Yan Wu

Rapid population increases in degraded habitats have been reported for the plateau pika (Ochotona curzoniae)—a small burrowing lagomorph endemic to the Qinghai–Tibet Plateau—challenging the ecological balance of alpine meadow ecosystems. Although previous studies have indicated that high-protein and sulfur-containing amino acid (particularly methionine) intake in degraded habitats may drive this expansion, whether methionine modulates the physiology of plateau pikas through the gut microbiota remains unclear. This study investigates the effects of dietary methionine on the gut microbiota, immunity, and reproductive physiological profiles in plateau pikas through controlled feeding and fecal microbiota transplantation (FMT) experiments. The results show that a high-methionine diet significantly enhanced cellular immunity in both sexes and humoral immunity in males, reduced the intensity of coccidian infection, and elevated GnRH, estradiol, progesterone, and testosterone levels. Microbiota analysis reveals that, while the dietary content of methionine does not alter the α-diversity of the gut microbiota, it does significantly affect the β-diversity, with enrichment of the genera Alistipes, Prevotella, and Prevotellaceae_UCG-001 observed in the high-methionine diet group. Fecal microbiota transplantation from high-methionine diet group pikas increased the relative abundances of Alistipes and Prevotella in female and male recipients, respectively. In parallel, these microbial shifts were accompanied by increased cellular immunity in both sexes and humoral immunity in males, reduced coccidian infection, and increased male reproductive traits. In contrast, female recipients showed no significant changes in reproductive traits. Metagenomic functional annotation showed that functional pathways involved in energy, amino acid metabolism, and carbohydrate metabolism exhibited lower abundance in female recipients, while those involved in amino acid and lipid metabolism exhibited higher abundance in male recipients following microbiota transplantation from high-methionine diet group donor pikas. Collectively, these findings suggest that improvements in immunity and reproductive physiological profiles induced by a high-methionine diet may partially contribute to the abundances of specific gut microbial taxa in plateau pikas.

The literature shows that maternal stress can influence behavior and immune function in F1. Yet, most studies on these are from the laboratory, and replicated studies on the mechanisms by which maternal stress drives individual characteristics are still not fully understood in wild animals. We manipulated high- and low-density parental population density using large-scale field enclosures and examined behavior and immune traits. Within the field enclosures, we assessed anti-keyhole limpet hemocyanin immunoglobulin G (anti-KLH IgG) level, phytohemagglutinin (PHA) responses, hematology, cytokines, the depressive and anxiety-like behaviors and prevalence and intensity of coccidial infection. We then collected brain tissue from juvenile voles born at high or low density, quantified mRNA and protein expression of corticotropin-releasing hormone (CRH) and glucocorticoid receptor gene (NR3C1) and measured DNA methylation at CpG sites in a region that was highly conserved with the prairie vole CRH and NR3C1 promoter. At high density, we found that the F1 had a lower DNA methylation level of CRH and a higher DNA methylation level of NR3C1, which resulted in an increase in the expression levels of the CRH mRNA and protein expression and further reduced the expression levels of the NR3C1 mRNA and protein expression, and ultimately led to have delayed responses to acute immobilization stress. Juvenile voles born at high density also reduced anti-KLH IgG levels and PHA responses, increased cytokines, and depressive and anxiety-like behaviors, and the effects further led to higher coccidial infection. From the perspective of population density inducing the changes in behavior and immunity at the brain level, our results showed a physiological epigenetic mechanism for population self-regulation in voles. Our results indicate that altering the prenatal intrinsic stress environment can fundamentally impact behavior and immunity by DNA methylation of HPA-axis genes and can further drive population fluctuations in wild animals.

Plateau pikas (Ochotona curzoniae) play a keystone role in the alpine meadow ecosystem on the Qinghai–Tibetan Plateau (QTP). For decades, QTP grasslands have become degraded to some degree, largely as a result of heavy livestock grazing. Concomitantly, the abundance of plateau pikas has increased dramatically as grassland degradation has altered the vegetation community structure and dominant species, shifting the plant nutrient contents toward higher protein conditions that favor them. Considerable research supports the hypothesis that the quantity and quality of food limit herbivore populations. Here, we examined the relationship between the availability of essential amino acids in the diets of plateau pikas and the degree of meadow degradation associated with livestock grazing intensity through a field survey, as well as the fitness of individuals by laboratory feeding experiments with 2 pelleted chows containing 0.26% and 0.45% methionine. Sulfur-containing methionine and cystine were the most limiting amino acids in the diets of pikas. During the pika breeding season, the concentrations of most essential acids, particularly methionine and cystine, were higher in heavily degraded meadows than in lightly and moderately degraded meadows. Individuals fed 0.45% methionine exhibited enhanced cell-mediated immunity, reduced intensity of coccidian infection, and increased concentrations of gonadotropin-releasing hormone, luteinizing hormone, estradiol, progesterone, and testosterone compared to those fed 0.26% methionine. These results showed that heavily degraded meadows provided relatively high-quality food that improved individual fitness, suggesting that the high-methionine food in the heavily degraded meadows may be a key factor in the generation and maintenance of high-density populations of plateau pikas.

To investigate the medication adherence of elderly hypertensive patients in community during the COVID-19 period and analyze its influencing factors. 392 elderly patients with hypertension were selected from two communities in Chengdu, Sichuan Province, and were investigated by demographic characters, circumstances in COVID-19 period, Morisky Medication Adherence Scale. chi-square test and binary logistic regression analysis were performed by SPSS 25.0 software. The medication adherence prevalence of elderly hypertensive patients from two communities in Chengdu was 43.37%. Binary logistic regression analysis showed that marital status, antihypertensive drug use during COVID-19 vaccination, antihypertensive drug use during COVID-19 treatment and emotional situation during the COVID-19 period were independent influencing factors of medication adherence of elderly hypertensive patients. During the COVID-19 period medication adherence among elderly hypertensive patients from two communities in Chengdu was poor.

Density dependence in reproduction plays an important role in stabilizing population dynamics via immediate negative feedback from population density to reproductive output. Although previous studies have shown that negative density‐dependent reproduction is associated with strong spacing behavior and social interaction between individuals, the proximal mechanism for generating negative density‐dependent reproduction remains unclear. In this study, we investigated the effects of density‐induced stress on reproduction in root voles. Enclosed founder populations were established by introducing 6 (low density) and 30 (high density) adults per sex into per enclosure (four enclosures per density in total) during the breeding season from April to July 2012 and from May to August 2015. Fecal corticosterone metabolite (FCM) levels, reproductive traits (recruitment rate and the proportion of reproductively active individuals), and founder population numbers were measured following repeated live trapping in both years. The number of founders was negatively associated with recruitment rates and the proportion of reproductively active individuals, displaying a negative density‐dependent reproduction. FCM level was positively associated with the number of founders. The number of founder females directly affected the proportion of reproductive females, and directly and indirectly through their FCM levels affected the recruitment rate; the effect of the number of male founders on the proportion of reproductive males was mediated by their FCM level. Our results showed that density‐induced stress negatively affected reproductive traits and that density‐induced stress is one ecological factor generating negative density‐dependent reproduction.

Growing evidence suggests that parasite-infected prey is more vulnerable to predation. However, the mechanism underlying this phenomenon is obscure. In small mammals, analgesia induced by environmental stressors is a fundamental component of the defensive repertoire, promoting defensive responses. Thus, the reduced analgesia may impair the defensive ability of prey and increase their predation risk. This study aimed to determine whether coccidia infection increases the vulnerability to predation in root voles, Microtus oeconomus (Pallas, 1776), by decreased analgesia. Herein, a predator stimulus and parasitic infection were simulated in the laboratory via a two-level factorial experiment, then, the vole nociceptive responses to an aversive thermal stimulus were evaluated. Further, a field experiment was performed to determine the overwinter survival of voles with different nociceptive responses via repeated live trapping. The coccidia-infected voles demonstrated reduced predator-induced analgesia following exposure to predator odor. Meanwhile, pain-sensitive voles had lower overwinter survival than pain-inhibited voles in enclosed populations throughout the duration of the experiment. Our findings suggest that coccidia infection attenuates predator-induced analgesia, resulting in an increased vulnerability to predation.

Predators and parasites have been important extrinsic factors influencing the fluctuation of small mammal populations. They can have non-additive effects on a shared group of preys or hosts, which can have important consequences for population dynamics. However, experimental studies incorporating the interactions between predation and parasites are scarce in small mammal populations. Here we systematically examined the synergistic effects of predators and coccidian parasites interaction on overwinter survival and likely mechanisms underlying the synergistic effects in the root vole (Microtus oeconomus). Our aim was to test the general hypothesis that predators and coccidia interact synergistically to decrease overwinter survival of root voles through mediating vole’s physiological traits and body conditions. We carried out a factorial experimental design, by which we manipulated the predator exclusion in combination with the parasitic removal in enclosures, and then measured fecal corticosterone metabolite (FCM) levels, immunocompetence, and body conditions in captured animals via repeated live trapping. We found a strong negative synergistic effect of predators and coccidia on survival. Importantly, we found that predators increased both the prevalence and intensity of coccidian infection in voles through immune suppression induced by predation stress, while increased coccidian infection reduced plasma protein and hematocrit level of voles, which may impair anti-predator ability of voles and lead to an increase in predation. Our finding showed when voles are exposed to both predation risk and infection, their synergistic effects greatly reduce overwinter survival and population density. This may be an important mechanism influencing population dynamics in small mammals.

Individuals in poor physiological condition are known to be more susceptible to infection that, once it occurs, further deteriorates the individuals' conditions, making them even more susceptible to infection and leading to death. This vicious synergy between the host condition and infection has recently been proposed to be among the key factors determining the oscillation characteristics in natural populations. Field studies that directly test such a hypothesis, however, are currently scarce, and the physiological traits involved remain largely unclear. In this field study, we systematically examined the synergistic effects of maternal stress and coccidian parasitic interaction on the physiological conditions and overwinter survival of offspring in the root vole (Microtus oeconomus) via repeated live trapping and measurements of faecal corticosterone metabolite (FCM) levels and immunocompetence in captured animals. We found that maternal density stress significantly increased FCM levels and both the prevalence and intensity of coccidian infection in offspring, significantly suppressed offspring immunocompetence and reduced offspring overwinter survival. Coccidian infection significantly potentiated increases in FCM levels and exacerbated the immune suppression induced by maternal density stress. Coccidian infection also significantly accelerated a decrease in overwinter survival and a population decline in maternal‐density‐stressed populations. Our findings indicate that both stress and immune systems are involved in the synergistic process through which stressors and parasites interact with the host to influence the fitness of individuals and cause a population decline in the natural environment. A plain language summary is available for this article.

The literature reveals that stress in early life or adulthood can influence immune function. As most studies on this are from the laboratory, there is a need for replicated studies in wild animals. This study aims to examine the effects of density stress during the maternal period and adulthood on immune traits of root vole (Microtus oeconomus) individuals. Four replicated high- and low-density parental populations were established, from which we obtained offspring and assigned each into four enclosures, two for each of the two density treatments used in establishing parental populations. The F1 offspring fecal corticosterone metabolite response to acute immobilization stress, anti-keyhole limpet hemocyanin immunoglobulin G (anti-KLH IgG) level, phytohemagglutinin (PHA)-delayed hypersensitivity and hematology at the end of the first breeding season, and prevalence and intensity of coccidial infection throughout the two breeding seasons, were tested. Density-induced maternally stressed offspring had delayed responses to acute immobilization stress. Density-stressed offspring as adults had reduced anti-KLH IgG levels and PHA responses, and the effects further deteriorated in maternally stressed offspring, leading to higher coccidial infection in the first breeding season than in the second. No correlations were found between immune traits or coccidial infection and survival over winter. These findings indicated that the combined density stresses during the maternal period and adulthood exhibited negative synergistic effects on immune traits. The synergistic effects lead to higher coccidial infection; however, this consequently reduced the risk of subsequent infection. The increased coccidial infection mediated by the synergistic effects may have an adaptive value in the context of the environment.