Yup - my bad - There are 3 colonies at t0 and 4 at t1, as both b's are seperate colonies. I may later thing about implementing colony merges, but that's a rather tricky business, as Grosberg et al. have shown that colony merging is largely determined by genetics (so, I may keep track of "original colony" later on) but that's a level of complexity that won't be necessary for what I want to do with this model. I'll take a look at the links, though - thanks!