Host sexual selection and cuckoo parasitism: an analysis of nest size in sympatric and allopatric magpie Pica pica populations parasitized by the great spotted cuckoo Clamator glandarius

Abstract

Magpies (Pica pica) build large nests that are the target of sexual selection, since males of early breeding pairs provide many sticks for nests and females mated to such males enjoy a material ¢tness bene¢t in terms of better quality territory and parental care of superior quality. Great spotted cuckoos (Clamator glandarius) preferentially parasitize large magpie nests and sexual selection for large nests is thus opposed by natural selection due to brood parasitism. Consistent with the hypothesized opposing selection pressures, in a comparative analysis of 14 magpie populations in Europe we found that nest volume was consistently smaller in sympatry than in allopatry with the great spotted cuckoo, in particular in areas with a high parasitism rate and high rates of rejection of mimetic model cuckoo eggs. These observations are consistent with the suggestion that magpies have evolved a smaller nest size in areas where cuckoos have exerted strong selection pressures on them in the recent past.

Brood-parasite interactions between great spotted cuckoos and magpies: a model system for studying coevolutionary relationships

“…A reduction in nest size is predicted to be caused by an increase in parasitic selection pressure. In accordance with the hypothesis, nest volume was on average reduced by 33.2% in areas of sympatry between parasite and host, as compared to areas of allopatry (J.J. Soler et al 1999b). Additionally, differences in the volume of magpie nests within different populations were correlated in a significant and negative manner with levels of parasitic selec-312 Fig.…”

“…Additional evidence of cuckoos selecting magpies with large nests comes from a study of 14 European magpie populations that vary in levels of parasitism (J.J. Soler et al 1999b). As nest size in magpies is a sexually selected character (J.J. Soler et al, in press, a), parasitic and sexual selection pressures should represent antagonistic forces working on the same character -the tendency to produce a nest of a certain size (Fig.…”

“…Fitness effects for parasites and hosts are shown for each of the strategies adopted by cuckoos and hosts tion pressure (e.g. prevalence of parasitism and ability of magpies to recognise foreign eggs) (J.J. Soler et al 1999b). (The latter analysis included a control for genetic distance between populations).…”

Brood parasitism by brown-headed cowbirds and the expression of sexual characters in their hosts

“…Therefore, individuals and/or species with more conspicuous sexual traits may be more prone to parasitism than birds with less conspicuous signals (e.g. Banks and Martin 2001;Soler et al 1995Soler et al , 1999.…”

“…If brood parasites use secondary sexual characters for host recognition, brood parasitism is a potential selection pressure that may raise evolutionary constraints against the products of sexual selection (e.g. Soler et al 1999). Consequently, selection pressures arising from brood parasitism may have favoured hosts to develop less elaborate sexual signals, allowing them to escape this pressure.…”