(d) Data analysis

All experimental data analyses were done using SPSS statistics v. 20. For each experiment, we measured the number of individuals on the two refuge zones at the end of the experiment (1200 s) and calculated the proportion of individuals on the most crowded refuge zone.

For the experimental portion of our study, we used a generalized linear model for proportional data, fixing the over-dispersion of the data using quasi-binomial error distribution and ‘Probit’ link function to determine whether the social context (group size variation) and the genetic variation (rover and sitter lines) affected aggregation behaviour.