DISSERTATION RESEARCH: Testing Behavioral Evolution in Response to Ecological Change in the Village Weaverbird (Ploceus Cucullatus)

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

Testing behavioral evolution in response to ecological change in the village weaverbird (Ploceus cucullatus). PI: Prof. Robert B. Payne Co-PI: David C. Lahti Behavior can evolve by natural selection, but testing this in wild populations is often difficult or impossible. The village weaverbird Ploceus cucullatus is a choice candidate for such a test, because historical events have fortuitously set the stage for an effective experiment. In the village weaverbird's home range in Africa, the diederik cuckoo Chrysococcyx caprius lays its eggs in weaverbirds' nests ("brood parasitism"). A hatched cuckoo promptly removes the weaverbird eggs or young from the nest. In 1999 and 2000, Lahti found that village weaverbirds throughout Africa eject from their nests eggs that are dissimilar from their own in color and spotting pattern, a behavior which is an effective defense against cuckoo parasitism. Their discrimination ability is finely tuned, which is necessary because the diederik cuckoo eggs mimic the appearance of weaverbird eggs. Humans introduced the village weaverbird from Africa into two islands where parasitic cuckoos do not exist: Mauritius, in the Indian Ocean, a century ago, and Hispaniola, in the Caribbean, about two centuries ago. Today there are large populations of the weaverbird in both places. Lahti will test quantitatively whether the weaverbirds' ability to discriminate against dissimilar eggs has declined in these two populations by "playing the cuckoo" and experimentally placing eggs into their nests. This experiment effectively imitates the environmental dangers of the weaverbirds' home range in a place where those dangers don't exist anymore. In this way the researchers can determine whether and to what extent the behaviors that evolved as a defense against those dangers have declined, since they are no longer needed.