Socioecological Correlates of Water Availability and Behavioral Strategies to Lactation in Wild Chimpanzees (Pan troglodytes)
Open Access DepositedOur preliminary analysis did not find such a relationship, but the temporal disconnect between the primary analysis and hydration status analysis (Chapter 2) highlight the need to more closely link habitat quality, daily behavior, and hydration status in the future. In Chapter 2, we investigated correlates of adult chimpanzee hydration status using a measure of urine concentration, urine specific gravity (USG). We found adults had higher USG in the dry season, but females had significantly higher USG during the dry season than males, suggesting females face hydration challenges associated with reproduction. Within females, those in middle lactation (with infants between 1.5 and 3 years of age) had significantly higher USG
Pilosof & Herrera M., 2010
McMichael et al., 2016
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I have used ‘we’ throughout this dissertation as two of these chapters are published (Chapters 2 and 3) and the first will certainly have co-authors. It is my ambition to accurately reflect the collaborative nature of this project. Hydration is essential for maintaining organismal health. Organisms may adopt a variety of strategies to maintain water balance depending on ecological or reproductive conditions. While numerous studies have investigated the socioecological correlates of water balance and availability in taxa such as Chiroptera (Adams & Hayes, 2008
physicians recommend a three-fold increase in water consumption during lactation (Institute of Medicine, 2005), and a failure to do so can lead to maternal dehydration (Bethancourt et al., 2021
Rosinger, 2015), but this has been an understudied topic in great apes. This dissertation integrated novel and long-term behavioral, physiological, ecological, spatiotemporal, and nutritional data to explore variation in water availability, hydration status, and water consumption behaviors in wild chimpanzees of the Kasekela community in Gombe National Park (GNP), Tanzania. GNP is the site of the longest running chimpanzee study in the world. The park experiences a high degree of variation in seasonality, vegetation, and elevation across the park, and females have varying access to food resources dependent upon their ranging patterns and dominance rank (Murray et al., 2006, 2007), providing an opportunity to study variation in water availability between individuals. Fluctuations in seasonality and elevation throughout the park may also impose an energetic and hydration burden on individuals. Additionally, chimpanzees typically demonstrate a female-biased dispersal pattern (Pusey & Packer, 1987), but the Kasekela community at GNP is unique in that females born here often do not disperse, presenting an opportunity to test the hypothesis that immigration may impose a hydration cost. In Chapter 1, we characterized spatiotemporal variation in water availability and quality (both in food and free-standing water) across Gombe National Park, Tanzania and explored how water access may vary between adult chimpanzees based on socioecological conditions. We found food-based water was more abundant in the wet season, and while there were also more streams available during this time, they were of much lower quality, than the fewer streams available in the dry season. We also found non-swollen females (without a full sexual swelling), high-ranking females, and resident females had higher water availability within their core areas. A clear future direction is to directly test for a relationship between core area water quality and hydration status
middle lactation is the period in which mothers are both carrying their growing offspring, which is energetically expensive, and still producing milk. This strongly suggests females have a dual challenge during this period. We also found low-ranking females had significantly higher USG than mid- and high-ranking females. Our results from Chapter 1 that high-ranking females have more water available within their core areas help explain this disparity in USG between females of different ranks. Lastly, in Chapter 3, we explored patterns of drinking frequency in lactating females and their young offspring, to identify the extent to which lactation and the dry season present a hydration burden to females and how they may compensate with increased drinking of free-standing water. Females drank significantly more water in the dry season, supporting results from Chapter 1 that food-based water is scarce, but stream water is higher quality during the dry season. We found lactation and rank effects here as well, with low-ranking females drinking significantly more water during late lactation than mid- and high-ranking females. Late lactation might prove the most challenging for low-ranking females, who have slower-developing offspring and later weaning ages than those of higher-ranks. Our work suggests habitat selection matters in terms of water availability, and low-ranking and immigrant females are relegated to lower-quality habitats. In females, these disparities in water access, compounded by hydration burdens associated with lactation, have physiological and behavioral effects. Taken together, our results demonstrate water is an important, but varying resource for chimpanzees, and should be considered in future investigations of primate space use, physiology, behavioral ecology, and conservation.
Newton, 1992). However recent work has shown water turnover, the daily gain and loss of water by an individual, in great apes is 30-50% higher than in humans, and apes consume more water per unit of metabolized food energy, despite an increased capacity for sweating in humans (Pontzer et al., 2021). Of the great apes, chimpanzees (Pan troglodytes) and bonobos (P. paniscus) have the highest water turnover, demonstrating a lower capacity to conserve water and suggesting that ape water balance is more complicated than previously thought.Chimpanzees present a compelling biological model to investigate variation in water availability and hydration status. Chimpanzees live in fission-fusion societies in which parties change in size and composition frequently. This is thought to reduce feeding competition (Wrangham, & Smuts, 1980), but may also allow individuals to alter behavior to minimize dehydration risk. A recent study found chimpanzees living in a dry savannah habitat (Fongoli) and lowland rainforest (Taï) both showed physiological markers of dehydration, suggesting that water is limiting for chimpanzees across varied environments (Wessling et al., 2018), but the extent to which this varies between individuals based on socioecological factors has yet to be explored. Chimpanzee mothers invest heavily in their offspring. Infants depend exclusively on their mothers for nutrition until six months of age, and the average weaning age is approximately five years (Lonsdorf et al., 2020). Great apes have the most dilute milk (consisting of 85-90% water) and the most protracted lactation period of all NHP (Hinde & Milligan, 2011). The hydration challenge associated with milk production is well-documented in humans
Ryu et al., 2021), there have been relatively few studies in non-human primates (NHP). NHP are generally understood to get most of their hydration requirements from water in foods, and it has been assumed that food-bound water is sufficient to maintain water balance (Glander, 1978
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