Sarcoptes scabiei infestation does not alter the stability of ectoparasite communities

Abstract

Background: The host represents a heterogeneous ecosystem where multiple parasite species co-occur and interact with each other for space and resources. Although these interactions may rule the features of an infracommunity and may shape the infracommunity response to external perturbations, the resilience of ectoparasite communities to new infestations remains poorly explored.

Methods: We analysed the composition of the ectoparasite communities found on 214 individual Iberian ibexes (Capra pyrenaica) inhabiting the Sierra Nevada Natural Space, southern Spain. Using classification and regression trees, we explored how the presence of Sarcoptes scabiei (a highly contagious mite), the off-host environment and the host sex govern the prevalence and abundance of lice and ticks. Null model analysis was applied to assess the impact of S. scabiei on the structure of the ectoparasite communities.

Results: Our results suggest that S. scabiei infestation acts in tandem with off-host environment and host sex to define the prevalence and abundance of lice and ticks. We also provided evidence for differences in species co-occurrence only at the early stages of S. scabiei infestation. Regarding species diversity, we recorded that ectoparasite communities in scabietic ibexes reached a high richness faster than those in healthy individuals.

Conclusions: Even though we show that ectoparasite burden is correlated with S. scabiei infestation, off-host environment and host sex, the species response to S. scabiei infestation and climate seem to be highly variable and influenced by ectoparasite life-history traits. Ectoparasite communities also appear resilient to perturbations which is in agreement with what was previously reported for endoparasites. Future refinement of sample collection and the incorporation of ecological and epidemiological-related variables may allow us to establish causal effects and deepen the knowledge about the mechanisms and consequences of ectoparasite interactions.

Keywords: Capra pyrenaica; Community ecology; Ecosystem engineer; Multiparasitism; Sarcoptes scabiei.

Fig. 1

Wild ibexes exhibiting different stages of mange severity. a Healthy ibex with no evidence of skin lesions (continuous microhabitat). b Mildly infested ibex presenting extensive alopecia on the face, abdomen, elbow and knees (loss of microhabitat). No evidence for hyperkeratotic and parakeratotic lesions. c Advanced case of S. scabiei infestation accompanied by an almost complete alopecia on the face, ears and neck (microhabitat becomes divided into several patches). Note thick crusts on the muzzle which may indicate the deficiency of a hypersensitivity response

Fig. 2

Classification (left) and regression (right) trees from analyses to assessing the influence of S. scabiei infestation, environment and host sex on the prevalence and abundance of lice and ticks. Each node represented by the variable abbreviation (variable names as shown in Table 2) defines a split of the dataset and the branches define the path taken by each observation. Ellipses represent the terminal nodes of the tree model. The terminal nodes of classification tree models (left) indicate if an ectoparasite species is present (1) or absent (0) in relation to S. scabiei infestation, environment and host sex. The terminal nodes of regression tree models (right) express the variations in ectoparasite abundance in relation to the aforementioned variables. The prediction error rate for each model is presented in bold. Abbreviations: PERCT, prediction error rate for classification trees; PERRT, prediction error rate for regression trees

Fig. 3

Species accumulation curves showing the rates at which new parasite species are found (species richness) as a function of sampling effort measured as the total number of parasites (abundance) in healthy, mildly infested and severely infested hosts

Fig. 4

Schematic representation of the preferential use of specific microhabitat areas (shaded in grey) by lice and ticks, and the spread of S. scabiei infestation in ibexes. The divergence in space use between lice, ticks and S. scabiei and the existence of unoccupied microhabitat patches even during the S. scabiei infestation are some reasons to explain the high prevalence and abundance of particular species in scabietic ibexes. Key: 1, face; 2, neck; 3, chest; 4, back; 5, shoulder; 6, costal area; 7, lumbar sacra; 8, flanks; 9, pelvis; 10, abdomen; 11, elbow; 12, carpus; 13, groin; 14, tarsus. Different shades of grey indicate a gradient of intensity of mite infestation, light (mild infestation) to dark (severe infestation). The spread of S. scabiei and the areas of the body of Iberian ibex follow partially the division of [15]