Internal head morphology of minor workers and soldiers in the hyperdiverse ant genus Pheidole

Canadian Journal of Zoology,Volume 96, Issue 5, Page 383-392, May 2018. In the hyperdiverse ant genus Pheidole Westwood, 1839, the worker caste evolved into two morphologically distinct subcastes: minor workers and soldiers. The evolution of soldiers, which are larger in size than minor workers and have disproportionately larger heads, are thought to be key to Phediole ’s success. Although many studies have focused on external anatomy, little is known about their internal anatomy. We therefore used microCT imaging and quantitative three-dimensional image analysis to reconstruct the major glands of the head, the musculature, nervous system, and digestive organ of minor workers and soldiers of four Pheidole species. We expected these tissues to scale isometrically and to be proportionally larger in soldiers relative to the minor workers. Surprisingly, we found that the nervous system, cephalic gland, and digestive organ volume are absolutely and relatively s maller in soldiers, whereas muscle volume is absolutely and relatively larger, than in minor workers. This may reflect individual-level trade-offs, where muscles grow at the expense of all other cephalic organs. Alternatively, this relationship may reflect the specialization of internal anatomy in e ach subcaste to enhance division of labour at the colony level. Future studies should test these alternative hypotheses across a larger number of Pheidole species.
Source: Canadian Journal of Zoology - Category: Zoology Authors: Source Type: research