ORIGINAL ARTICLE Repeatability and reproductive consequences of boldness in female gray seals Christine M. Bubac 1 & David W. Coltman 1 & W. Don Bowen 2,3 & Damian C. Lidgard 3 & Shelley L. C. Lang 2 & Cornelia E. den Heyer 2 Received: 24 July 2017 /Revised: 12 May 2018 /Accepted: 23 May 2018 # Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract Wild animals show consistent individual variation in behavior across time and/or contexts, now referred to as animal personality. While this variability may have important ecological and evolutionary implications, how and why variation in animal personality is maintained in a natural population remains unclear. In this study, we assessed the influence of environmental and biological sources of variation on behavioral responses measured along the shy-bold continuum in a long-lived, iteroparous marine mammal, the gray seal (Halichoerus grypus). Between 2008 and 2016, 469 females from the Sable Island, Nova Scotia breeding colony of gray seals were given a boldness score in response to a human approach, designed to stimulate maternal defense of offspring. Using generalized linear mixed-effects models (GLMM) in a Bayesian framework, we show that boldness is highly repeatable between and within years. There were age differences in boldness, with younger females being less bold than older, more experienced females providing some support for the life history trade-off hypothesis. We further used GLMMs to assess sources of variation on offspring weaning mass. We found that young females that were bolder produced heavier pups than shyer counterparts, and that pups produced by bolder females were on average ~ 2 kg heavier than pups of shy females. These results provide further evidence that personality influences life history strategies, and illustrates the evolutionary potential of animal personality in response to selection. Significance statement Consistent individual differences in behavior influence various aspects of ecology including species interactions, species distri- butions, and life history strategies. However, how and why this individual variation is maintained in a natural population remains uncertain. In this study, we assessed the influence of boldness, specifically maternal defense of offspring, on a component of reproductive success in a long-lived marine mammal. We showed highly repeatable behavioral differences, and found that boldness varied with age, with younger individuals being less bold than older individuals. Younger individuals that were bolder produced heavier offspring than shyer counterparts. Our study contributes to an under-represented group of animals, wild marine mammals, in the personality literature, and further prompts the investigation into the proximate and ultimate factors influencing personality in an ecologically important marine predator. Keywords Boldness . Animal personality . Life history . Gray seal . Pinniped . Halichoerus grypus Introduction Understanding the origin and extent of biological variation in natural populations is critical to the study of evolution. Recently, considerable attention has been given to the evolu- tionary and ecological implications of variation in animal per- sonalities. Broadly defined as repeatable individual differ- ences in behavioral responses over time or across different contexts or both (Gosling 2001; Réale et al. 2007), animal Communicated by L. Rendell Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00265-018-2515-5) contains supplementary material, which is available to authorized users. * Christine M. Bubac bubac@ualberta.ca 1 Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada 2 Population Ecology Division, Bedford Institute of Oceanography, Dartmouth, Nova Scotia, Canada 3 Biology Department, Dalhousie University, Halifax, Nova Scotia, Canada Behavioral Ecology and Sociobiology (2018) 72:100 https://doi.org/10.1007/s00265-018-2515-5