Using common gardens to understand the response of marine populations to temperature change
Growing multiple populations in a common garden environment is a time-honored experimental approach to examine the genetic and environmental causes of phenotypic variation. Originally used primarily with terrestrial plants, common gardens are now widely utilized across a variety of ecosystems, and when combined with recent advances in genomics and modeling, they offer a powerful tool for understanding responses to global change. To guide future work in this field and facilitate cross-ecosystem comparisons, we conducted a meta-analysis quantifying individual growth and/or survival responses to temperature in marine populations grown in a common garden environment. We identified over 30 studies manipulating temperature in marine algal, plant, invertebrate, or vertebrate populations from a wide range of latitudes. We then examined whether differences in sensitivity to temperature could be explained by a suite of predictor variables including taxonomic group, population latitude, population mean annual temperature, and/or the difference between experimental temperature and population mean annual temperature.
Overall, the magnitude of sensitivity to temperature was greater for survival than growth, most likely because growth experiments are restricted to the range of temperatures over which individuals can both survive and grow. Despite this difference, population latitude, taxonomic group, and the difference between experimental temperature and mean annual temperature explained variation in population responses for both growth and survival. When the experimental temperature was less than mean annual temperature, sensitivity to temperature change generally increased with population latitude. However, when the experimental temperature was greater than mean annual temperature, intermediate latitudes generally exhibited the greatest sensitivity. We also assessed evolutionary shifts in reaction norms between pairs of populations across eleven studies that tested three or more temperatures. We found that evolutionary shifts in the mean, slope, and curvature of growth reaction norms correlates with greater differences in mean annual temperature between the two populations. This relationship was stronger among studies with invertebrates and algae than vertebrates, suggesting that microevolution of vertebrates is less common. Shifts in survivorship reaction norms were not significantly correlated with latitude, taxa, or differences in mean annual temperature, suggesting that evolutionary change in reaction norms for growth is more common than for survivorship.