Host-Parasite Interactions and Population Dynamics of Rock Ptarmigan.

Mark S Boyce,Ute Stenkewitz,Gunnar Stefánsson,Karl Skírnisson,Ólafur K Nielsen

doi:10.1371/journal.pone.0165293

Mark S Boyce, Ute Stenkewitz + Show 3 more

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https://doi.org/10.1371/journal.pone.0165293

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Abstract

Populations of rock ptarmigan (Lagopus muta) in Iceland fluctuate in multiannual cycles with peak numbers c. every 10 years. We studied the ptarmigan-parasite community and how parasites relate to ptarmigan age, body condition, and population density. We collected 632 ptarmigan in northeast Iceland in early October from 2006 to 2012; 630 (99.7%) were infected with at least one parasite species, 616 (98%) with ectoparasites, and 536 (85%) with endoparasites. We analysed indices for the combined parasite community (16 species) and known pathogenic parasites, two coccidian protozoans Eimeria muta and Eimeria rjupa, two nematodes Capillaria caudinflata and Trichostrongylus tenuis, one chewing louse Amyrsidea lagopi, and one skin mite Metamicrolichus islandicus. Juveniles overall had more ectoparasites than adults, but endoparasite levels were similar in both groups. Ptarmigan population density was associated with endoparasites, and in particular prevalence of the coccidian parasite Eimeria muta. Annual aggregation level of this eimerid fluctuated inversely with prevalence, with lows at prevalence peak and vice versa. Both prevalence and aggregation of E. muta tracked ptarmigan population density with a 1.5 year time lag. The time lag could be explained by the host specificity of this eimerid, host density dependent shedding of oocysts, and their persistence in the environment from one year to the next. Ptarmigan body condition was negatively associated with E. muta prevalence, an indication of their pathogenicity, and this eimerid was also positively associated with ptarmigan mortality and marginally inversely with fecundity. There were also significant associations between fecundity and chewing louse Amyrsidea lagopi prevalence (negative), excess juvenile mortality and nematode Capillaria caudinflata prevalence (positive), and adult mortality and skin mite Metamicrolichus islandicus prevalence (negative). Though this study is correlational, it provides strong evidence that E. muta through time-lag in prevalence with respect to host population size and by showing significant relations with host body condition, mortality, and fecundity could destabilize ptarmigan population dynamics in Iceland.

Highlights

Parasite communities of wildlife species have rarely been studied over an extended time period [1]
We look at the combined parasite community and focus on six known pathogenic parasite species, namely Eimeria muta and Eimeria rjupa, intestinal microparasites that can cause coccidiosis [27], Capillaria caudinflata, a helminth known to cause capillariasis in Icelandic ptarmigan [28], Trichostrongylus tenuis, a helminth known to cause trichostrongylosis in grouse [3] [29], Metamicrolichus islandicus, a skin mite that can cause mange, and Amyrsidea lagopi, an amblyceran chewing louse that can cause feather damage [30]
The Anderson and May model [4] [31] identified low aggregation of parasites within the host population, parasite-induced host mortality and reduction in host reproductive potential, respectively, as well as time delays in parasite reproduction and transmission as the major regulating or destabilizing qualities that parasites can have on host population dynamics

Summary

Introduction

Parasite communities of wildlife species have rarely been studied over an extended time period [1]. Parasites can influence population dynamics by affecting host body condition, fecundity, and survival, and host-parasite interactions are known to be one of the driving forces of multiannual cycles in animal populations (e.g., [4] [5] [6] [7] [8] [9]). Cycles have been reported in a variety of herbivorous species in northern latitudes including moths, hares, lemmings, voles, and grouse [9] [10], and are well documented for species in the genus Lagopus. Lagopus) in Norway, have been reported to affect demographic parameters including body condition and breeding success of the host, and were negatively associated with changes in numbers of the ptarmigan population [12] [13] Parasites of willow ptarmigan (L. l. lagopus) in Norway, have been reported to affect demographic parameters including body condition and breeding success of the host, and were negatively associated with changes in numbers of the ptarmigan population [12] [13]

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