KINGSOLVER, JG*; IZEM, R; RAGLAND, G; UNC-Chapel Hill; UNC-Chapel Hill; UNC-Chapel Hill: Selection and variation in size and growth in fluctuating thermal environments

Most organisms experience a range of temperature conditions during their growth and development. How do fluctuating temperature conditions affect patterns of genetic variation and natural selection on growth rate and size? We address this question in three ways. First, an analysis of field selection studies indicates that directional selection favoring increased overall size is common in many systems—that bigger is frequently better. Second, we describe a statistical analysis that quantifies whether there is substantial genetic variation in overall growth or size across temperatures, or whether such variation is temperature-dependent. We apply this analysis to data on thermal reaction norms for insect growth and size. Third, we use a recent theoretical model to examine how selection on thermal reaction norms relates to environmental temperatures during selection. The model suggests a means of distinguishing selection on final size or development time from selection on temperature-specific growth rates. We illustrate the approach using data on thermal reaction norms for growth rate of Pieris rapae caterpillars.