Tamarin and marmoset mating systems: Unusual flexibility

Recent studies of wild tamarins and marmosets have shown that at least one species exhibits variable mating patterns, including cooperative polyandry, monogamy and, more rarely, polygyny. Polyandry is thought to occur because the high frequency of twinning and the relatively high weights of infants in these species make the rearing of infants unusually difficult. Nonreproductive helpers (older offspring) and polyandrous males may serve as alternative sources of the extra help needed with infant care. The apparent causes of facultative polyandry in saddle-back tamarins are quite different from those of the cooperative polyandry that has been studied in some bird species.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27403/1/0000436.pd

Facultative polyandry and the role of infant-carrying in wild saddle-back tamarins ( Saguinus fuscicollis )

Wild saddle-back tamarins ( Saguinus fuscicollis ) in southeastern Peru have a variable mating system that can differ both between territories at any one time and within territories over time. Groups are usually monogamous or cooperatively polyandrous, but are occasionally even polygynous. This study addressed the following questions: why does this population contain both monogamous and polyandrous groups simultaneously? What factors determine whether specific groups are monogamous or polyandrous? The data from this study population tentatively support the hypothesis that adults should mate monogramously only if they have nonreproductive helpers (usually older offspring) to help rear infants. Without helpers, the reproductive success of both males and females is hypothesized to be higher, on average, if they mate polyandrously than if they mate monogamously. The proposed benefits of polyandry to males and females differ quantitatively, but in both cases benefits stem from the help that males provide in rearing young. The following results support this hypothesis. (1) Lone pairs were never seen to attempt breeding, and calculations suggest that the costs of lactation and infant-carrying are too great for lone pairs to have a high probability of being able to raise twin offspring (the normal litter size). (2) Polyandrous males and nonreproductive offspring contributed substantially to infant care, particularly infant-carrying (fig. 2). (3) Adult males carried infants approximately twice as often as did lactating females, presumably because of the combined costs of (a) lactation (Fig. 3) and (b) infant-carrying (Fig. 4). The proximate causes of cooperative polyandry in S. fuscicollis appear to be different from those responsible in several bird species, showing that cooperative polyandry is a complex phenomenon.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46876/1/265_2004_Article_BF00572631.pd

A comparative perspective on the evolution of tamarin and marmoset social systems

Tamarins and marmosets (callitrichids) present an unusual opportunity for study of the determinants of primate social systems, because both the mating and infant care patterns of callitrichids are variable, even within individual populations. In this paper, I briefly describe three characteristics of callitrichid social systems that distinguish them from most other primates: extensive male parental care, helping by nonreproductive individuals, and variable mating patterns. I then discuss the evolution of these characteristics and of the frequent twinning exhibited by callitrichids. I suggest that an ancestor of modern callitrichids gave birth to a single offspring at a time, mated monogamously, and had significant paternal care. The idea that males of this ancestral form must have provided paternal care, even though only single infants were born, derives from a comparison of litter/mother weight ratios in modern primate species. Twinning perhaps then evolved because of a combination of dwarfing in the callitrichid lineage, leading to higher litter/mother weight ratios, and a high infant mortality rate, and because the extensive paternal care already present facilitated the raising of twins. I propose that the helping behavior of older offspring may have coevolved with twinning, because helpers would have increased the chances of survival of twins, and the presence of twins would have increased the benefits of helping. Finally, the high costs of raising twins and the variability of group compositions, especially the fact that some groups would not have had older offspring to serve as helpers, may have selected for facultative polyandry in saddle-back tamarins ( Saguinus fuscicollis ) and perhaps in other callitrichid species. Both helping and cooperative polyandry have been extensively studied in bird species, and I apply some of the conclusions of these studies to the discussion of the evolution of callitrichid social systems.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44556/1/10764_2005_Article_BF02193696.pd

Dynamics and Causes of Facultative Polyandry in Saddle-Back Tamarins (Saguinus Fuscicollis) (Peru).

Cooperative polyandry, where a single breeding female lives with two or more males who mate with her and subsequently help care for her young, occurs in a small but diverse array of animals, yet its causes are not well understood. In my dissertation research I studied the dynamics and causes of cooperative poly and ry in wild saddle-back tamarins living in Amazonian Peru. This species has unusually variable mating patterns: some groups are polyandrous, whereas others are monogamous, or even, rarely, polygynous. My seven-year study of this population showed that the ultimate cause of poly and ry in this species is, most probably, the high cost of raising infants. Lone male-female pairs are unlikely to be able to raise infants, and normally, adults either mate monogamously and are helped with infant care by nonreproductive helpers (older offspring) or mate polyandrously, with both males aiding with infant care. Demographic data showed that offspring exhibit helping behavior for some of the same reasons as do nonreproductive helpers in many bird species. The interactions between adult group members suggested that (1) the social relationships between polyandrous males are primarily affiliative and cooperative rather than aggressive, and (2) adult males make a greater investment than do females in the relationships between males and females. I suggest that polyandrous males are rarely aggressive towards each other because they benefit from each others' presence, and that the behaviors that increase a male's proximity to the female and increase her readiness to copulate with him have evolved as a form of indirect male-male competition for matings. Adults of both sexes contributed substantially to offspring care. Males carried infants twice as much, on average, as did females, and also groomed young more, spent more time in vigilance behavior, and remained in closer proximity to juveniles than did females, who performed all the energetically costly lactation. These results confirm the suggestion, based on descriptions of parental care patterns in some cooperatively polyandrous bird species, that cooperative and noncooperative forms of poly and ry are very different, since in noncooperative poly and ry males perform all or almost all of the offspring care.Ph.D.ZoologyUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/161534/1/8720271.pd

Agamas exhibit behavioral syndromes: bolder males bask and feed more but may suffer higher predation

According to basic evolutionary theory, individuals within a population should adapt their behavior in response to their current physical and social environment. However, there is now evidence from a diverse range of taxa that behavior is instead constrained by individuals' broad behavioral syndromes or personalities. Bold individuals are generally shown to take greater risks than shy individuals. Theory suggests that there should be fitness trade-offs associated with personalities. We aimed to answer the following 3 questions using the Namibian rock agama (Agama planiceps) as a study species: 1) Is the boldness of individual male agamas repeatable? 2) Do male agamas show a behavioral syndrome? and 3) Are there any possible fitness trade-offs associated with individual behavioral syndromes. We measured boldness of 30 male agamas by quantifying flight initiation distance. We found that individual agama behavior was significantly consistent through time. Also, bolder males were found to spend significantly more time basking and moving throughout their home ranges in sight of predators, indicating a behavioral syndrome in this species. Bolder males also had larger home ranges and fed more than shyer males but suffered higher levels of tail loss, possibly due to predation. The rates of visual signaling in the form of assertion displays of bolder and shyer males did not differ. We suggest that males of this species show a significant behavioral syndrome that may lead to fitness trade-offs. Copyright 2010, Oxford University Press.