Maternal density stress and coccidian parasitism: Synergistic effects on overwinter survival in root voles

Abstract

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 http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13129/suppinfo is available for this article.

Effects of parasites and predators on nociception: decreases analgesia reduces overwinter survival in root voles (Rodentia: Cricetidae)

“…Meanwhile, each vole in the PA-group was treated with a single orogastric gavage dose of 0.1 mL combina-torial anthelmintic comprising 6.25 × 10 -4 mL diclazuril solution (Weierkong, Sichuan) and a 2 mg ivermectin tablet (Weierkong). Combinatorial anthelmintics can effectively expel nematodes, cestodes, and coccidia (Yang et al 2018).…”

“…Second, we selected the models as described in our previous study (Yang et al 2018). Briefly, parsimonious models were selected based on the QAICc values, which allows a compromise between bias and precision when the global model does not fit the data (Anderson et al 1994) and incorporates a variance inflation factor.…”

Does density-induced stress promote density-dependent reproduction in root voles? Two field experiments

“…The animal was, then, released at the point of capture after handling. The F1 offspring born in the enclosures were captured at 20-30 days of age and moved to the laboratory for use in subsequent experiments (Bian et al, 2015;Yang et al, 2018).…”

“…The collected samples were, then, frozen in ice, transported to the laboratory, and stored in a -20degC freezer until analysis. FCM was measured following the methods outlined by Yang et al (2018), previously validated for root voles. First, the collected faecal samples were lyophilised (Labconco, Kansas City, MO, USA) for 14-18 h, ground into particles, and homogenised in 0.5 mL NaOH solution (0.04 M).…”

“…Our previous papers have reported that high parental population density was approximately three times higher compared with low parental population density at the end of the experimental period in 2012 (Bian et al, 2015). Moreover, the population under high-density conditions showed higher mean faecal corticosterone metabolite (FCM) levels than the population under low-density conditions in both 2012 (Bian et al, 2015) and 2015 (Yang et al, 2018). In this study, we present unpublished data from the same parental populations in 2012 and 2015, which include recruitment and proportion of reproductive conditions and the numbers of male and female founders in both years.…”