Population expansion and individual age affect endoparasite richness and diversity in a recolonising large carnivore population

Abstract

The recent recolonisation of the Central European lowland (CEL) by the grey wolf (Canis lupus) provides an excellent opportunity to study the effect of founder events on endoparasite diversity. Which role do prey and predator populations play in the re-establishment of endoparasite life cycles? Which intrinsic and extrinsic factors control individual endoparasite diversity in an expanding host population? In 53 individually known CEL wolves sampled in Germany, we revealed a community of four cestode, eight nematode, one trematode and 12 potential Sarcocystis species through molecular genetic techniques. Infections with zoonotic Echinococcus multilocularis, Trichinella britovi and T. spiralis occurred as single cases. Per capita endoparasite species richness and diversity significantly increased with population size and changed with age, whereas sex, microsatellite heterozygosity, and geographic origin had no effect. Tapeworm abundance (Taenia spp.) was significantly higher in immigrants than natives. Metacestode prevalence was slightly higher in ungulates from wolf territories than from control areas elsewhere. Even though alternative canid definitive hosts might also play a role within the investigated parasite life cycles, our findings indicate that (1) immigrated wolves increase parasite diversity in German packs, and (2) prevalence of wolf-associated parasites had declined during wolf absence and has now risen during recolonisation.

Figure 1. Relevant effectors of helminth species richness and diversity (Shannon index) in wolves from the CEL population.

Helminth species richness (a,b) and helminth diversity (c,d) vary with wolf age significantly decreasing from pups to yearlings (n_pup = 21, n_yearling = 16, n_adult = 14) and increase with wolf population size (n_3packs = 1, n_7packs = 1, n_14packs = 8, n_18packs = 11, n_25packs = 14, n_31packs = 16). Dots represent outliers. Box plot edges depict the quartiles for number of helminths species (a,b) and the Shannon index (c,d). Whiskers extend to non-outlier extremes. Statistical significance was calculated using a general linear model.

Figure 2. Helminth prevalence of CEL wolves in relation to their geographic origin.

‘Native’ wolves (grey bars) had a significantly lower prevalence of the tapeworm T. hydatigena (p = 0.010) and a significantly higher prevalence of the lung nematode C. aerophila than ‘immigrants’ (black bars) (p = 0.044). Statistical significance was calculated using the Fisher’s exact test.

Figure 3. Sarcocystis spp. prevalence of CEL wolves in relation to their geographic origin.

‘Native’ wolves (grey bars) had a significantly higher S. gracilis prevalence than ‘immigrant’ wolves (p value = 0.031) (black bars). Statistical significance was calculated using the Fisher’s exact test.