Biology Reference
In-Depth Information
CHAPTER SIX
Flatfish: An Asymmetric
Perspective on Metamorphosis
Alexander M. Schreiber
1
Laboratory of Vertebrate Metamorphosis, St. Lawrence University, Biology Department, Canton, New York,
USA
1
Corresponding author: e-mail address: aschreiber@stlawu.edu
Contents
1.
Introduction
168
2. Genetic Basis of Flatfish Asymmetry
169
3. Metamorphic Asymmetry of the Brain, Sensory Organs, and Behavior
178
4. Asymmetric Craniofacial Remodeling and the Basis of Eye Migration
181
5. Flatfish Evolution: A Developmental Perspective
187
Acknowledgments
188
References
188
Abstract
The most asymmetrically shaped and behaviorally lateralized of all the vertebrates, the
flatfishes are an endless source of fascination to all fortunate enough to study them.
Although all vertebrates undergo left
-
right asymmetric internal organ placement dur-
ing embryogenesis, flatfish are unusual in that they experience an additional period of
postembryonic asymmetric remodeling during metamorphosis, and thus deviate from
a bilaterally symmetrical body plan more than other vertebrates. As with amphibian
metamorphosis, all the developmental programs of flatfish metamorphosis are ulti-
mately under the control of thyroid hormone. At least one gene pathway involved
in embryonic organ lateralization (nodal-lefty-pitx2) is re-expressed in the larval stage
during flatfish metamorphosis. Aspects of modern flatfish ontogeny, such as the gradual
translocation of one eye to the opposite side of the head and the appearance of key
neurocranial elements during metamorphosis, seem to elegantly recapitulate flatfish
phylogeny. This chapter highlights the current state of knowledge of the developmen-
tal biology of flatfish metamorphosis with emphases on the genetic, morphological, be-
havioral, and evolutionary origins of flatfish asymmetry.
