Endoreduplication underlies body size variation in monomorphic ants

In ants, morphological variation is particularly important, as it constitutes a key mechanism underlying the division of labor. Despite this, relatively few studies have addressed the proximate cellular mechanisms responsible for worker size variation. Endoreduplication represents a promising contributor to morphological diversity, as it is a process with a well-established cellular basis.

In this study, we investigated whether endoreduplication can account for variation in body size in monomorphic ants, analogous to patterns previously reported in polymorphic species. We tested whether body size correlates with the level of endoreduplication in workers of three monomorphic ant species that differ in ecology, colony structure, and life-history traits. The analysis showed that individual worker size was positively correlated with nuclear DNA content (C-value), both in the overall linear mixed-effects model (LMM) and in species-specific analyses. As an additional finding, the C-value level exhibited body-part specificity, reaching the highest values in the abdomen.

Our results demonstrate that endoreduplication contributes to body size variation not only in ants with distinct worker subcastes, but also in species with subtle size variability. This suggests that endoreduplication represents an evolutionarily ancient and potentially widespread mechanism, which may have served as a developmental foundation for the evolution of advanced polymorphism in ants.