GROWTH TO DEATH IN LIZARDS

Abstract

Negative relationships between growth rate and survival have been demonstrated in many organisms, often reflecting risks associated with increased foraging rates. More puzzling, however, are recent reports that rapid growth early in life may lower survival rates much later in life, presumably because fast-growing animals allocate resources among different body components in ways that later compromise their survival. If widespread, such delayed effects may modify our interpretation of the evolution of life histories and phenotypic plasticity. Previous reports of this phenomenon are derived mostly from laboratory studies, generally on rodents or humans. We provide the first evidence from an experimental study in the field: neonatal lizards were exposed to different thermal conditions in seminatural enclosures at two different elevations (within their natural thermal regime). This arrangement allowed relatively higher and lower levels of food intake, which modified the neonates' growth rates (because lizards at more benign thermal conditions could forage more frequently). When later released into the wild, the individuals that grew more rapidly as neonates experienced much higher mortality than did slower-growing conspecifics, regardless of the elevation at which they had been kept.