A general theory of genital homologies for the Hexapoda (Pancrustacea) derived from skeletomuscular correspondences, with emphasis on the Endopterygota

Abstract

No consensus exists for the homology and terminology of the male genitalia of the Hexapoda despite over a century of debate. Based on dissections and the literature, genital skeletomusculature was compared across the Hexapoda and contrasted with the Remipedia, the closest pancrustacean outgroup. The pattern of origin and insertion for extrinsic and intrinsic genitalic musculature was found to be consistent among the Ectognatha, Protura, and the Remipedia, allowing for the inference of homologies given recent phylogenomic studies. The penis of the Hexapoda is inferred to be derived from mediallyfused primary gonopods (gonopore-bearing limbs), while the genitalia of the Ectognatha are inferred to include both the tenth-segmental penis and the ninth-segmental secondary gonopods, similar to the genitalia of female insects which comprise gonopods of the eighth and ninth segments. A new nomenclatural system for hexapodan genitalic musculature is presented and applied, and a general list of anatomical concepts is provided. Novel and refined homologies are proposed for all hexapodan orders, and a series of groundplans are postulated. Emphasis is placed on the Endopterygota, for which finegrained transition series are hypothesized given observed skeletomuscular correspondences.

The evolution of Zoraptera

“…As clade 2a includes many species with unknown character states, the independent occurrence of the spiral in clades 2a and 2b is not conclusive. An asymmetric configuration of the genitalia is a commonly observed feature in Polyneoptera (Huber et al ., ), but a symmetrical condition is considered as ancestral for the group (Helm et al ., ; Boudinot, ). The ancestral state of Zoraptera was probably symmetric according to our estimate (Fig.…”

“…Consensus on structural homologization in zorapteran genitalia was not evident, and researchers used different terminologies based on varying interpretations in the literature. A reliable assessment of homologies is still pending, a point also emphasized in Boudinot's () first comprehensive synthesis of insect male genitalia. As this turned out to be too ambiguous for characters (3) and (6), they were not scored for terminals outside of Zoraptera.…”

Synonymization of the male-based ant genusPhaulomyrma(Hymenoptera, Formicidae) withLeptanillabased upon Bayesian total-evidence phylogenetic inference

“…Of the 11 terminals recovered in this latter subclade, only Leptanilla TH01 was included in Borowiec et al (2019). Noonilla (BPP = 0.9769) is sister to a clade of highly distinctive male morphospecies, recovered with maximal support (BPP = 1), that are immediately recognizable by bizarre metasomal processes (heretofore hypothesized to be extensions of the gonocoxae sensu Boudinot [2018] [Boudinot 2015: Fig. 10D]) and a comb-like row of robust bristles on the protibia (Fig.…”

“…Scanning electron microscopy was undertaken using a Hitachi TM4000 tabletop microscope. Morphological terminology follows the Hymenoptera Anatomy Ontology (Yoder et al 2010), with some exceptions being derived from Bolton (2003) and Boudinot (2018). The character coding scheme was binary and non-additive (Pleijel 1995).…”

Copulatory function and development shape modular architecture of genitalia differently in males and females

“…The observation that modularity and integration are stable is not surprising considering that the copulatory interactions and the segmental origins of genital parts are both thought to be constant across Pentatomidae (Genevcius and Schwertner 2017), and perhaps in insects as a whole (Boudinot 2018). Nevertheless, closer inspection of the degrees of within‐ and between‐module correlations reveal some level of lability, especially in males (Fig.…”