A Saki Saga: Dynamic and Disruptive Relationships among Pithecia aequatorialis in Ecuador

Abstract

Saki monkeys live in socially monogamous groups and in groups containing more than one same-sex adult. As part of a 10-year study of equatorial sakis (Pithecia aequatorialis) in Ecuador, we documented the immigration of a second adult male into a group containing a resident male-female pair that had associated with one another for seven years and the resident female's two daughters. In the first month after immigration, the resident male spent more time closer to and grooming his putative adult daughter than the resident female, and the two males were seen performing a cooperative territorial display. After two months, the resident male interacted more with the resident female than with his putative adult daughter, while that daughter interacted more with the immigrant male and copulated with him. After three months, the males left the group together and associated with an unfamiliar female, leaving the resident females and a neonate behind. The resident male then paired with a new female, while the immigrant male joined another group, again as a second male. Compared to other socially monogamous primates, sakis appear to have a more variable social system whereby additional males can join established groups and form relationships with putatively unrelated males.

Delayed Dispersal and Immigration in Equatorial Sakis (Pithecia aequatorialis): Factors in the Transition from Pair- to Group-Living

“…We have been regularly monitoring the study group since November 2003 [Di Fiore et al, 2007;Porter et al, 2015;Van Belle et al, 2015]. At the time of the adult male's immigration, the group contained the original adult female present since the onset of the study (hereafter the "resident female") and her 3 offspring: a 5-year-old daughter ("adult daughter") born between November 5 and 26, 2006, a 1.5-year-old daughter ("juvenile daughter") born between March 9 and 15, 2010, and a 1-month-old infant of unknown sex born between November 15 and December 3, 2011.…”

“…For example, pair members are sometimes observed to interact frequently with extra-group individuals, including engaging in extra-pair copulations [Birkhead et al, 1995;Cohas et al, 2007;Jones et al, 2012;Barelli et al, 2013;Bonadonna et al, 2014]. Interactions with extra-group individuals can also result in turnover of resident adults within pairs, through either replacement by floaters (i.e., solitary individuals without a territory) or by "divorce" as a pair member leaves a group to pursue new mating opportunities elsewhere [Palombit, 1994;Choudhury, 1995;Ens et al, 1996;Otter and Ratcliffe, 1996;Morton et al, 2000;Lardy et al, 2010;Fernandez-Duque and Huck, 2013;Pérez-Staples et al, 2013;Porter et al, 2015]. Occasionally, putatively unrelated animals also immigrate into established groups and remain as additional breeding adults [Davies, 1992;Palombit, 1994;Brockelman et al, 1998;Seddon et al, 2003;Lappan, 2007], thus changing a social system from pair-living to group-living.…”

“…Sakis have been reported to retain adult offspring [Thompson et al, 2010;Norconk, 2011] and to accept putatively nonrelated adult immigrants into the group [Porter et al, 2015]. In Suriname, white-faced sakis ( P. pithecia ) living in groups with multiple same-sex adults are argued to form "primary dyads" between particular male-female pairs .…”

The ecological value of long-term studies of birds and mammals in Central America, South America and Antarctica

“…The following studies cover factors including resource availability and other ecological conditions and their influence on mating system formation, social organization, and reproductive success from a long-term perspective. Since 2003, the 'Comparative Socioecology of Monogamous Primates' study in Yasuní National Park and Biosphere Reserve in eastern Ecuador (76°08′ W, 0°38′ S) and Formosa Province, Argentina (58°11′W, 25°58′S) has revealed insights into ecological and social factors influencing social monogamy in primate species including owl monkeys (Aotus azarai), red titi monkeys (Callicebus discolor), and equatorial sakis (Pithecia aequatorialis) [31][32][33]. One theme that has emerged from this work is that intrasexual conflict plays an important role in social dynamics and reproductive success in some species but not others.…”

“…It was also shown that male intruders initiated the splitting up of male-female pairs and in some cases resulted in the death of expelled individuals, observations consistent with strong intra-sexual conflict in this species. In contrast, a focal study of one equatorial saki group and one red titi monkey group in Yasuní National Park suggests that intrasexual conflict is low and groups vary in social composition [32,34]. Monkey groups are continually being tracked (e.g.…”