CONVERGENT EVOLUTION OF WEAKLY ELECTRIC FISHES FROM FLOODPLAIN HABITATS IN AFRICA AND SOUTH-AMERICA

An assemblage of seven gymnotiform fishes in Venezuela was compared wi th an assemblage of six mormyriform fishes in Zambia to test the assum ption of convergent evolution in the two groups of very distantly rela ted, weakly electric, noctournal fishes. Both assemblages occur in str ongly seasonal floodplain habitats, but the upper Zambezi floodplain i n Zambia covers a much larger area. The two assemblages had broad diet overlap but relatively narrow overlap of morphological attributes ass ociated with feeding. The gymnotiform assemblage had greater morpholog ical variation, but mormyriforms had more dietary variation. There was ample evidence of evolutionary convergence based on both morphology a nd diet, and this was despite the fact that species pairwise morpholog ical similarity and dietary similarity were uncorrelated in this datas et. For the most part, the two groups have diversified in a convergent fashion within the confines of their broader niche as nocturnal inver tebrate feeders. Both assemblages contain midwater planktivores, micro phagous vegetation-dwellers, macrophagous benthic foragers, and long-s nouted benthic probers. The gymnotiform assemblage has one piscivore, a niche not represented in the upper Zambezi mormyriform assemblage, b ut present in the form of Mormyrops deliciousus in the lower Zambezi a nd many other regions of Africa.