Variation in inflammation as a correlate of range expansion in Kenyan house sparrows |
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Authors: | Lynn B Martin Jennifer L Alam Titus Imboma Andrea L Liebl |
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Institution: | (1) Department of Integrative Biology, University of South Florida, 4202 E. Fowler Avenue, SCA 110, Tampa, FL 33620, USA;(2) Department of Ornithology, National Museum of Kenya, Nairobi, Kenya |
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Abstract: | Many introduced animals harbor fewer parasites than native ones. This “enemy release” can select for individuals that bias
resources away from parasite resistance traits, including immune functions, and towards traits that enhance success in new
areas. One vertebrate example that supports this hypothesis involves house sparrows (Passer domesticus) and Eurasian tree sparrows (Passer montanus) introduced to St. Louis, MO, USA, over 150 years ago. Since ca. 1850, house sparrows have colonized most of North America
whereas tree sparrows have expanded little from the area of introduction. The more successful house sparrows now exhibit weaker
inflammatory responses than the less successful tree sparrows, which supports the possibility that diminished investments
in immune defense may have been conducive to the initial colonization by the more successful species. The goal of the present
study was to determine whether damped inflammation generally facilitates invasion by comparing inflammatory markers between
house sparrows invading Kenya and a native congener. House sparrows arrived in Mombasa, Kenya, about 50 years ago whereas
rufous sparrows (Passer ruficinctus) are native but ecologically similar. We predicted that if inflammation mediated invasion success, Kenyan house sparrows
would mount weaker inflammatory responses than the native species. Complete Freund’s adjuvant (CFA), a strong inflammatory
stimulus, increased body mass in house sparrows, a result unprecedented in any other vertebrate. Haptoglobin (Hp), a multi-functional
acute phase protein, was elevated by CFA in both species but rufous sparrows maintained more Hp than house sparrows irrespective
of treatment. Lysozyme, a broadly effective antimicrobial enzyme, was reduced by CFA in both species, but not differentially
so. Corticosterone was unaffected by CFA in either species, but elevated in both relative to free-living individuals. |
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