Anatomy and evolution of the head of Dorylus helvolus (Formicidae: Dorylinae): Patterns of sex‐ and caste‐limited traits in the sausagefly and the driver ant

Abstract

Ants are highly polyphenic Hymenoptera, with at least three distinct adult forms in the vast majority of species. Their sexual dimorphism, however, is overlooked to the point of being a nearly forgotten phenomenon. Using a multimodal approach, we interrogate the near total head microanatomy of the male of Dorylus helvolus, the “sausagefly,” and compare it with the conspecific or near‐conspecific female castes, the “driver ants.” We found that no specific features were shared uniquely between the workers and males to the exclusion of the queens, indicating independence of male and worker development; males and queens, however, uniquely shared several features. Certain previous generalizations about ant sexual dimorphism are confirmed, while we also discover discrete muscular presences and absences, for which reason we provide a coarse characterization of functional morphology. Based on the unexpected retention of a medial carinate line on the structurally simplified mandible of the male, we postulate a series of developmental processes to explain the patterning of ant mandibles. We invoke functional and anatomical principles to classify sensilla. Critically, we observe an inversion of the expected pattern of male‐queen mandible development: male Dorylus mandibles are extremely large while queen mandibles are poorly developed. To explain this, we posit that the reproductive‐limited mandible phenotype is canalized in Dorylus, thus partially decoupling the queen and worker castes. We discuss alternative hypotheses and provide further comparisons to understand mandibular evolution in army ants. Furthermore, we hypothesize that the expression of the falcate phenotype in the queen is coincidental, that is, a “spandrel,” and that the form of male mandibles is also generally coincidental across the ants. We conclude that the theory of ant development and evolution is incomplete without consideration of the male system, and we call for focused study of male anatomy and morphogenesis, and of trait limitation across all castes.

Evolution and systematics of the Aculeata and kin (Hymenoptera), with emphasis on the ants (Formicoidea: †@@@idae fam. nov., Formicidae)

“…2010). Mandibular gape was potentially modified through enlargement of the dorsal craniomandibular condyle (Richter et al ., 2019, 2020, 2021, submitted; Boudinot et al . 2021; Gronenberg et al ., 1998; Zhang et al ., 2020), although the specific biomechanical consequences of this derivation have yet to be explicitly addressed.…”

“…Published observations of apodeme presence include Brachyponera (Ponerinae), Dorylus (Dorylinae), Formica (Formicinae), and Wasmannia (Myrmicinae) (Richter et al . 2019, 2020; Boudinot et al . 2021); published observations of absence among crown ants are confined to the Leptanillomorpha, including Opamyrma (Yamada et al .…”

“…; Burmese amber; maximally supported as Ponerini in present analyses). Formicinae crown: offset 97.0 Ma ([1] Formicinae indet. ; Burmese amber; maximally supported as Formicinae in present analyses; [2] † Kyromyrma neffi Grimaldi et al ., 2000; Raritan amber; maximally supported as crown Formicidae in present analyses). Oecophylla (Formicinae) stem: 44.0 Ma († Oecophylla eckfeldiana Dlussky et al ., 2008, Eifel formation; shared autapomorphies with Oecophylla ; sister to extant species in combined-evidence tip-dating analysis of Boudinot et al . 2021).…”

“…Oecophylla (Formicinae) stem: 44.0 Ma († Oecophylla eckfeldiana Dlussky et al ., 2008, Eifel formation; shared autapomorphies with Oecophylla ; sister to extant species in combined-evidence tip-dating analysis of Boudinot et al . 2021).…”

Corrieopone nouragues gen. nov., sp. nov., a new Ponerinae from French Guiana (Hymenoptera, Formicidae)

“…In profile, clypeal projection with a broad anteroventral face (avf, Fig. 39A–D ), which extends ventroposteriorly (i.e., obliquely) from the clypeal dorsal face in almost 90 degrees; the ventralmost point of this anteroventral face meets the “true” clypeal ventral face (= surface of the clypeal infold in Boudinot et al 2021 ; vf, Fig. 39A–D ).…”