9622827 McCUNE The needlefishes (family Belonidae), so-named because of their long needle-like jaws, are fast, predatory fishes found mainly in tropical marine waters. Over the past century, biologists have been intrigued by striking changes of body shape that needlefishes undergo during their life span: juveniles have a long lower jaw, but later develop into adults with long upper and lower jaws. Curiously, adults of the closely-related halfbeak fishes (family Hemiramphidae), have a long lower jaw but never develop the long upper jaw, and thus resemble juvenile needlefishes. Halfbeaks may have arisen from needlefish-like ancestors, or vice versa, through changes in developmental timing (heterochrony) of upper and lower jaw growth. Several needlefish species inhabit South American freshwater rivers. These fish may have invaded freshwater from the Atlantic Ocean, the Pacific Ocean, or both - and the biogeographic patterns among needlefish may also apply to other organisms found in this region. Interpretations of these developmental and biogeographic patterns depends on basic knowledge of how needlefish species are related to one another (a genealogy of species), and this knowledge currently is inadequate. In this study, Nathan Lovejoy, under the supervision of Amy McCune and Richard Harrison, will investigate the relationships of needlefishes by comparing DNA sequences from different species. Specimens of most species are available; a South American collecting trip will complete the list. Mitochondrial and nuclear genes will be amplified from fish tissue samples using the Polymerase Chain Reaction, and the DNA sequences of these genes will be used to construct phylogenetic trees. The resulting insights into needlefish biology will illuminate both the origins of the extraordinary diversity of aquatic species in the tropics, and the mechanisms producing dramatically different body-shapes among these species.
