A differential response in the reproductive system and energy balance of spiny mice Acomys populations to vasopressin treatment

The African spiny mouse ( Acomys spp.) as an emerging model for development and regeneration

The African spiny mouse ( Acomys spp.) is an emerging animal model with remarkable biological characteristics that make it a subject of interest for a broad range of research fields. Typically a desert species adapted to a low-calorie diet, spiny mice develop diabetes-related symptoms when switched to high-energy diets. Spiny mice undergo relatively long gestation periods and have small litters of highly developed pups, making them an adequate model for late organogenesis and perinatal biology. Recently, they have been shown to have remarkable healing and regeneration capabilities, which make them unique among mammals. In this work, we describe our experience in housing a colony of African spiny mice and cover all basic aspects of feeding, maintenance and breeding for research purposes.

Characterizing the reproductive transcriptomic correlates of acute dehydration in males in the desert-adapted rodent, Peromyscus eremicus

BACKGROUND

The understanding of genomic and physiological mechanisms related to how organisms living in extreme environments survive and reproduce is an outstanding question facing evolutionary and organismal biologists. One interesting example of adaptation is related to the survival of mammals in deserts, where extreme water limitation is common. Research on desert rodent adaptations has focused predominantly on adaptations related to surviving dehydration, while potential reproductive physiology adaptations for acute and chronic dehydration have been relatively neglected. This study aims to explore the reproductive consequences of acute dehydration by utilizing RNAseq data in the desert-specialized cactus mouse (Peromyscus eremicus).

RESULTS

We exposed 22 male cactus mice to either acute dehydration or control (fully hydrated) treatment conditions, quasimapped testes-derived reads to a cactus mouse testes transcriptome, and then evaluated patterns of differential transcript and gene expression. Following statistical evaluation with multiple analytical pipelines, nine genes were consistently differentially expressed between the hydrated and dehydrated mice. We hypothesized that male cactus mice would exhibit minimal reproductive responses to dehydration; therefore, this low number of differentially expressed genes between treatments aligns with current perceptions of this species' extreme desert specialization. However, these differentially expressed genes include Insulin-like 3 (Insl3), a regulator of male fertility and testes descent, as well as the solute carriers Slc45a3 and Slc38a5, which are membrane transport proteins that may facilitate osmoregulation.

CONCLUSIONS

These results suggest that in male cactus mice, acute dehydration may be linked to reproductive modulation via Insl3, but not through gene expression differences in the subset of other a priori tested reproductive hormones. Although water availability is a reproductive cue in desert-rodents exposed to chronic drought, potential reproductive modification via Insl3 in response to acute water-limitation is a result which is unexpected in an animal capable of surviving and successfully reproducing year-round without available external water sources. Indeed, this work highlights the critical need for integrative research that examines every facet of organismal adaptation, particularly in light of global climate change, which is predicted, amongst other things, to increase climate variability, thereby exposing desert animals more frequently to the acute drought conditions explored here.

Arginine vasopressin plasma levels change seasonally in African striped mice but do not differ between alternative reproductive tactics

Arginine vasopressin (AVP) is an important hormone for osmoregulation, while as a neuropeptide in the brain it plays an important role in the regulation of social behaviors. Dry habitats are often the home of obligately sociable species such as meerkats and Damaraland mole-rats, leading to the hypothesis that high plasma AVP levels needed for osmoregulation might be associated with the regulation of social behavior. We tested this in a facultative sociable species, the African striped mouse (Rhabdomys pumilio). During the moist breeding season, both solitary- and group-living reproductive tactics occur in this species, which is obligatory sociable in the dry season. We collected 196 plasma samples from striped mice following different reproductive tactics both during the moist and the dry season. Solitary mice did not have lower AVP levels than sociable mice, rejecting the hypothesis that peripheral AVP is involved in the regulation of alternative reproductive tactics. However, we found significantly higher AVP levels during the dry season, with AVP levels correlated with the abundance of food plants, the main source of water for striped mice. Plasma AVP levels were not correlated with testosterone or corticosterone levels. Our study underlines the important role that AVP plays in osmoregulation, particularly for a free ranging mammal living under harsh arid conditions.

A comparative study of reproductive and metabolic responses to administration of exogenous melatonin and aldosterone in xeric and mesic spiny mice populations

A comparative study of reproduction revealed differences between desert-adapted Acomys russatus and Mediterranean Acomys cahirinus populations with respect to the environmental cues used for reproductive activity. Long day (LD) conditions were noted as initial reproductive cue for both populations. This research is a follow-up affects comparative endocrine and metabolic study in regards to reproduction where LD-acclimated mice were treated with, exogenous aldosterone (ALDO) and melatonin (MLT). Only the reproductive system of A. russatus females was significantly affected by both hormones. In A. cahirinus females, MLT decreased leptin levels, while in A. russatus, a treatment with both hormones increased leptin levels. In A. russatus males, MLT affects both reproductive and metabolic functions. However, in A. cahirinus males, ALDO and MLT treatments caused an increase in leptin levels, and a decrease in free fatty acid (FFA) levels, respectively. Correlations between leptin and FFA in general were affected by both MLT and ALDO treatments in A. russatus males and A. cahirinus females. Our results support the general idea, that although the reproductive system of A. russatus responded to an osmotic stress, in our case expressed by ALDO treatment, which can be considered as an ultimate signal, where, photoperiod changes are an initial signal.

Long-day photoperiod interacts with vasopressin and food restriction to modulate reproductive status, and vasopressin receptor expression of male Golden spiny mice

We tested the effects of photoperiod, water and food availability on body-mass, reproductive status, and vasopressin mRNA receptor 1a (Avpr1a) expression in males of desert-adapted golden spiny mice, Acomys russatus. In experiment 1, Males were acclimated to short-day (SD; 16D:8L) or long-day (LD; 8D:16L) with either saline (control) or vasopressin treatment for three weeks. The results of this experiment revealed that under control conditions, SD-mice increased body-mass by ~5% while LD-mice decreased it by ~4%. SD had no effect on reproductive status and leptin levels, whereas LD-males increased testes mass and serum testosterone, but had no effect on leptin levels. Vasopressin administration decreased LD-induced reproductive enhancement. Since no consistent effect of SD treatment was found on reproductive status, experiment 2 was carried out only on LD-acclimated males kept under 75% food restriction from ad libitum, with saline or leptin treatment. Body-mass, testes mass, serum testosterone, leptin concentrations, and Avpr1a mRNA expression, were measured. Food restriction remarkably decreased body-mass with more potent effect in leptin-treated males showing enhanced reproductive status and significant increase in serum leptin compared with controls. Avpr1a expression was significantly up-regulated in LD, vasopressin, and food restricted males, with higher hypothalamic levels compared with testes. We conclude that in A. russatus LD-photoperiod interacts with water and food availability to advance reproductive responses. Avpr1a is suggested to integrate nutritional and osmotic signals to optimize reproduction by modulating reproductive and energetic neuroendocrine axes at the central level. The interaction between photoperiod and other environmental cues is of an adaptive value to desert-adapted small rodents for timing reproduction in unpredicted ecosystems as extreme deserts.

Effects of photoperiod and food restriction on the reproductive physiology of female California mice

Many temperate-zone animals use changes in photoperiod to time breeding. Shorter term cues, like food availability, are integrated with photoperiod to adjust reproductive timing under unexpected conditions. Many mice of the genus Peromyscus breed in the summer. California mice (Peromyscus californicus), however, can breed year round, but tend to begin breeding in the winter. Glial cells may be involved in transduction of environmental signals that regulate gonadotrophin releasing hormone I (GnRH) activity. We examined the effects of diet and photoperiod on reproduction in female California mice. Mice placed on either short days (8L:16D) or long days (16L:8D) were food restricted (80% of normal intake) or fed ad libitum. Short day-food restricted mice showed significant regression of the reproductive system. GnRH-immunoreactivity was increased in the tuberal hypothalamus of long day-food restricted mice. This may be associated with the sparing effect long days have when mice are food restricted. The number of GFAP-immunoreactive fibers in proximity to GnRH nerve terminals correlated negatively with uterine size in ad libitum but not food restricted mice, suggesting diet may alter glial regulation of the reproductive axis. There was a trend towards food restriction increasing uterine expression of c-fos mRNA, an estrogen dependent gene. Similar to other seasonally breeding rodents, short days render the reproductive system of female California mice more susceptible to effects of food restriction. This may be vestigial, or it may have evolved to mitigate consequences of unexpectedly poor winter food supplies.

Photoperiodicity and increasing salinity as environmental cues for reproduction in desert adapted rodents

Understanding the ways environmental signals, regulate reproduction and reproductive behavior of desert adapted rodents is a major gap in our knowledge. In this study, we assessed the roles of photoperiod and diet salinity, as signals for reproduction. We challenged desert adapted common spiny mice, Acomys cahirinus, males and females with osmotic stress, by gradually increasing salinity in their water source - from 0.9% to 5% NaCl under short and long days (SD and LD, respectively). Photoperiodicity affected testosterone levels, as under LD-acclimation, levels were significantly (p<0.05) higher than under SD-acclimation. Salinity treatment (ST) significantly reduced SD-acclimated male body mass (W(b)) and testis mass (p<0.005; normalized to W(b)). ST-LD-females significantly (p<0.005) decreased progesterone levels and the numbers of estrous cycles. A reduction in white adipose tissue (WAT) to an undetectable level was noted in ST-mice of both sexes under both photoperiod regimes. Receptors for vasopressin (VP) and aldosterone were revealed on testes of all male groups and on WAT in control groups. Our results suggest that photoperiod serves as an initial signal while water availability, expressed by increased salinity in the water source, is an ultimate cue for regulation of reproduction, in both sexes of desert-adapted A. cahirinus. We assume that environmental changes also affect behavior, as water seeking behavior by selecting food items, or locomotor activity may change in extreme environment, and thus indirectly affect reproduction and reproductive behavior. The existence of VP and aldosterone receptors in the gonads and WAT suggests the involvement of osmoregulatory hormones in reproductive control of desert adapted rodents.

Physiological adaptations of small mammals to desert ecosystems

Adaptations of animals to the xeric environment have been studied in various taxonomic groups and across several deserts. Despite the impressive data that have been accumulated, the focus in most of these studies is mainly on the significance of one variable at a time. Here, we attempt to integrate between responses of several physiological systems, challenged by increasing diet and water salinity and extreme temperatures, acquired in different studies of thermo and osmo-regulatory adaptations, of small rodents, to the xeric environment. Studies have shown differential thermoregulatory responses to increased dietary salinity, which were attributed to habitat and habits of the relevant species. In the thermoregulatory studies, a potential adaptive significance of low metabolic rate was demonstrated. From an evolutionary point of view, the most important adaptation is in the timing of reproduction, as it enables the transfer of genetic properties to the next generation in an unpredictable ecosystem, where reproduction might not occur every year. Results in this aspect show that increased dietary salinity, through an increase in vasopressin plasma levels, plays an important role as a regulator of the reproductive system. We assume that the amount of food existing in the habitat and the amount of reserves in the animal in the form of white adipose tissue are important for reproduction. Photoperiod affects all studied physiological responses, emphasizing the importance of pre-acclimation to seasonal characteristics. We summarize the existing data and suggest neuro-endocrine pathways, which have a central role in these adaptations by affecting thermoregulation, osmoregulation and reproduction to create the optimal response to xeric conditions. These hypotheses can be used as the basis for future studies.

Photoperiod interacts with food restriction in performance in the Barnes maze in female California mice

Food restriction has been reported to have positive effects on cognition. This study examines how another environmental factor, daylength, can alter the impact of food restriction on the brain and behavior. Female California mice (Peromyscus californicus), housed on either long days (16 h of light and 8 h of darkness) or short days (8 h of light and 16 h of darkness), were restricted to 80% of their normal baseline food intake or provided with food ad libitum. Testing in a Barnes maze revealed that the effects of food restriction depended on photoperiod, and that these effects differed for acquisition vs. reversal learning. During acquisition testing, food restriction increased latency to finding the target hole in short-day mice but not in long-day mice. In reversal testing, food restriction decreased latency to finding the target hole in long-day mice but not in short-day mice. Latency to finding the hole was positively and independently correlated with both errors and time spent freezing, suggesting that changes in both spatial learning and anxiety-like behavior contributed to performance. Short days increased hippocampal expression of the synaptic protein, synapsin I, which was reversed by food restriction. Short days also reduced plasma corticosterone levels, but diet had no effect. There was no effect of diet or photoperiod on hippocampal expression of the glial marker, glial fibrillary acidic protein. The present findings suggest that, in female California mice, the differential effects of food restriction on acquisition and reversal learning are photoperiod-dependent. These results justify further testing of the relationship between food restriction and hippocampal synapsin I in the context of spatial learning.