Caste Determination in a Polymorphic Social Insect: Nutritional, Social, and Genetic Factors

TLDR

The study investigates how diet, social environment, and genetics influence size and caste differentiation in the Florida harvester ant Pogonomyrmex badius. Researchers examined larval diet composition using stable isotope ratios (δ13C, δ15N, C:N) and assessed colony size effects on worker and gyne morphology. The results show that larval diet composition differs among castes, with majors and gynes having higher nitrogen content and trophic position, colony size influences only minor worker size, about 19 % of patrilines bias caste production, and genetic factors affect both caste determination and size within castes, indicating that environmental, social, and genetic influences interact in a caste‑specific manner.

Abstract

We examined how dietary, social, and genetic factors affect individual size and caste in the Florida harvester ant Pogonomyrmex badius, which has three discrete female castes. The diet that a larva consumed, as indicated by delta(13)C, delta(15)N, and C:N, varied with caste. Both N content and estimated trophic position of dietary input was higher for major than for minor workers and was highest for gynes (reproductive females). The size and resources of a colony affected the size of only minor workers, not that of gynes and major workers. Approximately 19% of patrilines showed a bias in which female caste they produced. There were significant genetic effects on female size, and the average sizes of a major worker and a gyne produced by a patriline were correlated, but neither was correlated with minor worker size. Thus, genetic factors influence both caste and size within caste. We conclude that environmental, social, and genetic variation interact to create morphological and physiological variation among females in P. badius. However, the relative importance of each type of factor affecting caste determination is caste specific.