Evidence for a novel host selection strategy in the Shiny cowbird Molothrus bonariensis

MAHLER, B.; LOVETTE, I. J.; CONFALONIERI, V. A.; REBOREDA, J.C.

Tours

Congreso; XI International Behavioral Ecology Congress; 2006

Obligate brood parasites can be host-specialists, i.e. they lay their eggs in the nests of only one species, or host-generalists, i.e. they lay their eggs in the nests of more than one species. In the latter, in turn, individual females can be specialists if they parasitize only one host species, forming host-specific races or lineages, or generalists, if they parasitize more than one host species. The aim of this study was to analyze the strategies used by individual females of the host-generalist Molothrus bonariensis (Shiny cowbird) to select their hosts. In order to do that we studied the variation patterns of a 1154 bp fragment of mitochondrial DNA, belonging to the control region. We collected samples of Shiny cowbirds’ eggs or chicks found in four different hosts (House Wren, Chalk-browed Mockingbird, Brown and Yellow Marshbird, and Rufous-collared Sparrow) in three locations of Buenos Aires province. We studied 101 individuals and found 15 different haplotypes. The genetic variation patterns showed that females that parasitize the nests of the House Wren are genetically different from females using the nests of the other three species. These results suggest that females are not selecting for a particular host species, but for a particular nest type, as the House Wren is the only cavity nester, whereas the other three species are open cup nesters. This is the first time that such a nest selection pattern is described for an obligate brood parasite.