Tolerance as a Parasite Defense in a Colonial Bird

University Of Tulsa, Tulsa OK

Investigators

Abstract

All living organisms must defend themselves from disease-causing parasites and pathogens to which they are exposed. The typical way that such defense occurs is by resisting the pathogen or parasite, often through an immune response. Resistance by the host is the basis for much of modern medicine, in which the immune response is enhanced or replaced by various therapies. However, another defense is the tolerance of the parasite or pathogen without mounting any resistance, which (under certain circumstances) can be beneficial to the host, in part because tolerance does not require the host to incur the physiological cost of mounting an immune response. Plants are well known to tolerate various pathogens, but the ability of animals to tolerate parasites has only recently been recognized. This project documents how a colonial bird, the cliff swallow, has rapidly evolved (over 30 years) the ability to tolerate large numbers of blood-feeding parasitic bugs. By comparing the effects of these parasites on the birds in the 1980s versus their effects today, insight into conditions that favor the development of tolerance as a parasite defense in a social animal will be gained. The results will have wide relevance to understanding ways that animals (including humans) can potentially minimize the negative effects of parasites and the diseases sometimes associated with those parasites. Parasite tolerance has been established as a key host defense in plant-parasite systems, but few empirical studies have explored the role of tolerance in animal host-parasite relationships. This research seeks to study the ecology and evolution of tolerance defense strategies against parasites in colonially nesting cliff swallows (Petrochelidon pyrrhonota) and their principal parasite, the swallow bug (Hemiptera: Cimicidae: Oeciacus vicarius). The work builds on a long-term field study and the relatively recent adoption of new nesting sites by cliff swallows where they have come into greater contact with their nest parasites. During the 1980s, bugs exerted severe effects on cliff swallow reproductive success, but subsequent observation suggests that the birds may have evolved greater tolerance to parasitism in the intervening 30 years. This research seeks to establish whether cliff swallows now better tolerate parasites and how the birds? anti-parasite behavior may be changing as a result. The novelty of this work is that it is the first to examine temporal changes in tolerance within a natural population. This research will involve undergraduate students and a postdoctoral scientist, and participation by a community college faculty member will facilitate involvement of urban minority students. Because enhancing tolerance by the host may be more effective in fighting inflammatory and autoimmune diseases than prescribing antibiotics (a strategy that promotes resistance to parasites), this research will encourage non-scientists to think about tolerance as a treatment option.