Date Published: February 8, 2017
Publisher: Public Library of Science
Author(s): Manabi Paul, Anindita Bhadra, Dan Weary.
Parent-offspring conflict theory predicts the emergence of weaning conflict between a mother and her offspring arising from skewed relatedness benefits. Empirical observations of weaning conflict have not been carried out in canids. In a field-based study on free-ranging dogs we observed that nursing/suckling bout durations decrease, proportion of mother-initiated nursing bouts decrease and mother-initiated nursing/suckling terminations increase with pup age. We identified the 7th – 13th week period of pup age as the zone of conflict between the mother and her pups, beyond which suckling solicitations cease, and before which suckling refusals are few. We also report for the first time milk theft by pups who take advantage of the presence of multiple lactating females, due to the promiscuous mating system of the dogs. This behaviour, though apparently disadvantageous for the mothers, is perhaps adaptive for the dogs in the face of high mortality and competition for resources.
Maternal care in the form of nursing is an obligatory behaviour in mammals, at least in the early stages of development of the young. While in some species like hooded and harped seals, nursing occurs for a few days , in others it continues for months, and in the case of humans, can continue well beyond the natural weaning period . Nursing is a highly energy intensive behaviour, and makes heavy demands on the maternal resources, with the mothers often losing weight substantially during nursing [3,4]. Mammalian species are typically iteroparous, so mothers need to strike a balance between their investments in current offspring and lifetime reproductive success. Parent-offspring conflict (POC) theory suggests the emergence of a zone of conflict over weaning between the mother and her offspring, due to skewed cost-benefit ratios from relatedness estimates . Various models and empirical tests have validated this theory in contexts as diverse as brood size optimization, reproduction, resource sharing, mate choice, etc. [6,7]. POC in mammals can begin even before the offspring is born, as is evident in the case of preeclampsia (pregnancy induced hypertension) in humans, which is induced by the high energy demands of the fetus . Weaning is a complex process, and it has been argued that weaning occurs through mutual agreement between the mother and offspring, rather than through a situation of conflict . In polytocous species, within litter variations in suckling abilities and weight gain of the offspring add to the complications involved in understanding the dynamics of the weaning process.
According to the predictions of POC theory, a mother is expected to invest in LRS, such that her chances of increasing fitness are high . Kin selection theory suggests that individuals can increase their inclusive fitness benefits by investing in the survival of close kin . Thus, while mothers are expected to show conflict towards their offspring over weaning in order to maximize direct fitness, they can benefit by additionally providing altruistic care to the offspring of related females to ensure indirect fitness benefits. The duration of time allocated to a behaviour is a good estimate of investment in the behaviour in terms of time activity budgets of individuals, and we considered the time spent in nursing as a measure of investment by the mothers and allomothers. Though the use of nursing duration as a measure of investment by mothers has been debated, it continues to be used as an indirect measurement of maternal investment [27,28]. Moreover, since we compared nursing/ suckling durations for the same set of individuals over time, this could be considered as a reliable marker for changing interest of the mothers and pups in suckling. Suckling duration reduced as the pups grew older, which could be due to the reduced interest of the mothers to nurse as well the increased efficiency of pups to extract milk. There is also evidence that the physiological needs of pups change rapidly in the first 3–4 weeks of age, determining their milk intake .