Morphological and histological characters of penile organization in eleven species of molossid bats

Abstract

The penis is the reproductive organ that ensures efficient copulation and success of internal fertilization in all species of mammals, with special challenges for bats, where copulation can occur during flight. Comparative anatomical analyses of different species of bats can contribute to a better understanding of morphological diversity of this organ, concerning organization and function. In this study, we describe the external morphology and histomorphology of the penis and baculum in eleven species of molossid bats. The present study showed that penile organization in these species displayed the basic vascular mammalian pattern and had a similar pattern concerning the presence of the tissues constituting the penis, exhibiting three types of erectile tissue (the corpus cavernosum, accessory cavernous tissue, and corpus spongiosum) around the urethra. However, certain features varied among the species, demonstrating that most species are distinguishable by glans and baculum morphology and glans histological organization. Major variations in glans morphology were genus-specific, and the greatest similarities were shared by Eumops species and N. laticaudatus. The greatest interspecific similarities occurred between M. molossus and M. rufus and between Eumops species. Save for M. molossus and M. rufus, morphology of the baculum was species-specific; and in E. perotis, it did not occur in all specimens, indicating that it is probably under selection. In the histological organization, the most evident differences were number of septa and localization of the corpora cavernosa. In species with a baculum (Molossus, Eumops and Nyctinomops species), the corpora cavernosa predominantly occupied the dorsal region of the penile glans and is associated with the proximal (basal) portion of the baculum. In species that do not have a baculum (Cynomops, Molossops and Neoplatymops species), the corpora cavernosa predominantly occupied the ventro-lateral region of the glans.

Morphological changes associated with Nile crocodile (Crocodylus niloticus) phallic glans inflation

“…Although amniote phalli share homologous embryonic origins, morphogenetic processes, and molecular genetic mechanisms associated with early development (Brennan, 2016a; Gredler, 2016), their adult morphologies across major amniote lineages are quite diverse (Eberhard, 2010). Three lineages, turtles (Kelly, 2004; McDowell, 1983; Zug, 1966), crocodylians (Johnston et al, 2014; Moore, Spears, Mascari, & Kelly, 2016; Otaño, Imhof, Bolcatto, & Larriera, 2010; Tavalieri et al, 2019; Ziegler & Olbort, 2007), and mammals (Akbari, Babaei, & Goodarzi, 2018; Baskin et al, 2018; Comelis, Bueno, Góes, Taboga, & Morielle‐Versute, 2018; Cunha et al, 2014; Phillips, Wright, Gradie, Johnston, & Pask, 2015), have conspicuous glans structures on the distal phallus. In these taxa, the glans contains inflatable spongiform tissues that expand during sexual arousal and change the overall shape of the distal penis.…”

Histomorphology of the glans penis in Vespertilionidae and Phyllostomidae species (Chiroptera, Mammalia)

“…It has been suggested that male genitalia are subject to more rapid divergent evolution than any other structure in the animal kingdom, and therefore, numerous investigations have analyzed the morphology of male intromittent organs using different approaches, such as gross morphology (Comelis, Bueno, Góes, Taboga, & Morielle‐Versute, ; Hooper & Musser, ; Long, ; Ryan, , 1991b), histology (Comelis et al, ; Comelis, Bueno, Góes, & Morielle‐Versute, ; Herdina, Herzig‐Straschil, Hilgers, Metscher, & Plenk Jr, ; Ryan, , ), three‐dimensional reconstruction (Comelis et al, ; Herdina et al, ; Herdina, Kelly, et al, ; Herdina, Plenk Jr, et al, ), and the genetic basis of size and shape divergence (Schultz, Ingels, et al, ; Schultz, Lough‐Stevens, et al, ).…”

“…In mammals, most morphological variation occurs at the distal end of the male copulatory organ, that is, the glans penis, which has species‐specific morphology (Bradley, Schmidly, & Owen, ; Comelis et al, , ; Hooper, ; Hooper & Musser, ; Hosken & Stockley, ; Ramm, ). Contributing to the variation in penile morphology in mammals is the baculum, or penis bone, which has been described as “the most diverse of all bones” and varies in length, width, and shape across Mammalia (Burt, ; Romer, ).…”

“…The histological characterization of the penile anatomy, particularly of the glans, has allowed to determine the origin and development of the baculum, its specific mechanical functions in bats, and the organization of the penile tissues in the absence of the baculum (Comelis et al, ; Glucksmann, Ooka‐Souda, Miura‐Yasugi, & Mizuno, ; Herdina, Kelly, et al, ; Herdina, Plenk Jr, et al, ; Kelly, ; Murakami & Mizuno, ; Smith & Madkour, ).…”

“…In Chiroptera, most studies concerning the glans penis were focused on species of the most specious family of Chiroptera, the Vespertilionidae, where all analyzed species possess baculum inside the glans (Brown, Genoways, & Jones Jr., ; Comelis et al, ; Hamilton Jr., ; Herdina et al, ; Hill & Harrison, ; Hosken et al, ; LaVal, ; Wimsatt & Kallen, ). In taxa of Molossidae, the studies identified some species with—and some species without baculum inside glans, besides inter‐ and intra‐specific morphological variation in the size and presence of the os penis (Brown, ; Comelis et al, ; Ryan, , ).…”