| Summary: | 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.
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