Ecological correlates of ectoparasite load in a rodent: Complex roles of seasonality

Effects of individual characteristics and seasonality and their interaction on ectoparasite load of Daurian ground squirrels in Inner Mongolia, China

Understanding the drivers of parasite distribution is vital for ecosystem health, disease management, and vector monitoring. While studies note the impact of host sex, size, behavior, and season on parasite load, concurrent assessments of these factors and their interactions are limited. During the spring, summer and autumn seasons from 2021 to 2023, we trapped Daurian ground squirrel (Spermophilus dauricus), a small rodent species that inhabits eastern Asian grasslands in Inner Mongolia and collected their ectoparasites. Using machine learning Lasso regression, we pinpointed factors affecting tick and flea abundance on S. dauricus. We then analyzed these factors and their seasonal interactions with a mixed negative binomial generalized linear model. Our study revealed significant but inconsistent seasonal effects on the load of ectoparasites. The tick load was significantly higher in spring and summer compared to autumn, while the flea load was higher in summer and autumn but lacked statistical significance. Furthermore, individual factors that influence the flea and tick load were moderated by seasonal effects, with a male bias in flea parasitism observed in spring. Significant interactions were also found among seasonality, sex, and body weight. The load of male squirrel fleas was positively correlated with body weight, with the highest increase observed in spring. On the contrary, the flea load of female squirrels showed a negative correlation with body weight, significantly decreasing in the autumn with increasing weight. Significant interactions were observed between season and survival status, with hosts exhibiting higher tick load during autumn survival. Our findings underscore the importance of considering seasonal variation in parasitism and the interactions between seasonal dynamics and host biological traits in shaping parasite distributions.

O-GlcNAcylation of SERCA protects skeletal muscle in hibernating Spermophilus dauricus from disuse atrophy

Long-term inactivity of skeletal muscle results in muscular disuse atrophy; however, hibernating animals do not experience muscular disuse atrophy during the hibernation period. The molecular mechanism underlining the anti-atrophy effect in these animals is unclear. O-linked N acetyl-β-D-glucosaminylation (O-GlcNAcylation) and its effect on cell signaling pathways are important mechanisms underlying muscular disuse atrophy; thus, in this study, we investigated O-GlcNAcylation changes during hibernation in Spermophilus dauricus to explore the role of O-GlcNAcylation in the muscle disuse atrophy resistance of hibernating animals. The results showed that during hibernation, the muscle fiber cross-sectional area and ratio of muscle fiber did not change, and the morphological structure of the muscle remained intact, with normal contractile function. The level of O-GlcNAcylation decreased during hibernation, but quickly returned to normal in the periodic arousal stage. The O-GlcNAcylation level of sarcoplasmic/endoplasmic reticulum calcium ATPase 1 (SERCA1) decreased, whereas its activity increased. The decrease in O-GlcNAcylation of SERCA could result in the decreased binding of phospholamban to SERCA1, thus decreasing its inhibition to SERCA1 activity. This in turn can inhibit muscle cell calcium overload, maintain muscle cell calcium homeostasis, and stabilize the calpain proteolytic pathway, ultimately inhibiting skeletal muscle atrophy. Our results demonstrate that periodic arousal along with returning O-GlcNAcylation level to normal are important mechanisms in preventing disuse atrophy of skeletal muscle during hibernation.

Relationship between climatic factors and the flea index of two plague hosts in Xilingol League, Inner Mongolia Autonomous Region

Climatic factors are closely associated with the occurrence of vector-borne diseases, and they also influence the distribution of vectors. The occurrence of plague is closely related to the population dynamics of fleas and their host animals, as well as climatic conditions. This study focused on Xilingol League, utilizing climatic and flea index data from 2012 to 2021. Spearman correlation and "Boruta" importance analysis were conducted to screen for climatic variables. A generalized additive model (GAM) was employed to investigate the influence of climatic factors and rodent density on the flea index. GAM analysis revealed distinct trends in flea index among different rodent hosts. For Meriones unguiculatus, the flea index declined with increased density and with higher humidity, yet rose with greater lagged sunshine duration. For Spermophilus dauricus, an initial increase in flea index with density was observed, followed by a decrease, and a rise in the index was noted when ground temperatures were low. This study reveals the nonlinear interactions and lag effects among climatic factors, density, and flea index. Climatic factors and density variably influence the flea index of two Yersinia pestis hosts. This research advances the prediction and early warning efforts for plague control, providing a theoretical basis for rodent and flea eradication strategies.

Complex effects of testosterone level on ectoparasite load in a ground squirrel: an experimental test for the immunocompetence handicap hypothesis

BACKGROUND

The immunocompetence handicap hypothesis suggests that males with a higher testosterone level should be better at developing male secondary traits, but at a cost of suppressed immune performance. As a result, we should expect that males with an increased testosterone level also possess a higher parasite load. However, previous empirical studies aimed to test this prediction have generated mixed results. Meanwhile, the effect of testosterone level on parasite load in female hosts remains poorly known.

METHODS

In this study, we tested this prediction by manipulating testosterone level in Daurian ground squirrels (Spermophilus dauricus), a medium-sized rodent widely distributed in northeast Asia. S. dauricus is an important host of ticks and fleas and often viewed as a considerable reservoir of plague. Live-trapped S. dauricus were injected with either tea oil (control group) or testosterone (treatment group) and then released. A total of 10 days later, the rodents were recaptured and checked for ectoparasites. Fecal samples were also collected to measure testosterone level of each individual.

RESULTS

We found that testosterone manipulation and sex of hosts interacted to affect tick load. At the end of the experiment, male squirrels subjected to testosterone implantation had an averagely higher tick load than males from the control group. However, this pattern was not found in females. Moreover, testosterone manipulation did not significantly affect flea load in S. dauricus.

CONCLUSIONS

Our results only lent limited support for the immunocompetence handicap hypothesis, suggesting that the role of testosterone on regulating parasite load is relatively complex, and may largely depend on parasite type and gender of hosts.

The current distribution of tick species in Inner Mongolia and inferring potential suitability areas for dominant tick species based on the MaxEnt model

BACKGROUND

Ticks are known to transmit a wide range of diseases, including those caused by bacteria, viruses, and protozoa. The expansion of tick habitats has been intensified in recent years due to various factors such as global warming, alterations in microclimate, and human activities. Consequently, the probability of human exposure to diseases transmitted by ticks has increased, leading to a higher degree of risk associated with such diseases.

METHODS

In this study, we conducted a comprehensive review of domestic and international literature databases to determine the current distribution of tick species in Inner Mongolia. Next, we employed the MaxEnt model to analyze vital climatic and environmental factors influencing dominant tick distribution. Subsequently, we predicted the potential suitability areas of these dominant tick species under the near current conditions and the BCC-CSM2.MR model SSP245 scenario for the future periods of 2021-2040, 2041-2060, 2061-2080, and 2081-2100.

RESULTS

Our study revealed the presence of 23 tick species from six genera in Inner Mongolia, including four dominant tick species (Dermacentor nuttalli, Ixodes persulcatus, Dermacentor silvarum, and Hyalomma asiaticum). Dermacentor nuttalli, D. silvarum, and I. persulcatus are predominantly found in regions such as Xilin Gol and Hulunbuir. Temperature seasonality (Bio4), elevation (elev), and precipitation seasonality (Bio15) were the primary variables impacting the distribution of three tick species. In contrast, H. asiaticum is mainly distributed in Alxa and Bayannur and demonstrates heightened sensitivity to precipitation and other climatic factors. Our modeling results suggested that the potential suitability areas of these tick species would experience fluctuations over the four future periods (2021-2040, 2041-2060, 2061-2080, and 2081-2100). Specifically, by 2081-2100, the centroid of suitable habitat for D. nuttalli, H. asiaticum, and I. persulcatus was predicted to shift westward, with new suitability areas emerging in regions such as Chifeng and Xilin Gol. The centroid of suitable habitat for H. asiaticum will move northeastward, and new suitability areas are likely to appear in areas such as Ordos and Bayannur.

CONCLUSIONS

This study provided a comprehensive overview of the tick species distribution patterns in Inner Mongolia. Our research has revealed a significant diversity of tick species in the region, exhibiting a wide distribution but with notable regional disparities. Our modeling results suggested that the dominant tick species' suitable habitats will significantly expand in the future compared to their existing distribution under the near current conditions. Temperature and precipitation are the primary variables influencing these shifts in distribution. These findings can provide a valuable reference for future research on tick distribution and the surveillance of tick-borne diseases in the region.