Maternal Infanticide and Cannibalism in Moustached Tamarin

Infanticide and cannibalism are two extreme behaviors seen in primates. Though extreme, the persistence of these behaviors in primates suggest that they are adapted for and had evolved to serve different purposes. Infanticide and cannibalism can be considered as both reproductive and survival strategies. Infanticide has always been associated with males killing off the progeny of former dominant males to make females more sexually receptive and to shorten the birth interval. Cannibalism, on the other hand, is not as sinister as it has always portrayed to be but just a coping mechanism. Ingestion of body parts, usually own offspring, is a response to cope with food scarcity. Lack of food resources would inevitably result in the death of the offspring thus cannibalization returns the caloric investment back into the mother. A new paper by Culot et al. (2011) has documented a case of infanticide and cannibalism in a wild female moustached tamarin (Saguinus mystax).

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:

Culot, L. Lledo-Ferrer, Y. Hoelscher, O. Lazo, FJJM. Huynen, C. Heymann EW. 2011. Reproductive failure, possible maternal infanticide, and cannibalism in wild moustached tamarins, Saguinus mystax. Primates 52(2): 179-186.

Hrdy, SB. 1979. Infanticide among animals: A review, classification, and examination of the implications for the reproductive strategies of females. Ethology and Sociobiology 1(1): 13-40.

Having Brothers Delays Menstruation and Sexual Activity in Sisters

Hey girls, your brother will not only pull out your Barbie's head but he will also delay your sexual maturation as well ... allegedly. A interesting study by two behavioral ecologists (Milne & Judge, 2010) on contemporary western society of Australian adults found that:

Girls with older brothers experience a delay in menstruation.
Girls with older brothers (but with no older sisters) started their menstruation at a mean age of 13.6 years while girls with older brothers and older sisters started their menstruation at a mean age of 13.3 years. Girls with no older brothers (with or without older sisters) started their menstruation at a mean age of 12.7 years. The more older brothers the girls had, the older they were when they started their periods. However, the age of the brothers does not effect the results.

Girls with younger brothers experienced a delay in first sexual activity.
Girls with one or more younger brothers experienced their first sexual activity up to two years later than girls without any younger brothers.

Neither younger nor older brothers influenced the fitness of their sisters. 
Brothers do not affects number of pregnancies, number of children, age at first pregnancy or the firstborn of their sisters.

It is thought that having boys in subsistence and preindustrial societies require more resources than girls, therefore imposing a constraint on lifetime reproductive success. Results from Milne & Judge (2010) were unusual for a society that has plenty of resources because it shows evidence that having brothers negatively affect their sister's sexual maturation. However, having brothers do not influence the reproductive fitness of their sisters. The authors posit that brothers in contemporary Australian are not associated with reproductive fitness due to their sisters having a long period of independence before child bearing. Dr. Judge said that she prefer not to speculate too much of the study as the study was very basic and straightforward. She emphasized that the delay in sexual maturation should not be interpreted as something negative.

Possible reason why younger sisters are experiencing a delay in first sexual activity.

Important to note that the study interviewed only 273 (n) adults between the age of 18 - 75. Out of the total 197 are females and 76 are men. It would be interesting to see results of the study from a bigger sample size because the study essentially represents the western society of Australia (N) as a whole, so the sample size (n) should be bigger. I don't know off hand the population size of western society of Australia, but the Australian population is currently 22,434,156 (current as of August 24, 2010 from Australian Bureau of Statistics). So I would be interested to see if the trend holds up to a bigger sample size, where (n) is at least over 1000. Also, would sisters of twins (with younger twin brother or older twin brother) exhibit the same delay in sexual maturation as well?

References:
Milne, F.H. Judge, D.S. 2010. Brothers delay menarche and the onset of sexual activity in their sisters. Proceedings of The Royal Society B DOI: 10.1098/rspb.2010.1377

Edwards, L. 2010. Having brothers delays sexual maturation in women. Physorg.com Retrieved August 23, 2010 http://www.physorg.com/news201419637.html

Effects Of Global Warming On Endangered Primate Species

A study was done by Penn State Graduate students Ruscena Wiederholt and Biology professor Eric Post on how the effects of global warming, such as El Niño and El Niña, on endangered primate species. Focusing on New World Monkeys, Wiederholt and Post studied the trend of abundance and population dynamics in four genera of Atelines: the muriqui (Brachyteles hypoxanthus, formerly B. arachnoides) of Brazil, the woolly monkey (Lagothrix lagotricha) in Colombia, Geoffroy's spider monkey (Ateles geoffroyi) of Barro Colorado Island in Panama, and the red howler monkey (Alouatta seniculus) in Venezuela.

The results of the team's analyses were spectacular. All four monkey species showed drops in abundance relating to large-scale climate fluctuations. Even though the monkey populations were separated by large distances, the three fruit-eating species had synchronous responses to large-scale warming. During El Niño warming events, trees produced more fruit than usual. Then, during the subsequent La Niña cooling events, the trees produced much less fruit, resulting in a local scarcity or even famine.


Some ecologists have speculated that high production of fruit during El Niño events may have been triggered by the increase in solar radiation, despite lower-than-usual rainfall. However, high productivity during an El Niño event might also use up the stored reserves of the trees, which would have difficulty recovering during the subsequent La Niña events, when weather was wet, cloudy, and cool. This mechanism would explain why the fruit-eating monkeys showed a delayed response to the El Niño events after a lag of one or two years.

Howler monkeys also showed declines with warm and dry El Niño events, but their population fall was out of sync with that of the fruit-eating species. The mechanism is not yet clear, but Wiederholt has some ideas. She notes, "Primate researchers have seen elevated adult female mortality and lowered birthrates among red howlers in drought years. Since leaf flush often occurs at the start of the wet season, a prolonged dry season might delay the availability of this resource for the howlers and perhaps cause them nutritional stress."


Warmer temperatures also may cause leaves -- the howlers' primary food -- to mature faster, which would accelerate the leaves' acquisition of toxins and other chemical defenses against monkeys. The factor that the scientists found was most influenced by changes in climate was the monthly maximum number of tree species that were fruiting. Climate changes also were highly correlated with the monthly maximum number of species that were flowering and with annual seed production. The length of the dry season also was highly correlated with annual flower production. Thus, vegetation responses to climatic conditions substantially altered the food resources available to primates, which in turn influenced the decline or rise in monkey abundance.

Read the rest of the article from EurekAlert!