Geographic differences in the body sizes of adult Romalea microptera

Abstract

We compared adult body size among six populations of the flightless lubber grasshopper Romalea microptera from south Florida, USA. The most distant populations were 113 km apart. We tested whether size differences among populations are correlated with local mean precipitation or temperature, and specifically investigated whether smaller average size is correlated with climate-related short-growth season, as has been shown for other grasshoppers. We found significant size differences among the populations for both males and females. Mean body size of R. microptera was greatest for a central population at Shark Valley South, declined toward the northwest, and less strikingly, toward the south. R. microptera females had a greater mean size at sites with high precipitation in May and low precipitation in November, suggesting that earlier onset of the wet season is positively associated with mean size. Further, mean size increased with increasing mean minimum temperature in January. These differences in adult size of R. microptera suggest that differences in local environments lead either to evolution of local differentiation in adult size or local differences in growth and development that result in differential expression of phenotypic plasticity in adult size.