Reproduction, aging and mortality rate in social subterranean mole voles (Ellobius talpinus Pall.)

Defining the link between oxidative stress, behavioural reproductive suppression and heterothermy in the Natal mole-rat (Cryptomys hottentotus natalensis)

Sub-lethal effects, such as oxidative stress, can be linked to various breeding and thermophysiological strategies, which themselves can be linked to seasonal variability in abiotic factors. In this study, we investigated the subterranean, social living Natal mole-rat (Cryptomys hottentotus natalensis), which, unlike other social mole-rat species, implements heterothermy seasonally in an attempt to avoid exercise-induced hyperthermia and relies solely on behavioural reproductive suppression to maintain reproductive skew in colonies. Subsequently, we investigated how oxidative stress varied between season, sex and breeding status in Natal mole-rats. Oxidative markers included total oxidant status (TOS measure of total peroxides present), total antioxidant capacity (TAC), OSI (oxidative stress index) and malondialdehyde (MDA) to measure oxidative stress. Breeding and non-breeding mole-rats of both sexes were captured during the summer (wet season) and winter (dry season). Seasonal environmental variables (air temperature, soil temperature and soil moisture) had a significant effect on TOS, OSI and MDA, where season affected each sex differently. Unlike other social mole-rat species that use both physiological and behavioural means of reproductive suppression, no oxidative costs to reproduction were present in the Natal mole-rats. Males had significantly higher MDA than females, which was most apparent in summer (wet season). We conclude that the significant oxidative damage in males is a consequence of exercise-induced oxidative stress, exacerbated by increased burrow humidities and poorer heat dissipation abilities as a function of body mass. This study highlights the importance of both breeding and thermophysiological strategies in affecting oxidative stress.

Characteristics of settlements of the northern mole vole (Ellobius talpinus) in the Kamianska Sich National Nature Park

Preserved and protected within the territory of the Kamyanska Sich National Nature Park areas of psammophytic steppe are natural habitats of the highly specialized and stenotopic northern mole vole Ellobius talpinus. Studies of recent settlements of the species have revealed their strong preference for slopes of riparian balkas and upper terraces of the Kamiansko-Mylivska section of the Kakhovka Reservoir covered with psammophytic vegetation. As places for colonies, these rodents definitely prefer dry loess-sandy soils of light composition, avoiding shrubbery and dense grass due to the danger of disguising in them flying and terrestrial predators. A total of 14 "living" colonies of the northern mole vole were registered, 9 of which were defined as small-family settlements (less than 100 m2). The other five colonies had a clearly multi-family structure and a large area (680–1720 m2), within which spatially isolated clusters of emissions were traced hypothetically perceived as separate family constructions (up to 270 m2). According to these landmarks, some large settlements contained 3 to 9 networks of family burrows located at a distance of 57 to 106 m. Five small uninhabited settlements (45–70 m2) were also recorded with signs of last year emissions. These settlements were located on the periphery of large colonies, 108–219 m far from the nearest emissions of "living" settlements. Estimates of the total number of inhabitants of the 14 "living" settlements in the territory of the Kamianska Sich National Nature Park range from 50 to 200 individuals. As of July 2021, the number of reproductive adults in the registered colonies of the species is 40–50, while the number of young of the current year of birth should be estimated at least 100–120 individuals. Colonies of the northern mole vole are characterized by the presence in their vicinities of spring ephemeroids such as T. hypanica, T. schrenkii, B. versicolor, and C. reticulatus, which are indicator species of primary virgin steppe biotopes. The results of surveys of northern mole vole colonies and ecological assessments of protected natural habitats of the Kamianska Sich National Nature Park provide grounds for a favourable prognosis of further preservation of the last range segment of the species in the territory of Right-Bank Ukraine.

Plasma oxidative stress in reproduction of two eusocial African mole-rat species, the naked mole-rat and the Damaraland mole-rat

One of the most prominent life-history trade-offs involves the cost of reproduction. Oxidative stress has been proposed to be involved in this trade-off and has been associated with reduced life span. There is currently an unclear relationship between oxidative cost and the reproduction-longevity trade-off. The current study, using a non-lethal and minimally invasive (only a single blood sample and no euthanasia) method, investigated whether an oxidative cost (oxidative stress) to reproduction would be apparent in two long-lived eusocial mole-rats, the naked mole-rat (NMR), Heterocephalus glaber, and the Damaraland mole-rat (DMR), Fukomys damarensis, where breeding colony members live longer than non-breeder conspecifics. We measured the direct redox balance in plasma by measuring the oxidative stress index (OSI) based on the ratio of total oxidant status and total antioxidant activity in breeders and non-breeders of both sexes, in the two species. NMR had significantly higher OSI between breeders and non-breeders of each sex, whereas DMR showed no significant differences except for total antioxidant capacity (TAC). The mode of reproductive suppression and the degree of reproductive investment in NMR may explain to some degree the redox balance difference between breeders and non-breeders. DMR show minimal physiological changes between breeders and non-breeders except for the mode of reproduction, which may explain some variations in TAC and TOS values, but similar OSI between breeders and non-breeders.

Age-related differences in physiology and survival of northern red-backed voles (Myodes rutilus) in captivity

Age-related deterioration of physiological functions is one of the most evident manifestations of ageing. In wild populations of some species, including murid rodents, lifespans are substantially modified by environmental signals that affect an individual's response to such challenges as unfavourable climatic conditions, parasitic load etc. But the real impact of ageing on natural mortality of most species remains obscure. To clarify how age affects the responsiveness of organisms to environmental challenges, we performed longitudinal laboratory observations of wild-derived northern red-backed voles (Myodes rutilus). We fixed individual longevity and measured metabolic indexes (basal and maximal metabolic rates), ability to maintain body temperature under acute cooling, plasma corticosterone, indexes of acquired and innate immunity in the same individuals of 3-4, 6-7 and 9-10 months old. The maximum estimated lifespan was about 2 years 8 months, which is considerably older than in nature, but less than 30% of individuals passed the one-year milestone. Regardless of the intense mortality, in the first year of life, animals did not demonstrate any age-related deterioration in physiological functions, except leucocyte number. No consistency in any individual physiological index was found. As the individual longevity of red-backed voles varied between years of captivity, we suggest that the welfare and lifespan of wild animals in captivity may be affected by the environmental conditions in the period preceding removal of the animal from the wild.

Reproduction and mortality rates in ecologically distinct species of murid rodents

The trade-off between reproduction and somatic maintenance is one of the most studied concepts of modern evolutionary ecology. This theory predicts a negative relationship between maximum species longevity and total reproductive output. However, studies performed on natural animal populations have found contradictory results, probably due to the unlikelihood of wild animals gaining both maximum longevity and maximum potential fecundity. A comparison of the mortality rates and reproductive output of four ecologically distinct rodent species of Cricetidae family that were maintained in the laboratory in controlled conditions revealed the different life-history tactics of subterranean social mole voles and three related aboveground species: hydrophilic water voles, arid dwarf hamsters and steppe lemmings. Regardless of the relatively higher mortality rates at early ages in mole voles, this species has considerably higher maximum species longevity and smaller litter sizes that do not depend on calendar age, whereas in dwarf hamsters and water voles clear negative correlations between female age and litter size were detected. Steppe lemmings, as a semi-social arid species, shared some life-history tactics with both mole voles and aboveground non-social rodents.

Reproduction, ageing, and longevity in two species of laboratory rodents with different life histories

Social subterranean rodents of the Bathyergidae family are known to have extended longevity and some signs of negligible senescence, although the manifestation of these traits depends on the reproductive status of individuals. Such enormous life history peculiarities are usually explained by the specificity of a subterranean way of life. If so, all subterranean rodents, regardless of their taxonomic position, are expected to have higher maximum lifespans and shorter senescence periods than the related above-ground species. In this study we compared the mortality rates and age-related reproductive activity and physical conditions in two sympatric rodents of the Cricetidae family: subterranean mole voles and above-ground dwarf hamsters. Mole voles have a maximum lifespan that is as high as two times the maximum lifespan of the dwarf hamsters; however, only a few mole voles outlasted the maximum lifespan of dwarf hamsters. Dwarf hamsters were generally more fecund than mole voles, which manifests both in a higher number of litters and larger litter sizes. Neither species demonstrated a significant age-related decline in litter size or muscle strength, although there were negative trends for dwarf hamsters. We conclude that some evidence of extended longevity and slow ageing do occur in mole voles, but due to the relatively short "subterranean" phylogenetic history of the species, this evidence is not as pronounced as in the social species of Bathyergidae family.

Variability of whipworm infection and humoral immune response in a wild population of mole voles (Ellobius talpinus Pall.)

Restricted mobility and spatial isolation of social units in gregarious subterranean mammals ensure good defence mechanisms against parasites, which in turn allows for a reduction of immunity components. In contrast, a parasite invasion may cause an increased adaptive immune response. Therefore, it can be expected that spatial and temporal distribution of parasites within a population will correlate with the local variability in the host's immunocompetence. To test this hypothesis, the intra-population variability of a whipworm infestation and the humoral immune response to non-replicated antigens in mole voles (Ellobius talpinus Pall.), social subterranean rodents, was estimated. Whipworm prevalence in mole voles increased from spring to autumn, and this tendency was more pronounced in settlements living in natural meadows compared to settlements in man-made meadows. However, humoral immune response was lowest in animals from natural meadows trapped in autumn. Since whipworm infestation does not directly affect the immunity of mole voles, the reciprocal tendencies in seasonal dynamics and spatial distribution of whipworm abundance and host immunocompetence may be explained by local deterioration of habitat conditions, which increases the probability of an infestation.

Make haste slowly: reproduction in the Zaisan mole vole (Ellobius tancrei)

Mole voles are the most specialized subterranean members of the subfamily Arvicolinae. We assess the basic reproductive parameters of the Zaisan mole vole (Ellobius tancrei Blasius, 1884) and compare our data with the characteristics reported for other Ellobius species and surface-dwelling voles. In most respects, reproduction of the E. tancrei follows the pattern that is typical for voles. Females undergo postpartum estrus, but rarely combine pregnancy with lactation. The rate of embryonic and postembryonic growth (0.13 and 0.54 g/day, respectively) are slightly lower, whereas the relative neonate and weanling masses (8% and 40% of maternal mass, respectively) are slightly higher than the respective values predicted for non-subterranean arvicolines. The combination of these trends results in the protracted pregnancy and lactation (both ∼30 days). The age at first breeding is delayed (>2.5 months). Despite heavy weanlings, total maternal investment per litter in E. tancrei is low due to small litter size (2.31). Although the species of Ellobius are similar to each other by the parameters of developmental time, they vary by litter size, total investment per litter, and possibly by relative neonate body mass. This is consistent with the idea that when body-size effect is removed, fecundity variables and degree of precociality at birth are dissociated from timing variables.