Geographic Variation in Somatic Growth of Redside Shiner

Abstract

The geographic variation in growth rate and resulting body size is poorly known for most fish species. In this paper, we used data derived from otoliths to describe patterns of growth in redside shiners Richardsonius balteatus from seven native populations across the southern portion of its range, and we compare growth with latitude, elevation, and growing season to determine which of these environmental factors best predicts the growth patterns among these populations. To determine whether observed differences in growth resulted from environmental or genetic variation, we conducted a common-environment experiment on fish from three of the seven populations that showed contrasting patterns between latitude and length of growing season. Redside shiners exhibited about a 60% difference in size at age among populations in their natural environments. Growing season length was the best predictor of body size among these populations (Akaike weight = 0.78). In a common environment, temperature-specific growth rates differed among populations, indicating that some of the observed differences in size at age among populations are genetically based. Although populations of redside shiners with shorter growing seasons exhibited higher field growth rates than expected, the pattern of variation in individual growth rates among populations in a common environment was not consistent with either a countergradient variation model or a local adaptation model of growth.