Is Compensatory Growth Costly?

Abstract

1. Compensatory growth is well-studied and exhibited across a variety of taxa, including plants, invertebrates, and a variety of vertebrates. Compensatory mechanisms allow individuals to recover from adverse conditions, potentially enhancing survival and fitness. However, to compensate for a low body condition, individuals may allocate energetic resources to a few physiological functions, affecting the ability of other bodily functions to perform efficiently. Such costs associated with compensatory growth are shown in previous studies, and are expected to be strongest at early life stages. The allocation of resources to accelerate body growth may be traded-off against other essential physiological processes, such as bone growth, immunocompetence, and tissue repair. 2. We quantified short and long-term consequences of differential body growth rates in a wild population of yellow-bellied marmots, Marmota flaviventer, obligate hibernators with a short active season. We used mass measurements collected from 2002-2014 to calculate individual growth trajectories, and estimated annual survival from 688 females at distinct life stages (142 adults, 239 yearlings, 643 juveniles) distributed along a mild elevational gradient (165 m). We also estimated longevity utilizing 322 longitudinal mass measurements throughout the lifespan of 72 females. 3. We found that increased mass gain rate, coupled with the demands of a harsher higher- elevation environment, reduced annual survival in the young cohort. Older individuals with accelerated mass gain had higher survival, regardless of location in the elevational gradient. Collectively, we found that rapid mass gain had no effect on longevity. 2 4. Thus, while adults may benefit from accelerated mass gain, it may be that younger individuals pay a price. This cost in the younger cohort varies according to environmental conditions. Developing individuals face conflicting demands of structural vs. fat reserve growth, and one may be prioritized over the other in adverse conditions. Therefore, the benefits and costs of rapid growth are age and site- specific, and the costs are concentrated in young individuals in harsh environments. Furthermore, the costs of accelerated growth in this species may be exerted in the short-term, rather than paid later in life.

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