Fig. 4: Cerebello-cerebral scaling may be primate-general.
Data were split into strepsirrhine and haplorhine (a–e) and ape and non-ape (f–i) subsets. Separate PGLS regressions were performed in these groups. Importantly, none of the grade shifts were significant as assessed by phylogenetic ANCOVA (Pr > F are given for the varying slopes, intercept, or both). For strepsirrhines, a slightly higher intercept was observed for cerebellar scaling relative to the cerebrum (a; main analysis). When regressed against body mass, cerebella scaled similarly between groups (b), whereas the cerebral PGLS had a slightly lower intercept in strepsirrhines relative to haplorhines (c). This showed the opposite pattern relative to the main PGLS (a). Within the brain however, cerebellar volumes appeared to be more influential on the regression in (a). The jump in intercept for strepsirrhines in cerebellar PGLS mirrored the main PGLS (d), while cerebra scaled virtually identically between groups (e). For apes/non-apes, it appeared that ape cerebella were relatively large (f; main analysis). This (merely visual) shift was slightly accentuated by restricting the analyses to haplorhines as in Barton and Venditti35. (g). Ansiform regressions on the rest of cerebellar (h) and cerebral (i) volumes revealed no differences. Together, the lack of significant differences in any pANCOVA argue for primate-general scaling. Nstrepsirrhine = 9; Nhaplorhine = 25 (a–e); Nape = 7; and Nnon-ape = 27 (f); Nape = 7; and Nnon-ape = 18 (g); and Nape = 5 and Nnon-ape = 8 (h, i).
