Adaptive theory predicts that mothers would be advantaged by adjusting the sex ratio of their offspring in relation to their offspring's future reproductive success. Studies investigating sex ratio variation in mammals, including humans, have obtained notoriously inconsistent results, except when maternal condition is measured around conception. Several mechanisms for sex ratio adjustment have been proposed. Here, we test the hypothesis that glucose concentrations around conception influence sex ratios. The change in glucose levels resulted in a change in sex ratios, with more daughters being born to females with experimentally lowered glucose, and with the change in glucose levels being more predictive than the glucose levels per se. We provide evidence for a mechanism, which, in tandem with other mechanisms, could explain observed sex ratio variation in mammals.

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The Pacific walrus (Odobenus rosmarus divergens) is a candidate to be listed as an endangered species under United States law, in part, because of climate changerelated concerns. While the population was known to be declining in the 1980s and 1990s, its recent status has not been determined. We developed Bayesian models of walrus population dynamics to assess the population by synthesizing information on population sizes, age structures, reproductive rates, and harvests for 1974-2015. Candidate models allowed for temporal variation in some or all vital rates, as well as density dependence or density independence in reproduction and calf survival. All selected models indicated that the population underwent a multidecade decline, which began moderating in the 1990s, and that annual reproductive rate and natural calf survival rates rose over time in a density-dependent manner. However, selected models were equivocal regarding whether the natural juvenile survival rate was constant or decreasing over time. Depending on whether juvenile survival decreased after 1998, the population growth rate either increased during 1999-2015 or stabilized at a lesser level of decline than seen in the 1980s. The probability that the population was still declining in 2015 ranged from 45% to 87%.Key words: Pacific walrus, Odobenus rosmarus divergens, Bayesian, hidden process model, integrated population model, survival, reproduction, population growth rate, demography, density dependence.Population models are useful tools to evaluate the dynamics of wildlife populations, but they present the inevitable tradeoff between realism and tractability. In particular, environments are not constant, and neither are the population dynamics of the animals that inhabit those environments. Yet modelers often make the simplifying assumption that vital rates are constant over time (Williams 2013) because parameters of such models are easier to estimate when data are limited. In reality, vital rates do vary over time, whether in a density-dependent manner (where rates at one time step depend on the size of the population at a previous time step) or in a density-independent manner. While constancy of vital rates may be a useful 1

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