The distribution of allogrooming among female Japanese macaques (Macaca Fuscata Yakui)
Allo-grooming is the main behaviour primates use to establish and maintain amicable social relationships and, for this reason, it has been intensively studied in the last three decades. Notwithstanding this, conclusive data on the factors affecting allo-grooming distribution and on its benefits are still scarce. This Thesis thus aimed to analyse the importance of the following factors in the distribution of allo-grooming among female Japanese macaques (Macaca fuscata yakui): environmental variables, seasonal changes in food abundance and group size. This study also aimed to analyse some possible benefits of allo-grooming, namely, the reciprocation of allo-grooming (considered to be beneficial for the removal of parasites), tolerance over food and agonistic support. Data were collected on 28 females living in two groups of different size (N = 21 and around 50, respectively), on Yakushima Island, Japan. Allo-grooming was not affected by ambient temperature or relative humidity, suggesting that this behaviour is so important for the maintenance of amicable social relationships that it became independent from environmental variables (while this did not happen for behaviours related to pelage care but lacking any social function, such as self-grooming). Allo-grooming distribution and reciprocation were unaffected by seasonal changes in food abundance. Conversely, group size affected allo-grooming: females in the large group spent more time allo-grooming and were more selective in their choice of grooming partners. Finally, allo-grooming increased the chances of agonistic support against a male aggressor and it also favoured tolerance near food sources. The findings of this Thesis indicate that allo-grooming is relatively resilient to mild, short-term changes of habitat characteristics, while it may be affected by group size. They also highlight the importance of this behaviour for the establishment and maintenance of amicable social relationships and for obtaining social benefits (e.g. tolerance) other than allo-grooming itself.
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