TRANSMISSION DYNAMICS AND HOST-PARASITE INTERACTIONS OF TRICHOSTRONGYLUS-TENUIS IN RED GROUSE (LAGOPUS-LAGOPUS SCOTICUS)

Two components of the transmission dynamics of Trichostrongylus tenuis in red grouse are examined and quantified, namely parasite transmissi on rate and density-dependent reductions in egg production. Age-intens ity data for birds of known age suggest that the rate of parasite upta ke increases during the first 6 mo of a bird's life and this increase reflects an increase in feeding rate with age and exhibits no signs of self-cure. Analysis of these age-intensity curves permits us to estim ate the transmission rate of the free-living infective stages. Reinfec tion rates of adults treated to reduce parasite intensities were not s ignificantly different from infection rates of naive immature grouse. Secondary infections continued to rise over a period of 18 mo and this suggests that there is no strong host-mediated response against the p arasite. Any density-dependent reduction in parasite fecundity is prob ably very weak and would act through interspecific competition between parasites. Initial analysis of worm egg production in relation to the intensity of worm infection found weak evidence of density-dependent suppression of egg production at high worm intensities. However, a mor e rigorous analysis found that such a relationship suffered from Type I errors and was a consequence of the aggregated distribution of the p arasites. Any density-dependent suppression of parasite egg production is too weak to be detected and would only occur at high worm intensit ies. The potential density-dependent reductions in fecundity on the po pulation dynamics of T. tenuis and red grouse are examined using a mat hematical model. The model suggests that the presence of density-depen dent reductions in worm fecundity could produce significant reductions in the propensity of the grouse-nematode system to exhibit population cycles. The sustained cycles observed in the long-term dynamics of th e grouse populations in the study area suggest that density-dependent reductions in worm fecundity and establishment are either absent or on ly operating at levels that are not detectable in field studies.