Sexual selection on body size and shape in the western harvester ant, Pogonomyrmex occidentalis cresson

Mating in social insects has generally been studied in relation to reproduc tive allocation and relatedness. Despite the tremendous morphological diver sity in social insects, little is known about how individual morphology aff ects mating success. We examined the correlation of male size and shape wit h mating success in the western harvester ant, Pogonomyrmex occidentalis. L arger males had significantly higher mating success in two independent coll ections of males at mating aggregations. We also detected significant linea r and nonlinear selection on aspects of male shape that were consistent acr oss years. These shape components are independent of size, suggesting that male mating success is a complex function of size and shape. Successful mal es had elongate thoraxes and short mandibles relative to males collected at random at the lek. Overall, mated males also had longer postpetioles relat ive to body size, but there was also evidence of nonlinear selection on rel ative postpetiole length in both years. We found no evidence of assortative mating based on size or multivariate shape measures in either year, but in one year we found weak assortative mating based on some univariate traits.