Research Training Program

Alexandre Cunha Ribeiro
Universidade de São Paulo
Ribeirão Preto, Brazil

Richard P. Vari, Ph.D.
Supervising Scientist
Department of Systematic Biology
Division of Fishes

"It was a great experience working in my favorite field, Phylogenetic Biogeography, in one of the best museums."

Phylogeny of the genus Oligosarcus Günther: A preliminary survey

The genus Oligosarcus comprises 16 species that occur in most of the major drainages of the south central portions of South America. Members of the genus are small to mid-sized fishes (about 40 to 200 mm) occurring mainly in streams. With the exception of O. schindleri, collected from a tributary of Río Charape which flows into the Rio Madeira of the Amazon basin, all Oligosarcus species occur outside the Rio Amazonas basin and no species of the genus have been collected north of 15º S (Menezes, 1988). Little ecological information on Oligosarcus is available although life history studies of a few species report that they range from omnivores to fish predators. Information on intrageneric relationships for Oligosarcus was effectively nonexistent and biogeographic hypotheses as a consequence were not grounded on phylogenetic information. Data from a series of osteological systems examined demonstrates that the genus is monophyletic, provides insight into likely sister groups to Oligosarcus, and partially resolves the interrelationships within the genus. The results of this study indicate that the fragmentation of the genus Oligosarcus into mostly allopatric species is congruent with a hypothesis of speciation associated with somewhat recent vicariant events as evidenced by the lack of sympatry between sister groups, a situation contrary to that in many other fish species in that region. The sister-group relationship between O. pintoi and O. planaltinae suggested by the results is consistent with the idea that the High-Paraná is a endemic area. However, the recognition of "lowland species" and "plateau species" groups as postulated by Menezes (1988) is not supported by the phylogeny, since some of the "plateau species" are more closely related to a subunit, but not all of the "lowland species."

This research was supported by the Alice Eve Kennington Endowment.

Letter of Gratitude