Arrilton Araújo

Body weight of wild and captive common marmosets (callithrix jacchus)

Captive studies and occasional trappings of wild individuals indicate that callitrichids have small size and body weight and lack sexual dimorphism. We compared body weights of captive and wild Callithrix jacchus obtained by repeatedly weighing subjects from two populations in Brazil. We obtained captive data by routinely weighing 138 individuals from the Universidade Federal do Rio Grande do Norte colony and wild data via regular trapping of 243 individuals in 15 free-ranging groups from IBAMAs field site in Nísia Floresta. We assigned all subjects to one of four age classes—infant, juvenile, subadult, and adult—according to their birth dates or size, reproductive status, and dental development. There is no significant difference between males and females in any of the four age classes, but captive subjects were heavier than wild ones in all age classes but infant. Reproductive and nonreproductive adult females showed no statistical difference in weight. These results accord with previous reports of lack of body size sexual dimorphism in common marmosets and suggest that differences between wild and captive common marmosets are not constitutional, but are instead a consequence of diet and physical activity. The absence of weight difference between reproductive and nonreproductive females suggests that any possible advantage from high rank is outweighed by the costs of reproduction in common marmosets.

Two Breeding Females within Free-Living Groups May Not Always Indicate Polygyny: Alternative Subordinate Female Strategies in Common Marmosets (Callithrix jacchus)

The mating system of callitrichids has been reported to be monogamous, polygynous and polyandrous. In Callithrix jacchus, groups with 2 breeding females and groups with 1 breeding female have been reported. Our purpose was to evaluate the occurrence of occasional reproduction by subordinate females in free-ranging C. jacchus groups characterized as monogamous. Four groups were monitored at a field site of IBAMA-Brazil for between 20 and 72 months. We recorded the birth of 7 sets of twins to subordinate females that had never reproduced before. Sexual activities were recorded opportunistically: dominant females copulated with only the resident male, while subordinates copulated with extra-group males. We suggest these were essentially monogamous groups that occasionally had 2 reproductive females. Between-group copulations seem to be an alternative strategy used by the subordinates. Despite the costs, there would probably be benefits as a result of scanning for vacancies for reproductive positionsin neighbouring groups and the establishment of ties with extra-group males that might become a reproductive partner in the future.

Mating Systems and Female–Female Competition in the Common Marmoset, Callithrix jacchus

Mating systems in callitrichids are flexible, but usually only one female breeds. Reproductive skew models suggest that either dominant individuals can control the incidence of subordinate reproduction, and that when subordinates breed, it represents a concession from the dominant individual (Optimal Skew Model (OSM)), or alternatively, that subordinates breed because dominants are unable to control them (Incomplete Control Model (ICM)). We present data both from a captive study and a long term field study to test which model better explains mating systems and female-female competition in Callithrix jacchus. A 10-year study of a wild population allowed us to identify three possible mating systems occurring in groups: monogyny, monogyny with breeding attempts from subordinates (pseudo-polygyny), and polygyny. Comparison of interbirth intervals and time to produce a surviving offspring indicated that polygyny is costly to females, suggesting that females should benefit from monopolization of reproduction. Data from an experimental captive study indicated that dominant females are not always able to physiologically and/or behaviorally suppress subordinate females’ reproduction. The literature suggests that helpers are necessary to ensure the survival of dominant females’ offspring; however, our field data show that not all adults help equally. A few individuals, mostly adult males, participate significantly more in infant care than other helpers, suggesting that dominant females gain little by retaining subordinate females in their groups. These results indicate that dominant females are not able to control subordinates’ reproduction, suggesting that the flexibility of C. jacchus mating systems is better explained by ICM than by OSM.

Reproduction and aging in marmosets and tamarins.

This chapter presents data on the relations between reproduction and aging in both captive and free-ranging marmosets and tamarins. The relationship is examined from two perspectives. First, the relation of age to physiological impairments in reproductive function is explored. Callitrichid females, in common with many other nonhuman primates, begin to display anovulation associated with follicular depletion at a point relatively close to the maximum life span. Unlike Old World primates, however, they continued to display significant steroidogenic activity in the ovary. There are age effects on some reproductive output variables, such as litter size and inter-birth interval, though the effects are often small. Like other mammals, male marmosets display a change in levels of androgens with age, although the magnitude of the decrease is not large and they actually mount an elevated response to GnRH challenge as they age. We also examined whether age affects either the establishment or maintenance of a breeding position, the factors most important in determining lifetime reproductive success. Infant mortality did increase with increasing parturitions, suggesting that there may have been aging or parturition effects on lactation. Generally, marmoset females were well past the age of sexual maturity at the beginning of the tenure and approaching 8-9 years at the end of it. Reproductive decline did not appear to be a gradual process, but a rather abrupt one, often causing the dismantling of the group. There are potentially interesting relations among maternal age, mass and declining reproductive performance, given the known importance of mass as a determinant of reproductive success in female callitrichids.

Male and female breeding strategies in a cooperative primate.

Marmosets are cooperative breeders organized as extended family groups, but breeding is generally restricted to a single pair. Breeding competition is fierce in female marmosets; males, on the other hand, show low levels of intragroup aggression. We investigated male and female breeding strategies and the resulting reproductive output in 9 wild groups. Reproductive output, tenure of breeding animals, identification of the breeding system, breeding position replacements, migration and infanticide were recorded; also, we recorded grooming and aggression. Replacement of the breeding male or female was observed on nine occasions. On four occasions, the son of the breeding male inherited the breeding post, but we never observed inheritance of a breeding post by a daughter. Mostly, females attained a breeding post by immigrating to a group that had a breeding vacancy. Our results showed that Callithrix jacchus males and females use different strategies to attain a breeding position and maintain it for as long as possible. These strategies prolong the tenure of the breeding position, which is the best way to produce a large number of offspring. This article is part of a Special Issue entitled: Neotropical Behaviour.

Seasonal activity of Dinoponera quadriceps Santschi (Formicidae, Ponerinae) in the semi-arid Caatinga of northeastern Brazil

Seasonal activity of Dinoponera quadriceps Santschi (Formicidae, Ponerinae) in the semi-arid Caatinga of northeastern Brazil. We studied seasonal foraging patterns of the queenless ant D. quadriceps (Formicidae, Ponerinae) for 24 months in a Caatinga area of northeastern Brazil, an ecosystem characterized by strong climatic changes throughout the year, in order to determine if regulation of worker activity is based on environmental conditions (air temperature, relative humidity, precipitation) and/or food resources (potential prey: Coleoptera, Diptera, Hemiptera, Hymenoptera, Lepidoptera, Orthoptera, Araneae, Chilopoda and Diplopoda). Foraging activity of D. quadriceps varied over the course of both years, with the highest frequency occurring from May to August, corresponding to the late rainy season and early dry season. This foraging activity was negatively correlated with temperature and positively correlated with the availability of potential prey, but not with total abundance of soil arthropods or with rainfall and relative humidity. Diet composition, in relation to the main taxonomic prey groups, seems to be common to the species, regardless of habitat. Our results suggest that D. quadriceps workers adjust foraging activity to the most suitable period of the year, to avoid thermal stress and increase efficiency. Thus, they present an appropriate behavioral response to seasonal fluctuations in the Caatinga.

Emigration as a Reproductive Strategy of the Common Marmoset (Callithrix jacchus)

Demographic studies provide critical data for understanding the evolution, ecology, social organization and mating systems of primates. One influence on the demographic structure of a population is the pattern of emigration of individuals from their natal groups. In cooperative breeders, the offspring may stay in their natal group even after maturity, and many researchers are investigating the possible ecological and social factors responsible for this pattern and the resulting reproductive skew that occurs within these populations. In Callithrix jacchus, the common marmoset individuals disperse from their natal groups as adults, females disperse more frequently than males, and dispersals are more frequent during the rainy season than during the dry season. However, neither group size nor tertiary sex ratio is correlated with dispersal. Captive animals that undergo experimental procedures that simulate natural conditions after emigration (isolation from a group followed by movement into a new environment) trigger different physiological and behavioral responses in each sex. Males increased significantly in cortisol levels after separation, and upon placement in a new environment together with other males, they intensified their affiliative relationships and cooperated in tasks to acquire food. Females were less affected by isolation (as measured by changes in cortisol levels) and significantly increased piloerection and scent-marking behaviors when they were moved (as dyads) to a new environment. These differences suggest that males and females have evolved different strategies for dispersal and breeding success, and the dynamics of social relationships between females seem to be the main determinant of the demographic profile of common marmoset populations. Moreover, besides adaptations related to reproduction, females show additional behavioral and physiological mechanisms that may be selected to cope with social isolation following emigration.

Testicular Volume and Reproductive Status of Wild Callithrix jacchus

The social relationship dynamic among callitrichid females is well known. Breeding exclusivity by dominant females involves female-female competition, usually resulting in the inhibition of subordinate reproduction. However, the strategies to maintain the male breeding position are still unclear. Researchers have observed no overt aggression between males, and differences in testosterone levels between dominant and subordinate individuals do not correlate with differences in reproductive success. In Callithrix monogamy is the predominant mating system, and testicular size is compatible with the absence of sperm competition. We analyzed testicular volume during development in 95 individuals at different ages (infant n = 12, juvenile n = 9, subadult n = 15, and adult n = 59). We also investigated if the ratio between testicular volume and body mass correlates with breeding position in the social group. The ratio was significantly higher in breeding males and a positive correlation between body mass and testicular volume is significant only for nonbreeding males. The findings suggest that testicular size varies with male reproductive status in the social group and that the enlargement of testicular volume in breeding common marmoset males seems to be a result of proximate causes and to depend on social and reproductive contexts acting together or separately.

Social Organization in Callithrix jacchus: Cooperation and Competition

Abstract Callithrix jacchus are small anthropoid primates, endemic to Brazil. They are considered cooperative breeders as it takes more than the parents to rear the offspring. Their mating system is usually monogamous but two breeding female groups have also been reported. Marmoset females, unlike other female mammals, compete for breeding positions both behaviorally and physiologically and competition often involves leaving the group. Males, on the other hand, are philopatric, and show low levels of aggression. C. jacchus social system is characterized by competition by females, meant to enforce breeding monopolization, and cooperation by males, which provides support for the communal rearing of infants and the success of this system depends upon the balance between the two.Callithrix jacchus are small anthropoid primates, endemic to Brazil. They are considered cooperative breeders as it takes more than the parents to rear the offspring. Their mating system is usually monogamous but two breeding female groups have also been reported. Marmoset females, unlike other female mammals, compete for breeding positions both behaviorally and physiologically and competition often involves leaving the group. Males, on the other hand, are philopatric, and show low levels of aggression. C. jacchus social system is characterized by competition by females, meant to enforce breeding monopolization, and cooperation by males, which provides support for the communal rearing of infants and the success of this system depends upon the balance between the two.

Reproductive tactics of sexes and fitness in the dragonfly, Diastatops obscura.

Abstract The sexual selection strategies of territorial Odonata that do not present courtship behavior is still not completely understood, especially the role of the females. Diastatops obscura Fabricius (Odonata: Libellulidae) females participate in mate selection in a passive manner, allowing copulation with the first male that captures them and afterwards choosing whether to oviposit or not. This study introduces the idea of female passive choice as an adaptative tactic in intersexual selection. Also discussed is the adaptative value of this tactic and its flexibility according to environmental conditions and reproductive strategies adopted by the males. A natural population of Diastatops obscura was observed in the Pitimbu River of northeast Brazil. Focal continuous and ad libitum techniques were used to record attempted copulation, copulation, and oviposition behavior, in addition to registering male territoriality. An estimate of individual reproductive success (IRS) was obtained by recording 187 reproductive events. Territorial males, mainly occupying areas near the river margin, achieved greater copulation and oviposition success (IRS = 0.371) than did satellite males (IRS = 0.028). Females that copulated with territorial males experienced, for the most part, only one copulation and oviposition event, while those that copulated with satellite males fled or performed a second copulation with a territorial male. Thus, the best tactic adopted by the D. obscura males was to occupy a territory providing the greatest access to females, while the females used passive choice for fitness optimization.