Understanding parasite strategies: a state-dependent approach?

Abstract

Understanding and predicting parasite strategies is of interest not only for parasitologists, but also for anyone interested in epidemiology, control strategies and evolutionary medicine. From an ecological and evolutionary perspective, parasites are an important feature of their hosts' selective environment, and may have diverse roles, ranging from the evolution of host sex to host-sexual selection behavior. Generally, it is the hosts and their biology that have been the focus of these evolutionary investigations, but we approach the subject from the parasites' perspective, illustrating the sophistication of parasite strategies in dealing with contrasting and unpredictable environments.

What Makes a Host Profitable? Parasites Balance Host Nutritive Resources against Immunity

“…1a) differed between colonies and years, which agrees with the idea that host exploitation rate is a dynamic process that can fluctuate over space and time (Lively 1999). Although the importance of incorporating measures of parasite performance (and in turn fitness) in host-parasite coevolutionary scenarios has been stressed in recent studies (Sukhdeo and Bansemir 1996;Poulin and Combes 1999;Thomas et al 2002), we still know little about the relative effects of host immunocompetence, nutritional status, and other phenotypic traits on parasite fitness (e.g., Clayton et al 1999;Jokela et al 1999;Møller 2000;Roulin et al 2001;Blanford et al 2003;Pulkkinen and Ebert 2004;Krasnov et al 2005;De Bellocq et al 2006;Tseng 2006) in comparison to our knowledge of the effects of parasites on host fitness (Combes 2001). However, the present study is of importance because it highlights that the understanding of parasite strategies is a necessary step toward an appraisal of the outcome and evolution of hostparasite interactions.…”

“…Apart from the present study, maximal parasite fitness on hosts in intermediate condition has been found in two endoparasite species, namely, microsporidian (Bedhomme et al 2004) and malarial parasites (Lambrechts et al 2006) infesting mosquitoes. Although host condition is expected to have greater effects on the behavior of endoparasites because they cannot move from one host to another (Sukhdeo and Bansemir 1996;Poulin and Combes 1999;Thomas et al 2002), the same can be true in ectoparasites, as shown here. The louse fly Crataerina melbae is flightless and has a vertical transmission in the colony due to nest reuse by their hosts, and prolonged periods of poor weather are the major factor modulating nestling body condition in the whole colony.…”

“…Thus, louse flies (and parasites in general) may balance different host qualities when choosing, first, which host to go to/stay on, and second, how to exploit host resources. Altogether, this study suggests that parasites may show plastic and complex behavioral responses in the different steps of host-parasite interactions, hence emphasizing the need to take into account behavioral plasticity by parasites to appraise the whole diversity of host-parasite relationships (Sukhdeo and Bansemir 1996;Poulin and Combes 1999;Thomas et al 2002).…”

Biological implications of the phenotypic plasticity in the Schistosoma mansoni - Nectomys squamipes model

“…Vertebrate hosts behave as biological filters to parasites selecting phenotypes and genotypes within natural populations 8 . Hence, parasites may recognize the physiological and biochemical conditions of their hosts that are of selective importance 36 . The ability to adjust growth and reproduction to immediate local conditions would have been of great interest adaptive value to parasites 30 .…”

“…It must be also emphasized that S. mansoni adult worms might detect signals from their environment and responding appropriately in a state-dependent manner could greatly enhance its fitness 36 . The present study highlights the importance of water rat as a reservoir host for S. mansoni strains that might contribute to dispersion of schistosomiasis mansoni in Brazil.…”