Dai Shizuka
Allee Awardee for the best student presentation at the 2009 ABS Annual Meeting held in Pirenópolis, Brazil, 22-26 June.
General Research Interests of Dai Shizuka
One of my major research goals is to identify a major ecological puzzle or problem and trying to understand how learning -- a fundamental and ubiquitous process in behavior -- might play a role in these contexts. In my dissertation work, I focus on life history evolution and social conflicts within families. American coots, a common waterbird in North America, provides an interesting study system because parents face two major challenges to optimizing family size each year: brood parasitism and sibling competition. In particular, my presentation at the 2009 Animal Behavior Society conference focused on the role of learning in a unique host defense strategy against brood parasitism - parasitic chick rejection.
Topic of 2009 ABS Conference talk:
Over 2000 years ago, Aristotle first noted cuckoos do not make their own nests, but lay eggs in nests of other birds, who then raise their chicks (The History of Animals, Book IX Part XX). In the centuries since, the natural history of interactions between brood parasites and their hosts have been the focus of much interest, and detailed research has revealed how coevolutionary arms races between brood parasites and hosts fuel fascinating adaptations such as egg mimicry and egg recognition. Yet one question—why do hosts regularly fail to reject parasitic chicks after they hatch?—has eluded general explanations, and remained as a major evolutionary puzzle.
In my research, I show that parasitic chick recognition and rejection have evolved as a host defense in an unlikely system—conspecific brood parasitism—and demonstrate that costs of learning errors (Lotem 1993) may be a major driver the evolution of chick rejection. Combining field experiments with a long-term observational study, I show that American coots (Fulica americana) use the first-hatched chicks of the brood as referents for recognizing brood parasites among the later-hatched chicks of the same brood. When we experimentally replace host chicks with foreign chicks on the first day of hatching, we can induce parents to reject their own later-hatched chicks, paying the cost of learning errors. However, coots rarely pay this cost in nature because parasites rarely hatch on the first day, partly due to specific host defenses during the egg stage that delay hatching of parasitic chicks compared to host chicks. By ensuring that they have a pure reference of only their own chicks on the first hatching day, many coots gain the benefit of rejecting parasitic chicks while minimizing the risk of learning errors that would induce them to reject their own chicks.
This simple rule—learn the first-hatched chicks as your own—works well with coots, but could be detrimental to hosts of obligate brood parasites such as cuckoos and cowbirds. Because most obligate brood parasites have evolved to hatch early, hosts that are parasitized would mistakenly learn the parasitic chicks as their own. Therefore, by hatching early, brood parasites may not only gain a head start in parental provisioning, but also prevent chick rejection as host defense through the effects of learning errors.
