Monday, August 6, 2007 - 2:30 PM

COS 8-4: Spatial variation in adult body size of lubber grasshoppers: Patterns and mechanisms

Jason E. Jannot, Jessica Brinton, Kevin Kocot, Amanda Solliday, Andrew Thurman, Olcay Akman, and Steven A. Juliano. Illinois State University

Correlations between body size and latitude or altitude are a common phenomenon both within and among animal taxa. We present data demonstrating an unusual longitudinal cline in adult size of lubber grasshoppers (Romalea microptera) in sub-tropical Florida. We tested whether this longitudinal size cline could result from variation in any of three life history traits: size at hatching; growth rate during development; and duration of nymphal development. Field surveys indicated that adult body size (thorax length, femur length) of both males and females increases along a west-east cline. A laboratory study indicated that size at hatching did not differ between one large-bodied (eastern) population and one small-bodied (western) population. Field surveys of nymphal growth and development in six populations indicated that growth rate (mass increase per day) was higher in two small-bodied (western) populations relative to all other populations. Nymphal development was faster in small-bodied (western) populations relative to large-bodied (eastern) populations. However, our survey could not separate the potential effect of inter-population differences in development time from inter-population differences in hatching time. Our data suggest the longitudinal size cline could be caused by inter-population differences in development time and that growth rate and size at hatching play less of a role in producing the longitudinal cline. Future work will test the roles of natural selection and neutral processes (e.g., genetic drift, dispersal) in producing the longitudinal size cline.