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Primate Infanticide: Outline

Background

Primate infanticide, the killing of young by an individual of the same species, can be explained by a series of five hypotheses: exploitation, resource competition, parental manipulation, sexual selection, and social pathology (Hrdy, 1979).

Outside/external/non-related/non-familial

Resource Competition

o   Overall occurrence of feticide and infanticide is higher / increases when resource competition is high / availability of resources is lower (Zipple 2017)

o   When other groups invade a social structure, resource competition increases, and infanticide rate is higher (Zipple 2017)

o   Easy to eliminate infants because they are mostly defenseless, and entire social group is to benefit from the infant’s death if resources are scarce enough (Hrdy 1977)

o   Sometimes this involves cannibalism; killing the infant not only leaves more resources for group but is also a food source on its own (this is seen in gorillas) (Hrdy 1977)

o   More infanticide when it is xenophobic (from an invading group) because a foreign infant is easiest to eliminate when resources are scare (Hrdy 1977)

Role of Social Organization

·      In mammals, interaction between the sexes is usually limited to the female estrous or copulation. However, in non-human primates, these male-female bonds persist past the estrous. These social relationships are hypothesized to protect from male infanticide (Palombit, 1999).

·      It is hypothesized that this year- round association serves to lower the probability of infanticide by other males (Van Schaik and Kappeler, 1997).

·      Many primates live in multifemale groups, and it has been proposed that these females live together to reduce the risk of infanticide through paternity confusion ( Van Schaik and Kappeler, 2002).

Sexual Competition                          

·      Infanticide can be used by males to increase reproductive success when a male takes over a troop of females. This behavior has been observed in langurs. The females whose infants were killed exhibited estrous behavior and copulated with the new leader.  (Hrdy S, B, Male-Male Competition and Infanticide Among the Langurs (Presbytis Entellus) of Abu, Rajasthan. Folia Primatol 1974;22:19-58)

·      Infanticide by a male taking over a female group in one-male breeding units has also been observed in red-tailed monkeys (Struhsaker 2010) and blue monkeys (Butynski 1982).

·      This has also been observed in species that live in multimale breeding groups, the red howler and the mantled howler.(Parmigiani and vom Saal 2016)

Familial/internal/intra/related

Sibling

·      A lack of research on infanticide among siblings in primates may infer that it has never been observed.

Maternal Infanticide

·      Maternal infanticide is rare in non-human primates, and has been reported less than a handful of times.

·      Maternal infanticide has been reported once in S. fuscicollis and once in Callicebus nigrifrons, and four times in Saguinus mystax (Culot, 2011).

·      It is proposed that maternal infanticide occurs when the mother assesses the probability for infant survival based on previous infant deaths (Culot, 2011).

Paternal Infanticide

·      DNA analysis of wild Japanese macaques study showed males wouldn’t attack their own offspring or offspring of a female they mated with, only non familial (Soltis 2000)

·      Females form bonds with males so they will not kill offspring, because male primates will not commit infanticide of their own offspring (Palombit 1999)

·      Opie (2013) also says monogamy is so paternal infanticide will not occur

Counter Adaptations

·      Many primate species have developed counter strategies to reduce the likelihood of infanticide from male-female sexual competition in accordance with the Red Queen Hypothesis.

·      Defense: social and physical

·      Female “friendships” with males in chacma baboons may serve to protect infants from infanticidal individuals (Palombit et al., 1997)

·      Social monogamy: Males remain with mated females through weaning in order to protect their offspring from infanticidal males

·      Territoriality: females actively defend territory from potentially infanticidal females, seen in chimpanzees (Agrell et al., 1998)

·      Paternity Confusion: Females and males utilize paternity confusion to reduce the chance of a male she has mated with from killing her offspring.

·      Concealed ovulation: female catarrhine primates such as Hanuman langurs have evolved an extended estrous state with variable ovulation in order to conceal which mating likely resulted in fertilization (Hestermann et al., 2001).

·      Promiscuous mating: females mate with multiple males (mating patterns such as polyandry, promiscuous in multi-male multi-female) (Clarke et al., 2009)

·      Female chacma baboons prefer polyandry when threat of intragroup infanticide is low (Clarke et al., 2009)

·      Post-conception mating:  similar to promiscuous mating, in some primate species females are proceptive during first and second trimester in order to increase paternity confusion (Engelhardt et al., 2007)

·      Female synchrony: when many females are fertile at the same time it becomes impossible for one male to monopolize all females (Henzi et al., 2010)

·      Males utilize paternity confusion: Mating concessions: high ranking males will allow lower ranking males access to receptive females in order to protect his own offspring from immigrant males (Henzi et al., 2010)

·      Reproduction suppression:

·      Bruce Effect: Female primates may abort the pregnancy when presented with a new male as seen in langurs, baboons, and gibbons possibly in order to avoid any added investment when infanticide is likely (van Schaik & Janson, 2000).

·      Counter to the counterstrategies:

·      Counter to paternity confusion:

·      Mate-guarding, consortships, pair-bonding, all of which increase paternity certainty often in the case of mate-guarding and consortship through physical coercion or intimidation.

See Also

·      Infanticide (zoology)

·      Infanticide in humans

Sroivas (talk) 02:37, 17 February 2017 (UTC)