Population structure and speciation of Neotropical fishes

The population structure of many temperate fish species has been characterized by studies of mtDNA diversity; however, the phylogeography of South American taxa is virtually unknown. This is unfortunate since the Neotropics host the world’s most diverse fish fauna (estimated at 25% of all fish species), and a phylogeographic perspective could provide important clues for understanding speciation, gene flow, and life history patterns. Our lab is studying the population structure of several different Neotropical fish taxa, including needlefishes, cichlids, and electric knifefishes.

Cano Caicara, Apure State, Venezuela.
An excellent locality for Potamorrhaphis guianensis

We published the first phylogeographic study of South American fish species, an investigation of mitochondrial DNA diversity in the needlefish genera Potamorrhaphis, and Pseudotylosurus (Lovejoy and de Araújo, 2000). Ongoing surveys of genetic variation in the three described Potamorrhaphis species indicate a vast amount of genetic variation underlies a rather conservative morphology. For example, in the widespread species, Potamorrhaphis guianensis, we have identified more than 10 distinctive haplotype clades, and extensive sampling suggests that these clades have distinct geographic boundaries and may represent reproductively isolated populations.

A school of Potamorrhaphis guianensis

Stuart Willis, a recent graduate student in the lab, studied population structure and speciation in the Neotropical cichlid genus Cichla . For his MSc degree, Stu conducted fieldwork throughout northern South America (primarily Venezuela), and is investigating mitochondrial and nuclear genetic diversity in relation to river drainage patterns and water chemistry. He hopes to understand patterns of mechanisms of diversification in Cichla.

Our phylogenetic investigation of electric knifefishes of the genus Gymnotus also includes a phylogeographic component. Electric knifefishes offer a unique opportunity to consider species recognition systems in relation to intraspecific genetic variation and geography. For example, do widespread species have identical electric-organ discharges in different parts of their ranges? If discharges do differ across ranges, do these differences correspond to genetic breaks between populations?

Our studies suggests that a complex interplay of ecological and geographical factors determine patterns of intraspecific genetic structure and diversity. We are continually expanding the taxonomic, geographical, and genetic aspects of this study—for example, we are currently incorporating AFLP (amplified fragment-length polymorphism) DNA fingerprinting technology to assess patterns of nuclear variation. Our findings are providing significant insight into the evolution of diversity in the tropics; as well, we are contributing useful data for conservation genetics and fisheries management, since some of our target species are important food and sport fishes.

The Atures rapids, near Puerto Ayacucho, Venezuela.
A possible geographic barrier for Neotropical fishes.

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