The ultimate database to (re)set the evolutionary history of primate genital bones

Abstract

Scientific literature concerning genital bones in primates consists of both ancient works (dating back to the nineteenth century) and more recent revisions/meta-analyses, which, however, are not always so detailed or exhaustive. Based on a thorough analysis, several conflicting data, inaccurate references, and questionable claims have emerged. We generated a binary matrix of genital bone occurrence data, considering only data at the species level, based on (1) a rigorous literature search protocol, (2) raw data (collected exclusively from primary literature), (3) an updated taxonomy (often tracing back to the species taxonomic history) and (4) new occurrence data from scanned genitals of fresh and museum specimens (using micro-computed tomography-micro-CT). Thanks to this methodological approach, we almost doubled available occurrence data so far, avoiding any arbitrary extension of generic data to conspecific species. This practice, in fact, has been recently responsible for an overestimation of the occurrence data, definitively flattening the interspecific variability. We performed the ancestral state reconstruction analysis of genital bone occurrence and results were mapped onto the most updated phylogeny of primates. As for baculum, we definitively demonstrated its simplesiomorphy for the entire order. As for baubellum, we interpreted all scattered absences as losses, actually proposing (for the first time) a simplesiomorphic state for the clitoral bone as well. The occurrence data obtained, while indirectly confirming the baculum/baubellum homology (i.e., for each baubellum a baculum was invariably present), could also directly demonstrate an intra-specific variability affecting ossa genitalia occurrence. With our results, we established a radically improved and updated database about the occurrence of genital bones in primates, available for further comparative analyses.

When the Utility of Micro-Computed Tomography Collides with Insect Sample Preparation: An Entomologist User Guide to Solve Post-Processing Issues and Achieve Optimal 3D Models

“…This has allowed samples from different sources to be used and further exploited, from a morphological/functional/evolutionary perspective [40,41].…”

Over and beyond the Primate baubellum Surface: A “Jewel Bone” Shielded in Museums

“…Based on the bias found in the literature about variation in genital morphology, which returns data and discussions mostly limited to the male's genital external and internal features (e.g., penile length and complexity of distal morphology, the size, and shape of keratinized spines, baculum occurrence, length, and width, descriptive morphology [85,86]), we considered it mandatory (and fair) to enhance and initiate implementing the literature status of the baubellum (as for occurrence, external and internal morphology, length, and shape quantification data). The paucity of studies on the baubellum (as well as the clitoris) is even more striking by considering that: (a) it is not limited to the primate order but it also applies to upper taxonomic levels (i.e., mammals) and (b) although baculum (and penis) and baubellum (and clitoris) are homologous structures (i.e., they share ontogeny), most scientific efforts have been always and unjustifiably focused on just the male counterpart ( [73,[86][87][88][89][90][91], but see the most recent [43,92,93]).…”

“…Therefore, data acquisition from museum collection specimens represents a kind of post-mortem sampling that prevents the depletion of protected wild primate populations. In addition, museum collections are even more valorized when non-disruptive 3D scanning is applied since it allows both to produce advanced data from historic material (either exhibited or hidden in basements) and also to protect the integrity of samples thus available for future research to come [42,43]. The baubellum still represents a wide and worthy topic to investigate.…”

“…The use of micro-CT allowed us to overcome museum policy constraints and to investigate both anatomy and morphology while keeping samples fully preserved for future research. Although the study of genital bones in primates has always suffered a widespread omission of both occurrence and morphology data in both sexes, a notable bias disproportionally favors male data, making the study of baubella even more urgent (see [43] for more details). In this study, we apply micro-CT focusing on primate baubella to contribute to investigating the morphology and shape variation of this neglected bone.…”

Female Genital Variation Far Exceeds That of Male Genitalia: A Review of Comparative Anatomy of Clitoris and the Female Lower Reproductive Tract in Theria

“…Despite clear sexual dimorphism, some aspects of the clitoris covary with penile characters across species. Variation in the presence of the Os clitoridis (baubellum or clitoral bone) to some extent follows variation of the Os penis , the baculum ( Lough-Stevens et al 2018 ; Spani et al 2021 ). Both phalli also appear to covary in the extent of bifurcation.…”