Sex-specific associations between reproductive output and hematozoan parasites of American kestrels

Abstract

Parasites have the potential to decrease reproductive output of hosts by competing for nutrients or forcing hosts to invest in immune function. Conversely, reproductive output may affect parasite loads if hosts allocate resources to reproduction such that allocation to immune function is compromised. Both hypotheses implicitly have a temporal component, so we sampled parasites both before and after egg laying to examine the relationship between reproductive output (indexed using a combined measure of clutch size, egg volume, and initiation date) and blood parasite loads of American kestrels (Falco sparverius). Parasite loads measured prior to egg laying had no adverse effects on subsequent reproductive output. Females that previously had large reproductive outputs subsequently had lower parasite intensities than those whose outputs were smaller, suggesting that females were capable of allocating energy to both forming clutches and reducing parasite loads. Because male kestrels provide most of their mate's energetic needs before, during, and after egg laying, mate choice by females may have consequences for their parasite loads. Females choosing high-quality mates may not only have increased reproductive output, but may also obtain sufficient resources from their mates to enable them to reduce their parasite burdens. Males whose mates had large reproductive outputs were more likely to subsequently be parasitized and have more intense infections. For individual males sampled both before and after egg laying, those whose mates had larger reproductive outputs were also more likely to become parasitized, or remain parasitized, between sampling periods. Increased parasite loads of males may be one mechanism by which the costs of reproduction are paid.

Reduced blood parasite prevalence with age in the Seychelles Warbler: selective mortality or suppression of infection?

“…In many bird species, females invest more in reproduction than do males (Trivers 1972); hence, females may be more likely to have blood parasites than males (e.g. Dawson and Bortolotti 2001). Experimental evidence is, however, lacking.…”

Unravelling causality from correlations: revealing the impacts of endemic ectoparasites on a protected species (tuatara)

“…Recapture studies also allow tests of the alternative hypothesis that lower fitness leads to increased susceptibility to parasites (Appleby et al 1999 ;Clobert et al 2000). However, relatively few studies have used temporal patterns to test both hypotheses (but see : Dawson and Bortolotti, 2001 ;Beldomenico et al 2008). Studies that investigate sequential associations between infection and indicators of host fitness may also reveal the temporal nature of parasite impacts on hosts.…”

Plasmodiuminfections of red-billed gulls (Larus scopulinus) show associations with host condition but not reproductive performance

“…There was no evidence to support an association between Plasmodium infection and decreased reproductive performance in redbilled gulls, although we note that missing data for some covariates may have limited discriminatory power. Observational studies have generally not provided strong support for a relationship between haemosporidian infection and reproductive performance, leading some authors to suggest that despite the potential severity of primary infections, chronic infections typical of wild-caught individuals might be relatively benign (Shutler et al 1999;Dawson & Bortolotti 2001;Bensch et al 2007). In contrast, medication experiments in passerines have demonstrated associations between experimental reduction of Haemoproteus or Plasmodium parasitaemia and increased clutch size, hatching success and/or fledging success (Merino et al 2000;Marzal et al 2005;Knowles et al 2010).…”

“…Oppliger et al 1997;Nordling et al 1998;Dawson & Bortolotti 2001;Schrader et al 2003). According to resource allocationbased theory, energetic trade-offs occur when limited resources must be apportioned to the competing interests of reproductive effort and immune system function (Gustafsson et al 1994;Sheldon & Verhulst 1996;French et al 2009).…”