As described in a recently published paper in Biology Letters, the Philippine Tarsier (Tarsius syrichta) has been found to communicate through extremely high pitched vocalisations in the ultrasound domain, undetectable by human ear. These presumed mute primates baffled primatologists… How can such lack of calls be observed when closely related species are clearly dependent on frequent vocal signals within the group? However the mystery was solved when upon further inspection, these little guys could be heard communicating among the highest frequency levels detected from any terrestrial mammals. It is now thought the extremes of these calls could allow conspecifics to communicate whilst remaining undetected by predators or prey and/or allow individuals to be more easily heard through background noise.

(Ramsier et al. 2012) Primate communication in the pure ultrasound.
DOI: 10.1098/rsbl.2011.1149

Pairs of chimpanzees (Pan troglodytes) where placed into testing rooms, separated by a mesh barrier. One individual had access to 30 tokens, divided into two separate colours – all of which could be given to the experimenter in exchange for food. Half of these when exchanged resulted in a selfish outcome in which only the individual handing the token received a reward, whereas the other half resulted in an altruistic outcome where both individuals received an equal reward. The individual handing the tokens to the experimenter was rewarded regardless.

If chimpanzees where choosing under a system driven by selfish interests, there should be a preference towards the choice where only the individual in control of the tokens receives a reward, and if the choice was purely random, each token would be expected to be seen 50% of the time. However, it was found that pairs where significantly more likely to share a reward (displaying prosocial behaviour), than choose the selfish option.

Victoria Hornera, J. Devyn Cartera, Malini Suchaka, and Frans B. M. de Waal (2011). Spontaneous prosocial choice by chimpanzees Proceedings of the National Academy of Sciences : 10.1073/pnas.1111088108

Moustached Tamarin (S. mystax) from The Bronx Zoo, New York City. Photo from Wikipedia.

S. mystax belong to the Callitrichid family, and like all Callitrichids has an interesting reproductive strategy unlike those of other primate families. Callitrichids form multimale-multifemale group and has a polyandrous (one female, multiple male) mating system. Callitrichids are the only primate family that consistently give birth to twins. The gestation period for S. mystax is 6 months. Usually, only one dominant female is reproductively active and shares offspring rearing responsibilities with multiple males in the group. However, an unstable dominance hierarchy among females might lead to multiple births within the group and will compromise the survivability of both the group and the offspring from stress, less parental investment and lack of food resources.

The researchers were studying how help from male moustached tamarins in the same group and the absence of female competition ensure the survival of offspring when they observed a female cannibalizing an infant. Necropsy and genetic analyses were used to rule out diseases and to determine paternity. They found that the infant has no diseases and did not die from trauma (falling from tree). Instead, it was a healthy infant and was being cannibalized by its own mother.

The mother was seen biting and then eating the head of its own infant during a period when another female was pregnant and gave birth just 1 month later. Before that, the perpetrator had given birth to twins three times successfully when four to five adult and subadult males were present in the group. Although we do not know for certain that the infant was alive when the mother started biting it, our field observations preceding the event suggest it probably was. The possible infanticide case and the two cases of births and early death of the infants occurred while only two to three adult males were present in the group. This could be the second case of maternal infanticide reported in the genus Saguinus and the similar circumstances suggest a common pattern. Culot et al. (2011).

Five common hypotheses proposed by Hrdy (1979) were used by the authors to try to explain maternal infanticide and cannibalism in this scenario. These hypotheses are resource competition, sexual selection, social pathology, exploitation, and parental manipulation.

The resource competition and sexual selection hypotheses were rejected because it was maternal infanticide, and not infanticide from another female. The social pathology hypothesis was rejected because it predicts infanticide restricted in areas that are disturbed by humans. The study group was habituated and had many successful births, therefore social pathology was ruled out. The exploitation hypothesis was also reject because the mother did not kill her infant to exploit its meat. Observation shows that the mother only consumed the brain and parts of the infant’s neck.

The parental manipulation hypothesis was accepted because the authors think that it best explains the scenario. The offspring was not pathological nor did it fell from the tree. Instead, it was a healthy infant that was killed by its own mother. According to Hrdy (1979), victim of parental manipulation does not necessarily have to be defective but also born “at the wrong place in the wrong time”.

The authors concluded that parental manipulation is the best explanation for this possible maternal infanticide scenario. Parental manipulation strategy can happen in a group with poor capacity to raise the offspring from multiple breeding females, birth intervals that are shorter than 3 months, and low infant survival probability due to physical injuries or weakness.

References:

Lingual view (side that touches the tongue) of Mescalerolemur horneri partial mandible.
Scale bar equals 2 mm. Photo from Kirk & Williams (2011).

Anywho … A fossil primate from the Eocene Epoch was discovered in Devil’s Graveyard badlands of West Texas by Anthropologists Christopher Kirk and Blythe Williams. Named Mescalerolemur horneri, this new fossil primate lived about 43 million years ago is a member of the extinct group, adapiforms, that are found all over the Northern Hemisphere. Mescalerolemur looked like a modern-day greater dwarf lemur and weighs about 370 grams.

Interestingly enough, Mescalerolemur are more closely related to Eurasian and African adapiforms than those from North America. Darwinius masillae, famously known as Aunt Ida, was a Eurasian adapiform. Another interesting fact to point out is that Mescalerolemur had unfused mandibular symphysis, similar to those of Strepsirrhines (lemurs, lorises and galagos). The authors posit that this is definitive evidence that adapiforms are more similar to Strepsirrhines than Haplorrhines (humans are Haplorrhines). Kirk &Williams (2011) published their findings on Journal of Evolution: New adapiform primate of Old World affinities from the Devil’s Graveyard Formation of Texas (PDF). You can also read more about the discovery at EurekAlert: Anthropologist discovers new fossil primate species in West Texas.

Originally posted on The Prancing Papio.

Coquerel-Sifaka at the Maryland Zoo in Baltimore, Photo: Kristin Abt

Read the press release for more information!

The Duke Lemur Center manages the United States’ Coquerel’s Sifaka population and provides more information about the species: Coquerel’s Sifaka

A recent article in the journal, Zoo Biology, discusses the current lack of gum enrichment for certain primate species in a captive setting that is in contrast to their wild behavior. Huber and Lewis (2011) surveyed zoos at an international scale to assess the occurrence and methods of “gum-based enrichment.”

Patas Monkey at Woodland Park Zoo (Photo: Kristin Abt)

Golden Lion Tamarin at National Zoo (Photo: Kristin Abt)

They identify numerous primates that feed on gums in varying amounts in the wild, including galagos and lorises, marmosets and tamarins, and members of Cercopithecinae.  Because enrichment aims to promote species-typical behaviors in a non-natural environment, the items that are offered should be primarily selected based on whether or not they contribute to this aim.

This study obtained responses from 46 zoos, 27 of which feed gum to at least some of their primates. The greatest disparity between wild gum-feeding and captive gum-provisioning was for cercopithecines. They identify patas monkeys as obligate gumnivores; therefore, they specifically highlight the need for the development of enrichment programs utilizing gum for this species. Also, they highlight the need to provide enrichment devices that simulate how primates feed on gum in the wild as opposed to free-feeding in dishes.

Patas Monkey Exhibit (Photo: Kristin Abt)

Huber and Lewis (2011) take a focused approach to assessing an area of enrichment within zoos that can have a marked management impact. This study shows the value of applied research to enhance the ability of zoos and other facilities to care for their collections in a manner more representative of the wild experience.

Reference:

Huber, H. F. & Lewis, K. P. (2011). “An assessment of gum-based environmental enrichment for captive gumnivorous primates.” Zoo Biology 30: 71-78.

Although experimentation testing these types of numerical skills are not new, previous studies used edible items where the subject may eat the amount of food on the plate in which they choose – this experiment yielded only a 69% success rate in this study, and showed that the impulsiveness to gain a reward that they could see impaired their judgement when making a choice. Therefore previous studies may have underestimated the animals’ ability.

More information at; BBC – Earth News

Schmitt, V. & Fischer, J. Representational format determines numerical competence in monkeys. (2011). Nat. Commun. 2:257 DOI: 10.1038/ncomms1262.

A vervet monkey. Photo from Wikipedia.

Here’s what the researchers did in the field. They used playbacks of recorded vervet monkey (subjects) alarm calls from concealed speakers. Equal amount of alarm calls for leopard, eagle and snake were used. These alarm calls were recorded from known adult male, adult female and juvenile vervet monkeys in the field. Trials were done when subjects were on the ground and also when they were in the trees. These trials were conducted in the absence of predators to eliminate visual cues from the caller.

Alarm calls were broadcasted in different amplitudes to mimic natural alarm calls. In succession from loudest to lowest amplitudes are alarm calls for leopard, eagle and snake. Subsequently, leopard calls have the lowest pitch while snake calls have the highest pitch. To control for the possible effects of amplitude, the researchers broadcasted alarm calls that do not differ significantly in the amplitudes for all three predators.

Table from Seyfarth et al. (1980). Click on illustration for its original size

The alarm call playbacks showed two types of responses. First, subjects of any sex and age looked at the direction of the speaker and spent more time scanning their environment once an alarm call was made for more than 10 seconds. The researchers believe that they might be scanning for additional cues from the “caller” and the subject’s surrounding.

Second, each alarm calls seem to elicit a distinct response from the subjects. Remember the trials were done when the subjects were on the ground and on the trees? When subjects were on ground, leopard calls were more likely to make them run up into the trees and eagle calls made them look up and run into cover (bushes) Snake calls made them look down. When subjects were on the trees, leopard calls were more likely to make them run higher in trees and to look down. Eagle calls made them look up and sometimes run out of trees. Snake calls made them look down.

From the results, Seyfarth et al. (1980) posit that vervet monkey alarm calls alone do elicit different responses. It’s hard to tease out whether these alarm calls symbolize the predator ”leopard” or a command ”run up tree”. However, we can postulate that these alarm calls are rudimentary semantic signals used to warn other conspecific of impending danger. For those that are not familiar with semantics, it refers to the meaning of a symbol, sign, word or phrase. In this case, vervet monkey alarm calls are semantic signals because it conveys a specific meaning.

Reference:

Seyfarth, RM. Cheney, DL. Marler, P. 1980. Monkey responses to Three Different Alarm Calls: Evidence of Predator Classification and Semantic Communication. Science 210(4471): 801-803.

Originally posted on The Prancing Papio.