Tempo and mode of morphological evolution in the ant reproductive caste
Raquel Divieso Roman Rodrigues, Raquel Divieso Roman Rodrigues , Marcio Roberto Pie
Departamento de Zoologia, Universidade Federal do Paraná, Curitiba, Brazil; Departamento de Zoologia, Universidade Federal do Paraná, Curitiba, Brazil ; Departamento de Zoologia, Universidade Federal do Paraná, Curitiba, Brazil
One of the characteristics required for an organism to be considered eusocial is the division of labor in the colony. In the vast majority of ant species, the reproductive caste is typically winged and almost exclusively responsible for the reproduction of the colony. Differences in size and shape between the sexes can vary greatly among species, and usually the winged female (queen) has a larger body size than the male. This asymmetry should have a profound impact on the selective pressures for different morphological traits within and among castes. However, the processes that drive sexual size dimorphism in ants are still poorly explored. In this study we compared the morphological variation in males and queens of 678 species of ant across 191 genera and 15 subfamilies. Six measurements were obtained from each specimen: eye length, distance between the eyes, head width, head length, mesossoma length and pronotum width. Using these traits, we explore the tempo and mode of morphological evolution in ant reproductive castes. Our main goals were: (1) to characterize morphological variation within and among ant reproductive castes; (2) to estimate the degree of phylogenetic signal in male and female traits; (3) to test whether different sexes display differences in their rates of evolution. Morphological variation in each reproductive caste were explored using principal component analyses. Our results indicate different evolutionary rates for five of the six characteristics analyzed, all faster in queens, the size of the eye with a rate twice as fast. In particular, although body size had a fundamental role in explaining morphological evolution in the reproductive caste, males and females tend to follow drastically different allometric rules. The processes that drive these patterns of body size in association with caste dimorphism are discussed.