Comparison of acrophase data between groups of subjects. This diagram shows acrophase distribution of one subject on the left and another subject on the right side. For each subjects a mean vector, representing the long-term mean acrophase was calculated (see Figure 1). The clock plot in the middle shows the end points of these mean vectors for all subjects; vectors from the two subjects are highlighted by a red box. Two groups are shown: subjects with pigment dispersion are represented by red circles, the ones without by blue crosses. Again the analysis of time series and other circular data requires special methods, so for second-order analysis (i.e. comparing group means from already aggregated individual data), the group mean was calculated similarly to the individual mean by averaging the x- and y-coordinates. The significance of the differences of the mean angles among groups was tested using a parametric test according to Batschelet and Hotelling.