Breeding versus survival: proximate causes of abrupt population decline under environmental change in a desert rodent, the midday gerbil (Meriones meridianus)

Flexible males, reactive females: faecal glucocorticoid metabolites indicate increased stress in the colonist population, damping with time in males but not in females

Individuals colonizing new areas at expanding ranges encounter numerous and unpredictable stressors. Exposure to unfamiliar environments suggests that colonists would differ in stress levels from residents living in familiar conditions. Few empirical studies tested this hypothesis and produced mixed results, and the role of stress regulation in colonization remains unclear. Studies relating stress levels to colonization mainly use a geographical analysis comparing established colonist populations with source populations. We used faecal glucocorticoid metabolites (FGMs) to assess both spatial and temporal dynamics of stress levels in an expanding population of midday gerbils (Meriones meridianus). We demonstrated that adult males and females had higher FGM levels in newly emerged colonies, compared with the source population, but differed in the pattern of FGM dynamics post-foundation. In males, FGM levels sharply decreased in the second year after colony establishment. In females, FGM levels did not change with time and remained high despite the decreasing environmental unpredictability, exhibiting among-individual variation. Increased stress levels of colonist males damping with time post-colonization suggest they are flexible in responding to immediate changes in environmental uncertainty. On the contrary, high and stable over generations stress levels uncoupled from the changes in the environmental uncertainty in female colonists imply that they carry a relatively constant phenotype associated with the reactive coping strategy favouring colonization. We link sex differences in consistency and plasticity in stress regulation during colonization to the sex-specific life-history strategies.

Multi-assay approach shows species-associated personality patterns in two socially distinct gerbil species

We aimed to investigate whether two closely related but socially distinct species of gerbils differ in personality patterns. Using a suit of multivariate repeated assays (docility test, dark-light emergence test, startle test, novel object test, elevated platform test, and stranger test), we assessed contextual and temporal consistency of docility, boldness, exploration, anxiety, and sociability in the solitary midday gerbil, Meriones meridianus, and social Mongolian gerbil, M. unguiculatus. We revealed contextually consistent and highly repeatable sex-independent but species-specific personality traits. Species differed in temporal repeatability of different behaviours, and contextual consistency was more pronounced in solitary M. meridianus than in social M. unguiculatus. This finding contradicts the social niche specialization hypothesis, which suggests that personality traits should be more consistent in more social species. Instead, we hypothesize that social complexity should favour more flexible and less consistent behavioural traits. The habituation effect indicative of learning abilities was weak in both species yet stronger in social M. unguiculatus, supporting the relationship between the sociality level and cognitive skills. In both species, only a few different behavioural traits covaried, and the sets of correlated behaviours were species-specific such that the two species did not share any pair of correlated traits. Between-species differences in personality traits, habituation, and behavioural syndromes may be linked to differences in sociality. The lack of prominent behavioural syndromes is consistent with the idea that context-specific individual behavioural traits might be favoured to allow more flexible and adequate responses to changing environments than syndromes of correlated functionally different behaviours.

Establishment of an Animal Model Scheme of Strongyloides stercoralis-Infected Meriones meridianus

Studying parasitic nematodes, which generate a massive hazard to animal health, is more difficult than studying free-living nematodes as appropriate animal models are essential, and the relationship between parasites and hosts is extremely complex. Strongyloides stercoralis is an intestinal nematode parasite that mainly infects dogs, humans and other primates. Currently, S. stercoralis worms needed for research mainly rely on their natural host, the dog. This study explored a method of using Meriones meridianus as a model for S. stercoralis. The immunosuppressed M. meridianus were infected with S. stercoralis subcutaneously, and post-parasitic, first-stage larvae (PP L1) were detected in the faeces, with more larvae in female gerbils. In addition, parasitic females (PFs), third-stage larvae (L3s) and rhabditiform larvae were found primarily in the small intestines and lungs of infected gerbils. The PFs and auto-infective third-stage larvae (aL3s) obtained from M. meridianus are morphologically identical to those obtained from beagles and Meriones unguiculatus. Moreover, the infection of S. stercoralis caused changes to biochemical indicators in the serum and in the physiology of M. meridianus. The results demonstrated that M. meridianus can be infected by S. stercoralis, and this model provides a great tool for exploring the biological processes of this parasite and its interaction with the host.

Sustained population decline of rodents is linked to accelerated climate warming and human disturbance

Background

During the past three decades, sustained population decline or disappearance of cycles in small rodents have been observed. Both anthropogenic disturbance and climate warming are likely to be potential drivers of population decline, but quantitative analysis on their distinct effects is still lacking.

Results

Using time series monitoring of 115 populations (80 populations from 18 known rodent species, 35 mixed populations from unknown species) from 1980 in China (spanning 20–33 yrs), we analyzed association of human disturbances and climate warming with population dynamics of these rodent species. We found 54 of 115 populations showed a decreasing trend since 1980, and 16 of 115 showed an increasing trend. Human disturbances and climate warming showed significant positive associations with the population declines of most rodent species, and the population declines were more pronounced in habitats with more intensified human disturbance such as cities and farmlands or in high-latitude regions which experienced more increase of temperature.

Conclusions

Our results indicate that the large-scale sustained population decline of small mammals in various ecosystems driven by the rapid increase of both climate warming and human disturbance is likely a signal of ecosystem dysfunction or transition. There is an urgent need to assess the risks of accelerated climate warming and human disturbance imposes on our ecosystems.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12862-022-02056-z.

The effect of grazing on winter survival of midday gerbil (Meriones meridianus) of different genders

The objective of this study was to investigate the effects of grazing on midday gerbil (Meriones meridianus) population characteristics and survival of animals of different genders. The experiment used a randomized complete block design and was conducted in Alxa Left Banner, Inner Mongolia, China, in 2002 (The agricultural reclamation plots set up in 1994). From April 2006 to October 2010, midday gerbils were live-trapped in 3 light grazing plots, 3 overgrazed plots, and 3 grazing exclusion plots. The quantity of vegetation was investigated in the two different grazing intensity areas and grazing exclusion area to determine the relationship between gerbils and plant food availability. The results suggested that there was higher gerbil density, individual body mass, and daily body mass growth rate in the grazing exclusion sites than the other sites across the whole year. Females had higher survival in grazing exclusion areas than in other treatments, but the males' survival showed the opposite pattern. Our results indicated that grazing negatively influenced the midday gerbil population by reducing food availability. Grazing influenced the survival rates of male midday gerbils positively, but had negative effects on females. The reason for gendered differences in survival rates of midday gerbils requires further investigation.

Rodent burrow network dynamics under human-induced landscape transformation from desert to steppe in Kalmykian rangelands

Rodents play an important role in rangelands through the engineering of extensive burrow systems, which provides key habitats for many animal and plant species. We have analyzed the long-term variation in the abundance and distribution of rodent burrows in grazing ecosystems of southern Russia (Kalmykia) under the landscape change from desert to steppe caused by the drastic reduction of livestock after the collapse of the USSR in the early 1990s. We conducted burrow surveys in the "desert" (1980) and "steppe" (2017) periods on 19 3-km transects. We found considerable changes in burrow abundance and distribution, as well as evidence of desert habitat fragmentation and isolation caused by the expansion of tall-grass communities. Burrows of the open-dwelling diurnal ground squirrel (Spermophilus pygmaeus), the dominant and the keystone species during the "desert" period, almost completely disappeared from the rodent burrow network by 2017, indicating significant habitat loss. In contrast, the burrows of the folivorous social vole (Microtus socialis) which was rare in the 1980s, became abundant and ubiquitously distributed. The burrow density of the desert-dwelling psammophilous midday gerbil (Meriones meridianus) decreased, while the distances between occupied patches increased, indicating desert habitat fragmentation and loss of population connectivity. Burrows of the folivorous tamarisk gerbils (M. tamariscinus) were recorded only sporadically in both 1980 and 2017. The observed changes in the rodent burrow network, the key component of grazing ecosystems, correlate with rodent species ecology and can have long-term and important consequences for ecosystem functioning.