Morphological traits correlated with resource partitioning among small characin fish species coexisting in a Neotropical river

Abstract

Body shape variation should play a central role in determining the feeding ability of a fish species. We tested whether variations in feeding resource use of sympatric and closely related fish species could be explained by differences in ecologically relevant metrics, such as body morphology, trophic apparatus or combinations thereof. Fish were sampled at 14 sampling sites from Pelotas River and tributaries, Upper Uruguay, Brazil. The stomach contents of five species of Characidae (Astyanax and Bryconamericus) were analysed by the volumetric method. A geometric morphometric approach was used together with internal morphological traits to predict their patterns of prey use. Significant differences in body depth, snout and caudal peduncle lengths were found. Concomitant pronounced variations were verified to occur among species in structures related to digestion and absorption. Increased numbers of cusps, more pyloric caeca and higher intestinal coefficient values were observed in species that consumed greater proportions of plants. The opposite trends occurred in species that consumed greater proportions of insects. Mixed linear models indicated that the characin species differed significantly in the use of algae, aquatic insects, terrestrial insects, plant remains/seeds and detritus. Dietary differences reflected in low trophic niche overlap. Partial least squares regression results indicated strong correlations between morphological divergences and the corresponding variations in species diet. These outcomes combined confirm that the morphological traits that best enables the exploration of certain resource were an important factor in the resource‐related divergence and were the underlying reasons for these species' respective feeding modes.

Trophic morphology features allow Astyanax endemic species coexistence in a Neotropical river system

“…The species analysed in this study were recorded to have trophic segregation in co‐occurrence in different reservoirs and rivers, showing low food overlap in lower Iguaçu River (Delariva & Neves, 2020; Mise et al ., 2013; Pini et al ., 2019). They also co‐occur in Salto Osório and Salto Santiago reservoirs (Supporting Information, Figure M2) and probably have trophic segregation in both reservoirs.…”

“…Astyanax congener species from other locations also presented differences in their gill rakers according to their life strategies ( e.g ., feeding habits) (Delariva & Neves, 2020; Ornelas‐García et al ., 2018). Different from this study's findings, shorter gill rakers were mainly correlated with predatory and omnivorous habits, whereas longer gill rakers were present in species which preferred food of plant origin (Ornelas‐García et al ., 2018).…”

“…Astyanax congener species from other locations also presented differences in their gill rakers according to their life strategies (e.g., feeding habits) (Delariva & Neves, 2020;Ornelas-García et al, 2018).…”

Resource use by omnivorous fish: Effects of biotic and abiotic factors on key ecological aspects of individuals

“…Dietary composition showed that Astyanax lineatus is an omnivorous species with a tendency to insectivory, consuming both terrestrial and aquatic insects. Omnivory is common for fish of the Astyanax genus, with variation in the frequency of insectivory and herbivory, and this plasticity may be one of the explanations for the high diversity (174 species) and wide distribution in the Neotropical region (Delariva & Neves, 2020;Fricke et al, 2020). (Winemiller et al, 2008).…”

Seasonality and interspecific competition shape individual niche variation in co‐occurring tetra fish in Neotropical streams

“…Among these similar co‐occurring species, small characids (tetra fish) exhibit a striking diversity in morphology and life history across species, but also conspicuous variation within populations (Bonato et al., 2017; Garita‐Alvarado et al., 2018; Silva et al., 2017). South American small‐sized characids, mainly Asyanax, Psalidodon , and Bryconamericus species, are omnivorous generalist fish commonly found in the water column of streams (Bonato et al., 2017; Delariva & Neves, 2020; Neves et al., 2018). Characid species are considered as opportunistic foragers due to their ability to shift their diets according to the seasonal abundance of resources (Corrêa et al., 2011; Juncos et al., 2015; Neves et al., 2018; Silva et al., 2017).…”