About 83% of the pygmy marmoset population lives in stable troops of two to nine individuals, including a dominant male, a breeding female, and up to four successive litters of offspring. The modal size of a standard stable troop would be six individuals.[4] Although most groups consist of family members, some may also include one or two additional adult members. Members of the group communicate using a complex system including vocal, chemical, and visual signals. Three main calling signals depend on the distance the call needs to travel. These monkeys may also make visual displays when threatened or to show dominance. Chemical signaling using secretions from glands on the chest and genital area allow the female to indicate to the male when she is able to reproduce. The female gives birth to twins twice a year and the parental care is shared between the group.
The pygmy marmoset has been viewed as somewhat different from typical marmosets, most of which are classified in the genera Callithrix and Mico, and thus is accorded its own genus, Cebuella, within the family Callitrichidae. It is listed as Vulnerable by the International Union for Conservation of Nature. The biggest threats to the species are habitat loss and the pet trade.[5]
Evolution and taxonomy
There has been debate among primatologists concerning the proper genus in which to place the pygmy marmoset. An examination of the interstitial retinol binding protein nuclear gene (IRBP) in three marmoset species showed that Callithrix as constructed in the 1990s also needed to include C. pygmaea to be monophyletic, and that the times of separation of pygmaea and the argentata and jacchus species groups from one another are less than 5 million years ago, as might be expected for species of the same genus.[6] However, subsequent separation of the argentata and jacchus species groups into different genera (the argentata group having been moved to Mico) justifies maintaining a separate genus for the pygmy marmoset, as Callithrix is no longer paraphyletic.[3]There are two subspecies described by Colin Groves of the pygmy marmoset:[1][2]
- Cebuella pygmaea pygmaea – Northern/Western pygmy marmoset
- Cebuella pygmaea niveiventris – Eastern pygmy marmoset
The evolution of this species diverged in terms of body-mass from typical primates, with a high rate of body-mass reduction. This involves large decreases in pre-natal and post-natal growth rates, furthering the thought that pro-genesis played a role in the evolution of this animal.[8]
Physical description
The pygmy marmoset is the world's smallest monkey.
The pygmy marmoset is one of the world's smallest primates, being the smallest true monkey, with a head-body length ranging from 117 to 152 mm (4.6 to 6.0 in) and a tail of 172 to 229 mm (6.8 to 9.0 in). The average adult body weight is just over 100 grams (3.5 oz) with the only sexual dimorphism of females being a little heavier.[9][10] The fur colour is a mixture of brownish-gold, grey, and black on its back and head and yellow, orange, and tawny on its underparts. Its tail has black rings and its face has flecks of white on its cheeks and a white vertical line between its eyes.[10] It has many adaptations for arboreal living including the ability to rotate its head 180 degrees and sharp claw-like nails used to cling to branches and trees.[11][12] Its dental morphology is adapted to feeding on gum, with specialised incisors that are used to gouge trees and stimulate sap flow. Its cecum is larger than usual to allow for the greater period of time gum takes to break down in the stomach.[12] The pygmy marmoset walks on all four limbs and can leap up to 5 m (16 ft) between branches.[11][13]
Ecology
Geographic range and habitat
The pygmy marmoset can be found in much of the western Amazon Basin, in Brazil, Colombia, Ecuador, Peru, and Bolivia. The western pygmy marmoset, Cebuella pygmaea pygmaea, occurs in the state of Amazonas, Brazil, eastern Peru, southern Colombia, and north-eastern Ecuador. The eastern pygmy marmoset, C. p. niveiventris, is also found in Amazonas, but also in Acre, Brazil, eastern Peru, and northern Bolivia. The distribution of both subspecies is often limited by rivers. It typically lives in the understory of the mature evergreen forests and often near rivers.[3] Population density is correlated with food tree availability. It can be found between ground level and about 20 metres (66 ft) into the trees but generally does not enter the top of the canopy. It is often found in areas with standing water for more than three months of the year.[10]Diet
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Specialised claws allow the pygmy marmoset to cling to trees while feeding.
Pygmy marmosets have adapted insect-like claws, known as tegulae, to engage in a high degree of claw-clinging behaviors associated with plant exudate exploitation. Exudate is any material that oozes out of a plant, including gum, sap, resin, and latex.[15] Claw-clinging is primarily used during feeding, but also during plant exudate foraging.[13]
Behaviour
Pygmy marmosets at the Rostock Zoo.
Social systems
Infant pygmy marmosets, along with their parents, twin, and other siblings, form cooperative care groups. Babbling, or vocalizing, by the infant marmoset is a key part of its relationships with its family members and is a major part of its development. As the infant develops, the babbling gradually changes to resemble and eventually become adult vocalization. There are many similarities between the development of vocalization in infant pygmy marmosets and speech in infant humans. Vocalizing gives the infant advantages such as increased care and allows the entire family to coordinate their activities without seeing each other.[21]
Pygmy marmosets live in groups of two to nine individuals.
The pygmy marmoset is a non-seasonal breeder and usually gives birth to twins once or twice a year.[23] However, single births occur 16% of the time and triplet births 8% of the time.[17] The pygmy marmoset is usually monogamous though there is some variation within the species in terms of breeding systems. Polyandry also occurs as male marmosets are responsible for carrying the infants on their backs. Having a second male to carry the offspring can be beneficial as marmoset litters are often twins and decreases the cost to any particular male. The daily range of the pygmy marmoset, however, is relatively small, which decreases the rate of polyandry.[24]
Male and female pygmy marmosets show differences in foraging and feeding behavior, although male and female dominance and aggressive behavior varies within the species. Males have less time to search out food sources and forage due to the constraints of their infant caring responsibilities and predator vigilance. Without an infant to carry, female pygmy marmosets have greater freedom to forage, giving them an apparent feeding priority. This priority may serve to compensate mothers for the energetic costs of carrying and lactating for two offspring at a time. However, the fact that feeding priority is also given to females without offspring weakens the argument. Instead, female feeding priority may have evolved through sexual selection. Females may choose mates who invest more time in infant care and predator vigilance. Such males have less time to look for food, allowing the female feeding priority.[25]
Communication
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Groups use contact calls to stay together when foraging, feeding, and travelling.
Environmental factors play a role in communication by affecting the frequency of the signal and how far the signal can travel and still be audible to communicate the desired message. Since the pygmy marmoset is often found in the rain forest, plant life and the humid atmosphere add to the normal absorption and scattering of sound. Because low frequency calls are affected less by the disturbances than their high frequency counterparts, they are used for communication across longer distances.[19] The pygmy marmoset changes the characteristics of its calls when its social environment is changed. Adult marmosets will show modifications in the structure of their calls which mimic that of their group members. In addition to changes of existing calls, novel calls may be heard from marmosets after pairing.[26]
The pygmy marmoset has other ways to communicate information about matters such as the female's ovulatory state. New World monkeys do not show genital swelling during ovulation as female Old World monkeys do. Instead, a lack of female aggression towards males can serve as a signal of ovulation. Scent glands on its chest, anus, and genitals are also rubbed on surfaces which leave chemical signals about the reproductive state of the female.[27] The pygmy marmoset also performs visual displays such as strutting, back-arching, and piloerection when it feels threatened or to show dominance.[28]
Conservation
It is listed as a Vulnerable species by the International Union for Conservation of Nature. The species was originally listed on Appendix I by CITES due to wildlife trade but has since been downgraded to Appendix II. It is threatened by habitat loss in some areas of its range, and by the pet trade in others (i.e. Ecuador).[3]Interaction between humans and the pygmy marmoset is associated with a number of behavioral changes in the animal including social play and vocalization, both of which are important to communication between animals in the species. Particularly in areas of heavy tourism, pygmy marmosets have a tendency to be less noisy, less aggressive, and less playful with other individuals. They are also pushed into higher strata of the rainforest than they would normally prefer. Tourism in areas native to the pygmy marmoset is also correlated with increased capture of the animal. Due to its small size and relatively docile nature, captured pygmy marmosets are often found in exotic pet trades.[29] Capture causes even more behavioral variations, including a decrease in both the number and the sound level of vocalizations.[30] Pygmy marmosets can also be found at local zoos, where they exist in groups.[31]
In popular culture
- Fingerlings, the hit toy of Christmas 2017 produced by WowWee, are based on pygmy marmosets.[32]
As pets
Finger monkeys’ (pygmy marmoset) value is associated with them being the smallest primate in the world. New-born pygmy marmosets are usually 5–6 inches (130–150 mm) tall, and weigh from 100 grams (3.5 oz).[33] Although these primates are not in danger of extinction, they are rare to find in the market for purchase. Prices range from $1,000 to $4,000.[33] Generally, a Pygmy Marmoset’s life-span is from 15 to 20 years, they are known to have a shorter life in the wild mainly because they fall off of trees.[34]Another expense for these creatures as pets is the necessary essentials in order to maintain them. Creating an environment similar to that of where they are from is important.[35] For food, these creatures as pets are often fed fruits, insects, and smaller lizards.[36] As pets, a baby pygmy marmoset needs to be fed every two hours for at least two weeks [33]. Understanding their natural diet is also important because it helps maintain their good health from the necessary protein, calcium and other nutritional sources they need in order to survive.
In the United States, each state has different regulations when it comes to owning one of these creatures.[33] Another factor that needs to be considered is that a regular veterinarian might not be able to help provide medical evaluations or care; one would need to seek out a veterinarian with a primate specialization.[37] In South America it is illegal to either import or export these creatures. Understanding the laws within those countries is important when it comes to considering owning or taking care of a pygmy marmoset. Many people do not agree that pygmy marmosets should be pets.[35] The argument is usually that they have a longer life-span when they are in good care from a human.[36]
Binomial name
Cebuella pygmaea
Spix, 1823
Geographic range
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