Reproduction In Small Mammals Research Articles

Overview of Hantavirus Infections in the World, the Epidemiological Situation on Hemorrhagic Fever with Renal Syndrome in the Russian Federation in 2021, and Forecast for 2022

The paper presents a description of the epidemiological situation on Hantavirus infection incidence in the countries around the world. Comparative analysis of the intensity and dynamics of the epidemiological process of hemorrhagic fever with renal syndrome (HFRS) in the Russian Federation by Federal Districts in 2021 has been carried out and forecast of the HFRS incidence for 2022 prepared. The study has revealed that tense situation on incidence of hantavirus diseases was observed in the world in 2021. On the territory of the Russian Federation, there was a decrease in the HFRS incidence in 2021 (by 1.7 times compared to 2020). However, the results of epidemiological analysis of the HFRS incidence, epizootiological data and laboratory studies in certain Federal Districts of the Russian Federation indicate that the epidemiological situation on HFRS remains tense. High risk of HFRS infection is predicted in a number of regions of the country due to the favorable natural and climatic conditions in the winter period of 2021–2022 with a heavy snow cover, which contributed to the under-snow reproduction of small mammals, the main carriers of HFRS. The presence of infected rodents testifies to a high likelihood of complication of the epidemiological situation in areas of increased epidemic risk of HFRS.

Seasonality and climatic control of reproduction in wild-caught female Lesser Egyptian jerboa (Jaculus jaculus) from central Saudi Arabia

In arid regions, unpredictable rainfall patterns and extreme temperature variation occurs; this poses severe constraints on reproduction in small mammals. In the present study, the gonad morphometrics, gonadal histology and endocrine profiles of the female Lesser Egyptian jerboas (Jaculus jaculus) were studied over one year in a wild population from central Saudi Arabia. An unusual rainfall pattern occurred during this study period, with three out of four seasons receiving rainfall. Pregnant females were observed during every season when rainfall fell. Yet, a distinct reproduction pattern was also observed in the reproductive parameters of J. jaculus, likely entrained by ambient temperature and photoperiodic changes, with indicators of reproductive activity being at its highest during the winter months. Jaculus jaculus, appear to possess an endogenous circannual rhythm (seasonality) of breeding, entrained by ambient temperature and photoperiod. However, they have a plasticity to their breeding strategy, which allows them to breed opportunistically. As global warming takes effect, many species which currently inhabit temperate regions may experience desertification. Understanding how species that inhabit deserts today are adapted to these harsh conditions may allow researchers to identify temperate species that are more at risk to climatic changes due to global warming.

The pattern of reproduction in the Libyan jird (Meriones libycus; Rodentia: Muridae) from central Saudi Arabia in the absence of rainfall

The reproductive pattern of the Libyan jird (Meriones libycus Lichtenstein, 1823) from central Saudi Arabia was investigated in the absence of rainfall. In this study, body mass, morphometry of the reproductive tract, the histology of the reproductive organs, and the hormone concentrations of males and females were studied over 12 consecutive months in a wild population of the Libyan jird from central Saudi Arabia. Previous studies have found the breeding season of the Libyan jird from the Sahara desert of Algeria to occur during the wet months of spring. In the absence of rainfall, temperature and photoperiod were found to be important activators of reproductive activity. The cooler temperatures and shorter days of winter triggered the onset of ovulation in females and increased testes size and seminiferous tubule diameter in males. Only two pregnancies were found during the sampling period, which occurred during the cooler winter and early spring and coincided with a rise in plasma progesterone concentration in females. The Libyan jird was found to shift its breeding to the cooler months of winter in the absence of rainfall. This study strengthens the findings that changes in rainfall and temperature in dry deserts are critical cues for the onset of reproduction in small mammals.

The effects of food and parasitism on reproductive performance of a wild rodent.

Food and parasitism can have complex effects on small mammal reproduction. In this study, we tested the effects of sex, food, and parasitism on reproductive performance of the Taiwan field mouse (Apodemus semotus). In a field experiment, we increased food availability for a portion of the mice in the population by providing sorghum seeds to a set of food stations. We reduced parasite intensity of randomly chosen mice through ivermectin treatment. We determined the number and quality of offspring for the mice using paternity analysis. We quantified seed consumption with stable carbon isotope values of mouse plasma and parasite intensity with fecal egg counts of intestinal nematodes and cestodes (FEC). In a laboratory experiment, we reduced parasite intensity of randomly chosen mice through ivermectin treatment. We quantified their immune functions by total white blood cell count, percent granulocyte count, and percent lymphocyte count through hematological analyses. We measured the FEC and energy intake of the mice. From the field experiment, the number of offspring in A. semotus increased with increasing seed consumption. Due to the trade‐off between number and quality of offspring, the offspring quality decreased with increasing seed consumption for the females. The ivermectin treatment did not affect offspring number or quality. However, the FEC was positively correlated with number of offspring. In the laboratory experiment, the percent lymphocyte/granulocyte count changed with parasite intensity at low energy intake, which was relaxed at high energy intake. This study demonstrated positive effects of food availability and neutral effects of parasitism on A. semotus reproduction. However, the benefits of food availability for the females need to take into account the offspring number–quality trade‐off, and at high infection intensity, parasitism might negatively affect offspring quality for the males. We suggest that food availability could mediate the relationships between parasite intensity and immune responses.

The reproductive biology of the Ethiopian hedgehog, Paraechinus aethiopicus, from central Saudi Arabia: The role of rainfall and temperature

We set out to test whether the Ethiopian hedgehog, Paraechinus aethiopicus is a seasonal or aseasonal breeder and assess which environmental cues bring about both reproductive recrudescence and its subsequent regression. In this study, the body mass, morphometry of the reproductive tract the histology of the reproductive organs and the hormone concentrations of males and females were studied over 12 consecutive months in a wild population of the Ethiopian hedgehog from central Saudi Arabia. Using these data we investigated the potential proximate environmental cues that may trigger the onset of reproduction. Temperature is important for the initial activation of the males by bringing about an increase in testosterone concentration. In female hedgehogs the first rains trigger the onset of reproductive activation with ovulation. In turn increased temperature brings about the final activation of the males with increased testes size and seminiferous tubule diameter. Pregnancies were first recorded in early spring and summer coinciding with a rise in plasma progesterone concentration that peaked in spring. The Ethiopian hedgehog was found to exhibit marked seasonal reproduction. This study strengthens the findings that changes in rainfall and temperature in the Middle East are crucial cues for the onset of reproduction in small mammals.

Effects of climate change on the reproduction and offspring sex ratio of plateau pika (Ochotona curzoniae) on the Tibetan Plateau

Exploring animals’ responses to climate change will improve our understanding of the ecological consequences of such a phenomenon. As the “third pole” of the earth, the Tibetan Plateau is sensitive to climate change. To explore the effects of climate change on the reproduction of small mammals in an arid environment, we tested the reproduction of a native species, plateau pika (Ochotona curzoniae), from 2005 to 2009 in Dawu, which is located east of the Tibetan Plateau. The breeding season of this population maintained a stable onset date, but the length of breeding season varied from 53 to 84 days. The April temperature and spring precipitation positively affected the length of the breeding season. The offspring sex ratio was female biased except in 2009, whereas the ratio of recruits per reproductive female (RRF) ranged from 2.7 to 4.4. The April temperature and the normalized difference vegetation index (NDVI) in June positively affected the offspring sex ratio, whereas the precipitation in cold seasons and May NDVI positively affected the RRF. Therefore, increased temperature, precipitation, and NDVI may extend the length of the breeding season, increase the sex ratio, and produce more offspring recruits.

Seasonal reproduction in the Arabian spiny mouse, Acomys dimidiatus (Rodentia: Muridae) from Saudi Arabia: The role of rainfall and temperature

In deserts where unpredictable rainfall arises and a large variation in temperature occurs, this poses severe energetic and water related constraints on reproduction in small mammals and makes the use of photoperiod as cue for reproduction unreliable. In the present study, the gonad morphometrics, gonadal histology and endocrine profiles of the Arabian spiny mouse (Acomys dimidiatus) were studied over 12 consecutive months in a field population from western Saudi Arabia in an attempt to assess the seasonality of reproduction and gain insights into the environmental cues that may trigger reproduction in this species. Although sperm was present throughout the year, most reproductive parameters exhibited a seasonal pattern with a minimum in winter in both sexes and pregnancies were observed from spring to autumn. Whereas testes volume, the number of corpora lutea and progesterone levels were correlated with temperature, all other reproductive parameters were correlated with rainfall. Thus, it appears that A. dimidiatus ceases to breed during winter and uses rainfall as an environmental cue to initiate reproduction in the study area. However, the species appears to have the ability to reproduce throughout the year, if favourable conditions arise.

Biotopic distribution, population structure, and some features of small mammal reproduction in Chisinau City

Comparative analysis of species composition, biotopic distribution, population structure, and reproduction of rodents and insectivores in Chisinau City was performed in October–November 2008 (3029 traps days, 715 animals). Sylvaemus sylvaticus appeared to be the most numerous and widely distributed species, the reproductive strategy of which consisted of intense reproduction in the summer. The second most abundant species was Microtus rossiaemeridionalis, which had a different reproductive strategy, with part of its population continuing to reproduce actively in the autumn. Urban woodlands are the most close to natural biotopes by the species composition. The highest number of animals was defined for meadows and gardens. No rodents and insectivores are found on lawns and waste grounds.

The physiological costs of reproduction in small mammals

Life-history trade-offs between components of fitness arise because reproduction entails both gains and costs. Costs of reproduction can be divided into ecological and physiological costs. The latter have been rarely studied yet are probably a dominant component of the effect. A deeper understanding of life-history evolution will only come about once these physiological costs are better understood. Physiological costs may be direct or indirect. Direct costs include the energy and nutrient demands of the reproductive event, and the morphological changes that are necessary to facilitate achieving these demands. Indirect costs may be optional 'compensatory costs' whereby the animal chooses to reduce investment in some other aspect of its physiology to maximize the input of resource to reproduction. Such costs may be distinguished from consequential costs that are an inescapable consequence of the reproductive event. In small mammals, the direct costs of reproduction involve increased energy, protein and calcium demands during pregnancy, but most particularly during lactation. Organ remodelling is necessary to achieve the high demands of lactation and involves growth of the alimentary tract and associated organs such as the liver and pancreas. Compensatory indirect costs include reductions in thermogenesis, immune function and physical activity. Obligatory consequential costs include hyperthermia, bone loss, disruption of sleep patterns and oxidative stress. This is unlikely to be a complete list. Our knowledge of these physiological costs is currently at best described as rudimentary. For some, we do not even know whether they are compensatory or obligatory. For almost all of them, we have no idea of exact mechanisms or how these costs translate into fitness trade-offs.

Introduction. Adaptation to the annual cycle

Most large organisms have an annual routine; that is to say they schedule activities in a regular way over the year. Like any behaviour, annual routines can be explained in terms of either their causation or their contribution to reproductive success, that is their evolutionary function. Previous

Effects of Thinning on Small Mammals in Oregon Coastal Forests

Because of fires and intensive logging practices, young forest stands dominate much of the landscape of the Pacific Northwest. Most young stands were reforested with Douglas-fir (Pseudotsuga menzeisii) trees at high densities. Researchers have proposed thinning of the densely stocked young stands as a means to improve habitats for vertebrates. However, effects of thinning intensity on forest-floor small mammals are not well understood. During 1994-1996, we conducted experimental and retrospective studies using pitfall trapping to assess effects of thinning intensity on abundance and reproduction of small mammals in Douglas-fir forests of the Oregon Coast Range, USA. In the experimental study, we assessed the short-term effects of thinning stands to moderate and to low tree densities on small mammals during the first 2 years following thinning. In the retrospective study, we assessed potential long-term effects of thinning by comparing relative abundance and reproductive performance of small mammals in previously thinned (7-24 years prior to the study) and unthinned stands. Among the 12 species of small mammals we examined in the experimental study, number of captures increased for 4 species and decreased for 1 within 2 years of thinning. However, responses were similar between moderately and heavily thinned stands. Among the 9 species we examined in the retrospective study, number of captures was greater for 5 species and lower for none in previously thinned than in unthinned stands. Furthermore, total number of small mammals captured was higher in previously thinned than in unthinned stands. Effects of thinning on 2 species, creeping voles (Microtus oregoni) and Pacific jumping mice (Zapus trinotatus), were consistent in the short and long term. The number of captures for both species increased in the first 2 years following thinning and was greater in stands thinned 7-24 years previously than unthinned stands. Number of western red-backed voles (Clethrionomys californicus) captured decreased within 2 years of thinning but was similar in stands thinned 7-24 years previously and in unthinned stands. Reproductive performances of deer mice (Peromyscus maniculatus) and creeping voles improved following thinning in the short term. In the retrospective study, reproductive performance of western red-backed voles was higher in thinned than in unthinned stands. Overall, thinning did not have substantial detrimental effects on any of the species we investigated and had positive effects on several. We suggest that thinning is a viable option to enhance habitat quality for several species of forest-floor small mammals in densely stocked, young Douglas-fir stands.

Effects of Tall Fescue Endophyte Infection and Population Density on Growth and Reproduction in Prairie Voles

The fungal endophyte (Neotyphodium coenophialum) infecting tall fesene grass (Festuca arundiuacea) can produce adverse effects when consumed by herbivores, Becent laboratory studies have produced conflicting results on effects of the endophyte on growth and reproduction of small mammals. We compared the growth and reproductive condition of prairle voles (Microtus ochrogaster) on plots of endophyte-infected and uninfected fescue to determine the effects of the endophyte under field conditions. Populations of voles on endophyte-infected plots exhibited a skewed sex ratio at low population densities. As densities increased in the second year of the study the sex ratios equalized on all grids, but female voles on the infected plots exhibited greater weights at sesxual maturity. Greater weight at sexnal maturity could be due to either a change in growth. rate or a change in the timing of reproductive maturation. No differences in the growth rates of voles were found, suggesting that the endophyte may delay the onset of sexual maturity in wild rodents.

Impact of photoperiod and melatonin on reproduction in small mammals

Our present view of the function(s) of the pineal gland has been derived primarily from a comparative approach using several small rodent species which show pronounced seasonal reproductive cycles. Although it had been known for several decades that these seasonal reproductive cycles are controlled by the photoperiod, the idea of a functional link between the pineal gland and mammalian photoperiodism in general, developed slowly. Today it is well established that the pineal gland and one of its compounds, namely melatonin, convey the photoperiodic message. The gonadotropic effect(s) of the pineal gland and of melatonin certainly are of major importance for an adequate adaptation of the animals to a seasonally changing environment. However, photoperiod not only has a strong impact on the reproductive system, but also on many other organs and physiological functions. All functions which appear to be controlled by the photoperiod can be influenced by modifying the output signal of the pineal gland, i.e. melatonin. The major importance of the pineal organ in small mammals seems to be the precise temporal and sequential coordination of all of these functions, in order to meet the varying energetic demands of the different seasons.

Ecology of Small Mammals in Coastal Heathland at Anglesea, Victoria

Aspects of ecology and reproduction of small mammals in a heathland community near Anglesea were investigated in the field by means of mark-recapture trapping. Population size, animal movements and reproductive state were estimated. The floristic and structural habitat preferences were also determined. The most common species were Antechinus stuartii, A. minimus maritimus, Sminthopsis leucopus, Rattus fuscipes assimilis and R. lutreolus. For Antechinus the populations were maximal throughout February-June (A. stuartii) and December-June (A. minimus) inclusive. A marked decline in numbers of Antechinus during late winter and early spring was associated with the total loss of males from the population. The maximal numbers of animals (per hectare) were 21 (A. stuartii), 14 (A. m. maritimus), 14 (R. f. assimilis) 7 (R. lutreolus), and 8 (S. leucopus). Young were born to A. m. maritimus during August, and 1 month later to A. stuartii. R. f. assimilis bred during late winter and spring, and S. leucopus from September to November. None of the species showed an overall preference for any floristic or structural vegetation type. This study confirms male 'die-off' in A. m. maritimus. The data also indicate that the difference in breeding times of A. m. maritimus between Anglesea and Dartmoor, Vic., is due to climatic or habitat differences rather than to sympatry with A. stuartii.

Relationship between feeding habits, climate and reproduction of small mammals in Meru National Park, Kenya

SummaryThe relationship between rainfall, temperature, diet, and breeding activity was investigated in Acomys percivali Dollman, A. wilsoni Thomas, Tatera nigricauda (Peters), and Elaphantulus rufescens (Peters), inhabiting a semi‐arid region of central Kenya. Insects formed the major resource base of all four species. There was little variation in the food habits of Elephantulus during the year, but the diets of the other three species showed predictable seasonal changes. Insects were the major food item during the dry seasons, and seeds were most frequently consumed during the month‐long period after the end of the rains. Tatera also showed a significant increase in consumption of plant stem and leaf material during the rains. Tatera exhibited the most pronounced seasonal changes in food habits and also had a pronounced seasonal pattern of breeding activity. The other three species showed less seasonal variation in food habits and no detectable seasonal variation in breeding activity. However, the dichotomy of seasonal v. continuous breeding was also associated with the dichotomy of altricial v. precocial young, and so the results are equivocal. Other evidence suggests that the inhibition of breeding during the dry season may be more related to the increase in temperature.RésuméLes relations entre les chutes de pluie, la température, les régimes alimentaires et les activités de reproduction de Acomys percivali Dollman, A. wilsoni Thomas, Tatera nigricauda (Peters) et Elephantulus rufescens (Peters) ont étéétudiés dans une région semi‐aride du Kenya. Les insectes forment la base des ressources pour toutes ces espèces. II y a peu de variations dans le régime alimentaire de Elephantulus au long de l'année mais celui des trois autres espèces présente des variations saisonnières prévisibles. Les insectes constituent la nourriture principale durant les saisons sèches et les graines sont plus fréquemment consommées durant une longue période après la fin des pluies. Tatera manifeste les changements saisonniers de comportement alimentaire et une période d'activité reproductrice saisonnière. Les trois autres espèces présentent moins de variation saisonnière dans leur régime alimentaire et aucune variation saisonnière décelable dans l'activité reproductrice. Cependant la dichotomie entre reproduction continue ou saisonnière est aussi associéà la dichotomie jeunes tardifs ou précoces. Les résultats sont donc équivoques. Une autre évidence suggère que l'inhibition de la reproduction durant la saison sèche peut être davantage en relation avec l'augmentation de la température.

Studies on the pelvis in British Muridae and Cricetidae (Rodentia)

The morphology and its variation of the bony pelvis in British species of Muridae and Cricetidae have been studied. The investigation began with the application of a mensural method for demonstrating sexual dimorphism and it is shown that for all species except those of Rattus the male os coxa can be distinguished from the female over a wide range of ages. During the study it became obvious that there are ranges of morphological variation in os coxae both inter‐ and intraspecific. There are constant interpecific differences which allow identification of os coxae of these rodents at least to genus and in many cases to species. Detailed descriptions of the morphology of the os coxa of each species are given together with an identification key. Intraspecific variation is mainly sex‐dependent and comprises sexual dimorphism, male pubertal changes and female parturition changes. The changes in the male are from epicene, through pubertal, to post‐pubertal phase, with the first of these resembling the agonadal, female, form and the last with a posterior border thickened and tuberculate in relation to the hypertrophied penis and its associated glands and musculature. These phases are not equally obvious in all species, but the pelvis in all except Rattus and Mus shows some evidence of the sexual development of the animal. In females the form of the pelvis may be modified during successive pregnancies to allow a wider pelvic outlet for parturition. Resorption and remoulding of the female pelvis allows the recognition of non‐parous, uniparous and multiparous animals in all Cricetid species, in Micromys and, more doubtfully, in Mus, but not in Apodemus and Rattus. Non‐sex‐dependent intraspecific variation, comprising differences in rugosity related to muscularity is also described.The observations are discussed in relation to earlier experimental work, to the need for basic research on small mammal reproduction and population structure, and to the use of the pelvis in the analysis of osteological assemblages, such as occur in owl pellets.