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.