Franziska Mattle

Experimentally Induced Polygyny in Callitrichids: Comparison between Callithrix and Callimico
The aim of this PhD project is, to investigate the socio-sexual strategies and their underlying motivations in two "socially flexible" species of the family Callitrichidae, the common marmoset (Callithrix jacchus) and the Goeldi's monkey (Callimico goeldii). For both species reports exist about wild groups living polygynously, i.e. two breeding females are present at the same time. Marmosets have twins and the father is the main care giver from the day of birth on. Goeldi's monkeys have singletons and the mother is the main care giver. The Callimico male does not begin to care for the infant until three weeks postpartum, and it is the female who controls male access to the infant. Based on these characteristics of their reproductive biology, it is to be expected that in Callithrix females, competition over males should be more intense than in Callimico. To test these hypotheses, a series of experiments is conducted in captivity: sister pairs of each species are removed from their native families. They are followed through three consecutive social stages by behavioural observations and sex steroid monitoring: (1) sister pairs (socially neutral); (2) encounters with an opposite-sexed conspecific (social competition); (3) permanent reunion of the trio with full physical contact (sexual competition).

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