Abstract
Although rare within the context of 30 000 species of extant fishes, scale-feeding as an ecological strategy has evolved repeatedly across the teleost tree of life. Scale-feeding (lepidophagous) fishes are diverse in terms of their ecology, behaviour, and specialized morphologies for grazing on scales and mucus of sympatric species. Despite this diversity, the underlying ontogenetic changes in functional and biomechanical properties of associated feeding morphologies in lepidophagous fishes are less understood. We examined the ontogeny of feeding mechanics in two evolutionary lineages of scale-feeding fishes: Roeboides, a characin, and Catoprion, a piranha. We compare these two scale-feeding taxa with their nearest, non-lepidophagous taxa to identify traits held in common among scale-feeding fishes. We use a combination of micro-computed tomography scanning and iodine staining to measure biomechanical predictors of feeding behaviour such as tooth shape, jaw lever mechanics and jaw musculature. We recover a stark contrast between the feeding morphology of scale-feeding and non-scale-feeding taxa, with lepidophagous fishes displaying some paedomorphic characters through to adulthood. Few traits are shared between lepidophagous characins and piranhas, except for their highly-modified, stout dentition. Given such variability in development, morphology and behaviour, ecological diversity within lepidophagous fishes has been underestimated.
Highlights
Better minds than ours have pointed out the link between feeding morphology and diet, and many of the archetypes in evolutionary study are examples of the powerful links between2018 The Authors
ANOVAs of tooth aspect ratio showed that P. denticulata had longer and narrower teeth than Catoprion, which had stouter more spatulate teeth (0.96 ± 0.04 s.e. versus 0.85 ± 0.02 s.e. respectively, p = 0.013), at all sizes
Catoprion (10.0 mm ± 1.27 s.e.) have longer jaws than Pygopristis (6.04 mm ± 0.89 s.e., p < 0.001), which is reflected in Catoprion having lower jaw leverage at the anterior-most tooth compared to Pygopristis
Summary
Better minds than ours have pointed out the link between feeding morphology and diet, and many of the archetypes in evolutionary study are examples of the powerful links between2018 The Authors. There are cichlids in African rift lakes that allegedly specialize in eating the eyes of other cichlids [1,2] These fishes and sympatric scale-eating cichlids maintain a handedness polymorphism that allows half the population to deliver nasty surprises from the right side of prey while the other half operates on the left side [3]. Molluscivory represents a near monophagous dietary specialization associated with a narrow suite of morphological characters: large jaw muscles, and robust teeth and jaws [6,7]. Diet and morphology suffer a serious mismatch when the snail-slurping snake Sibon is grouped ecologically with mollusc-mauling myliobatine stingrays [8,9]; the former ratchet snails from their shells with elongate, gracile lower jaws, while the latter crush prey outright with stout jaws fused at the symphysis and pavement-like dentition
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