12/28/2023 0 Comments Baby western lowland gorillaIn gorillas, dispersal of females while they are pregnant is known to occur after group disintegration, when females are forced to find another male since they typically do not range on their own. With their strategy of voluntary secondary dispersal, female gorillas may be able to choose a better male before the death of the current silverback and protect their offspring from infanticide (Palombit 2015 Manguette et al. The infanticide rate after death of the silverback (leading to group disintegration) is quite high (12%) in western lowland gorillas at Mbeli (Breuer et al. However, cases of unweaned infants surviving after transferring together with their mother have been observed (Sicotte 2000 Stokes et al. Infanticide is often inferred after the silverback’s death and subsequent group disintegration when infants disappear soon after their mother’s transfer to a new silverback (Robbins et al. Infanticide by males has been directly observed or inferred in many populations of gorillas (Watts 1989 Yamagiwa et al. If a female transfers while pregnant or with an infant, the first and third criteria for infanticide are met, and the infant is at risk. 2005 Robbins and Robbins 2015 Sicotte 1993 Sicotte et al. However, when females disperse, the timing of their voluntary dispersal must be carefully calculated, as due to the risk of infanticide, they have only a very short window of time in which to leave their current group between weaning an infant and conceiving again (Sterck et al. When secondary dispersal occurs voluntarily, this ability to move between groups gives females an advantage over those of philopatric species as it allows them to reduce the risk of infanticide of their young (Lewis 2018). However, it may also occur involuntarily after group disintegration or female eviction and lead to infanticide if the females are pregnant or have unweaned offspring. Secondary dispersal (also referred to as transfer), which involves the movement of females between reproductive groups, is found in only a few mammals and is believed to represent female choice for a high-quality male where it occurs voluntarily (Harcourt and Stewart 2007 Lukas and Huchard 2014). Infanticide reduces the reproductive success of both parents, but it can increase the reproductive success of the infanticidal male if three conditions are met: there is a low probability that the infanticidal male sired the infant, the mother resumes reproduction sooner if the infant is killed, and the mother is likely to mate with the infanticidal male (Hrdy 1977 Smuts and Smuts 1993).įemale primates have developed several strategies to avoid infanticide, such as forming permanent associations with males that provide protection against other males, remaining with the father until weaning the infant, residing in a multi-male group, mating with multiple males to create paternity confusion, or joining a better protector male using secondary dispersal (Palombit 2015). in rodents, ungulates, carnivores, pinnipeds and primates (van Schaik 2000a). One clear example of sexual conflict suffered by reproductive females is infanticide by males (Lukas and Huchard 2014), which has been observed in a wide range of mammals, e.g. Social mammals exhibit a range of intersexual conflicts and compromises (Clutton-Brock 2007). These observations highlight the behavioural plasticity shown by female gorillas in response to sexual coercion by males. To our knowledge, these observations are the first to show that wild female western lowland gorillas can transfer voluntarily while pregnant without incurring infanticide by a new silverback. The females gave birth 5–6 months (gestation period 8.5 months) after their last transfer. The gorillas were observed from 1995 to 2015 at the Mbeli Bai research site in northern Republic of the Congo. We report here on three adult females that transferred voluntarily while pregnant multiple times between two groups yet their offspring were not killed by the new group’s silverback. In the few known cases of female gorillas transferring when pregnant (mainly after group disintegration), their offspring were killed. If females are pregnant or have unweaned offspring when the only male in the group dies, their offspring are vulnerable to infanticide by the new silverback that they join (via involuntary dispersal). By doing so they leave a weaker silverback near the end of his tenure and join a stronger silverback at an earlier stage of his own tenure, thereby mitigating the risk of infanticide if the former dies. Female gorillas have developed the rare strategy of secondary dispersal in which they transfer between reproductive groups during the limited time period between weaning an infant and conceiving the next one (voluntary dispersal). In many social species, after the alpha male has been replaced or the group disintegrates, a female’s infant is at risk of infanticide by a male.
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