Divergent Seasonal Reproductive Patterns in Syntopic Populations of Two Murine Species in Southern Spain, Mus spretus and Apodemus sylvaticus

Characterization of the Small Intestine in the Southern White-breasted Hedgehog (Erinaceus concolor) Using Histological, Histochemical, Immunohistochemical, and Scanning Electron Microscopic Techniques

The present study was designed to investigate the microscopic features of the small intestine in the southern white-breasted hedgehog (Erinaceus concolor). The histochemical profile of the small intestine was investigated using periodic acid Schiff (PAS), alcian blue (AB, pH 2.5), and aldehyde fuchsin. The expression of SOX9 was also evaluated immunohistochemically, and the detailed morphology of intestinal mucosa was studied by using a scanning electron microscope. The intestinal wall was composed of the tunica mucosa, tunica submucosa, tunica muscularis, and tunica serosa. Plica circulares and muscularis mucosa were present only in the duodenum. The jejunal villi were the tallest and the ileal villi were the shortest. From the duodenum to the ileum, the population density of goblet cells decreased significantly. The goblet cells throughout the small intestine reacted positively with PAS and AB. The expression rate of SOX9 was not statistically different between the three parts of the small intestine (p > 0.05). In conclusion, despite the general characteristics of the small intestine in this species of hedgehog, there were some differences when compared with other mammalian and rodent species. These findings provide a baseline for future detailed research on the digestive system of the hedgehog species and other mammalian species.

What do we know about blood-testis barrier? current understanding of its structure and physiology

Blood-testis barrier (BTB) creates a particular compartment in the seminiferous epithelium. Contacting Sertoli cell-Sertoli cell plasma membranes possess specialized junction proteins which present a complex dynamic of formation and dismantling. Thus, these specialized structures facilitate germ cell movement across the BTB. Junctions are constantly rearranged during spermatogenesis while the BTB preserves its barrier function. Imaging methods are essential to studying the dynamic of this sophisticated structure in order to understand its functional morphology. Isolated Sertoli cell cultures cannot represent the multiple interactions of the seminiferous epithelium and in situ studies became a fundamental approach to analyze BTB dynamics. In this review, we discuss the contributions of high-resolution microscopy studies to enlarge the body of morphofunctional data to understand the biology of the BTB as a dynamic structure. The first morphological evidence of the BTB was based on a fine structure of the junctions, which was resolved with Transmission Electron Microscopy. The use of conventional Fluorescent Light Microscopy to examine labelled molecules emerged as a fundamental technique for elucidating the precise protein localization at the BTB. Then laser-scanning confocal microscopy allowed the study of three-dimensional structures and complexes at the seminiferous epithelium. Several junction proteins, like the transmembrane, scaffold and signaling proteins, were identified in the testis using traditional animal models. BTB morphology was analyzed in different physiological conditions as the spermatocyte movement during meiosis, testis development, and seasonal spermatogenesis, but also structural elements, proteins, and BTB permeability were studied. Under pathological, pharmacological, or pollutant/toxic conditions, there are significant studies that provide high-resolution images which help to understand the dynamic of the BTB. Notwithstanding the advances, further research using new technologies is required to gain information on the BTB. Super-resolution light microscopy is needed to provide new research with high-quality images of targeted molecules at a nanometer-scale resolution. Finally, we highlight research areas that warrant future studies, pinpointing new microscopy approaches and helping to improve our ability to understand this barrier complexity.

Global change effects on Mediterranean small mammal population dynamics: Demography of Algerian mice (Mus spretus) along land use and climate gradients

Climate and land use change are key global change drivers shaping future species' distributions and abundances. Negative interactions among effects of drivers can reduce the accuracy of models aimed at predicting such distributions. Here we analyse how climate and land use affected population dynamics and demography of the Algerian mouse (Mus spretus), an open-land thermophilic Mediterranean small mammal. Change to a warmer and drier climate would facilitate the expansion of the species, whereas landscape change (forest encroachment following extensive land abandonment) would produce its retreat. We correlated abundance and demography parameters computed from captures obtained in 16 plots during a 10-years period (2008-2017; SEMICE small mammal monitoring) with climate, vegetation and land use change. Climate became warmer and dryer, and afforestation due to encroachment occurred in 81 % of plots. Expected positive effects of climate warming, derived from bioclimatic niche models, were counterbalanced by negative effects of both increasing hydric deficit and changes in vegetation and landscape structure. Abundance showed a slight but significant decline (-5 %). The species' range was more resilient to change, as shown by occupancy analyses, apparently due to strong local effects of vegetation structure on occupancy. This result highlighted that negative population trends would not necessarily produce range retractions. Simultaneously analysing both abundance trends and occupancy patterns may thus allow for deeper understanding and more accurate predictions of expected population trends in response to interacting global change drivers.

Seasonal changes in the expression of molecular markers of stallion germ cells

The economic impacts of infertility and subfertility of stallions greatly influence the horse breeding industry. Self-renewal and differentiation of spermatogonial stem cells are the initial processes to maintain an adequate sperm population. Thus, understanding these processes may provide useful information to reveal the causes and remedies of subfertile and infertile stallions. Stallions are seasonal breeders. About 50% of the sperm population is reduced during the non-breeding season (NBS) in stallions. The seasonal regulation of spermatogenesis renders stallions as ideal models to understand the process of sperm production. Furthermore, comparing internal and external factors related to spermatogenesis during the breeding season (BS) and NBS may provide a solution for subfertile/infertile stallions. It is especially pertinent to study the expression pattern of different protein markers during undifferentiated, differentiating, and differentiated spermatogonia. Deleted in azoospermia-like (DAZL), undifferentiated cell transcription factor 1 (UTF-1), and protein gene product 9.5 (PGP9.5) are the molecular markers expressed at different stages of spermatogenesis. However, whether the expression pattern of these molecular markers is similar throughout the year in stallion remains undetermined. The objectives of this study were to (1) investigate the expression pattern and localization of DAZL, UTF-1, and PGP9.5 within seminiferous tubules and (2) evaluate the relative mRNA levels of these three germ cell markers in stallion testes during BS and NBS. Immunohistochemistry was performed to check and compare the expression pattern and localization of DAZL, UTF-1, and PGP9.5 antibodies. Reverse transcription-quantitative PCR analysis was performed to calculate the relative mRNA expression levels in the testes. Testicular tissues from thoroughbred stallions were collected during routine castration that was carried out in field conditions. Immunostaining of germ cells with DAZL and UTF-1 in BS and NBS were not significantly different. However, the relative mRNA expression levels of DAZL and UTF-1 were significantly different in both groups. Interestingly, the immunolabeling and the relative mRNA expression of PGP9.5 were significantly different between BS and NBS. From these results, it is hypothesized that the expression level of these putative molecular markers might be gonadotropin-dependent in stallion testes.

Assessing the Effects of Landscape Change on the Occupancy Dynamics of the Greater White-Toothed Shrew Crocidura russula

Land-use change is the main driver of biodiversity loss in the Mediterranean basin. New socio-economic conditions produced a rewilding process so that cultural landscapes are being invaded by more natural habitats. We analyze the effects of landscape change on the demography and the spatial distribution of Crocidura russula in six protected areas of the western Mediterranean basin. The study was conducted in the period 2008–2020 on 19 live trapping plots representing the three main natural habitats of the area (scrubland, pinewood, and holm oak woodland). We used a multiscale approach to ensure that the scale of response matched landscape structure (from plot to landscape) using either vegetation profiles (LiDAR) and land use data obtained from years 2007 and 2017. Statistical models (multiple-season single-species occupancy models) showed that C. russula populations were strongly associated to habitat features at the plot level. These models were used to predict occupancy at sampling units for the whole study area (850 km²), showing contrasting trends that shifted at relatively small spatial scales (expansions and retractions of species ranges). Parks showing extreme scrubland encroachment (−8% of area) and afforestation (+6%) significantly reduced habitat suitability for shrews and reductions in occupancy (−5%). Results would indicate faster changes in the spatial distribution of the target species than previously expected on the basis of climate change, driven by fast landscape changes.

Cellular Modifications in Spermatogenesis during Seasonal Testicular Regression: An Update Review in Mammals

Simple Summary

The most common form of reproduction in mammals is seasonal reproduction. This ensures that offspring are born at the most suitable time for survival, due to the abundance of food and the optimal temperatures for early postnatal development. In males, one way to achieve this is to decrease or lose fertility over a given period. This loss is associated with a greater or lesser degree of spermatogenesis modification that affects both germ and Sertoli cells. This paper reviews the different cellular mechanisms that have been postulated in recent years to explain how the activity of the seminiferous epithelium decreases during the non-reproductive period.

Abstract

Testicular regression occurs during the non-breeding season in many mammals. This affects spermatogenesis, resulting in decreased or arrested activity. Both lead to a decrease or cessation in sperm production. In recent years, the cellular mechanisms that lead to infertility in males in non-reproductive periods have been studied in very different species of mammals. At the start of the present century, the main mechanism involved was considered as an increase in the apoptotic activity of germ cells during the regression period. The loss of spermatogonia and spermatocytes causes not only a decrease in spermatogenesis, but an arrest of the seminiferous epithelium activity at the end of regression. Recently, in some mammal species, it was found that apoptosis is the usual mechanism involved in epithelium activity arrest, although it is firstly atrophied by massive desquamation of the germ cells that are released from their binding with the Sertoli cells, and which are shed into the lumen of the seminiferous tubule. In other species, it has been shown that not only germ cell apoptosis, but also Sertoli cell apoptosis, including decreased proliferative activity, spermatophagy or autophagy, are involved in testicular regression. Furthermore, the most recent studies indicate that there are multiple patterns of seminiferous epithelium regression in seasonally breeding animals, which may not only be used by different species, but also by the same ones to reproduce in the best conditions, ensuring their survival. In conclusion, at this time, it is not possible to consider the existence of a paradigmatic cellular mechanism in the involution of the seminiferous epithelium applicable to all male mammals with seasonal reproduction, rather the existence of several mechanisms which participate to a greater or lesser extent in each of the species that have been studied to date.

Cell adhesion and immune response, two main functions altered in the transcriptome of seasonally regressed testes of two mammalian species

In species with seasonal breeding, male specimens undergo substantial testicular regression during the nonbreeding period of the year. However, the molecular mechanisms that control this biological process are largely unknown. Here, we report a transcriptomic analysis on the Iberian mole, Talpa occidentalis, in which the desquamation of live, nonapoptotic germ cells is the major cellular event responsible for testis regression. By comparing testes at different reproductive states (active, regressing, and inactive), we demonstrate that the molecular pathways controlling the cell adhesion function in the seminiferous epithelium, such as the MAPK, ERK, and TGF-β signaling, are altered during the regression process. In addition, inactive testes display a global upregulation of genes associated with immune response, indicating a selective loss of the "immune privilege" that normally operates in sexually active testes. Interspecies comparative analyses using analogous data from the Mediterranean pine vole, a rodent species where testis regression is controlled by halting meiosis entry, revealed a common gene expression signature in the regressed testes of these two evolutionary distant species. Our study advances in the knowledge of the molecular mechanisms associated to gonadal seasonal breeding, highlighting the existence of a conserved transcriptional program of testis involution across mammalian clades.

Habitat Suitability for Small Mammals in Mediterranean Landscapes: How and Why Shrubs Matter

Fires are usually seen as a threat for biodiversity conservation in the Mediterranean, but natural afforestation after abandonment of traditional land uses is leading to the disappearance of open spaces that benefit many species of conservation interest. Fires create open habitats in which small mammals can live under more favourable conditions, such as lower predation, interspecific competition, and higher food availability. We analysed the role of changes in shrub cover and shrub preference by small mammals along the Mediterranean post-fire succession. We used data (period 2008–2018) from 17 plots woodlands and post-fire shrublands present in the study area (Barcelona’s Natural Parks, Catalonia, NE Spain), and vegetation structure was assessed by LiDAR technology for modelling ground-dwelling small mammal preferences. The diversity, abundance, and stability of Mediterranean small mammal communities negatively responded to vegetation structural complexity, which resulted from the combined effects of land abandonment and recovery after wildfires. We suggest that biotic factors such as vegetation profiles (providing food and shelter) and their interaction with predators and competitors could be responsible for the observed patterns. Considering the keystone role of small mammals in the sustainability of Mediterranean forest, our results could be useful for management under the current global change conditions.

Sex Hormones in Hemolymph of Red King Crabs from the Barents Sea

Simple Summary

Well-known sex hormones, testosterone and 17β-estradiol, play a crucial role in the reproduction of vertebrates. Biochemical assays have detected these substances in a few crustaceans, and it has been hypothesized that these hormones are involved in the regulation of crustacean reproduction. Red king crab is a large commercially important species harvested both in their native areas (North Pacific) and in the area of its introduction (Barents Sea). The presence of 17β-estradiol and testosterone and fluctuations of their concentrations in relation to different factors have not yet been investigated. For this reason, we provided a pilot study to reveal the levels of sex hormones in hemolymph of red king crabs captured in the coastal Barents Sea. These hormones were detected in the crabs and we compared our data with previously published data involving a wide range of crustaceans. We found seasonal variations in the level of testosterone with the maximum in the spawning period. Our data expand the current knowledge about the red king crab physiology and may be used for the development of its aquaculture.

Abstract

The presence of vertebrate-related steroid sex hormones has been reported in both freshwater and marine crustaceans. However, despite the commercial importance of king crabs, many aspects of their endocrinology are still unknown. For this reason, we examined hemolymph samples of the red king crab Paralithodes camtschaticus from the Barents Sea population for the presence of testosterone and 17β-estradiol using radioimmunoassay. The mean testosterone concentration was 0.46 ± 0.04 (range 0.08–1.39) ng mL^–1, whereas the mean 17β-estradiol concentration was 1248.9 ± 91.4 (range 217.7–4100.1) pg mL^–1. In general, the levels of 17β-estradiol and testosterone in red king crabs were higher than reported for the hemolymph of amphipods, crabs, and shrimps from warm and temperate waters, probably because the king crabs analyzed were larger and heavier than the other crustaceans. The concentrations of sex steroids did not differ significantly between males and females and between immature and mature red king crabs. Seasonal variations in the level of testosterone with the maximum value in the spawning period (May) indicate a potential role of the sex hormones in the maturation and reproduction processes of red king crab. Taking into account the slow growth rate in P. camtschaticus, our data could be useful not only for further physiological studies but also for the development of reliable techniques for red king crab aquaculture.

Mediterranean Pine Vole, Microtus duodecimcostatus: A Paradigm of an Opportunistic Breeder

Simple Summary

In temperate zones of the Earth, some mammalian species reproduce seasonally whereas others do it continuously. Other species are summer breeders in the north and winter breeders in the south. Thus, the reproductive pattern seems not to be a species-specific but a population-specific trait. We investigated the reproduction pattern of the Mediterranean pine vole, Microtus duodecimcostatus, in the area around the city of Granada in Southern Spain, and found that individuals living in wastelands reproduce seasonally whereas those living in close poplar plantations (just 8 km apart) reproduce throughout the year, as did voles captured in wastelands and kept in captivity. These animals represent thus a paradigm of an opportunistic breeder as particular individuals stop breeding or not, depending on the environmental conditions they face at any moment. Sexually inactive male voles undergo complete testis inactivation and their sperm production is halted. The immune system in active testes is depressed, a phenomenon known as “immune privilege” that protect germ cells from autoimmune attack. We studied gene activity in active and inactive testes and our results indicate that such an immune privilege is lost in inactive testes, suggesting an important role for this process during testis regression.

Abstract

Most mammalian species of the temperate zones of the Earth reproduce seasonally, existing a non-breeding period in which the gonads of both sexes undergo functional regression. It is widely accepted that photoperiod is the principal environmental cue controlling these seasonal changes, although several exceptions have been described in other mammalian species in which breeding depends on cues such as food or water availability. We studied the circannual reproductive cycle in males of the Mediterranean pine vole, Microtus duodecimcostatus, in the Southeastern Iberian Peninsula. Morphological, hormonal, functional, molecular and transcriptomic analyses were performed. As reported for populations of other species from the same geographic area, male voles captured in wastelands underwent seasonal testis regression in summer whereas, surprisingly, those living either in close poplar plantations or in our animal house reproduced throughout the year, showing that it is the microenvironment of a particular vole subpopulation what determines its reproductive status and that these animals are pure opportunistic, photoperiod-independent breeders. In addition, we show that several molecular pathways, including MAPK, are deregulated and that the testicular “immune privilege” is lost in the inactive testes, providing novel mechanisms linking seasonal testosterone reduction and testis regression.