Preferential treatment of kin is widespread across social species and is considered a central prerequisite to the evolution of cooperation through kin selection. Though it is well known that, among most social mammals, females will remain within their natal group and often bias social behaviour towards female maternal kin, less is known about the fitness consequences of these relationships. We test the fitness benefits of living with maternal sisters, measured by age-specific female reproduction, using an unusually large database of a semi-captive Asian elephant ( Elephas maximus ) population. This study system is particularly valuable to an exploration of reproductive trends in a long-lived mammal, because it includes life-history data that span multiple generations, enabling a study of the effects of kinship across a female's lifespan. We find that living near a sister significantly increased the likelihood of annual reproduction among young female elephants, and this effect was strongest when living near a sister 0–5 years younger. Our results show that fitness benefits gained from relationships with kin are age-specific, establish the basis necessary for the formation and maintenance of close social relationships with female kin, and highlight the adaptive importance of matriliny in a long-lived mammal. This article is part of the theme issue ‘The evolution of female-biased kinship in humans and other mammals'.
For many animal species, immatures are less efficient foragers than their adult counterparts and must use multiple strategies to fulfill their nutritional needs through effective learning of social and feeding behaviour. To overcome these challenges, young animals are predicted to rely on adult relatives to gain foraging competency, partly because kin are more likely to tolerate the proximity of immatures, upon which socially facilitated learning of food selection and foraging skills depends. While evidence suggests that mothers improve the foraging success of their offspring, little is known about the potential contribution of fathers to the development of feeding skills. Here, we investigate the influence of both mothers and fathers on the foraging behaviour of young olive baboons (Papio anubis) in Laikipia, Kenya. Behavioural data were gathered via focal animal sampling and genetic relatedness was determined by microsatellite genotyping of non-invasively collected faecal DNA samples. We also conducted analyses to assess the nutritional and energetic content of staple foods consumed by the baboons. We found that, compared to when feeding near unrelated adults or alone, immatures were more likely to consume high energy foods when they were near their mothers and preliminary results suggest access to similar effects when near fathers. These data advance well-documented maternal influences on the foraging competence of offspring in a matrilocal society, and additionally suggest the importance (and possible long-term fitness benefits) of associations between offspring and their fathers.
BackgroundDemonstrating the impact that parents have on the fitness of their children is a crucial step towards understanding how parental investment has affected human evolution. Parents not only transfer genes to their children, they also influence their environments. By analyzing reproductive patterns within and between different categories of close relatives, this study provides insight into the genetic and environmental effects that parents have on the fitness of their offspring.MethodsWe use data spanning over two centuries from an exceptionally accurate Icelandic genealogy, Íslendingabók, to analyze the relationship between the fertility rates of close relatives. Also, using genetic data, we determine narrow sense heritability estimates (h2) to further explore the genetic impact on lifetime reproductive success. Finally, we construct four simulations to model the expected contribution of genes and resources on reproductive success.ResultsThe relationship between the reproduction of all full sibling pairs was significant and positive across all birth decades (r = 0.19) while the reproductive relationship between parents and offspring was often negative across many decades and undetectable overall (r = 0.00) (Fig. 1 and Table 1). Meanwhile, genetic data among 8,456 pairs of full siblings revealed a narrow sense heritability estimate (h2) of 0.00 for lifetime reproductive success. A resources model (following the rule that resources are transmitted from parents to children, distributed equally among siblings, and are the only factor affecting reproductive success) revealed a similar trend: a negative relationship between parent and offspring reproduction (r = − 0.35) but a positive relationship among full siblings (r = 0.28). The relationship between parent and offspring lifetime reproductive success (LRS) and full sibling LRS was strongly and positively correlated across time (r = 0.799, p < 0.001). Similarly, the LRS among full siblings was positively correlated with both the LRS among half siblings (r = 0.532, p = 0.011) and the relationship between the LRS of aunts and uncles with their nieces and nephews (r = 0.438, p = 0.042).DiscussionWe show that an individual’s lifetime reproductive success is best predicted by the reproduction of their full and half siblings, but not their parents, grandparents or aunts and uncles. Because all siblings share at least one parent, we believe parental investment has had an important impact on fitness. Overall, these results indicate that direct parental investment, but not genes, is likely to have had an important and persistent impact on lifetime reproductive success across more than two centuries of Icelandic history.
Using various forms of enrichment, animal care specialists encourage species-specific behaviors and discourage stereotypic behaviors. Within the zoo community, bears (Ursids spp.) are commonly housed, yet are prone to exhibiting stress-related behaviors. Here, we assess the effect of access to multiple habitats, including areas of off guest view, on the welfare of two American black bears (U. americanus) housed at the North Carolina Zoo. In this study, we looked at two behaviors, pacing and foraging to represent negative and positive welfare indicators. We performed logistic regressions to model the effect of access on these behaviors. Because having an animal visible to guests is important to consider when creating management plans, we also explored the effect of access on the bears’ visibility. We found that full access reduced the likelihood of pacing by an average of 13% and increased the likelihood of foraging by an average of 5%. Access to multiple areas reduced the probability of visibility by 57% for one individual but did not impact visibility of the other bear. This case study suggests the value of access to zoo animal welfare and should incite future research aimed at exploring the effects of access on various behavioral outcomes.
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