Figure 1. Images of P. badius and P. barbatus from www.antweb.org size-scaled for comparison (note scales on images). A and E are gynes, B and F are males, C, D, and G are workers. Images A-D photographed by A. Nobile, E-F by M. Esposito, and G by J. Fogarty. In order of letter A to G, specimen codes are casent0104422, casent104421, casent0103057, casent0103056, casent0914095, casent0914094, casent0102894.

I hypothesized that the worker caste of P. barbatus would be similar in shape to both males and gynes, as opposed to the traditional notion that females should clearly group to the exclusion of males. InP. badius , the gynes and major workers are very similar in basic visual appearance (shape and size) and appear to be co-regulated at the colony-level – that is, their production as a function of colony size is similar. While P. badius minors and males are not immediately clearly similar upon visual inspection, they also appear co-regulated at the colony level (Smith and Tschinkel 2006, Smith 2007). And thus forP. badius , it was hypothesized that increasing sexual dimorphism would be mirrored by increased worker dimorphism, with males/minors (small castes) and gynes/majors (large castes) grouping together in size-shape space.

In order to generalize the patterns seen across the twoPogonomyrmex species, where sexual dimorphism covaried with worker dimorphism, a generic-level comparison was conducted across two genera that have broad variation in sexual and worker dimorphism,Pogonomyrmex (sensu stricto ) and Pheidole . These two genera were also chosen as they met two other important criteria, 1) a high-quality molecular phylogeny was available, and 2) sufficient samples of all castes were available for measurement on Antweb.org. Based on the prior data on the two Pogonomyrmex species it was hypothesized that there would be a positive correlation (controlling for evolutionary history) between sexual dimorphism and worker di/poly-morphism. The use of these two genera have the potential to provide a strong hypothesis test for this correlation as the ancestral state in each case is opposite whereby ancestral Pogonomyrmexhave monomorphic workers and little sexual dimorphism and ancestral state of Pheidole is to high worker and sexual dimorphism.