Juvenile concentrations of <scp>IGF</scp>‐1 predict life‐history trade‐offs in a wild mammal

Abstract

Summary Early postnatal development can have profound effects on life‐history traits later in life. One mechanism hypothesized to mediate this relationship is the anabolic hormone, insulin‐like growth factor‐1 ( IGF ‐1). IGF ‐1 contributes importantly to postnatal growth, and thus offers a means by which environmental and genetic variation might direct organismal development, reproduction and survival. We tested whether juvenile concentrations of IGF ‐1 can predict intraspecific variation in life‐history traits later in life using longitudinal data from free‐living female spotted hyenas ( Crocuta crocuta) . We found that juvenile concentrations of IGF ‐1 predicted heavier juvenile mass, which in turn predicted greater survival to reproductive maturity. However, independent of mass, higher juvenile concentrations of IGF ‐1 predicted earlier age at first parturition and reduced longevity in adulthood. Our results highlight the importance of early postnatal development as a determination period in mammals and suggest that concentrations of IGF ‐1 during this sensitive period can be used to predict important later‐life trade‐offs between growth, reproductive fitness and life span in wild, long‐lived animals. A lay summary is available for this article.