RT Journal Article SR Electronic T1 Adult sex ratio bias in snowy plovers is driven by sex-specific early survival: implications for mating systems and population growth JF bioRxiv FD Cold Spring Harbor Laboratory SP 117580 DO 10.1101/117580 A1 Luke J. Eberhart-Phillips A1 Clemens Küpper A1 Tom E. X. Miller A1 Medardo Cruz-López A1 Kathryn H. Maher A1 Natalie dos Remedios A1 Martin A. Stoffel A1 Joseph I. Hoffman A1 Oliver Krüger A1 Tamás Székely YR 2017 UL http://biorxiv.org/content/early/2017/03/16/117580.abstract AB Adult sex ratio (ASR) is a central concept in population biology and a key factor in sexual selection, yet why do most demographic models ignore sex-biases? Vital rates often vary between the sexes and across life history, but their relative contributions to ASR variation remain poorly understood—an essential step to evaluate sex ratio theories in the wild and inform conservation. Here we combine structured two-sex population models with individual-based mark-recapture data from an intensively monitored polygamous population of snowy plovers. We show that a strongly male-biased ASR is primarily driven by sex-specific survival of juveniles, rather than adults or dependent offspring. This provides empirical support for theories of unbiased sex allocation when sex-differences in survival arise after the period of parental investment. Importantly, a conventional model ignoring sex-biases significantly overestimated population viability. We suggest that sex-specific population models are essential to understand the population dynamics of sexual organisms: reproduction and population growth is most sensitive to perturbations in survival of the limiting sex. Overall, our study suggests that sex-biased early survival may contribute towards mating system evolution and population persistence, with implications for both sexual selection theory and biodiversity conservation.SIGNIFICANCE STATEMENT Sex biases are widespread in nature and represent a fundamental component of sexual selection and population biology—but at which point in life history do these biases emerge? Here we report a detailed individual-based demographic analysis of an intensively studied wild bird population to evaluate the origins of sex biases and their consequences on mating strategies and population dynamics. We document a strongly male-biased adult sex ratio, which is consistent with behavioral observations of female-biased polygamy. Notably, sex-biased juvenile, rather than adult survival, contributed most to the adult sex ratio. Sex-biases also strongly influenced population viability, which was significantly overestimated when sex ratio and mating system were ignored. Our study therefore has implications for both sexual selection theory and biodiversity conservation.