Morphological Variation of Primary Reproductive Structures in Males of Five Families of Neotropical Bats

Sperm morphology and comparison morphometry measurements of two species of bats, Molossus molossus and Molossops temminckii (Chiroptera: Molossidae)

Sperm morphology is considered a species-specific character and has been used as a tool in the classification of numerous mammalian taxa. Neotropical bats have been poorly studied, and important aspects on sperm morphology have not been elucidated. The aim of the present study was to describe and compare the sperm morphology and morphometry of Molossus molossus and Molossops temminckii. A total of 14 adults specimens were analyzed from the Colección Mamíferos Lillo, Universidad Nacional de Tucumán: five M. molossus and nine M. temminckii. The epididymis were extracted and macerated in Farmer's solution, followed by a coloration with different stains. To carry out the description and morphometric analysis, microphotographs were taken under an optical, epifluorescence, and scanning electron microscope (SEM). A total of 50 sperm from each individual were measured for morphometric analysis. The length and width of the head, midpiece and tail were taken as variables. Sperm from M. molossus and M. temminckii were practically identical, both morphologically and morphometrically. In both species, a distal bulge was observed at the end of the intermediate piece in a percentage greater than 85%. The main characteristics shared between the species were: presence of acrosomal blebs in the upper half of the head of the spermatozoa; cephalic equatorial segment with filiform ornamentations; intermembrane space of head apex wedge-shaped; helical middle piece and annulus at the end of middle piece. In the present study, SEM allowed us to visualize structures, such as acrosomal vesicles, that were not detected with other types of microscopy. RESEARCH HIGHLIGHTS: The similarities in the sperm morphology between M. molossus and M. temminckii were observed with three types of microscopy: optical, epifluorescence and scanning electron, and supported by morphometric and statistical analyses.

Migratory testis, spermatogenesis and reproductive cycle of the neotropical broad-eared bat Nyctinomops laticaudatus (Molossidae)

We describe for the first time the displacement mechanism of migratory testis in Nyctinomops laticaudatus, which is little known in bats, in addition to histological analysis of its gonads. Data on testis anatomy and activity were obtained from 20 males. Males had migratory testes as they are displaced in the inguinal canals between intra and external abdominal positions. The displacement mechanism consisted of a testis ligament composed mainly of smooth muscle tissue attached to the cranial pole of the testis. Since the epididymis is closely tied to the testis, both organs are displaced together, regardless of the individual reproductive condition. Males and females showed seasonal monoestry, with a short mating period at the beginning of the dry season. The occurrence of breeding males was inversely proportional to rain and air temperature. At the mid-dry season, when air temperatures are also lower, males showed testis regressing, remaining in a reproductive hiatus for several months (rest/recrudescence) until the beginning of in the next dry season. Pregnant females were captured at the end of the dry season, and the birth of the young occurred during the rainy season, a time of greater food availability. Thus, females coordinated their reproductive phases to a more favorable period of the year for their survival and that of the offspring. Males associated their spermatogenic activity to a time of no environmental nor physiological restriction related to low air temperature.

Sperm production and seminal analyses in a Neotropical sperm-storing vespertilionid bat yellowish myotis (Myotis levis)

Yellowish myotis is a Neotropical vespertilionid bat that presents a seasonal reproduction. The sperm is produced in the Mature stage, stored in the Regressed stage and released in the Rest stage (mating period). Aiming to understand, for the first time, the relationship between testis and epididymis physiology in yellowish myotis reproduction, the spermatogenesis length, sperm production, and seminal parameters were herein evaluated. Fifty-one adult male bats were captured in Santuário do Caraça, Minas Gerais, Brazil. The gonads were collected in the Maturing and Mature stages for histomorphometric and immunohistochemical analyses, whereas the epididymis was evaluated in all reproductive stages for seminal studies. Our results demonstrated that the yellowish myotis spermatogenic process is fast, lasting 31.70 ± 0.15 days. Despite the low Sertoli cell efficiency (6.60 ± 1.23), the high numbers of Sertoli cells per testis enable an elevated sperm production in the Mature stage. The sperm concentration, vitality, and motility presented the highest values in the Regressed stage; however, in this period, an increased incidence of sperm morphological defects was detected. In the following period (Rest stage), a drastic reduction of defective sperm was observed, suggesting quality control of sperm before the mating period. Furthermore, the epididymis ability to maintain a long-term sperm-storage was observed in 26.7% of the bats in the Maturing stage. In summary, yellowish myotis presented a fast and high sperm production during the Mature stage. These sperms are stored and selected before mating period.

The process of testicular regression also impacts the physiology of the epididymis of the bat Molossus molossus, although with a delay in epididymal response due to sperm storage

Responsible for post-testicular maturation, concentration, protection and sperm storage, the epididymis is an organ that can be easily subdivided into three segments: caput, corpus and cauda. Each epididymal region displays different morphology and functions within the sperm maturation process. Despite the great importance of this organ, studies on its morphology and hormonal control in bats remain scarce. Thus, the aim of this study was to morphologically analyze the epididymis of the bat Molossus molossus (Chiroptera: Molossidae), in order to evaluate its morphological and morphometric variations, as well as some aspects of its hormonal control during the annual reproductive cycle. For this purpose, 60 sexually adult males were used in this study, comprising five specimens collected monthly for one year to form 12 sample groups. The epididymis was subjected to morphological, morphometric and immunohistochemical analyses. The results demonstrated that the processes of total testicular regression and posterior recrudescence suffered by M. molossus also impacts the physiology of the epididymis, however, a delay in the epididymal response is seen due to the storage of sperm. Similar to other mammals, the epididymis of M. molossus has a large predominance of principal and basal cells. The epididymal seasonal variations appear to be directly correlated to rainfall and photoperiod, but not to temperature. Meanwhile, epididymal physiology appears to be regulated, at least partially, by the expression of the androgen receptor in epithelial cells, which has agonist effects on cell proliferation.

Descrição e variação sazonal na histomorfometria epididimária de Dermanura cinerea (Chiroptera: Phyllostomidae) em um fragmento de Mata Atlântica no Nordeste do Brasil

RESUMO Esse estudo objetivou avaliar sazonalmente a histomorfometria do epidídimo de Dermanura cinerea (Gervais, 1856) em um fragmento de Mata Atlântica no nordeste do Brasil. Foram utilizados 18 espécimes machos adultos capturados por redes de neblina. As coletas ocorreram mensalmente ao longo de dezoito meses, durante duas noites consecutivas e os dados meteorológicos foram fornecidos pelo Instituto Nacional de Meteorologia. Depois de eutanasiados, os espécimes tiveram os epidídimos coletados e esses órgãos foram fixados e processados. As lâminas histológicas foram coradas por Hematoxilina - Eosina e analisadas em microscopia óptica. Os parâmetros morfométricos analisados foram as áreas do túbulo, do lúmen e do epitélio das regiões do segmento inicial, cabeça, corpo e cauda do epidídimo. Os dados histomorfométricos obtidos foram submetidos às análises no teste U de Mann-Whitney. Os resultados revelaram que D. cinerea apresentou espermatozoides em todas as regiões do epidídimo, exceto no segmento inicial. As maiores médias das áreas tubular, do lúmen e do epitélio nas quatro regiões, foram constatadas durante os meses secos. Portanto, D cinerea apresentou maior sensibilidade na região da cauda do epidídimo, ao longo dos meses com baixos índices pluviométricos. Isso indica que as condições ambientais apresentam considerável influência sobre a morfofisiologia epidídimária dessa espécie, sobretudo, em relação ao armazenamento de espermatozoides na cauda desse órgão, em área de Mata atlântica do nordeste brasileiro.

Three-Dimensional and Histological Observations on Male Genital Organs of Greater Horseshoe Bat, Rhinolophus ferrumequinum

Anatomy of bat genital organs has been conventionally studied by gross and microscopic observations to date. Here, we employ both histological observation and diceCT (diffusible iodine-based contrast-enhanced computed tomography) to study the detailed three-dimensional morphological structure of the male genital organs in bats, using the greater horseshoe bat, Rhinolophus ferrumequinum. This is the first study to three-dimensionally describe the whole reproductive organs of bats in detail. Our highly resolved three-dimensional reconstruction reveals that the male organs of R. ferrumequinum consist of paired testes, epididymides, deferent ducts, and five accessory genital glands. The boundary between the ampullary and vesicular glands has been difficult to identify in previous observations, but our diceCT imaging allowed us to clearly differentiate the two. We found that the ampullary gland is located at the terminal part of the deferent ducts, and the vesicular gland lies distal to the ampullary glands. This species possesses a single and carrot-shaped urethral gland, which is not found in most chiropteran families. The presence of the urethral gland in this species and its secretions suggest that after copulation this species is capable of forming a vaginal plug, which can seal the female’s vaginal orifice to block the entrance of spermatozoa from other males. The presence of the urethral gland and elongated epididymal tail and the fact that some individuals can terminate their hibernation and reactivate imply forced copulation on hibernating females can occur in R. ferrumequinum.

Evaluation of reproductive parameters in male Neotropical bats during dry and rainy months in a specific area of the Cerrado biome

The aim of this study was to analyse the reproductive aspects of male bats of three common species of the Phyllostomidae family: Artibeus lituratus, Platyrrhinus lineatus and Sturnira lilium, during dry and rainy months in a specific area of the Cerrado biome. Body weight was significantly higher during the dry months for S. lilium. The gonadosomatic index (GSI) and testicular weight were not significantly different between dry and rainy periods. The tubular parameters were significantly bigger in A. lituratus than in the other two species during both periods. No difference in the tubular/interstitial ratio was observed in any of the species during both periods. In both periods, all sperm cells and germ cell developmental stages were visible on seminiferous tubules whereas sperm cells were observed in epididymides of all sampled animals. The percentage of morphologically normal sperm was low (35%-60%), with no difference between periods. Spermatozoa from A. lituratus presented a leaf-shaped head, while the head was round-shaped in the other two species. In conclusion, our data suggest that males from the three studied species did not present reproductive latency during the most critical weather periods (dry and rainy months) in the metropolitan region of Brasilia, Brazil.

Estágio reprodutivo, histologia e morfometria sazonal do testículo de Dermanura cinerea (Chiroptera: Phyllostomidae) em fragmento de Mata Atlântica no Litoral Sul de Pernambuco, Brasil

RESUMO Esse estudo analisou o estágio reprodutivo, a histologia e a morfometria dos testículos de Dermanura cinerea (Gervais, 1856) em fragmento de Mata Atlântica no Litoral Sul de Pernambuco. Os espécimes foram capturados por redes de neblina e as coletas ocorreram mensalmente, ao longo de duas noites consecutivas, durante 18 meses. Os dados meteorológicos foram agrupados em meses chuvosos e secos. Foram utilizados 18 espécimes adultos, os quais foram classificados em machos com testículos descendentes e não descendentes. Para as análises histológicas, os testículos foram coletados, fixados e processados seguindo a técnica histológica de rotina. As lâminas obtidas foram coradas por Hematoxilina-Eosina. Nas análises morfométricas foram mensuradas a área de ocupação do compartimento tubular e intertubular, quantificados o número de células de Leydig, de Sertoli, de espermatócitos e de espermátides alongadas. Os dados morfométricos foram submetidos às análises estatísticas. Dermanura cinerea apresentou maior atividade de produção espermática em meses secos e maior produção hormonal em meses chuvosos. Essas informações estão relacionadas também com o padrão reprodutivo das fêmeas e com a elevação nos índices pluviométricos, já que é um fator determinante na mediação da disponibilidade alimentar das espécies frugívoras, como D. cinerea em área de Mata Atlântica de Pernambuco.

Reproductive biology of Artibeus fimbriatus Gray 1838 (Chiroptera) at the southern limit of its geographic range

Abstract Bats of the Phyllostomidae family exhibit different reproductive patterns in Neotropical regions and the strategy adopted depends on the regional climate. Here we studied the reproductive biology of Artibeus fimbriatus at the southern limit of their distribution in Brazil. This region has no rainy season, and the climate is characterized by high temperatures and variable photoperiods. We examined 129 A. fimbriatus females over several months, and used histological procedures where necessary in order to determine whether bats were pregnant. Females exhibited a long reproductive period and were pregnant from June until February. The reproduction events were found to be dependent on the photoperiod, but independent of annual accumulated precipitation. Our results show that at the southern limit of their distribution, A. fimbriatus exhibit seasonal-dependent reproductive patterns, with parturition events occurring during spring and summer, in which the days are longer and temperature is warmer.

Impact of the Processes of Total Testicular Regression and Recrudescence on the Epididymal Physiology of the Bat Myotis nigricans (Chiroptera: Vespertilionidae)

Myotis nigricans is a species of vespertilionid bat, whose males show two periods of total testicular regression within the same annual reproductive cycle in the northwest São Paulo State, Brazil. Studies have demonstrated that its epididymis has an elongation of the caudal portion, which stores spermatozoa during the period of testicular regression in July, but that they had no sperm during the regression in November. Thus, the aim of this study was to analyze the impact of the total testicular regression in the epididymal morphophysiology and patterns of its hormonal regulation. The results demonstrate a continuous activity of the epididymis from the Active to the Regressing periods; a morphofunctional regression of the epididymis in the Regressed period; and a slow recrudescence process. Thus, we concluded that the processes of total testicular regression and posterior recrudescence suffered by M. nigricans also impact the physiology of the epididymis, but with a delay in epididymal response. Epididymal physiology is regulated by testosterone and estrogen, through the production and secretion of testosterone by the testes, its conduction to the epididymis (mainly through luminal fluid), conversion of testosterone to dihydrotestosterone by the 5α-reductase enzyme (mainly in epithelial cells) and to estrogen by aromatase; and through the activation/deactivation of the androgen receptor and estrogen receptor α in epithelial cells, which regulate the epithelial cell morphophysiology, prevents cell death and regulates their protein expression and secretion, which ensures the maturation and storage of the spermatozoa.

Structure, histochemistry and seasonal variations of the male reproductive accessory glands in the Pallas’s mastiff bat, Molossus molossus (Chiroptera: Molossidae)

Due to their wide geographical distribution, bats suffer considerable influence from abiotic factors on their reproductive strategies, detected through behavioural or functional assessment of the gonads and accessory glands. The present study aimed to characterise anatomically and morphologically the reproductive accessory glands (RAGs) of Molossus molossus (Molossidae) and evaluate their seasonal variations. The RAGs were removed, fixed, sectioned after histological processing and submitted to the following stains: haematoxylin–eosin, periodic acid­–Schiff (PAS) and Gömöri’s reticulin. Our data demonstrated that the RAGs of M. molossus are composed of a semi-lobed prostatic complex associated with the urethra and a pair of inguinal bulbourethral glands. Histology and three-dimensional reconstruction of the prostatic complex demonstrated the existence of two regions: ventral and dorsal (named according to the position around the urethra). The two regions had distinctive morphological and histological differences, with the ventral region being the most prominent and the dorsal formed by four lobes. Considering the seasonal evaluation, we can infer that the prostatic complex of M. molossus is active throughout the seasons in São Paulo State (Brazil) and, although each of the prostatic regions has inherent characteristics, they synchronise to establish the main reproductive peak in spring (early rainy season).

Ultrastructure of spermatogenesis in the short-tailed fruit bat, Carollia perspicillata (Chiroptera: Phyllostomidae: Carollinae)

Among species of the Chiroptera, spermatogenesis and the fully differentiated spermatozoa differ in morphological and ultrastructural detail. This study therefore aimed to ultrastructurally characterize the spermatogenesis and the spermatozoa of Carollia perspicillata (Phyllostomidae) and compare the process with other species of bats and mammals. The differentiation of spermatogonia is similar to other bats and to Primates, with three main spermatogonia types: Ad, Ap, and B. Meiotic divisions proceed similarly to those of most mammals and spermiogenesis is clearly divided into 12 steps, in the middle of the range of developmental steps for bats (9-16 steps). The process of acrosome formation is similar to that found in Platyrrhinus lineatus, with the acrosome formed by two different types of proacrosomal vesicles. The ultrastructure of the spermatozoon is similar to other bats already described and resembles the typical mammalian sperm model; however, its morphology differs from other mammals such as marsupials and rodents, on account of a simpler spermatozoon head morphology, which indicates a pattern that is more closely related to the sperm cells of humans and other primates. Our data demonstrated that spermatogenesis in C. perspicillata presents great ultrastructural similarities to P. lineatus. This pattern is not surprising, because both species belong to the same family (Phyllostomidae); however, it is observed that C. perspicillata presents some characteristics that are more closely related to phylogenetically distant species, such as Myotis nigricans (Vespertilionidae), which is a fact that deserves attention.