Friendly or Powerful? Fatted male phenomenon of collin’s squirrel monkeys

In species where sexual selection operates, reproduction is heavily influenced by morphological and behavioral traits that ultimately affect their copulation rates and reproductive success. Two of the most conspicuous of those traits are the sexual size dimorphism, the permanent or temporary enlargement of males, as in the case of squirrel monkeys. In this research, we unveil some central aspects regarding the “fatted male phenomenon” of the Amazonian Collins’ squirrel monkey, Saimiri collinsi. Closely monitoring four captive social groups under controlled conditions, we used a combination of techniques, observing their reproductive behavior, their social dominance and their social network power for more than 15 consecutive months.