Dai Shizuka

I am an evolutionary ecologist, with broad interests in the mechanisms that facilitate or constrain social evolution. My research lies  at the intersection of life history theory, evolutionary conflicts and cognitive ecology. Here are some of my major research interests at the moment:

(1) What are the roles of learning and recognition in ecological and evolutionary processes?

In my dissertation research, I demonstrate that American coots (Fulica americana) have an ability to do what most birds seem unable to do: recognize and reject brood parasitic chicks. More shockingly, they do this despite the fact that parasitism occurs within species, and thus parasitic chicks look much like their own. Through experiments and theory, I confirm a theory proposed 15 years ago -- that cost of learning errors can constrain host adaptations, and that when these costs are alleviated, chick recognition can evolve (Lotem 1993). But critically, a detailed understanding of the mechanism of learning is necessary for untangling these costs of errors and benefits of recognition.

This work has led me to further ponder the ubiquitous role of learning mechanisms in ecological and evolutionary processes. Equally important is the ecology of information in which organisms evolve, which ultimately influences the evolution of learning. I seek to combine field experiments and theory to further understand learning processes in the contexts of host-parasite coevolution, speciation and family dynamics.

(2) How to conflicts within families affect life history strategies?

Raising a family is challenging. Conflicts of interest arise between parents, who seek to optimize family size each breeding season, and offspring, who seek to maximize the amount of care they receive (to a point). How parents manage their investment in the face of these conflicts has been a focus in evolutionary theory.

In stark contrast to some well-known examples of parents who do not intervene in sibling conflict (e.g., boobies, hyenas), American coots have a decidedly active -- and aggressive -- strategy of parental intervention.  My research shows that parental behaviors such as parental aggression, brood division and favoritism act as mechanisms for parental control that allow adults to optimally invest in their offspring. In the process, parents create a "favoritism hierarchy", that is distinct from the competitive hierarchy created by hatching asynchrony. The degree to which parents compensate for competitive asymmetries among offspring allows them to facultatively adjust their brood size.

By using coots as a counter-example to many well known systems in which parents do not intervene in sibling conflict, I seek to expand the scope of how we understand parent-offspring conflict theory and life history theory in birds.

(3) Winter social strategies of migrant birds

I am also working on a collaborative project with Bruce Lyon and Alexis Chaine, integrating signalling strategies and overall wintering strategies of a migrant, the golden-crowned sparrow (Zonotrichia atricapilla). We consider plumage signalling, winter singing, flocking and space use as a global strategy, through which individuals seek to maximize their survival and condition during the non-breeding season -- which takes up most of their lives. This research, conducted on the UCSC campus, has also been a major source of undergraduate mentorship. 

Photos by B. Lyon

Publications:

Shizuka, D. and B. E. Lyon. In Review. Coots learn to recognize and rejecti brood parasitic chicks.

Dickinson, J.L., M. Euparadorn, K. Greenwald, C. Mitra and D.Shizuka. 2009. Cooperation and competition: Nepotistic tolerance and intrasexual aggression in western bluebird winter groups. Animal Behavior 77: 867-872. 

Shizuka, D. and B.E. Lyon. 2008. Improving the reliability of molecular sexing using a W-specific marker. Molecular Ecology Resources 8: 1249-1253.

Shizuka, D. and J.L. Dickinson. 2005. Using molt limits to age Western Bluebirds. Journal of Field Ornithology 76(2):193-196.

in preparation:

Shizuka, D. and B.E. Lyon. Benefits of rejection, costs of errors, and synergistic host defense against brood parasite eggs and chicks.

Shizuka, D. and B.E. Lyon. Parental intervention compensates for hatching asynchrony.

Shizuka, D., A. Marcus, S. Kim, P.L. Koch, and B.E. Lyon. A stable isotope approach to understanding regulation of clutch size.

Chaine, A.S., K.A. Tjernell, D. Shizuka and B.E. Lyon. Multiple badges of status in winter social flocks. 

Pelayo, J.T., K.R. Mehl, J.J. Taylor, W.L. Reed, C.L. Amundson, D. Shizuka, B.E. Lyon and T.W. Arnold. Assessement of nape tags for marking offspring of precocial waterbirds.