Game on for host birds and parasitic cuckoos
Biological arms races between host birds and avian brood parasites - in this case the cuckoo bird - drive evolution, leading to fresh 'signatures' (egg patterns) for the hosts and forgeries for the parasites, a new British-South African study shows. Presented in the journal Proceedings of the Royal Society B: Biological Sciences, the findings reveal significant changes in phenotypic diversity and behaviour of birds. Experts know that as brood parasitic birds, cuckoos lay eggs that mimic those of their hosts in order to fool the latter into accepting the 'alien' egg and raising the cuckoo chick as one of their own. But researchers from the University of Cambridge in the United Kingdom and the University of Cape Town in South Africa have discovered that some bird species parasitised by the African cuckoo finch have upped the ante by evolving their defence mechanisms to beat the cuckoo at its own game. An example of this is how the host females lay eggs of varied types, colours and patterns in the nests. Thanks to these egg signatures, the cuckoos have a much harder time of laying forgeries that could pass muster and trick the hosts into accepting them. The female cuckoo finch cannot change the look of her egg, thus practically failing in her attempt to match her egg to those of the female host. 'As the cuckoo finch has become more proficient at tricking its hosts with better mimicry, hosts have evolved more and more sophisticated ways to fight back,' explains Dr Claire Spottiswoode from the Department of Zoology at Cambridge, and the Percy FitzPatrick Institute of African Ornithology at Cape Town, the lead author of the study. 'Our field experiments in Zambia show that this biological arms race has escalated in strikingly different ways in different species. Some host species - such as the tawny-flanked prinia [Prinia subflava] - have evolved defences by shifting their own egg appearance away from that of their parasite. And we see evidence of this in the evolution of an amazing diversity of prinia egg colours and patterns. 'These variations seem to act like the complicated markings on a banknote: complex colours and patterns act to make host eggs more difficult to forge by the parasite, just as watermarks act to make banknotes more difficult to forge by counterfeiters.' A different plan of action for another cuckoo finch host, the red-faced cisticolas (Cisticola erythrops), is based not on laying significantly different eggs but on being very discriminate in what it accepts and rejects. In this case, the red-faced cisticola has such a brilliant discrimination skill that it can spot even the most sophisticated mimic among the other eggs. Commenting on varied strategies used by the host birds, Dr Martin Stevens, also from Cambridge's Department of Zoology and study author, says: 'Our experiments have shown that these different strategies are equally successful as defences against the cuckoo finch. Moreover, one species that has done a bit of both - the rattling cisticola [a Cisticola chiniana] - appears to have beaten the cuckoo finch with this dual strategy, since it is no longer parasitised. The arms race between the cuckoo finch and its host emphasises how interactions between species can be remarkably sophisticated especially in tropical regions such as Africa, giving us beautiful examples of evolution and adaptation.'For more information, please visit:University of Cambridge:http://www.cam.ac.uk/Percy FitzPatrick Institute of African Ornithology:http://www.fitzpatrick.uct.ac.za/Proceedings of the Royal Society B: Biological Sciences:http://rspb.royalsocietypublishing.org/
Countries
United Kingdom, South Africa