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.

Annual reproductive cycle of males of the great fruit-eating bat, Artibeus lituratus: Testicular variations, abiotic regulation and sperm analysis

Artibeus lituratus is one of the most well-known bat species in the Neotropics, probably due to its high abundance and the ability to inhabit urban areas. It plays an important ecological role in the ecosystem due to its ability to disperse seeds, which contributes to the regeneration of degraded areas. Actually, the species has been used as an important experimental model for ecotoxicological studies of the impact of pesticides on male reproduction. Despite that, the reproductive pattern of A. lituratus is still controversial due to inconsistent descriptions of the reproductive cycle. Thus, the aim of the present work was to evaluate the annual variations of the testicular parameters and sperm quality of A. lituratus and analyze their responses to annual variations in abiotic factors in the Cerrado area in Brazil. Testes of five specimens were collected each month for one year (12 sample groups) and submitted to histological, morphometric, and immunohistochemical analyses. Analyses of the sperm quality were also performed. Results demonstrate that A. lituratus presents a continuously active process of spermatogenesis throughout the year, with two significant peaks in spermatogenic production (September-October and March), which indicates a bimodal polyestric pattern of reproduction. These reproductive peaks seem to be related to an increase in proliferation and, consequently, in the number of spermatogonia. Conversely, seasonal variations in testicular parameters are correlated with annual fluctuations in rainfall and photoperiod but not with temperature. In general, the species presents smaller spermatogenic indexes with a similar sperm quantity and quality to other bat species.

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.

Duration of the seminiferous epithelium cycle in the frugivorous bat Artibeus lituratus

The seminiferous epithelium goes through multiple changes which enables the differentiation of a spermatogonia in a fully mature spermatozoon. The timing of these changes is species-specific and influences the duration of the reproductive cycles. Bats are among wild mammals whose coordination between male and female reproductive cycles are imperative, since most females show seasonal preferences, even in the Tropics. This seasonal variation demands constant sperm production ready for spermiation in order to guarantee its genetic dispersion and reproduction success. Despite their abundance, little is known about the duration of reproductive cycles in Neotropical bat species, a relevant information for the species management and for conservational strategies regarding anthropogenic and climate influences on bats reproduction. In this study, we aimed at characterizing the stages of the seminiferous epithelium cycle (SEC) of the fruit bat Artibeus lituratus and to determine its duration based on the immunohistochemical analysis of the bromodeoxyuridine (BrDU) activity. SEC stages were characterized according to the tubular morphology method and the frequency of each stage was estimated. After intratesticular injections of BrDU, the animals were euthanized at different times, and the estimation of SEC duration was performed by observing the most advanced germ cells in the seminiferous epithelium. The most advanced stained cells after 2 days of BrdU injection were the primary spermatocytes in pachytene, transitioning from stages 1-2 of the SEC. Within 2 days, we found a progression of 30.42% of the SEC, and an entire cycle lasted 6.58 days on average. Considering that 4.5 seminiferous epithelium cycles are necessary for the whole spermatogenic processes to be completed, the total length of spermatogenesis in A. lituratus was estimated at 29.61 days. Our findings support a pattern of bimodal seasonal polyestry for this species, with rapid spermatogenic cycles.

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 functions in Desmodus rotundus: A comparison between seasons in a morphological context

Reproductive seasonality in Neotropical bats has been assessed to the better understand their reproductive behavior. This knowledge is especially important for the control of Desmodus rotundus population as it is a transmitter of rabies virus. Therefore, we aimed to evaluate the functional activity of testis and epididymis of D. rotundus in dry and rainy seasons under a morphological approach. We observed an increase in tubular diameter and epithelial height of the seminiferous tubules during the rainy season. In the latter, additionally, stereological analysis of the testis showed increased proportion of seminiferous epithelium and reduced percentage of lumen. The sperm number in caput/corpus epididymis increased in rainy season, whereas sperm count and transit time were reduced in cauda region. These alterations were probably related to the recovery of epithelium activities after mating season in dry season. Despite altered nuclear and cytoplasm parameters of Leydig cells between seasons, the volume and number of these cells were constant. Moreover, no change in serum testosterone levels, daily sperm production, and apoptotic index were observed, which indicates that the reproductive pattern in D. rotundus does not change between seasons. Our study offers a baseline for the management of vampire bat population as an attempt to control rabies disease.

Ultrastructure and morphometric features of epididymal epithelium in Desmodus rotundus

The blood-feeding behavior of Desmodus rotundus made this bat a potential vector of rabies virus and a public health issue. Consequently, the better understanding of its reproductive biology becomes valuable for the development of methods to control its population. In this study, we described morphological aspects of epithelial cells in D. rotundus' epididymis using light and transmission electron microscopy methods. The duct compartment was the main component of initial segment (83%), caput (90%), corpus (88%) and cauda (80%) regions. The epithelium lining the duct presented a progressive decrease in its height from initial segment to cauda regions. Moreover, the morphology of each cell type was the same along the entire duct. Similarly to rodents, columnar-shaped principal cells were the most abundant cell type throughout the epididymis, followed by basal and clear cells. Differently in rat and mice, the frequency of clear cells did not increase in the epididymis cauda, whereas the proportion of principal and basal cells was greater in this region. Furthermore, D. rotundus presented goblet-shaped clear cells with the nucleus located in the apical portion of the epididymal epithelium. This cellular portion also presented electron-lucid vesicles of different sizes that may correspond to vesicles enriched with proteins related to proton secretion. In addition to the findings regarding clear cells' structural organization, basal cells presented scarce cytoplasm and no axiopodia. Taken these findings together, we suggest that the mechanism of luminal acidification may have other pathways in D. rotundus than those described in rodents.

The spermatogenic process of the common vampire bat Desmodus rotundus under a histomorphometric view

Among all bat species, Desmodus rotundus stands out as one of the most intriguing due to its exclusively haematophagous feeding habits. However, little is known about their spermatogenic cycle. This study aimed at describing the spermatogenic process of common vampire bats through testicular histomorphometric characterization of adult specimens, spermatogenic production indexes, description of stages of the seminiferous epithelium cycle and estimative of the spermatogenic process duration. Morphometrical and immunohistochemical analyzes for bromodeoxiuridine were conducted under light microscopy and ultrastructural analyzes were performed under transmission electron microscopy. Vampire bats showed higher investment in gonadal tissue (gonadosomatic index of 0.54%) and in seminiferous tubules (tubulesomatic index of 0.49%) when compared to larger mammals. They also showed a high tubular length per gram of testis (34.70 m). Approximately half of the intertubular compartment was found to be comprised by Leydig cells (51.20%), and an average of 23.77x10⁶ of these cells was found per gram of testis. The germline cells showed 16.93% of mitotic index and 2.51% of meiotic index. The overall yield of spermatogenesis was 60% and the testicular spermatic reserve was 71.44x10⁷ spermatozoa per gram of testis. With a total spermatogenesis duration estimated at 37.02 days, vampire bats showed a daily sperm production of 86.80x10⁶ gametes per gram of testis. These findings demonstrate a high sperm production, which is commonly observed in species with promiscuous mating system.

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).

Evaluation of the cell population of the seminiferous epithelium and spermatic indexes of the bat Sturnira lilium (Chiroptera: Phyllostomidae)

Due to the scarcity of information about patterns of spermatogenesis in bats, this study aimed to provide information on the testicular activity of the bat Sturnira lilium along the annual seasons. Thus, a series of morphometrical and stereological analyses were made using the testes of adult S. lilium in order to achieve a better understanding of the sperm production dynamics. Light and transmission electron microscopy analyses were performed in testicular fragments of animals captured during dry and rainy seasons. The testes followed the pattern of organization described for other mammals, and there were no morphological differences between organs collected either in dry or in rainy seasons. Each tubular cross-section in stage 1 was made of 0.5 type-A spermatogonia, 4.4 primary spermatocytes in preleptotene/leptotene, 3.7 in zygotene, 11.9 in pachytene, 35.6 round spermatids and 8.5 Sertoli cells. The mitotic and meiotic indexes were 15.4 and 2.9 cells, respectively, while the spermatogenesis yield was 68.7 cells. The testicular sperm reserves was 37.61×10⁶ cells, and daily sperm production per gram of testis averaged 209.68×10⁶ cells, both highest averages occurring in the rainy season. S. lilium male bats have a continuous reproductive pattern, high spermatogenesis yield and low support capacity by the Sertoli cells.

Two periods of total testicular regression are peculiar events of the annual reproductive cycle of the black Myotis bat, Myotis nigricans (Chiroptera: Vespertilionidae)

Myotis nigricans presents few and controversial reproductive data, which indicate geographical variation in reproduction. Thus, this study aimed to evaluate the seasonal modifications in testicular and epididymal morphologies in a tropical environment, submitting these organs to morphometric and immunohistochemical analysis. The observations revealed that this species presents two peaks of spermatogenic activity followed by two periods of total testicular regression (a quiescent pre-pubertal-like morphology, where only Sertoli cells and spermatogonia could be observed), in the same annual reproductive cycle, which seem to be only indirectly influenced by abiotic factors. This testicular behaviour seems to be synchronised with the caput and corpus epididymidis, but not with the cauda epididymidis, which presents aspects of sperm storage in May–June. The control of this variation seems to be directly linked to the expression of the androgen receptor, since, throughout the year, it is high in periods of testicular recrudescence and low in periods of deactivation. It is not thought to be directly linked to apoptosis, which is more pronounced in periods of recrudescence than in periods of regression.

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.

Stages and duration of the seminiferous epithelium cycle in the bat Sturnira lilium

Knowledge of the stages that compose the seminiferous epithelium cycle (SEC) and determination of the duration of spermatogenic processes are fundamental for the accurate quantification of the dynamics of spermatogenesis. The aim of this study was to characterize the stages that compose the SEC of the bat Sturnira lilium, including evaluation of the average frequency of each of these stages throughout the year and calculation of the duration of the spermatogenic process. An ultrastructural characterization of the formation of the acrosomal cap was also performed. Testicular fragments were processed for morphological and immunohistochemical analysis as well as ultrastructural analysis using transmission electron microscopy. According to the tubular morphology method, the SEC in S. lilium is divided into eight stages, following the pattern found in other mammals. Primary spermatocytes were found at zygotene in stage 1 of the cycle. There was no variation in frequency of each of the stages over the seasons, with stage 1 being the most frequent, and stage 7 the least frequent. The duration of one seminiferous epithelium cycle was 3.45 days, and approximately 15.52 days were required for the development of sperm from spermatogonia. Ultrastructural characterization allowed the formation of the acrosomal cap in round spermatids to be monitored. In conclusion, the stages that compose the SEC in S. lilium are generally similar to those described for other mammals, but the duration of the spermatogenic process is shorter than previously recorded for mammals. The presence of primary spermatocytes at zygotene in stage 1 of the cycle is probably due to the longer duration of this stage.