Ecomorphology of Neotropical Electric Fishes: An Integrative Approach to Testing the Relationships between Form, Function, and Trophic Ecology

Abstract

Synopsis The relationship between form and function is thought to play an integral role in structuring broad-scale patterns of morphological evolution and resource utilization. In ecomorphological studies, mechanical performance is widely understood to constrain the evolution of form and function. However, the relationship between form, function, and resource utilization is less clear. Additionally, seasonal fluctuations in resource availability may further complicate patterns of resource use. How organisms cope with these complexities, and the effect of these factors on broadscale patterns of morphological evolution is also poorly understood. Here we use three-dimensional geometric morphometrics, biomechanics, stable isotope analysis, and gut-content analysis to study trophic evolution in a clade of riverine-adapted electric fishes from a region with high seasonal variability; the Amazon River. We find significant and phylogenetically structured relationships among measures of trophic ecology and skull shape. We also recover a significant relationship between the mechanical advantage of the mandible and trophic position, where species feeding at higher trophic levels have narrower jaws with lower mechanical advantages, and species feeding at lower trophic levels have deeper jaws with higher mechanical advantages. Our results indicate that selection is driving the evolution of mandible shape and performance toward specialization on different trophic ecologies.

Ecomorphological divergence and habitat lability in the context of robust patterns of modularity in the cichlid feeding apparatus

“…This trend is consistent with the adaptive value of these traits with respect to feeding kinematics. Indeed, the trend in functionally relevant components of anatomical structures exhibiting fast rates and high evolvability has been noted in other teleosts groups (i.e., Electric fishes [52,53], cichlids, pomacentrids, centrarchids, and labrids [54]), and may reflect a general trend across organisms [55,56]. In terms of disparity, it is notable that the tooth-plate module exhibited the highest levels for both the mandible and lower pharyngeal jaw.…”

Global patterns and predictors of trophic position, body size and jaw size in fishes

“…Predators generally had longer jaws than fishes feeding at a lower TP and, although gape size is not directly related to jaw length, the positive association was consistent with predictions of TP increasing with gape size (Arim et al., 2007). Longer jaws can increase gape‐distance for prey capture, increase mouth closing speeds, or increase suction feeding velocities in predators (Hulsey & Garcia de Leon, 2005), while shorter jaws maximize bite force needed to feed on hard‐bodied prey items (Ferry et al., 2015; Westneat, 2004; Evans et al, 2019). The shape of the nonlinear association showed that top predators rarely had small jaw sizes, while species with extremely long jaws were not commonly omnivorous, herbivorous or detritivorous.…”

Role of morphology in shaping the feeding niche of fishes inhabiting Eastern Himalayan torrential rivers of West Bengal, India

“…For evaluating the phylogenetic independence of morphological characters, we tested for the “phylogenetic signal” of trait values among species. For this, we constructed a phylogenetic tree using the maximum likelihood (ML) method based on the cytochrome oxidase‐I (COX‐I) sequences of the species (Blomberg et al, 2003; Evans et al, 2019). The best ML tree using DNA substitution models (Arenas, 2015) was inferred based on Akaike's Information Criterion (AIC) values after which Abouheif's C‐ mean test for serial independence was employed (Abouheif, 1999).…”