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<p>The Navajini is a clade of Neotropical electric fishes specialized to inhabit deep river channels in the lowland Amazonian, with species that exhibit high craniofacial disparity and a highly conservative post-cranial body shape. This study investigates the morphological, ecological, and developmental factors contributing to phenotypic diversification in this clade. By integrating 3D geometric morphometrics, phylogenetic comparative methods, and ancestral state estimation within a robust phylogenetic framework, we examine the evolution of skull shape across the group. Our approach combines high-resolution micro-CT scanning with multivariate analyses to identify major axes of craniofacial disparity, and to assess how these patterns relate to ecology, sexual dimorphism, and phylogenetic history. Rather than being randomly distributed or purely environmentally plastic, key traits such as lower jaw elongation, opercle morphology, and maxilla orientation exhibit strong phylogenetic signal and structural consistency within genera. We explore how certain lineages have accessed distinct regions of craniofacial morphospace, likely by means of trophic specialization and developmental shifts. Sexual dimorphism emerges as a major contributor to morphological disparity in some but not all subclades. These results highlight repeated evolutionary trajectories among taxa that share similar ecological roles or mating strategies. Together, these findings provide new insights into the processes driving phenotypic evolution in one of the most morphologically diverse lineages of Neotropical freshwater fishes.</p>

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Lineage Diversity and Craniofacial Disparity of Navajini (Gymnotiformes, Apteronotidae) in Deep River Channels of Tropical South America

  • 期刊论文

  • 发表日期：

    2026年3月17日

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  • Jonathan G. Allen,
  • Taylor L. Fisher,
  • James S. Albert

摘要

The Navajini is a clade of Neotropical electric fishes specialized to inhabit deep river channels in the lowland Amazonian, with species that exhibit high craniofacial disparity and a highly conservative post-cranial body shape. This study investigates the morphological, ecological, and developmental factors contributing to phenotypic diversification in this clade. By integrating 3D geometric morphometrics, phylogenetic comparative methods, and ancestral state estimation within a robust phylogenetic framework, we examine the evolution of skull shape across the group. Our approach combines high-resolution micro-CT scanning with multivariate analyses to identify major axes of craniofacial disparity, and to assess how these patterns relate to ecology, sexual dimorphism, and phylogenetic history. Rather than being randomly distributed or purely environmentally plastic, key traits such as lower jaw elongation, opercle morphology, and maxilla orientation exhibit strong phylogenetic signal and structural consistency within genera. We explore how certain lineages have accessed distinct regions of craniofacial morphospace, likely by means of trophic specialization and developmental shifts. Sexual dimorphism emerges as a major contributor to morphological disparity in some but not all subclades. These results highlight repeated evolutionary trajectories among taxa that share similar ecological roles or mating strategies. Together, these findings provide new insights into the processes driving phenotypic evolution in one of the most morphologically diverse lineages of Neotropical freshwater fishes.