504 J. Parasitol., 93(3), 2007, pp. 504–510  American Society of Parasitologists 2007 PATTERNS OF GASTROINTESTINAL PARASITISM AMONG FIVE SYMPATRIC PRAIRIE CARNIVORES: ARE MALES RESERVOIRS? Aaron J. Wirsing, Fernando C. C. Azevedo*, Serge Larivie `re†, and Dennis L. Murray‡ Department of Biological Sciences, Marine Biology Program, Florida International University, Biscayne Bay Campus MSB 351, North Miami, Florida 33181. e-mail: wirsinga@fiu.edu ABSTRACT: Male vertebrates are believed to be disproportionately vulnerable to parasites, but empirical support for this contention is mixed. We tested the hypothesis of higher levels of parasitism in males with the use of counts of gastrointestinal helminths in 5 sympatric mammalian carnivores (American badgers, coyotes, red foxes, raccoons, striped skunks) from central Saskatchewan. Parasite burdens for females and males of each host species were compared with the use of prevalence (percentage of hosts infected), intensity (parasites per infected host), and overdispersion (proportion of heavily infected hosts that were male). Of 30 comparisons (13 each for prevalence and intensity, 4 for overdispersion), male bias was detected 8 times (27%), whereas female bias was detected only once (3%), adding some support to the notion that male mammals are more susceptible to parasitism. However, most of the statistical comparisons we undertook revealed no sexual bias (n = 21, 70%), suggesting that differential patterns of infection are not ubiquitous in mammals. Moreover, when detected, the magnitude and direction of bias varied among host species, helminth species, and metrics of infection. We conclude that sympatric and ecologically similar mammal species will not always share the tendency for males to be more susceptible to parasitism, and that studies incorporating multiple parasites and metrics of infection are more likely to detect sex bias. Parasites tend to aggregate in particular hosts within species across a variety of taxa (Shaw and Dobson, 1995; Wilson et al., 1996; Shaw et al., 1998). Skewed parasite distributions within host populations are known to derive from individual differences in exposure and susceptibility (Wilson et al., 2002), but host traits consistently associated with heightened contact and vulnerability have been difficult to identify (Perkins et al., 2003). These traits are of wide interest, for parasite skew has important implications for the dynamics and stability of host populations, the responsiveness of host populations to parasite control measures, and the mechanisms of parasite transmission (Anderson and May, 1985; Bundy, 1988; Perkins et al., 2003). In mammals, 1 trait often associated with vulnerability to parasitism is host sex (Poulin, 1996). Specifically, males have been hypothesized to be more prone to infection than females because: (1) their comparably large size and tendency to roam widely may render them easier and more accessible targets (Poulin, 1996; Arneberg, 2002; Moore and Wilson, 2002; Wil- son et al., 2002), (2) testosterone allegedly suppresses immune function (Folstad and Karter, 1992), and/or (3) they should be expected to invest heavily in short-term mating success rather than longevity (Rolff, 2002). This hypothesis has received em- pirical support (Poulin, 1996; Schalk and Forbes, 1997). How- ever, not all analyses have documented a male bias (e.g., Stien et al., 2002), and observed levels of bias often have been small (typically 5%), raising questions about biological significance (Wilson et al., 2002; Skorping and Jensen, 2004). Thus, the notion that males in many mammal populations serve as res- ervoirs for parasites, i.e., tend to be more heavily burdened, remains contentious and, given that relevant data are scarce, merits further consideration. We explored patterns of gastrointestinal parasitism in 5 sym- patric prairie carnivore species, i.e., American badgers (Taxidea Received 25 September 2006; revised 1 December 2006; accepted 4 December 2006. * Department of Fish and Wildlife Resources, University of Idaho, Mos- cow, Idaho 83843. † Cree Hunters and Trappers Income Security Board, 2700 Boulevard Laurier, Sainte-Foy, Quebec G1V 4K5, Canada. ‡ Department of Biology, Trent University, Peterborough, Ontario K9J 7B8, Canada. taxus), coyotes (Canis latrans), red foxes (Vulpes vulpes), rac- coons (Procyon lotor), and striped skunks (Mephitis mephitis). For each carnivore, helminth parasite communities in both sex- es were quantified and compared to test the generality of the hypothesis that male mammals are more susceptible to parasit- ism than their female counterparts. In the absence of overall gender differences in parasite burdens, certain members of 1 sex may nevertheless act as reservoirs for parasites; thus, var- iance with respect to susceptibility may be greater in 1 sex than the other even if mean levels of infection are equivalent (Per- kins et al., 2003; Ferrari et al., 2004; Skorping and Jensen, 2004). Therefore, we addressed both mean parasite loads for males and females and the tendency of heavily infected indi- viduals to belong to a particular sex. Importantly, particular parasites may possess ecological or life history attributes that typically lead them to burden (or preclude them from burden- ing) 1 sex more heavily irrespective of gender-specific patterns of susceptibility in their hosts (Reimchen and Nosil, 2001). By extension, such parasites should be expected to overburden the same sex (or to burden the sexes equally) in all potential host species that are ecologically similar, i.e., that occupy similar niches, in a given environment (Altizer et al., 2003). Therefore, we also hypothesized that, even if the male carnivores in our system are not inherently more vulnerable to parasitism, spe- cific parasites sharing multiple host species should nevertheless manifest consistent distribution patterns, e.g., a consistent ten- dency to aggregate in males. MATERIALS AND METHODS Collection of specimens Between April and June of 2000 and 2001, carnivores were collected roughly 75 km southwest of Weyburn, Saskatchewan, Canada (49°24'N, 104°39'W; see Azevedo et al., 2006, for study-area details) as part of a predator control program initiated by the Delta Waterfowl Foundation. Importantly, the carnivore species sampled are characterized by consid- erable dietary (see Azevedo et al., 2006) and spatial overlap (S. Lari- vie `re, unpubl. obs.) and are not known to exhibit marked gender dif- ferences with respect to diet (F. Azevedo, unpubl. obs.) in the study area. Thus, opportunities for shared parasites to infect both sexes of all of their hosts presumably were roughly comparable. Carnivores were harvested according to the protocol described by Azevedo et al. (2006); all predator removal procedures conformed to standard protocols and were approved by the University of Saskatchewan Animal Care Com-