Complex growth rate evolution in a latitudinally widespread species

Abstract

The simultaneous effects of selective agents acting on somatic growth rates, their interactions, and their interactions with local environmental conditions that vary across a species’ geographic range are potentially complex and poorly known. This is particularly true of viviparous ectotherms whose offspring may be adapted to the gestation environment provided by their mothers. We studied multiple sources of growth rate variation in a widespread, viviparous reptile, including the effect of the maternal environment on growth following parturition. Females in early pregnancy were collected from replicate populations close to the tropical and temperate margins of this species’ range. These females completed gestation in either of two different, common environments designed to simulate the thermal and photoperiod environments at the sampling locations. Our experiments revealed complex growth rate evolution between the northern and southern extremes of E. quoyii’s geographic range and local adaptation of growth rates to maternal environments. Unique to this study was the manifestation of these growth rate differences, entrained in utero, but expressed following parturition and maintained through to maturity despite the presence of compensatory growth. In addition to providing the most complete picture to date of the evolution of somatic growth in a viviparous ectotherm, our study suggests that understanding local adaptation to maternal gestation environments, both in terms of mean growth rates and growth rate reaction norms, could change our understanding of how growth rates have evolved in other viviparous ectotherms. Indeed, such local adaptation may provide a selective advantage in the evolution of viviparity.