Flow gradient drives morphological divergence in an Amazon pelagic stream fish
Body shape and size variations are common in stream fishes, and morphological differences can have either a genetic or non-genetic basis. Flow has been indicated as one of the causes of intraspecific variation, and shifts in stream-fish body morphology are related to swimming performance and to individual fitness. Although populations in lotic versus lentic habitats have been compared, the effects of a flow gradient on fish shape are little studied. We tested differences in size, body shape and caudal-peduncle morphology of a pelagic fish that inhabits streams with different velocities in two basins, using geometric morphometrics to evaluate shifts in body morphology. Fish from lower-flow velocities had larger bodies that were deeper posteriorly; fish from higher-flow velocities were smaller and more streamlined. Shape variation among specimens was significantly influenced by the local velocity, with similar responses in fish body shape in the different basins. We showed that selective pressures generated by flow velocities affect fish shape in the same way in both basins. Fish body size, shape and caudal-peduncle morphology affect swimming performance, which could influence the energy costs for survival. Our results with a small pelagic characid help to elucidate questions on morphological predictions for fishes across flow regimes.
KeywordsGeometric morphometrics Natural variation Steady swimming Ecomorphology paradigm
The authors would like to thank Dr. Henrique Lazzarotto and MSc. Ana Clara Franco, who reviewed earlier versions of this manuscript; Janet Reid, who reviewed the final English version of the manuscript; and, to three anonymous reviewers who made valuable contributions to final revision of the manuscript. To Ane Mello and Heloisa Barreto for their assistance in laboratory work; to Rafael de Oliveira Marques, the researchers and students from the Laboratório de Ecologia de Peixes—UFRJ, the Laboratório de Limnologia—UFRJ and the Laboratório de Ecologia Aquática—NUPEM/UFRJ for their help during fieldwork; and to Ronilson Picanço and Mineração Rio do Norte (MRN) employees for logistical help with fieldwork. We are grateful to Dr. Cristiano Moreira, curator of fish collection of the Museu Nacional do Rio de Janeiro—UFRJ, for examination and deposition of voucher specimens in the Ichthyological Collection, and also to describe H. ericae as a homage to EPC. We also thank Dr. Brian Sidlauskas from the Oregon State University, for the encouragement to publish the data, preliminarily presented as a poster during the XXI EBI. This study is dedicated to the people of Moura, Água Fria and Boa Nova Communities (Oriximiná, Pará, Brazil).
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