Anne Hertel, Agnieszka Sergiel, Aimee Tallian, Nuria Selva, Andreas Zedrosser

Differences in resource allocation form the basis of life-history theory, however, realized phenotypes depend on local adaptations. Maternal reproductive expenditures, whether the absolute reproductive cost or the reproductive cost relative to maternal resources available affects population dynamics. To understand the nuance of maternal expenditures, we used a population of individually marked mother-offspring pairs of brown bears (Ursus arctos) with a unique phenotype in Scandinavia 1995–2019 to explain variation in both absolute and relative maternal expenditures. We used mass of yearling offspring as an indicator of absolute maternal expenditure and the difference in mass between mothers and their offspring as an indicator of relative maternal expenditure. If females prioritize reproduction, offspring mass will increase faster than maternal mass. Additionally, the mother-offspring mass difference will remain stable or decrease with increasing resource demands in mixed effects linear regression models and covariate to account for maternal body condition and diet as well as bear density and litter size. Maternal resources were not shared equally between mothers and offspring. Larger mothers invested relatively less in their offspring than smaller females, and when competition for resources increased, mothers passed the burden onto their offspring, rather than sacrificing their own condition to compensate.