University of Saskatchewan Saskatoon, Saskatchewan, Canada
Background/Question/Methods
Growth is one of the central life-history traits, due to the survival and reproductive advantages of fast growth. However, to finance the cost of synthesizing new tissues and maintaining a larger digestive system, growing individuals require a substantial amount of resources. Additionally, in the pre-weaning phase, growth rates are more related to maternal and litter size effects, and it is hypothesized that in the post-weaning phase, growth rates are more explained by the variation at the individual level and resource availability. In Columbian ground squirrels as well as other hibernating sciurids, juveniles sustain a linear increase in body mass for 4-5 weeks after they emerge from their natal burrows, followed by a plateau phase in which the energy acquired is primarily allocated to lipid synthesis and storage. To evaluate the effect of initial body mass, sex, and resource availability on the growth rates of Columbian ground squirrel juveniles, we took repeated measurements of their total body mass, fat, and fat-free mass using a quantitative magnetic resonance system since they emerged from their natal burrows until entry into hibernation (2018 and 2019). To evaluate the effect of resource availability, we provided ad-libitum food to targeted individuals using automatic pet feeders.
Results/Conclusions
During the linear phase of growth, the variation in fat and fat-free mass was explained only by the initial body mass, and the time interval between measurements (P< 0.002). In contrast, during the plateau phase of growth, levels of fat-free mass and fat mass were explained by resource availability, the initial body mass, and the time interval between measurements. Fed juveniles accumulated 1.7 times more fat compared to unfed juveniles. Sex was significant only to explain the variation in fat-free mass during the plateau phase of growth, since males on average attained a higher fat-free mass than females, and these differences were maintained in the fed and the unfed treatment. Given the limited time available for growth and fattening, the fed juveniles were able to allocate the additional food resources mainly towards fat deposition and partially towards the increase in structural size, which could increase their survival probability after hibernation.
