Jackson Powell
Jackson’s undergraduate research examined how natural selection acts on the whole phenotype of an organism, rather than one trait in isolation.  Selection on trait correlations may explain why species cannot adapt to stressful conditions at their range limit: different trait combinations can be favored under range-center versus edge conditions.  He explored the nonlinear effects of selection on trait correlations involved in surviving low-salinity stress in estuarine sea slugs.  At a range of salinities, he quantified body size, number of dorsal appendages called cerata (which affect surface area), and rate of circulation for individual slugs; he measured reproductive output for several weeks as a fitness proxy, and performed a multivariate selection analysis. He found a negative correlation between cerata # and beat rate was favored under benign conditions, but selected against at low salinity.  This may explain why range-edge populations evolve tolerance for low salinity stress during the rainy season, but lose that tolerance each summer.