Speciation by host switch in brood parasitic indigobirds

Abstract

A growing body of empirical and theoretical work supports the plausibility of sympatric speciation, but there remain few examples in which all the essential components of the process are well understood. The African indigobirds Vidua spp. are host-specific brood parasites. Indigobird nestlings are reared along with host young, and mimic the mouth markings of their respective hosts. As adults, male indigobirds mimic host song, whereas females use these songs to choose both their mates and the nests they parasitize. These behavioural mechanisms promote the cohesion of indigobird populations associated with a given host species, and provide a mechanism for reproductive isolation after a new host is colonized. Here we show that all indigobird species are similar genetically, but are significantly differentiated in both mitochondrial haplotype and nuclear allele frequencies. These data support a model of recent sympatric speciation. In contrast to the cuckoo Cuculus canorus, in which only female lineages are faithful to specific hosts, host switches have led to speciation in indigobirds because both males and females imprint on their hosts.

Differentiation of tundra/taiga and boreal coniferous forest wolves: genetics, coat colour and association with migratory caribou

“…Experimental and empirical studies on a diverse array of animals support natal habitat-based differentiation (Stamps 2001;Davis & Stamps 2004), and some observations support natal habitat-based dispersal, differentiation and fragmentation also in coyotes, a close relative of the grey wolf (Sacks et al 2005). Whereas random dispersal between different types of habitat will produce gene flow that limits local adaptation (Lenormand 2002), the combination of reduced gene flow and local adaptation facilitated by natal habitat-based dispersal might lead eventually to speciation (Sorenson et al 2003). The results of our study support a critical role for foraging ecology (a factor potentially linked to natal habitat-based dispersal) in explaining genetic and phenotypic patterns in North American wolves that may be similar to patterns in raptors, hyenas and killer whales where resident and migratory prey populations are found (Hofer & East 1993;Hoelzel 1994Hoelzel ,1998Lank et al 2003).…”

Coevolution is linked with phenotypic diversification but not speciation in avian brood parasites

“…Rapid genetic divergence may occur when different populations of a generalist species become more specialized on particular host species, or when they exploit, and specialize on, novel host species. For example, brood parasitic Vidua finches, Vidua spp., underwent sympatric speciation as they annexed novel host species [15]. Moreover, specialization on particular host species has led to genetic divergence within some cuckoo and honeyguide species into distinct host-specific races [16][17][18], and Krü ger et al [19] demonstrated that species of parasitic cuckoos had more subspecies than species of non-parasitic cuckoos.…”

“…Vidua finches and whydahs, on the other hand, impose lower costs on their hosts, because their young can be raised alongside the host chicks [15]. Differences in virulence between parasitic lineages may have repercussions in the coevolutionary interactions with their hosts, as selection for defences against parasitism is likely to be stronger in hosts of the more virulent species, leading to more rapid evolution of defences in hosts and counteradaptations in parasites [15].…”

Females that experience threat are better teachers

“…For example, reproductive isolation between indigobird (Vidua spp.) brood parasites is maintained because young males learn to mimic their host species' song and young females learn to prefer attributes of the host species nest and the learned song of the conspecific male [2]. Naive juvenile superb fairy-wrens (Malurus cyaneus) use social learning to recognize a brood parasite after observing experienced birds mob the cuckoo mount [3].…”