Phylogenetic study on relationships of the genus Anguilla

• Main Authors: Lin, Yeong-Shin, 林勇欣
• Other Authors: Chyng-Shyan Tzeng
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/45703805193900158386

碩士 === 國立清華大學 === 生命科學系 === 86 === Freshwater eels, the genus Anguilla Shaw of Family Anguillidae, containeighteen species (including three subspecies). The unique catadromouseels are born in remote sea abysses and their flat-body larvae driftingin ocean currents travel to the edges of continents and, then, migrateinto freshwater following metamorphosis for further growth. Therefore,appropriate spawning places and freshwater environments for juvenilegrowth may contribute to the distribution, speciation and dispersion ofeel species. Classifying freshwater eels is rather difficult owing to their similarmorphological appearance. Major criteria for classification consist ofproportion, coloration, dentition, and number of vertebrae. As generallyaccepted, a short dorsal fin and the absence of variegated markings areconsidered the primary monophyletic features. A majority of the Anguillaspecies is distributed throughout the Indo-Pacific region, particularlynear the equator, an area widely assumed to be the center of origin offreshwater eels. In contrast, only A. rostrata (Le Sueur, 1817) andA. anguilla (Linnaeus, 1758) inhabit the Atlantic Ocean. Of relevantinterest is how the Atlantic eels migrated all the way from the centerof origin to the Atlantic Ocean.In light of above concerns this study examines the phylogenetic relationshipsof freshwater eels covering more than half of the Anguilla species andemploying the entire cytochrome b gene to ensure the genetic variation.The close species in the phylogenetic tree do not share a similar colorationor the types of dorsal fin. Above characteristics imply that thesemorphological features might be unstable or have reoccurred duringevolutionary history.By combining the molecular results and geographical evidences, we speculatethat the origin of the genus Anguilla could be deduced to twenty millionyears ago. In addition, the ancestors of Atlantic eels may not havemigrated by the Tethys Seaway, but via the Central American isthmusinstead. The plate movement could provide another important factorfor eel speciation. In addition, this investigation presents an efficientmethod by RFLF analysis to identify the elvers for eel culture.