Using the incidence and impact of health conditions in guide dogs to investigate healthy ageing in working dogs.

This study aimed to use retirement data from working guide dogs to investigate healthy ageing in dogs and the demographic factors that influence ageing. Using a dataset of 7686 dogs spanning 20 years, dogs withdrawn for health reasons before they reached retirement were identified. Cases of retirement for old age, rather than for health reasons, were also recorded, as was the length of working life for all dogs. Specific health reasons were grouped into 14 different health categories. The influence of purebred or crossbreed, breed, and sex on the incidence of these health categories and the length of working life within each health category was considered. The majority (n = 6465/7686; 84%) of working guide dogs were able to function as guide dogs until they had worked for 8.5 years, when they retired. This working life might constitute a reference for the different breeds considered, with the exception of the German shepherd dog, which had a shorter working life. The most common reason for health withdrawals was musculoskeletal conditions (n = 387/1362; 28%), mostly arthritis. Skin conditions (mostly comprised of cases of atopic dermatitis) reduced working life most commonly (mean, approximately 5 years). Nervous sensory conditions (35% of which were cases of epilepsy) reduced working life by 3 years.

A branching process, its application in biology: influence of demographic parameters on the social structure in mammal groups.

Branching processes are widely used in biology. This theoretical tool is used in cell dynamics, epidemics and population dynamics. In population dynamics, branching processes are mainly used to access extinction probabilities of populations, groups or families, with the Galton-Watson branching process. Many mammal species live in socially-structured groups, and the smallest units of these groups are lineages (or families) of kin-related individuals. In many primate species, these lineages are matrilines, as females remain in their natal groups most of the time, whereas males generally disperse. Lineage parameters, such as numbers of matrilines, size of each matriline and average degree of relatedness, could strongly influence the genetic composition of groups. Evidence indicates that division along matrilines could induce substantial differentiation among fission groups. Here, we develop a novel mathematical model based on the branching process theory describing demographic dynamics of groups. The main result of this model is an explicit analytical expression of the joint distribution of numbers of lineages and sizes of socially-structured groups. We investigated the influence of parameters such as natality and mortality on the outcome of the process, including extinction probability. Finally, we discuss this theoretical result with respect to biological significance.

Amplification and oscillations in the FAK/Src kinase system during integrin signaling.

Integrin signaling is a major pathway of cell adhesion to extracellular matrices that regulates many physiological cell behaviors such as cell proliferation, migration or differentiation and is implied in pathologies such as tumor invasion. In this paper, we focused on the molecular system formed by the two kinases FAK (focal adhesion kinase) and Src, which undergo auto- and co-activation during early steps of integrin signaling. The system is modelled using classical kinetic equations and yields a set of three nonlinear ordinary differential equations describing the dynamics of the different phosphorylation forms of FAK. Analytical and numerical analysis of these equations show that this system may in certain cases amplify incoming signals from the integrins. A quantitative condition is obtained, which indicates that the total FAK charge in the system acts as a critical mass that must be exceeded for amplification to be effective. Furthermore, we show that when FAK activity is lower than Src activity, spontaneous oscillations of FAK phosphorylation forms may appear. The oscillatory behavior is studied using bifurcation and stability diagrams. We finally discuss the significance of this behavior with respect to recent experimental results evidencing FAK dynamics.