potential impacts on the clinical practice.

A multiscale mathematical model for oncolytic virotherapy.

One of the most promising strategies to treat cancer is attacking it with viruses. Oncolytic viruses can kill tumor cells specifically or induce anticancer immune response. A multiscale model for virotherapy of cancer is investigated through simulations. It was found that, for intratumoral virus administration, a solid tumor can be completely eradicated or keep growing after a transient remission. Furthermore, the model reveals undamped oscillatory dynamics of tumor cells and virus populations, which demands new in vivo and in vitro quantitative experiments aiming to detect this oscillatory response. The conditions for which each one of the different tumor responses dominates, as well as the occurrence probabilities for the other nondominant therapeutic outcomes, were determined. From a clinical point of view, our findings indicate that a successful, single agent virotherapy requires a strong inhibition of the host immune response and the use of potent virus species with a high intratumoral mobility. Moreover, due to the discrete and stochastic nature of cells and their responses, an optimal range for viral cytotoxicity is predicted because the virotherapy fails if the oncolytic virus demands either a too short or a very large time to kill the tumor cell. This result suggests that the search for viruses able to destroy tumor cells very fast does not necessarily lead to a more effective control of tumor growth.