Geographic Variation in Size and Oviposition Depths of Romalea microptera (Orthoptera: Acrididae) is Associated with Different Soil Conditions

Abstract

Abstract Intraspecific geographic variation in morphology and behavior can be indicative of populations that are adapted to local environmental conditions. Heterogeneity in the abiotic environment, such as soil conditions, can be an important driver of local adaptation. In south Florida, mean body sizes in populations of the lubber grasshopper Romalea microptera (Beauvois) (Orthoptera: Acrididae), increase from west to east. We tested how body size variation, population origin, and soil physical characteristics are associated with oviposition depth in the soil. In a laboratory experiment with homogeneous soil conditions, size-corrected oviposition depth (analysis of covariance) differed among three populations: females from a western population oviposited at the shallowest depths; females from an eastern population oviposited the deepest; and a central population oviposited at intermediate depths. A similar pattern also was observed in two field experiments conducted on two additional populations not used in the laboratory experiments. In addition, size-corrected oviposition depth in the field experiments declined with increasing soil compaction for both populations but the decline was significantly steeper for the eastern population. High soil moisture yielded significantly shallower size-corrected oviposition depth only for the eastern population. Female size was positively related to oviposition depth in both field experiments, but the relationship between female size and oviposition depth did not differ among populations (i.e., equal slopes). We suggest that local soil conditions might be an important selection pressure and behavioral cue in determining oviposition depth. Choice of vertical position of the egg pod within the soil is discussed as one possible mechanism by which females can influence offspring viability.