Testing Morphological Relationships Between Female and Male Copulatory Structures in Bats

The lower reproductive tract of female mammals has several competing functions including mating, tract health maintenance, and parturition. Diverse vaginal anatomy suggests interactions between natural and sexual selection, yet despite its importance, female copulatory morphology remains under-studied. We undertook a comparative study across the species-rich mammalian order Chiroptera (bats) with a focus on the suborder Yangochiroptera (Vespertilioniformes) to examine how female vaginal features may have coevolved with male penis morphology to minimize mechanical damage to their tissues during copulation. The penis morphology is diverse, presenting great potential for post-copulatory sexual selection and coevolution with the female morphology, but vaginas have not been carefully examined. Here we test the hypotheses that vaginal thickness and collagen density have coevolved with features of the male penis including the presence of spines and a baculum. We present histological data from females of 24 species from 7 families of bats, and corresponding data on male penis anatomy. We also examine the role of phylogenetic history in the morphological patterns we observe. We found evidence that female vaginal thickness has coevolved with the presence of penile spines, but not with baculum presence or width. Collagen density did not appear to covary with male penile features. Our findings highlight the importance of considering interactions between the sexes in influencing functional reproductive structures and examine how these structures have been under selection in bats.

The Core Concepts, Competencies and Grand Challenges of Comparative Vertebrate Anatomy and Morphology

Core concepts offer coherence to the discourse of a scientific discipline and facilitate teaching by identifying large unifying themes that can be tailored to the level of the class and expertise of the instructor. This approach to teaching has been shown to encourage deeper learning that can be integrated across subdisciplines of biology and has been adopted by several other biology subdisciplines. However, Comparative Vertebrate Anatomy, although one of the oldest biological areas of study, has not had its core concepts identified. Here, we present five core concepts and seven competencies (skills) for Comparative Vertebrate Anatomy that came out of an iterative process of engagement with the broader community of vertebrate morphologists over a 3-year period. The core concepts are (A) evolution, (B) structure and function, (C) morphological development, (D) integration, and (E) human anatomy is the result of vertebrate evolution. The core competencies students should gain from the study of comparative vertebrate anatomy are (F) tree thinking, (G) observation, (H) dissection of specimens, (I) depiction of anatomy, (J) appreciation of the importance of natural history collections, (K) science communication, and (L) data integration. We offer a succinct description of each core concept and competency, examples of learning outcomes that could be used to assess teaching effectiveness, and examples of relevant resources for both instructors and students. Additionally, we pose a grand challenge to the community, arguing that the field of Comparative Vertebrate Anatomy needs to acknowledge racism, androcentrism, homophobia, genocide, slavery, and other influences in its history and address their lingering effects in order to move forward as a thriving discipline that is inclusive of all students and scientists and continues to generate unbiased knowledge for the betterment of humanity. Despite the rigorous process used to compile these core concepts and competencies, we anticipate that they will serve as a framework for an ongoing conversation that ensures Comparative Vertebrate Anatomy remains a relevant field in discovery, innovation, and training of future generations of scientists.