Intraspecific Variation in the Mating System of Spectral Tarsiers

Abstract

Historically, a species' social system was perceived to be a fixed attribute and deviations were usually treated as aberrant or maladaptive. Over the last few decades, socioecologists have started to recognize that variation in social systems is normal and adaptive. Here I explore how ecological variation affects the mating system of a nocturnal primate, the spectral tarsier, Tarsius spectrum. Several studies of the spectral tarsier have illustrated variation in this species' mating system. Although most groups exhibit a monogamous mating system, a small proportion of the population consistently exhibits a polygynous mating system. I conducted this study at Tangkoko Nature Reserve in Sulawesi, Indonesia during 2007. I found that group size was highly variable, ranging from 2 individuals to as many as 8 individuals per sleeping site. Although most groups (21 of 26) were composed of a single adult male and a single adult female, ca. 19% of the groups contained 2 adult females. Three of the 5 groups with 2 adult females contained 2 young infants. As might be expected, polygynous groups were larger than were monogamous groups. The mean group size of monogamous groups was 2.9, whereas the mean group size of polygynous groups was 6.0. Polygynous groups were also more likely to use Ficus caulocarpa trees than were the monogamous groups. Polygynous groups consistently used more sleeping sites as well as larger diameter sleeping trees, than did monogamous groups. The large-diameter fig trees are ideal homes for the spectral tarsiers in that they offer multiple entrances and exits as well as protection from the elements. Polygynous and monogamous groups exhibited no differences in insect biomass available, home range size, or height of sleeping tree. These results support the hypothesis that ecological variation is an important determinant of mating system within spectral tarsiers.

Where are the beachmasters? Unexpectedly weak polygyny among southern elephant seals on a South Shetland Island

“…However, mating systems are the outcome of the reproductive strategies of members of a species rather than evolved characteristics of a species (Clutton-Brock 1989). Hence, they often vary in accordance with the prevailing social and ecological conditions (Carranza, Hidalgo De Trucios & Ena 1989, Bradley et al 2005, Gursky-Doyen 2010, Maher & Burger 2011, Jin et al 2016. This is exactly what we found in southern elephant seals, where pups born at Half Moon Beach in the South Shetland Islands appear to be fathered by a large number of males that each sire between one and a handful of offspring.…”

Defining the Low End of Primate Social Complexity: The Social Organization of the Nocturnal White-Footed Sportive Lemur (Lepilemur leucopus)

“…Among pair-living nocturnal primates fork-marked lemurs ( Phaner pallescens : Schülke and Kappeler 2003), dwarf lemurs ( Cheirogaleus medius : Fietz 1999), dwarf galagos ( Galagoides zanzibaricus : Nash and Harcourt 1986), tarsiers ( Tarsius spp. : Driller et al 2009; Gursky-Doyen 2010), woolly lemurs ( Avahi spp. : Harcourt 1991), and owl monkeys ( Aotus spp.…”

“…: Driller et al . 2009 ; Gursky-Doyen 2010 ), woolly lemurs ( Avahi spp. : Harcourt 1991 ; Norscia and Borgognini-Tarli 2008 ), and owl monkeys ( Aotus spp.…”

Ultrasonic Vocalizations by the Spectral Tarsier, Tarsius spectrum

“…Although most groups exhibit a monogamous social system, a few exhibit a polygynous social system [Gursky, 1994[Gursky, , 1995. They are known to exhibit long-term relationships with the same individual [Gursky-Doyen, 2010] but are also known to engage in occasional extra-pair copulations. The mating season is in May and November.…”