Testing the ecomorphological hypothesis in a headwater riffles fish assemblage of the rio São Francisco, southeastern Brazil

Abstract

The ecomorphology of 14 fish species resident in a headwater riffles area of the São Francisco river, southeastern Brasil, was analyzed and combined with diet and feeding behavior data, previously obtained by us. The three larger species groups formed in the ecomorphological analysis were found to reflect primarily microhabitat occupation in the following manner: a) nektonic characids with compressed bodies, lateral eyes and lateral pectoral fins, with diurnal and opportunistic feeding habits (Astyanax rivularis, Bryconamericus stramineus, and Bryconamericus sp.); b) nektobenthic characiforms and siluriforms with fusiform bodies and expanded pectoral fins, including sit-and-wait characidiins, predators of aquatic insect larvae (Characidium fasciatum and Ch. zebra), as well as the algae grazing parodontids (Apareiodon ibitiensis and Parodon hilarii), and also the heptapterid and trichomycterid catfishes that practice substrate speculation and feed on benthic aquatic insect larvae (Cetopsorhamdia iheringi, Imparfinis minutus, Rhamdia quelen, and Trichomycterus sp.); c) benthic species with depressed bodies, suctorial oral discs, dorsal eyes, and horizontal pectoral fins, represented by the periphytivorous loricariid catfishes (Hisonotus sp., Harttia sp., and Hypostomus garmani). Correlation between diet and general morphology was not significant in our analysis, unless when the analyzed set included only nektonic and benthic species, indicating that the lack of correlation between these factors is most pronounced in the group of nektobenthic species. The unequivocal case of morphological convergence found between the nektobenthic Characidiinae and Parodontidae is a clear example of the integration between phylogenetic information and ecomorphology, and provides a way to objectively identify cases of morphological and adaptive convergence and divergence. Furthermore, the general congruence between the ecomorphological results and the independently obtained ecological data about the analyzed fish species in their natural environment seems to be strong evidence in favor of the proposed predictive capabilities of the ecomorphological hypothesis.A ecomorfologia de 14 espécies de peixes residentes em um trecho de corredeiras do curso superior do rio São Francisco, sudeste do Brasil, foi analisada e combinada com dados de comportamento alimentar e dieta, previamente obtidos por nós. Os três principais agrupamentos ecomorfológicos de espécies identificados refletem a ocupação espacial de micro-hábitats da seguinte forma: a) caracídeos nectônicos com corpos comprimidos, olhos laterais e nadadeiras peitorais laterais, com hábitos noturnos e oportunistas alimentares (Astyanax rivularis, Bryconamericus stramineus e Bryconamericus sp.); b) nectobentônicos com corpos fusiformes e nadadeiras peitorais expandidas, que incluem os caracidiíneos predadores de espreita que se alimentam principalmente de larvas aquáticas bentônicas de insetos (Characidium fasciatum e Characidium zebra), parodontídeos pastadores de epilíton (Apareiodon...

Phylogenetic signal and major ecological shifts in the ecomorphological structure of stream fish in two river basins in Brazil

“…However, this observation does not imply that particular trophic or habitat specialization evolved in one clade only. For example, parodontids (Characiformes) are similarly algivorous/periphytivorous to loricariids (Siluriformes) (Casatti & Castro, 2006).…”

“…For each specimen, 18 morphometric measures were obtained and subsequently used to calculate 14 ecomorphological attributes, related to functional specializations of the fish to water flow, swimming ability, position in the water column, and prey size (Hora, 1930;Gosline, 1971;Webb, 1977;Gatz, 1979; Watson & Balon, 1984; Casatti & Castro, 2006). These 14 ecomorphological attributes were: compression index (CI), relative depth (RD), relative caudal peduncle length (RCPL), caudal peduncle compression index (CPCI), index of ventral flattening (IVF), relative area of the dorsal fin (RADF), relative area of the pectoral fin (RAPF), pectoral fin aspect ratio (PFAR), relative area of the caudal fin (RACF), relative head length (RHL), relative eye position (REP), relative mouth width (RMW), mouth orientation (MO) and fineness coefficient (FC).…”

“…High values indicate long fins, typical of fishes that swim for long distances (Watson & Balon, 1984), or pelagic fishes that swim constantly (Casatti & Castro, 2006).…”

“…A principal component is interpretable if it exceeds the eigenvalue randomly generated by the broken-stick model (Legendre & Legendre, 1998). For the selection of significant components, the broken-stick model is one of the methods with the most consistent results in ecological studies (Jackson, 1993) and is widely used in studies of ecomorphological structure (see: Casatti & Castro, 2006;Oliveira et al, 2010). Multivariate analyses were conducted using Primer v6 (Clarke & Gorley, 2006) and Statistica 7 (StatSoft Inc., 2004) software.…”

Morphological differentiation among migratory fish species from the Paraná River basin

“…Studies on morphology of Neotropical freshwater fish are restricted to the comparison between morphology and diet (Piorski et al 2005, Teixeira & Bennemann 2007, morphological variations under different environmental conditions (Monteiro & Neves 2003), and ecomorphology of fish from streams (Casatti & Castro 2006, Ferreira 2007. However, studies on the morphology associated with swimming performance for the Neotropical fish species are non-existent, with only information available for two migratory species, Leporinus reinhardti and Pimelodus maculatus, on swimming speeds and determination of swimming performance in the studies conducted by Santos et al (2007Santos et al ( , 2008.…”