Fig. 4

Chasing is affected by the sex of the play partner. a There were no sex differences in either same- or mixed-sex pairs in frequency of chasing behavior (Student’s t tests with Welch’s correction: ns = not significant). However, both males and females increased their chasing when in mixed- relative to same-sex pairs (paired t tests: *p < 0.05, **p < 0.01). b Separation of chasing behavior into individual days did not reveal a significant interaction between age and pair type (two-way repeated measures ANOVA). c Comparison of play on PN32 (familiar partner) and PN33 (novel partner) did not reveal an interaction between pair type and partner familiarity (two-way repeated measures ANOVA: ns = not significant)