DOMINANCE HIERARCHIES NEED LIGHT-DARKNESS TO DEVELOP ROBUST STABILITY - PowerPoint Presentation

1. DOMINANCE HIERARCHIES NEED LIGHT-DARKNESS TO DEVELOP ROBUST STABILITYINTRODUCTIONThe formation and maintenance of linear dominance hierarchies is characterized by a gradual polarization (increased steepness) of dominance ranks over time. Agonistic interactions are usually correlated to daily activity rhythms and both are controlled by light-entrained endogenous pacemakers (i.e., circadian clocks). Circadian clocks can be also entrained by social cues, but the mechanisms controlling such synchronized clock networks are still not fully understood.The burrowing behavioural rhythms of the Norway lobster (Nephrops norvegicus) are controlled by the circadian clock and lobsters develop lasting dominance relationships accompanied with rank related changes in burrowing behaviour.We are using this model to understand the effects of circadian social synchronization on the stability of dominance hierarchies. THE EXPERIMENTFour lobsters were housed in a tank (150x75x30 cm) provided with 4 burrows (Fig. 1) for 7 days in 12-12 light-darkness conditions followed by 6 days of constant darkness, to study the endogenous properties of their circadian clocks. We used steepness to measure the stability of dominance hierarchies and locomotor activity as output of the circadian clock. RESULTSPreliminary results indicated that after switching to constant darkness (DD), the stability of dominance hierarchies decreased (Fig. 2), but the rank position of lobster was maintained. Such results suggested that light-darkness is not a fundamental requirement for establishing and maintaining dominance relationships, however it is important to maintain robust stability in the dominance hierarchies.NEXT ACTIONSWe are now starting to measure the syncronization of circadian oscillations in locomotor activity (Fig. 3) among lobsters, in order to understand whether these two parameters are correlated to the observed decrease of stability of the hierarchyies.REFERENCESSbragaglia, V., Leiva, D., Arias, A., Antonio Garcia, J., Aguzzi, J. & Breithaupt, T. (2017). Fighting over burrows: the emergence of dominance hierarchies in the Norway lobster (Nephrops norvegicus). J. Exp. Biol. 220, 4624-4633.Bloch, G., Herzog, E. D., Levine, J. D. & Schwartz, W. J. (2013). Socially synchronized circadian oscillators. Proc. R. Soc. Lond. B. 280, 20130035.Matteo Chiarini1, Jose Antonio Garcia1, Jacopo Aguzzi1, Valerio Sbragaglia2,3 1 Marine Science Institute, Spanish National Research Council (ICM-CSIC), Barcelona, Spain2 Department of Biology and Ecology of Fishes, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany3 Institute for Environmental Protection and Research (ISPRA), Livorno, ItalySupported by CoB travel grant:Fig. 1 - A frame of the time-lapse videos used to score agonistic interactions. Colored lines represent the output of the automated tracking used to measure locomotor activity.Fig. 2 - Emergence of dominance hierarchy measured over the 13 days (N = 5). Points represent the significant values of steepness (randomization test). The red line represent a local smoothing function together with 95% confidence interval (shaded red contour). Fig. 3 - Representative locomotor activity of four cohoused lobsters. The alternation between the white (light) and grey (darkness) backgrounds represent the first 7 days in LD conditions, followed by 6 days of constant darkness (DD).DDDD