Scott Gilbert: Research
Download the PDF of How the Turtle Forms its Shell: A Paracrine Hypothesis of Carapace Formation from the Journal of Experimental Zoology.
We have three areas of research interest in developmental biology:
1. How the turtle got its shell: The development of an evolutionary novelty.
The turtle shell is a remarkable evolutionary novelty. It is composed of two main parts, the dorsal carapace and the ventral plastron. Between them, on the lateral sides, is a bridge. The carapace contains fifty bones and is supported by the ribs, which grow dorsolaterally rather than ventrally. The critical event in turtle development and evolution is thought to be the "ensnarement" of the ribs by the carapacial ridge, a bulge of ectoderm and mesoderm that resembles the limb bud. The bones of the shell are thought to be formed from the dermis by intramembranous ossification, with contributions from the ribs. We wish to test three hypotheses on the mechanisms governing turtle shell development: (1) that the carapace ridge forms by the co-option of the developmental program that forms the limb buds; (2) that the ribs induce intramembranous ossification in the dermis; and (3) that the dorsal growth of the rib cartilage precursors depends on their encountering the carapacial ridge. This work is supported by grants from the John Simon Guggenheim Foundation, the Howard Hughes Medical Institute, and the National Science Foundation.
The carapace (left) and plastron (right) of a 118-day red-ear slider hatchling. The shell bones of these farm-bred turtles are beginning to form and can be seen as the red stain. They form without a cartilagenous intermediate, similar to the way skull bones form. (From Gilbert et al., manuscript in preparation).
The second project concerns education in Developmental Biology. There are several components to this project. First, we have recently revised the textbook, Developmental Biology (Sinauer Associates, Sunderland, MA, 2006), for its eighth edition. This edition has new sections on the roles of paracrine factors in development, the development of aging, senescence, and regeneration, the influences of the environment on normal and pathological development, and the roles of development in evolution. This edition of the book is complemented by a website that allows us to (1) update the text and (2) to include material on the medical, ethical, and historical aspects of developmental biology. The website has been in existence since 1994, and it started as the creation of students in Scott's courses.
Second, while the Developmental Biology book focuses on the cellular and molecular aspects of development, a second volume, Ecological Developmental Biology, focuses on the ecological aspects of development. This is the first textbook in a new field concerning the interactions of the developing organism with its environment.
This has been an ongoing project and focuses on (1) the history of embryology with respect to genetics, and (2) the interactions between biology and society. We have edited two collections of essays in these areas:
Embryo of Trachemys scripta (red-ear slider turtle; about 4 weeks gestation) drawn from nature by A. Sonrel for Louis Agassiz (1857) Contributions to the Natural History of the United States II. The turtle egg may have been collected at Walden Pond by Henry David Thoreau, a friend of Agassiz.
Recent studies in the area include papers in the history of neural induction, the historiography of early genetics, feminist contributions to developmental biology, human cloning and embryonic stem cells; complexity and reductionism in contemporary embryology; and the roles of biology in the liberal arts curriculum.