Disease ecology in the Galápagos Hawk ( Buteo galapagoensis ): host genetic diversity, parasite load and natural antibodies

Abstract

An increased susceptibility to disease is one hypothesis explaining how inbreeding hastens extinction in island endemics and threatened species. Experimental studies show that disease resistance declines as inbreeding increases, but data from in situ wildlife systems are scarce. Genetic diversity increases with island size across the entire range of an extremely inbred Galápagos endemic bird, providing the context for a natural experiment examining the effects of inbreeding on disease susceptibility. Extremely inbred populations of Galápagos hawks had higher parasite abundances than relatively outbred populations. We found a significant island effect on constitutively produced natural antibody (NAb) levels and inbred populations generally harboured lower average and less variable NAb levels than relatively outbred populations. Furthermore, NAb levels explained abundance of amblyceran lice, which encounter the host immune system. This is the first study linking inbreeding, innate immunity and parasite load in an endemic, in situ wildlife population and provides a clear framework for assessment of disease risk in a Galápagos endemic.

Condition, innate immunity and disease mortality of inbred crows

“…Although information on immunity and inbreeding in other wild bird populations is scant, a negative relationship between inbreeding and immune response has also been documented in an island population of song sparrows (Melospiza melodia), using an assay of cellmediated immunity, which is one component of the avian acquired immune system (Reid et al 2007). Likewise, among island populations of Galapagos hawks (Buteo galapagoensis), Whiteman et al (2006) found that the NAb levels decreased with populationlevel genetic diversity, and individual ectoparasite abundance was negatively correlated with the level of NAbs.…”

“…Empirical evidence for disease costs of inbreeding has been documented in captive settings (e.g. Spielman et al 2004;Hawley et al 2005;Ross-Gillespie et al 2007;Charpentier et al 2008;Ilmonen et al 2008) as well as in an array of free-living taxa, including California sea lions (Zalophus californianus; Acevedo- Whitehouse et al 2003), Mediterranean striped dolphins (Stenella coeruleoalba; Valsecchi et al 2004), Galapagos hawks (Buteo galapagoensis; Whiteman et al 2006), Soay sheep (Ovis aries; Coltman et al 1999), harbour seals (Phoca vitulina; Rijks et al 2008) and American crows (Corvus brachyrhynchos; Townsend et al 2009a). In some studies, however, the relationship between inbreeding and disease is unclear (e.g.…”

“…Previous field studies have explored links between inbreeding and components of the immune response (Reid et al 2007), inbreeding and disease (e.g. Acevedo-Whitehouse et al 2003;Charpentier et al 2008;Townsend et al 2009a), immune response, condition and parasite load (Moller & Haussy 2007;Parejo & Silva 2009), and population-level genetic diversity, immune response and ectoparasite abundance (Whiteman et al 2006). To date, however, no studies have explicitly examined the links between inbreeding, immune response, condition and disease mortality of individuals in a wild, free-living population.…”

Nature of crop contents of an amblyceran pigeon louse, Colpocephalum turbinatum (Phthiraptera: Insecta)

“…Moreover, Whiteman and Parker (2004b) recorded negative relationship between body condition of Galapagos hawks and the abundance of C. turbinatum and suspected this relationship to be based on blood feeding habits of C. turbiantum . Whiteman et al (2006) further indicated that natural antibody titre of Galapagos hawks were found negatively correlated to the abundance of C. turbinatum (assuming that it feeds on skin and blood). Santiago et al (2008) also emphasized that C. turbinatum feeds on epidermal tissues and blood over most regions of body.…”

Field Investigation of Innate Immunity in Passerine Birds in Suburban Chicago, Illinois, Usa

“…This result suggests that bactericidal capacity tended to be lower for birds infested with chewing lice, which is consistent with a metaanalysis showing that brood manipulation (i.e., increased reproductive effort) decreased immune responsiveness and in- creased hematozoan parasitemia (Knowles et al, 2009). Additionally, Whiteman et al (2006) found that ectoparasite abundance on the Galapagos Hawk (Buteo galapagoensis) was negatively correlated with natural antibody titers, as measured by the hemolysis-hemagglutination assay. The lack of correlation between constitutive innate immunity and condition indices observed in this study is consistent with previous studies in birds (Palacios et al, 2009;Forsman et al, 2010), which suggest that the innate branch of the immune system is less sensitive to body condition than adaptive immunity.…”