Play Frequency and Modalities in Adult Bonobos

As a first step we compared the levels of play performed by adults with other adults and with immature individuals (excluding mother-offspring play from the analysis). The analysis showed no significant difference (Wilcoxon Exact test T = 6, ties = 0, n = 8, p = 0.11).

In the first observation session, adults directed play invitations (PINV) more frequently to each other than to immature subjects (Palagi 2006). In the following observation sessions (specifically, sessions 3 and 4), we also recorded the frequency of successful and unsuccessful play invitations (PINV and PINV ).

We compared the results obtained by the following ratio in order to assess whether the successful PINVs performed by adults toward other adults and toward immature individuals differed significantly. There proved to be no significant difference (Wilcoxon Exact test T = 10, n = 6, ties = 0, p = 0.99). Both age-matched and immature subjects responded with a similar motivation to the play invitations performed by adults (Fig. 3.1).

Then we carried out a comparison of the play modalities according to the age of playmates. In order to evaluate such a difference, we compared the following ratio between adult-adult and adult-immature combinations.

We found that adults used higher levels of contact play (C play) during play sessions with immature subjects, whereas during adult-adult sessions they preferred the locomotor modality (L play) (Wilcoxon Exact test T = 1, n = 8, ties = 0, p = 0.016) (Fig. 3.2).

1,00

successful PINV

unsuccessful PINV

Fig. 3.1 Proportion of successful play invitations showed by adult bonobos with other adults or immatures. A line with open dots represents an adult male, and a line with closed dots represents an adult female.

successful PINV

unsuccessful PINV

with other adults with immatures

Fig. 3.1 Proportion of successful play invitations showed by adult bonobos with other adults or immatures. A line with open dots represents an adult male, and a line with closed dots represents an adult female.

As for the occurrence of sexual contacts per play session, adult-adult dyads used sexual patterns more frequently than adult-immature dyads (Wilcoxon Exact test T = 1, n = 8, p = 0.016). The use of sexual patterns per play session is significantly more frequent in males than in females (Exact Mann Whitney U = 0, nm = 3, nf = 5, p = 0.036) (Fig. 3.3).

Play frequency among adults did not follow a random distribution in relation to the partner's sex (randomization ANOVA, one-way: F = 8.837, p = 0.007) (Palagi 2006). The frequency of play among bonobo females was higher than in malefemale dyads (t = 3.501, nff = 10, nmf = 15, p = 0.001). Males, on the other hand, never played together. Here, we provide an additional analysis which showed a difference in play modality according to the sex of the players. In order to evaluate the difference we compared the ratio (3.2) between female-female and male-female dyads. The randomization test for two independent samples showed that C play occurred with significantly higher frequency among female-female compared to male-female dyads (t = 3.841, nff = 10, nmf = 15, p = 0.0007) (Fig. 3.4).

contact play t l locomotor play

with other adults

Fig. 3.2 Proportion of contact play performed by adult bonobos with other adults or immatures. A line with open dots represents an adult male, and a line with closed dots represents an adult female.

contact play t l

with other adults locomotor play with immatures

Fig. 3.2 Proportion of contact play performed by adult bonobos with other adults or immatures. A line with open dots represents an adult male, and a line with closed dots represents an adult female.

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