Letters to Nature

Nature 422, 157-160 (13 March 2003) | doi:10.1038/nature01460; Received 18 November 2002; Accepted 21 January 2003

Escalation of a coevolutionary arms race through host rejection of brood parasitic young

Naomi E. Langmore1, Sarah Hunt2 & Rebecca M. Kilner3

  1. School of Botany and Zoology, Australian National University, Canberra, Australian Capital Territory 0200, Australia
  2. School of Biological Sciences, University of Bristol, Woodland Road, Clifton, Bristol, BS8 1UG, UK
  3. Department of Zoology, University of Cambridge, Downing Street, Cambridge, CB2 3EJ, UK

Correspondence to: Naomi E. Langmore1 Correspondence and requests for materials should be addressed to N.E.L. (e-mail: Email: naomi.langmore@anu.edu.au).

Cuckoo nestlings that evict all other young from the nest soon after hatching impose a high reproductive cost on their hosts1. In defence, hosts have coevolved strategies to prevent brood parasitism. Puzzlingly, they do not extend beyond the egg stage2, 3, 4, 5. Thus, hosts adept at recognizing foreign eggs remain vulnerable to exploitation by cuckoo nestlings6, 7. Here we show that the breach of host egg defences by cuckoos creates a new stage in the coevolutionary cycle. We found that defences used during the egg-laying period by host superb fairy-wrens (Malurus cyaneus) are easily evaded by the Horsfield's bronze-cuckoo (Chrysococcyx basalis), a specialist fairy-wren brood parasite. However, although hosts never deserted their own broods, they later abandoned 40% of nests containing a lone Horsfield's bronze-cuckoo nestling, and 100% of nests with a lone shining bronze-cuckoo nestling (Chrysococcyx lucidus), an occasional fairy-wren brood parasite. Our experiments demonstrate that host discrimination against evictor-cuckoo nestlings is possible, and suggest that it has selected for the evolution of nestling mimicry in bronze-cuckoos.