Abstract
In wildlife, endoparasite burden can be affected by host life history stage, environmental conditions, host abundance, and parasite co-infections. We tested the effects of these factors on gastrointestinal parasite infection in plains zebras (Equus quagga) in the Serengeti ecosystem, Tanzania, using fecal egg counts of two nematode families (Strongylidae and Ascarididae) and the presence/absence of cestode (Anoplocephalidae) eggs. We predicted higher egg counts of Strongylidae and Ascarididae, and increased likelihood of Anoplocephalidae infection in individuals (1) during energetically costly life history stages when resource allocation to immune processes may decrease and in young zebras after weaning because of increased uptake of infective stages with forage, (2) when climatic conditions facilitate survival of infective stages, (3) when large zebra aggregations increase forage contamination with infective stages, and (4) in individuals co-infected with more than one parasite group as this may indicate reduced immune competence. Strongylidae egg counts were higher, and the occurrence of Anoplocephalidae eggs was more likely in bachelors than in band stallions, whereas Ascarididae egg counts were higher in band stallions. Strongylidae and Ascarididae egg counts were not increased in lactating females. Strongylidae egg counts were higher in subadults than in foals. Regardless of sex and age, Ascarididae infections were more likely under wet conditions. Co-infections did not affect Strongylidae egg counts. Ascarididae egg counts in adult females were higher when individuals were co-infected with Anoplocephalidae. We present evidence that parasite burdens in plains zebras are affected by life history stage, environmental conditions, and co-infection.
Highlights
The mammalian intestinal tract is inhabited by a diverse and dynamic parasite community that is shaped throughout the host’s lifespan by interactions between various internal and external factors (Krecek et al 1987a; Behnke et al 2005; Graham 2008; Telfer et al 2010; Hayward et al 2011; Van der Wal et al 2014; Kappeler et al 2015)
We investigated factors shaping gastrointestinal parasite infection burdens and the occurrence of co-infections in plains zebras (Equus quagga Boddaert, 1785) in the Serengeti National Park, Tanzania, focusing on parasite taxa that are known to infect plains zebras in Africa and that rely on ingestion of infective stages for transmission, i.e., nematodes of the families Strongylidae and Ascarididae and cestodes of the family Anoplocephalidae (Krecek et al 1987b; Wambwa et al 2004; Turner and Getz 2010; Fugazzola and Stancampiano 2012; Cizauskas et al 2015)
Ascarididae eggs were observed in 31% of all samples, with egg counts in infected individuals ranging from 25 to 675 eggs per gram feces (EPG) in adults and from 25 to 1625 EPG in young zebras
Summary
The mammalian intestinal tract is inhabited by a diverse and dynamic parasite community that is shaped throughout the host’s lifespan by interactions between various internal and external factors (Krecek et al 1987a; Behnke et al 2005; Graham 2008; Telfer et al 2010; Hayward et al 2011; Van der Wal et al 2014; Kappeler et al 2015). Previous studies revealed substantial variation between individuals in terms of their burden of infection with various parasite taxa, the diversity of co-infecting parasite taxa, and how these measures change over time (Irvine et al 2000; Behnke et al 2005; Irvine 2006; Ferreira et al 2019) Individuals differ in their exposure to parasite infective stages, in their ability to mount immune responses to control or clear infections due to factors such as climatic conditions, age, and diet (Cattadori et al 2005; Behnke et al 2005; Råberg et al 2009; Turner and Getz 2010; Hayward et al 2011; Ferreira et al 2019). Immunological resistance to infections changes with age, being generally lower in young animals than adults (Dowling and Levy 2014; Simon et al 2015; Beirne et al 2016), suggesting that parasites that are controlled by adaptive immune responses may be more prevalent during early life stages
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