Meeting Abstract
The Tocantins River serves as the major drainage for the Tocantins and Araguaia watershed and was once a large (2,450km), contiguous system. The construction, and subsequent closure, of the Tucuruí Hydroelectric Dam (the major dam in the system) in 1984 established a large (~2,850km2) ‘permanent’ reservoir, eliminating the once historic streams, floodplains, and rapids that once occupied this length of the Tocantins river. Such dramatic anthropogenic change can either lead to the extirpation of local flora and fauna, or species may be able to adapt to local environmental changes. To explore the latter possibility, we used geometric morphometrics to evaluate changes in native cichlids, incorporating both museum specimens collected prior to the closure of the hydroelectric dam (≤ 1984) and specimens collected during 2017-18. A total of six species, distributed over four genera, were included, representing distinct ecomorphs, varying from large piscivorous fishes to relatively small opportunistic omnivores. While some lineages expressed subtle changes, more drastic morphological shifts were documented in others. Moreover, the morphological changes that we observed tended to be associated with functional aspects of anatomy, ranging from head shape and organization, to the body length to depth ratio. These data suggest that native cichlid populations have undergone rapid (≤ 50 years), and in some instances dramatic, morphological changes since the closure of the dam, and provide insights as to the ways that different fish ecotypes may respond to sudden, large scale hydrological alterations.
