Abstract

Current hypotheses concerning nematode reproduction strategies focus on the component population level (individuals in all hosts collectively) and predict that sex ratios should be female biased at low prevalence and mean intensity and approach 1:1 as prevalence and mean intensity increase. We observed sex ratios of nematodes at both the component and the infrapopulation level (within each host individual), using 46 white-fronted geese (WFG) and 16 Ross’ geese (RG) collected in 1999–2000 and 60 blue-winged teal (BWT) collected in 2002. Nematodes were removed from gizzard linings and identified, and the sex of each worm was recorded.

Three species were found in the WFG: Epomidiostomum crami (prevalence 96.7%, mean intensity 14.0, sex ratio 1 female: 1 male), Amidostomum spatulatum (75.0%, 6.5, 1.2:1), and A. anseris (31.7%, 2.5, 1.3:1); two species were found in Ross’ Geese: E. crami (87.5%, 13.6, 1.2:1), and A. anseris (68.8%, 4.1, 1.3:1). Blue-winged teal also contained three species: A. acutum (96.7%, 7.5, 1.1:1), Streptocara crassicauda (56.7%, 2.9, 2.9:1), and E. uncinatum (21.7%, 2.5, 1.9:1). At the infrapopulation level, sex ratios from WFG were E. crami (18% equal, 43% male biased, 32% female biased, and 7% single-sex infections), A. spatulatum (6%, 43%, 43%, 24%), and A. anseris (30%, 0%, 0%, 70%); sex ratios from RG were E. crami (8%, 38%, 38%, 16%) and A. anseris (10%, 20%, 20%, 50%). Within BWT, sex ratios were A. acutum (11%, 37%, 41%, 11%), S. crassicauda (15%, 0%, 18%, 67%), and E. uncinatum (8%, 0%, 23%, 69%). The trend of sex ratios within the component population to approach 1:1 as prevalence and mean intensity increased concur with predictions of models finding less female-biased sex ratios with increased prevalence and intensity of infection. At the infrapopulation level, the high incidence of single sex infections at low prevalence suggests that propagation of those component populations is achieved by fewer hosts than shown by component-level analyses and stresses the importance of infrapopulation dynamics in community-based evaluations.