Levy, E. J. | Search bioRxiv

bioRxiv2023

Early life drought predicts components of adult body size in wild female baboons

ObjectivesIn many taxa, adverse early-life environments are associated with reduced growth and smaller body size in adulthood. However, in wild primates, we know very little about whether, where, and to what degree trajectories are influenced by early adversity, or which types of early adversity matter most. Here, we use parallel-laser photogrammetry to assess inter-individual predictors of three measures of body size (leg length, forearm length, and shoulder-rump length) in a population of wild female baboons studied since birth. Materials and MethodsUsing >2,000 photogrammetric measurements of 127 females, we present a cross-sectional growth curve of wild female baboons (Papio cynocephalus) from juvenescence through adulthood. We then test whether females exposed to three important sources of early-life adversity - drought, maternal loss, or a cumulative measure of adversity - were smaller for their age than females who experienced less adversity. Using the animal model, we also test whether body size is heritable in this study population. ResultsProlonged early-life drought predicted shorter limbs but not shorter torsos (i.e., shoulder-rump lengths). Our other two measures of early-life adversity did not predict any variation in body size. Heritability estimates for body size measures were 36%-58%. Maternal effects accounted for 13%-22% of the variance in leg and forearm length, but no variance in torso length. DiscussionOur results suggest that baboon limbs, but not torsos, grow plastically in response to maternal effects and energetic early-life stress. Our results also reveal considerable heritability for all three body size measures in this study population.

ecology↗

bioRxiv2020

Comparing proportional and ordinal dominance ranks reveals multiple competitive landscapes in an animal society

Across group-living animals, linear dominance hierarchies lead to disparities in access to resources, health outcomes, and reproductive performance. Studies of how dominance rank affects these outcomes typically employ one of several dominance rank metrics without examining the assumptions each metric makes about its underlying competitive processes. Here we compare the ability of two dominance rank metrics--ordinal rank and proportional or standardized rank--to predict 20 distinct traits in a well-studied wild baboon population in Amboseli, Kenya. We propose that ordinal rank best predicts outcomes when competition is density-dependent, while proportional rank best predicts outcomes when competition is density-independent. We found that for 75% (15/20) of the traits, one of the two rank metrics performed better than the other. Strikingly, all male traits were better predicted by ordinal than by proportional rank, while female traits were evenly split between being better predicted by proportional or ordinal rank. Hence, male and female traits are shaped by different competitive regimes: males competitive environments are largely driven by density-dependent resource access (e.g., access to estrus females), while females competitive environments are shaped by both density-independent resource access (e.g. distributed food resources) and density-dependent resource access. However, traits related to competition for social and mating partners are an exception to this sex-biased pattern: these traits were better predicted by ordinal rank than by proportional rank for both sexes. We argue that this method of comparing how different rank metrics predict traits of interest can be used as a way to distinguish between different competitive processes operating in animal societies.

animal behavior and cognition↗