Abstract
It has been suggested that selection on melanocortin-1-receptor (MC1R) polymorphism, a common cause of melanic colour variation in vertebrates, results from pleiotropic effects of the gene in the immune system. Here we present the first test of whether MC1R variation is associated with differences in parasite abundance in a natural population. Bananaquits (Coereba flaveola) (Linnaeus, 1758) living on Grenada in the Caribbean exhibit a melanic plumage dimorphism as a result of a mutation in MC1R. The proportion of black individuals increases clinally towards the central, wetter parts of the island. We captured bananaquits through the cline and quantified parasite abundances. Avian malaria, feather mites, and mallophaga lice varied significantly in abundance across the cline; however, neither these infections, nor coccidia, nor arboviruses showed overall differences between the morphs. Feather mites tended to be more abundant on black individuals, in areas where the black morph was more common. This may result from differences in microhabitat use by the two morphs. These patterns do not support the idea that MC1R variation in itself results in differing susceptibility to parasites. © 2013 The Linnean Society of London
Highlights
Throughout the history of evolutionary biology there has been a fascination with polymorphisms (Bates, 1861)
Feather mites on black birds increased with the percentage of black birds at a site, and tended to be more abundant than on yellow birds, for which there was no relationship between mite abundance and the percentage of black birds at a site (Fig. 2A; Table 1)
Faecal samples were obtained from 39 birds that were well distributed across the cline, and between black and yellow morphs (21 and 18 samples, respectively)
Summary
Throughout the history of evolutionary biology there has been a fascination with polymorphisms (Bates, 1861). Since before the advent of molecular genetics they have represented model systems for studying natural selection in the wild, while simultaneously allowing inference about genotypes (Cain & Sheppard, 1954; Kettlewell, 1973), and providing the first and most resonant examples of evolution occurring in nature (Bates, 1861; Kettlewell, 1973). Significant strides have been made in determining the genetic basis of several prominent polymorphisms (Theron et al, 2001; Hoekstra & Nachman, 2003). This new genetic understanding is interesting in itself, it further highlights the fundamental.
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