Abstract
This study assesses the patterns of variation in body shape, and relations of morphological similarity among species of theTheraps–Paraneetroplusclade in order to determine whether body shape may be a trait in phylogenetic relations. A total of 208 specimens belonging to 10 species of theTheraps–Paraneetroplusclade were examined. The left side of each specimen was photographed; in each photograph, 27 fixed landmarks were placed to identify patterns in body shape variation. Images were processed by using geometric morphometrics, followed by a phylogenetic principal component analysis. The phylogenetic signal for body shape was then calculated. To determine the relations in morphological similarity, a dendrogram was created using the unweighted pair group method and arithmetic mean values, while a Procrustes ANOVA and post-hoc test were used to evaluate significant differences between species and habitats. We found three morphological groups that differed in body length and depth, head size, and the position of the mouth and eyes. The body shape analysis recovered the morphotypes of seven species, and statistical differences were demonstrated in eight species. Based on traits associated with cranial morphology,Wajpamheros nourissati(Allgayer, 1989) differed the most among the species examined. No phylogenetic signal was found for body shape; this trait shows independence from ancestral relatedness, indicating that there is little congruence between morphological and genetic interspecific patterns. As evidenced by the consistently convergent morphology of the species in theTheraps–Paraneetroplusclade, the diversification of the group is related to an ecological opportunity for habitat use and the exploitation of food resources. Although no phylogenetic signal was detected for body shape, there appears to be an order associated with cranial morphology-based phylogeny. However, it is important to evaluate the intraspecific morphologic plasticity produced by ecological segregation or partitioning of resources. Therefore, future morphological evolutionary studies should consider cranial structures related to the capture and processing of food.
Highlights
Among Neotropical freshwater fishes, evidence of diversity suggests that allopatric speciation models frequently apply to several clades and that there are few cases of sympatric speciation stemming from adaptive processes (Albert et al 2020)
Studies related to morphological diversity in South American cichlids have demonstrated that body shape and size variation have been the main axes of diversification, most notably the constant presence of morphological convergence between lineages (López-Fernández et al 2010, 2013)
Species located on the positive axis of PC1 include T. irregularis, P. bulleri, and R. lentiginosus; O. heterospila, M. argenteus, C. pearsei, and K. ufermanni were located on the negative axis; and C. intermedium, V. hartwegi, and W. nourissati were located on the middle axis
Summary
Among Neotropical freshwater fishes, evidence of diversity suggests that allopatric speciation models frequently apply to several clades and that there are few cases of sympatric speciation stemming from adaptive processes (Albert et al 2020). The main historical processes include river capture and sea-level oscillations, which fragment and merge fluvial networks In this scenario involving geographic changes and ecological heterogeneity, phenotypic variation has been an important attribute in morphological diversification and environmental adaptation (Albert et al 2020). Freshwater fish orders such as Siluriformes, Characiformes, Cyprinodontiformes, Gymnotiformes, and Cichliformes are the best examples of morphological diversity in the Neotropical region due to their high species richness and abundance (Albert et al 2020; Elías et al 2020). Morphological convergence is interpretable as evidence that natural selection has selected similar traits, providing strong evidence for the adaptive quality of said traits (Elmer and Meyer 2011; Losos 2011; Burress 2015)
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