South American electric knifefishes of the genus Archolaemus (Ostariophysi, Gymnotiformes): undetected diversity in a clade of rheophiles : GENUS ARCHOLAEMUS

Hydroelectric dams represent major investments and major sources of environmental and social impacts. Powerful forces surround the decision-making process on public investments in the various options for the generation and conservation of electricity. Brazil's proposed Belo Monte Dam (formerly Kararaô) and its upstream counterpart, the Altamira Dam (better known by its former name of Babaquara) are at the center of controversies on the decision-making process for major infrastructure projects in Amazonia. The Belo Monte Dam by itself would have a small reservoir area (440 km2) and large installed capacity (11, 181.3 MW), but the Altamira/Babaquara Dam that would regulate the flow of the Xingu River (thereby increasing power generation at Belo Monte) would flood a vast area (6140 km2). The great impact of dams provides a powerful reason for Brazil to reassess its current policies that allocate large amounts of energy in the country's national grid to subsidized aluminum smelting for export. The case of Belo Monte and the five additional dams planned upstream (including the Altamira/Babaquara Dam) indicate the need for Brazil to reform its environmental assessment and licensing system to include the impacts of multiple interdependent projects.

The Neotropical knifefish genus Gymnotus is the most broadly distributed and the most diverse (34+species) gymnotiform genus. Its wide range includes both Central and South American drainages, including the Amazon, Orinoco, and La Plata Basins. Like all gymnotiforms, Gymnotus species produce weak electric fields for both navigation and communication, and these fields exhibit interspecific variation in electric waveform characteristics. Both biogeography and electric signal evolution can profitably be analyzed in a phylogenetic context. Here, we present a total evidence phylogeny for 19 Gymnotus species based on data from the mitochondrial cytochrome b and 16S genes (1558 bp), the nuclear RAG2 gene (1223 bp), and 113 morphological characters. Our phylogenetic hypothesis resolves five distinct Gymnotus lineages. In a previous morphology-based analysis, the Central American Gymnotus cylindricus lineage was hypothesized as the sister group to all other Gymnotus species. In our analysis, the G. cylindricus lineage is nested within South American species, and molecular age estimates support a relatively recent origin for the clade in Central America. Phylogenetic optimization of electric signal waveforms indicate that the ancestral state in Gymnotus is a multiphasic (4+phases of alternating polarity) condition, and independent phase loss has occurred in multiple lineages. Gymnotus is a model group for understanding Neotropical diversification and the evolution of communication at a continental scale.