In riverine ecosystems, downstream drag caused by fast‐flowing water poses a significant challenge to rheophilic organisms. In neotropical rivers, many members of a diverse radiation of suckermouth catfishes (Loricarioidei) resist drag in part by using modified lips that form an oral suction cup composed of thick flesh. Histological composition and morphology of this cup are interspecifically highly variable. Through an examination of 23 loricarioid species, we determined that the tissue most responsible for lip fleshiness is collagen. We hypothesized that lip collagen content is interspecifically correlated with substrate and flow so that fishes living on rocky substrates in high‐flow environments have the largest, most collagenous lips. By mapping the amount and distribution of lip collagen onto a phylogeny and conducting ANOVA tests, we found support for this hypothesis. Moreover, these traits evolved multiple times in correlation with substrate and flow, suggesting they are an effective means for improving suction‐based attachment. We hypothesize that collagen functions to reinforce oral suction cups, reducing the likelihood of slipping, buckling, and failure under high‐flow, high‐drag conditions. Macroevolutionary patterns among loricarioid catfishes suggest that for maximum performance, biomimetic suction cups should vary in material density according to drag and substrate requirements.
Complex prey processing requires the repositioning of food between the teeth, as modulated by a soft tissue appendage like a tongue or lips. In this study, we trace the evolution of lips and ligaments, which are used during prey capture and prey processing in an herbivorous group of fishes. Pacus (Serrasalmidae) are Neotropical freshwater fishes that feed on leaves, fruits, and seeds. These prey are hard or tough, require high forces to fracture, contain abrasive or caustic elements, or deform considerably before failure. Pacus are gape‐limited and do not have the pharyngeal jaws many bony fishes use to dismantle and/or transport prey. Despite their gape limitation, pacus feed on prey larger than their mouths, relying on robust teeth and a hypertrophied lower lip for manipulation and breakdown of food. We used histology to compare the lip morphology across 14 species of pacus and piranhas to better understand this soft tissue. We found that frugivorous pacus have larger, more complex lips which are innervated and folded at their surface, while grazing species have callused, mucus‐covered lips. Unlike mammalian lips or tongues, pacu lips lack any intrinsic skeletal or smooth muscle. This implies that pacu lips lack dexterity; however, we found a novel connection to the primordial ligament which suggests that the lips are actuated by the jaw adductors. We propose that pacus combine hydraulic repositioning of prey inside the buccal cavity with direct oral manipulation, the latter using a combination of a morphologically heterodont dentition and compliant lips for reorienting food.
more » « less- NSF-PAR ID:
- 10392421
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- The Anatomical Record
- Volume:
- 306
- Issue:
- 2
- ISSN:
- 1932-8486
- Page Range / eLocation ID:
- p. 326-342
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
more » « less
Abstract Epibranchial organs (EBOs), found in at least five of the eight otomorphan families, are used to aggregate small prey inside the buccopharyngeal cavity and range in morphological complexity from a singular, small slit on the pharyngeal roof to several, elongated soft tissue tubes. Despite broad phylogenetic representation, little is known about the origin, development, or evolution of EBOs. We hypothesize that both heterochronic and heterotopic changes throughout the evolution of EBOs are at the root of their morphological diversity. Heterochrony is a foundational explanation in developmental studies, however, heterotopy, a developmental change in spatial or topographical relationships, can have even more profound effects on a given structure but has received relatively little attention. Here, we investigate how developmental mechanisms may drive morphological diversity of EBOs within otomorphan fishes. We compare early pharyngeal development in three species,
Anchoa mitchilli (Engraulidae) which has the most basic EBO,B. tyrannus (Clupeidae) which has a more complex EBO, andHypophthalmichthys molitrix (Cyprinidae) which has the most complex EBO yet described. Using branchial arch growth rates and morphological analyses, we illustrate how both heterochronic and heterotopic mechanisms are responsible for some of the phenotypic diversity seen in otomorphan EBOs. Importantly, we also identify conserved developmental patterns that further our understanding of how EBOs may have first originated and evolved across actinopterygian fishes. -
more » « less
ABSTRACT The masticatory apparatus has been the focus of many studies in comparative anatomy—especially analyses of skulls and teeth, but also of the mandibular adductor muscles which are responsible for the production of bite force and the movements of the mandible during food processing and transport. The fiber architecture of these muscles has been correlated to specific diets (e.g., prey size in felids) and modes of foraging (e.g., tree gouging in marmosets). Despite the well‐elucidated functional implications of this architecture, little is known about its ontogeny. To characterize age‐related myological changes, we studied the masticatory muscles in a large (
n = 33) intraspecific sample of a small, Malagasy primate,Microcebus murinus including neonatal through geriatric individuals. We removed each of the mandibular adductors and recorded its mass as well as other linear measurements. We then chemically dissected each muscle to study its architecture—fascicle length and physiological cross‐sectional area (PCSA) which relate to stretch (gape) and force capabilities, respectively. We observed PCSA and muscle mass to increase rapidly and plateau in adulthood through senescence. Fascicle lengths remained relatively constant once maximal length was reached, which occurred early in life, suggesting that subsequent changes in PCSA are driven by changes in muscle mass. Quadratic curvilinear models of each of the architectural variables of all adductors combined as well as individual muscles regressed against age were all significant. Anat Rec, 303:1364–1373, 2020. © 2019 American Association for Anatomy -
Killing them softly: Ontogeny of jaw mechanics and stiffness in mollusk‐feeding freshwater stingraysmore » « less
Abstract Durophagous predators consume hard‐shelled prey such as bivalves, gastropods, and large crustaceans, typically by crushing the mineralized exoskeleton. This is costly from the point of view of the bite forces involved, handling times, and the stresses inflicted on the predator's skeleton. It is not uncommon for durophagous taxa to display an ontogenetic shift from softer to harder prey items, implying that it is relatively difficult for smaller animals to consume shelled prey. Batoid fishes (rays, skates, sawfishes, and guitarfishes) have independently evolved durophagy multiple times, despite the challenges associated with crushing prey harder than their own cartilaginous skeleton.
Potamotrygon leopoldi is a durophagous freshwater ray endemic to the Xingu River in Brazil, with a jaw morphology superficially similar to its distant durophagous marine relatives, eagle rays (e.g.,Aetomylaeus, Aetobatus ). We used second moment of area as a proxy for the ability to resist bending and analyzed the arrangement of the mineralized skeleton of the jaw ofP. leopoldi P. leopoldi P. leopoldi P. leopoldi -
more » « less
Abstract Hypophthalmichthys molitrix ,
