Research Training Program

Amanda Cass
Mount Holyoke College
South Hadley, Massachusetts

Lynne R. Parenti
G. David Johnson
Supervising Scientists
Systematic Biology, Vertebrate Zoology
Division of Fishes

"It is said that the best way to learn is through total immersion, and that's exactly what the RTP is: Ten weeks of reading, writing, talking and doing systematics. On top of that, it's done under the guidance of prominent scientists and with access to all the resources in the world. What more could an aspiring systematist ask for?"

A preliminary survey of the dorsal gill arches of flatfishes (Pleuronectiformes) and an examination of potential phylogenetic consequences

The flatfishes are a large and diverse group of fishes including more than 570 species. All fishes in this group share three unique features, the most striking of which is their transformation from symmetrical free swimming young to asymmetrical adults who live, almost exclusively, on the sea floor. Due to their unusual development natural historians have studied flatfishes for centuries, but much about them is still unknown. One important question that remains unanswered is their relationships to each other. Flatfish relationships are of special interest to science in the study of the evolution of development; if their asymmetry can be understood, it will help scientists to explain the development of all other symmetrical animals. However, in order to understand this asymmetry it is necessary to know about its evolution, which requires knowledge of the relationships of living flatfishes. One structure which has been helpful in determining relationships of fishes, and has not yet been examined in flatfishes, is the gill arch complex. The gill arches are a structure located behind the mouth and beneath the braincase that supports the gill filaments (used in respiration) and toothplates (used for feeding). These arches are divided into two parts, the dorsal (top) and ventral (bottom) complexes. Though unique features can be found in both, the dorsal arches are often the more variable complex. During the course of this survey, members of each flatfish family were prepared for observation via treatment in a trypsin bath (to make soft tissues transparent) and staining (to make cartilage and bone opaque and brightly colored). The dorsal complexes of their gill arches were then removed for examination and documentation. These structures were found to vary widely across groups, and more than 20 consistent differences were recorded. Due to the large number of species and the dramatic variation observed, a complete survey was not possible; however, the observations made support previous suggestions of flatfish relationships. Considering the small number of taxa used in this study, it is likely that still more information can be obtained by examining the gill arches more closely and a more comprehensive study is planned for the future. The data obtained from these studies will bring science one step closer to understanding the evolution of these unusual fishes, and the evolution of development.

This research was supported by a grant from the National Science Foundation Research Experiences for Undergraduates program, Award Number DBI-02435123.

Letter of gratitude