Towards a Constructional Morphology of Cichlid Fishes (Teleostei, Perciformes)

Is lionfish ontogenetic dietary change mediated by morphological functionality?

Article

Full-text available

Jun 2023
HYDROBIOLOGIA

The objective of this study was to explore ontogenetic changes in functional morphological traits of the invasive lionfish (Pterois volitans) and to test if they were associated with the ontogenetic dietary shifts previously documented for this species. We calculated nine functional indices based on body morphology, six associated with fish locomotion and three with prey capture functionality. In juvenile fish, the morphology associated with feeding provides greater mechanical advantages during prey capture due to higher feeding speeds. In contrast, in adults’ locomotion is more efficient and is related to enhanced sustained swimming as the invader grows, but the suction index (related to the ability to generate flow rate to the mouth during feeding) decreases as lionfish grow bigger. Our results suggest ontogenetic changes in functional morphological features related to feeding and locomotion in the invader P. volitans, but these modifications do not seem to be the main driver of their ontogenetic dietary change.

Geometric morphometric comparison of the oral and lower pharyngeal jaws of the closely related cichlids Vieja bifasciata, V. breidohri, and V. hartwegi (Cichliformes: Cichlidae)

Article

Full-text available

Apr 2022

The systematics of the genus Vieja is complex because it contains many morphologically similar species that have little genetic differentiation. Examination of morphological traits can be useful for clarifying their taxonomic status. We analyzed the morphological variation of bones in the oral and lower pharyngeal jaws to determine whether these structures permit the differentiation of species and to study possible functional implications. Morphological differences were quantified using canonical variates analysis, MANOVA, and paired comparisons. Differences in the number of pharyngeal teeth in the lower pharyngeal jaw were determined using an ANCOVA. The shape of the premaxilla and lower pharyngeal jaw proved useful for the delimitation of these species. Although the morphological variation between V. breidohri and V. hartwegi is minimal, the shapes of their lower pharyngeal jaws differ in morphospace. Vieja bifasciata possesses more teeth in the lower pharyngeal jaw when compared to the other species. Variation in these bones may affect jaw biomechanics and influence feeding behavior. However, these morphological differences contradict the weak genetic differentiation observed. The geographic isolation of V. bifasciata is likely related to its morphological differentiation. The close phylogenetic relationship between V. breidohri and V. hartwegi likely explains their low morphological divergence.

Trophic divergence of Lake Kivu cichlid fishes along a pelagic versus littoral habitat axis

Article

Full-text available

Jan 2021

Local adaptation to the littoral and pelagic zones in two cichlid haplochromine fish species from Lake Kivu was investigated using morphometrics. Cranial variation and inferred jaw mechanics in both sexes of the two species across the two habitat types were quantified and compared. Comparisons of littoral versus pelagic populations revealed habitat‐specific differences in the shape of the feeding apparatus. Also, kinematic transmission of the anterior jaw four‐bar linkage that promotes greater jaw protrusion was higher in the pelagic zone than in the littoral zone for both species. Inferred bite force was likewise higher in pelagic zone fish. There were also sex‐specific differences in craniofacial morphology as males exhibited longer heads than females in both habitats. As has been described for other cichlids in the East African Great Lakes, local adaptation to trophic resources in the littoral and pelagic habitats characterizes these two Lake Kivu cichlids. Similar studies involving other types of the Lake Kivu fishes are recommended to test the evidence of the observed trophic patterns and their genetic basis of divergences.

Unprecedented Biting Performance in Herbivorous Fish: How the Complex Biting System of Pomacentridae Circumvents Performance Trade-Offs

Article

Full-text available

Jan 2021

It is well accepted that the complexity of functional systems may mitigate performance trade-offs. However, data supporting this theory are hard to find because they need to be based on a functional system with different complexity levels in closely related species. The Pomacentridae (damselfishes) provide an excellent opportunity to test this hypothesis because most of the species have two mouth-closing systems: the first using the adductor mandibulae, as in all teleost fishes, and the second relying on the ceratomandibular (cmd) ligament, a synapomorphic trait of the family. Interestingly, some pomacentrids have secondarily lost the cmd ligament during evolution and therefore have a less complex mouth-closing system. Using dissection, kinematic analysis, and mathematical modeling, we demonstrated that the possession of two mouth-closing systems enabled grazing damselfishes to have a forceful and extremely fast bite. This combination challenges a major functional trade-off in fish jaw dynamics, as systems better suited for force transmission are usually less suited for speed transmission, and vice versa. The combination of grazing behavior, small and robust lower jaws (conferring high biting force), and an ultrafast bite is unusual within actinopterygians. These attributes and their associated performance seem to be required conditions to colonize the ecological niche of farming, that is, the maintenance of small filamentous algae crops serving as both food and storage.

Trophic ecomorphology of cichlid fishes of Selva Lacandona, Usumacinta, Mexico

Article

Full-text available

Jul 2019
ENVIRON BIOL FISH

Neotropical cichlids exhibit great diversity of morphological traits associated with feeding, locomotion, and habitat use. We examined the relationship between functional traits and diet by analyzing a dataset for 14 cichlid species from rivers in the Selva Lacandona region, Usumacinta Basin, Chiapas, Mexico. Volumetric proportions of ingested food items were used to calculate diet breath and interspecific dietary overlap. Morphometric analysis was performed using 24 traits associated with feeding. Associations between morphological and dietary components were assessed using canonical correspondence analysis. The most common feeding guilds were omnivore, herbivore and carnivore (the latter consuming invertebrates and/or fish), with detritivores represented by relatively few species and strict piscivore by one species. Dietary overlap was highest among carnivores (P. friedrichsthalii and T. salvini), herbivores (C. intermedium and C. pearsei) and detritivore-herbivores (V. melanura and K. ufermanni). Dietary components were strongly correlated with several morphological traits, confirming patterns observed in other cichlids. For example, jaw protrusion and mandible length were positively correlated with consumption of fish and terrestrial invertebrates. A longer gut and a wider tooth plate on the lower pharyngeal jaw were correlated with ingestion of vegetation, algae and detritus. Findings confirmed a high degree of trophic specialization in certain species as well as interspecific divergence of functional traits associated with feeding among cichlids of the Usumacinta Basin, which is consistent with the idea that Middle American cichlids represent an adaptive radiation.

The anatomy, evolution and interrelationships of Devonian Dipnoans, with insights from the extant Australian lungfish, Neoceratodus forsteri

Thesis

Jan 2011

Alice M. Clement

The modem Australian fauna includes one of the most enduring extant vertebrate lineages, the Dipnoi, and this body of work examines their anatomy, evolution and relationships, with insights from the Australian lungfish, Neoceratodus forsteri. Through application of modern technology and techniques, this thesis provides comparative, ontogenetic, phylogenetic and functional insights into both fossil and extant lungfishes. Three recently discovered fossil taxa are discussed. These include the first Gondwanan species of a European genus (Rhinodipterus kimberleyensis, Clement 2012), and a primitive genus belonging to the holodontid family (Xeradipterus hatcheri, Clement and Long 2010b), both from the Late Devonian Gogo Formation of Western Australia. Also, a Middle Devonian genus from central Australia (Harajicadipterus youngi, Clement 2009) and a detailed examination of the postcranial anatomy of two lungfishes from Victoria (Howidipterus donnae and Barwickia downunda, Long 1992a) is included. Key findings include the first unequivocal marine lungfish with air-breathing adaptations, possible examples ofsympatric speciation driven by competition for trophic resources, and some of the earliest dipnoans to make the transition to freshwater in Australia. Cladistic analysis was employed to examine dipnoan interrelationships, with special emphasis on early Australian forms. The analysis suggests there were significant adaptive radiations of lungfishes in Devonian reefs, with three locally-evolving clades identified; the chirodipterids, holodontids and dipnorhynchids. The monophyly ofa number ofgenera found in Australian deposits, namely Chirodipterus and Griphognathus is not supported, whereas, the monophyly of Rhinodipterus is confirmed. The analysis suggests that air-breathing probably evolved only once within the Dipnoi. Partition homogeneity tests and Farris' successive weighting provide support for the hypothesis that anatomical characters relating to feeding, such as those of the dentition, jaw and palate, may be less reliable than some other, less convergence-prone traits. Basic jaw lever mechanics in conjunction with 3D bite-modelling software were used to estimate bite force and velocity in extant and fossil genera. Neoceratodus was shown to have a mid level mechanical advantage for its bite compared to earlier fossil forms, implying it has neither a particularly strong nor fast bite. The two main adductor mandibulae muscle portions, the temporalis and masseter, contribute similar forces, and effective mechanical advantage remains constant throughout ontogeny despite an observable shift in diet. Analysis of functional morphology illustrates a large variety of feeding ecomorphologies, and thus, inferred behaviours of Devonian lungfishes. Early members of this lineage were evidently capable of eating diverse prey types, and likely filled a wide range of ecological roles. An inherent ability to remodel plastic dental morphologies is supported as a mechanism by which the early lungfishes were able to evolve, adapt and exploit new niches throughout their long history.

Dissecting a potential spandrel of adaptive radiation: Body depth and pectoral fin ecomorphology coevolve in Lake Malawi cichlid fishes

Article

Full-text available

Nov 2018

The evolution of body shape reflects both the ecological factors structuring organismal diversity as well as an organism's underlying anatomy. For instance, body depth in fishes is thought to determine their susceptibility to predators, attractiveness to mates, as well as swimming performance. However, the internal anatomy influencing diversification of body depth has not been extensively examined, and changes in body depth could arise as a by‐product of functional changes in other anatomical structures. Using an improved phylogenetic hypothesis for a diverse set of Lake Malawi cichlid fishes, we tested the evolutionary association between body depth and the height of the pectoral girdle. To refine the functional importance of the observed substantial correlation, we also tested the coevolution of pectoral girdle height and pectoral fin area. The extensive coevolution of these traits suggests body depth in fishes like the Lake Malawi cichlids could diverge simply as a by‐product of being tightly linked to ecomorphological divergence in other functional morphological structures like the pectoral fins. This study uses an improved phylogenetic hypothesis for a diverse set of Lake Malawi cichlid fishes to test the evolutionary association between body depth, the height of the pectoral girdle, and the area of the pectoral fins. Body depth is often assumed to be functionally important and an adaptively diverging trait in many groups of fishes, but few studies, has examined the internal anatomy that gives rise to this trait. The evidence for extensive coevolution of body depth with pectoral fin morphology that we find for the Lake Malawi cichlids surprisingly suggests that body depth could often diverge simply as a by‐product of being tightly linked to ecomorphological divergence of other important anatomical structures such as the pectoral girdle.

Ontogenetic divergence generates novel phenotypes in hybrid cichlids

Article

Jan 2021

Hybridization is suggested to contribute to ecomorphological and taxonomic diversity in lacustrine East African cichlids. This is supported by studies demonstrating that genetic diversity within lake radiations has been influenced by hybridization events, leading to extensive phenotypic differentiation of genetically closely related species. Hybrid persistence and speciation in sympatry with gene flow can be explained by pleiotropy in traits involved in reproductive isolation; however, little attention has been given to how trait differentiation is established during hybrid ontogeny, and how this may relate to trophic and locomotor specialization. This study compares body shape changes in a Lake Victoria cichlid hybrid throughout its post‐hatch ontogeny to those of its parental species. Across the considered age/size categories, hybrids occupy a distinct and intermediate morphological space, yet where several transgressive traits emerge. A between‐group principal component analysis on body shapes across size categories reveals axes of shape variation exclusive to the hybrids in the youngest/smallest size categories. Shape differences in the hybrids involved morphological traits known to be implicated in trophic and locomotor specializations in the parental species. Combined, our findings suggest that phenotypic divergence in the hybrid can lead to functional differences that may potentially release them to some degree from competition with the parental species. These findings agree with recent literature that addresses the potential importance of hybridization for the unusually recent origin of the Lake Victoria cichlid super‐species flock.

“Simple” Biomechanical Model for Ants Reveals How Correlated Evolution among Body Segments Minimizes Variation in Center of Mass as Heads Get Larger

Article

Full-text available

May 2020
INTEGR COMP BIOL

The field of comparative biomechanics strives to understand the diversity of the biological world through the lens of physics. To accomplish this, researchers apply a variety of modelling approaches to explore the evolution of form and function ranging from basic lever models to intricate computer simulations. While advances in technology have allowed for increasing model complexity, great insight can still be gained through the use of low-parameter 'simple' models. All models, regardless of complexity, are simplifications of reality and must make assumptions; 'simple' models just make more assumptions than complex ones. However, 'simple' models have several advantages. They allow individual parameters to be isolated and tested systematically, can be made applicable to a wide range of organisms and make good starting points for comparative studies, allowing for complexity to be added as needed. To illustrate these ideas, we perform a case study on body form and center of mass stability in ants. Ants show a wide diversity of body forms, particularly in terms of the relative size of the head, petiole(s) and gaster (the latter two make-up the segments of the abdomen not fused to thorax in hymenopterans). We use a 'simple' model to explore whether balance issues pertaining to the center of mass influence patterns of segment expansion across major ant clades. Results from phylogenetic comparative methods imply that the location of the center of mass in an ant's body is under stabilizing selection, constraining the center of mass to the middle segment (thorax) over the legs. This is potentially maintained by higher correlated rates of evolution between the head and gaster on either end. While these patterns arise from a model which makes several assumptions/simplifications relating to shape and materials, they still offer intriguing insights into the body plan of ants across ∼75% of their diversity. The results from our case study illustrate how 'simple', low-parameter models both highlight fundamental biomechanical trends, and aid in crystalizing specific questions and hypotheses for more complex models to address.

A digital dissection of two teleost fishes: comparative functional anatomy of the cranial musculoskeletal system in pike ( Esox lucius ) and eel ( Anguilla anguilla )

Article

May 2019

Advances in X‐ray computed tomography (CT) have led to a rise in the use of non‐destructive imaging methods in comparative anatomy. Among these is contrast‐enhanced CT scanning, which employs chemical stains to visualize soft tissues. Specimens may then be ‘digitally dissected’, producing detailed, three‐dimensional digital reconstructions of the soft‐ and hard‐tissue anatomy, allowing examination of anatomical structures in situ and making accurate measurements (lengths, volumes, etc.). Here, we apply this technique to two species of teleost fish, providing one of the first comprehensive three‐dimensional (3D) descriptions of teleost cranial soft tissue and quantifying differences in muscle anatomy that may be related to differences in feeding ecology. Two species with different feeding ecologies were stained, scanned and imaged to create digital 3D musculoskeletal reconstructions: Esox lucius (Northern Pike), predominantly a suction feeder; and Anguilla anguilla (European eel), which captures prey predominantly by biting. Muscle cross‐sectional areas were calculated and compared between taxa, focusing on muscles that serve important roles in feeding. The adductor mandibulae complex – used in biting – was larger in Esox than Anguilla relative to head size. However, the overall architecture of the adductor mandibulae was also very different between the two species, with that of Anguilla better optimized for delivering forceful bites. Levator arcus palatini and sternohyoideus – which are used in suction feeding – are larger in Esox, whereas the levator operculi is larger in Anguilla. Therefore, differences in the size of functionally important muscles do not necessarily correlate neatly with presumed differences in feeding mode.

Pleiotropic jaw morphology links the evolution of mechanical modularity and functional feeding convergence in Lake Malawi cichlids

Article

Full-text available

Feb 2019

Complexity in how mechanistic variation translates into ecological novelty could be critical to organismal diversification. For instance, when multiple distinct morphologies can generate the same mechanical or functional phenotype, this could mitigate trade-offs and/or provide alternative ways to meet the same ecological challenge. To investigate how this type of complexity shapes diversity in a classic adaptive radiation, we tested several evolutionary consequences of the anterior jaw four-bar linkage for Lake Malawi cichlid trophic diversification. Using a novel phylogenetic framework, we demonstrated that different mechanical outputs of the same four jaw elements are evolutionarily associated with both jaw protrusion distance and jaw protrusion angle. However, these two functional aspects of jaw protrusion have evolved independently. Additionally, although four-bar morphology showed little evidence for attraction to optima, there was substantial evidence of adaptive peaks for emergent four-bar linkage mechanics and jaw protrusion abilities among Malawi feeding guilds. Finally, we highlighted a clear case of two cichlid species that have independently evolved to graze algae in less than 2 Myr and have converged on similar jaw protrusion abilities as well as four-bar linkage mechanics, but have evolved these similarities via non-convergent four-bar morphologies. © 2019 The Author(s) Published by the Royal Society. All rights reserved.

Ecomorphology of round goby, Neogobius melanostomus, predation on zebra mussels, Dreissena polymorpha

Thesis

Dec 2007

Janelle Morano

The functional performance of morphological characters may change through ontogeny, affecting the organism’s ecology. The fins and external structure of the round goby, Neogobius melanostomus, does not change through ontogeny, but the diet changes from soft-bodied native prey (benthic invertebrates, fish eggs, larvae) to hard-bodied zebra mussels, Dreissena polymorpha, when the gobies reach a standard length (SL) of 60-70 mm. To feed on D. polymorpha attached to substrate via byssal fibers, N. melanostomus uses oral jaws to remove mussels and pharyngeal jaws to process. By comparing the performance of the oral jaw bite force through ontogeny and correlating it to the byssal fiber attachment strength, it was concluded that smaller N. melanostomus are not capable of primarily feeding on D. polymorpha. Examining the pharyngeal jaws, the dentition changes with the diet shift, reflecting prey type. Morphological performance of N. melanostomus feeding apparatus is linked to feeding ecology.

PLASTICITY OF JAW AND SKULL MORPHOLOGY IN THE NEOTROPICAL CICHLIDS GEOPHAGUS BRASILIENSIS AND G. STEINDACHNERI

Article

Nov 1991
EVOLUTION

Peter Wimberger

I examined plasticity of jaw and skull morphology induced by feeding different diets in two species of the neotropical cichlid genus Geophagus. The two species possess different modes of development, which affect the size at which young begin feeding. I hypothesized that the difference in size at first feeding could lead to a difference in the amount of change inducible in the two species. The young of the substrate-spawning species, G. brasiliensis, which begin feeding at a smaller size, were predicted to be more plastic than those of the mouthbrooding species, G. steindachneri. The two diets used to induce differences were brine shrimp nauplii and chironomid larvae. Numerous measures of the jaw and skull differed significantly between groups fed the two diets but the amount of plasticity induced was small and would not present a problem for taxonomists. Contrary to my prediction, both the magnitude and pattern of plasticity induced in the two species was similar. Thus, mode of parental care and the size at which young begin feeding do not affect the degree of plasticity. Fish fed brine shrimp nauplii were longer in oral jaw region, but were shorter and shallower in the area behind the oral jaws. An additional group of G. brasiliensis was fed flake food to compare the results of this study to other studies. The differences in measures between fish fed brine shrimp diets and flake food diets were greater than those between fish fed brine shrimp and chironomid larvae. A possible role of plasticity for enhancing rather than retarding morphological evolution is discussed.

Labrid cleaner fishes show kinematic convergence as juveniles despite variation in morphology

Article

Full-text available

May 2017
J EXP BIOL

Cleaning, a dietary strategy in which ectoparasites or mucous are removed and consumed off other taxa, is performed facultatively or obligately in a variety of species. We explored whether species in the Labridae (wrasses, parrotfishes) of varying ecological specialization employ similar mechanisms of prey capture. In investigating feeding on attached prey among juveniles of 19 species of wrasses, we found that patterns of biting in wrasses are influenced by the interaction between the maxilla and a feature of the premaxilla which we term the maxillary crest. Premaxillary motion during biting appears to be guided by the relative size of the crest. In many cases, this results in a 'premaxillary bite' wherein the premaxillae rapidly move anteroventrally to meet the lower jaws and deliver a protruded bite. Cleaners in the Labrichthyini tribe, however, exhibited reduced or absent maxillary crests. This coincided with a distinct kinematic pattern of prey capture in these labrichthyine cleaners, coupled with some of the fastest and lowest-excursion jaw movements. Although evidence of kinematic specialization can be found in these labrichthyines (most notably in the obligate cleaners in Labroides), we found that facultative cleaners from other lineages similarly evolved reductions in excursions and timing. Convergence in feeding kinematics are thus apparent despite varying degrees of cleaning specialization and underlying morphological features.

Functional trait plasticity diverges between sexes in African cichlids: A contribution toward ecological sexual dimorphism?

Article

Full-text available

Nov 2023

Phenotypic plasticity enables development to produce multiple phenotypes in response to environmental conditions. Plasticity driven variation has been suggested to play a key role in adaptive divergence, and plasticity itself can evolve. However, the interaction of plasticity with the multiple levels involved with adaptive divergence is less understood. For example, sexual dimorphism can contribute adaptive variation through ecological sexual dimorphism (ESD), but the contribution of plasticity to this phenomenon is unknown. Therefore, to determine the potential contribution of plasticity to ESD, we used the adaptive radiation of Malawi cichlids. Two mouthbrooding species ( Labeotropheus fuelleborni and Tropheops “Red Cheek”) with differences in foraging tactics underwent foraging experiments using benthic and limnetic treatments while accounting for sex. Plasticity in craniofacial shape and three functionally important traits were measured. Plasticity was shown, but without any sex‐based differences in shape. However, for mechanical advantage traits of the mandible sex by diet interactions were found. This suggests that ESD, may be influenced by phenotypic plasticity that diverges between sexes. Given the involvement of the mandible in parental care in cichlids this may indicate that sexual divergence in plasticity may trade‐off against maternal care tactics.

Evolutionary Patterns of Modularity in the Linkage Systems of the Skull in Wrasses and Parrotfishes

Article

Full-text available

Sep 2023

Synopsis The concept of modularity is fundamental to understanding the evolvability of morphological structures and is considered a central framework for the exploration of functionally and developmentally related subsets of anatomical traits. In this study, we explored evolutionary patterns of modularity and integration in the 4-bar linkage biomechanical system of the skull in the fish family Labridae (wrasses and parrotfish). We measured evolutionary modularity and rates of shape diversification of the skull partitions of three biomechanical 4-bar linkage systems using 205 species of wrasses (family: Labridae) and a three-dimensional geometric morphometrics data set of 200 coordinates. We found support for a two-module hypothesis on the family level that identifies the bones associated with the three linkages as being a module independent from a module formed by the remainder of the skull (neurocranium, nasals, premaxilla, and pharyngeal jaws). We tested the patterns of skull modularity for four tribes in wrasses: hypsigenyines, julidines, cheilines, and scarines. The hypsigenyine and julidine groups showed the same two-module hypothesis for Labridae, whereas cheilines supported a four-module hypothesis with the three linkages as independent modules relative to the remainder of the skull. Scarines showed increased modularization of skull elements, where each bone is its own module. Diversification rates of modules show that linkage modules have evolved at a faster net rate of shape change than the remainder of the skull, with cheilines and scarines exhibiting the highest rate of evolutionary shape change. We developed a metric of linkage planarity and found the oral jaw linkage system to exhibit high planarity, while the rest position of the hyoid linkage system exhibited increased three dimensionality. This study shows a strong link between phenotypic evolution and biomechanical systems, with modularity influencing rates of shape change in the evolution of the wrasse skull.

The evolution of bite force and head morphology in scincid lizards: diet and habitat use as possible drivers

Article

Jun 2023

Diet and habitat use impose mechanical constraints that may impact head morphology and bite force. Skinks (Scincidae) comprise the largest family of lizards with ~1700 species currently described. They also show an important morphological and ecological diversity. Using phylogenetically informed analyses, we studied the interrelationships between ecology (diet, habitat use), head morphology and bite force in these lizards. Our results show a strong link between body size, bite force and diet, with herbivorous species being larger and biting harder than species from other dietary groups. Despite a lack of differences in body size and head morphology, omnivorous species bite harder than insectivorous species, in order to process the fibrous plant material that is part of their diet. Overall, lineages that evolved greater bite forces also showed an increase in relative head height allowing for more vertically oriented jaw muscles. Moreover, we find evidence for correlated evolution between bite force and head length: skinks that bite harder tend to have shorter jaws that likely provide a greater mechanical advantage when biting at the tip of the jaw. Surprisingly, habitat use does not appear to be correlated with morphological traits or bite force, but this needs to explored further.

Just below the surface, the pelagic haplochromine cichlids from the Lake Edward system

Article

Full-text available

May 2023
HYDROBIOLOGIA

The East African Great Lakes are inhabited by impressive radiations of cichlids that display a large variation in morphology, diet, colour pattern, and behaviour and have adapted to a large array of niches. Whilst most of these cichlids are bottom dwellers, a number of species have adapted to a pelagic environment and inhabit open waters. From the Lake Edward system, one pelagic species had been previously described, the zooplanktivorous Haplochromis pappenheimi. Our sampling revealed the Lake Edward system to be inhabited by two more pelagic species that were unknown to science and are formally described here, the zooplanktivorous Haplochromis pelagicus sp. nov. and the insectivorous H. aureus sp. nov. All three species seem mostly restricted to deepwater regions where the depth exceeds six metres in Lake Edward, except for H. pelagicus sp. nov., which also occurs in shallower regions of Lakes Edward and George and of the Kazinga Channel. Sexual dimorphism, mainly in head shape, was discovered in H. pappenheimi and H. pelagicus sp. nov. These differences suggest that females of these species have larger buccal cavities than males, which is most likely linked to female mouth brooding behaviour.

A reappraisal of the cranial and mandibular osteology of the spinosaurid Irritator challengeri (Dinosauria: Theropoda)

Article

Full-text available

Jan 2023
PALAEONTOL ELECTRON

Although originally described almost three decades ago, the holotype of Irritator challengeri from the Lower Cretaceous Romualdo Formation of Brazil still represents the most complete spinosaurid skull known to science. Here, we present a detailed description of the skull of Irritator based on digital reconstructions from medical and micro computed tomography (μCT) data. Segmentation reveals the near-complete palatal complex and braincase, an unusual morphology of the retroarticular process, a large, ventrally inclined surangular shelf and the tooth replacement pattern. The digitally reconstructed skull anatomy indicates a robust dentition, a field of binocular vision in front of the skull with an inclined snout orientation, a relatively weak but fast bite, as well as laterally spreading and rotating lower jaw rami during jaw opening. We modified an existing phylogenetic matrix of Tetanurae to account for new observations on the morphology of Irritator and analysed this using parsimony and Bayesian methods. Results support Spinosauridae as members of Megalosauroidea and recover a monophyletic Carnosauria (Megalosauroidea + Allosauroidea). Parsimony analysis recovers Monolophosaurus nested within Megalosauroidea as sister taxon to spinosaurids, but this is not supported by the Bayesian analysis. Bayesian time-calibration and evolutionary rate analysis indicate that spinosaurid evolution happened fast, despite a long ghost lineage of at least 35 million years. High evolutionary rates over a prolonged time can explain the highly derived skull morphology of spinosaurids. This study provides an in-depth look into the evolution of spinosaurid skull anatomy and refines our understanding of these specialized Mesozoic predators.

Contemporary phenotypic change in correlated characters in the African cyprinid, Rastrineobola argentea

Article

Mar 2018

Phenotypes reflect a complex interplay between the direct and indirect effects of multiple selective pressures; adaptive responses in individual traits may therefore be constrained by architectonic considerations and correlations with other traits. We explored whether and how three suites of neighbouring structures (respiratory, trophic and cranial) have changed over time in Rastrineobola argentea, a small pelagic cyprinid fish that is endemic to the Lake Victoria Basin in East Africa. We compared museum specimens from 1966 to modern (2010) specimens, spanning a period of almost 50 years of strong anthropogenic change in the lake, including increased frequency and extent of hypoxia and anoxia, and a dramatic restructuring of the lacustrine fish community and food-web. We found that modern R. argentea had significantly larger gills, wider heads, and shorter and more tightly packed gill rakers than their historical counterparts. Larger gill size probably represents a direct, adaptive response to more frequent bouts of hypoxia over time; the increase in head width and decrease in raker spacing may reflect correlated (and potentially maladaptive) responses to the increase in gill size. Integrative studies such as this are key to unravelling complex interactions between phenotypes and the environment.

Coevolution of the premaxillary ascending process and jaw protrusion in Lake Malawi cichlid fishes

Article

Full-text available

Aug 2022
HYDROBIOLOGIA

Variation in jaw protrusion is critical to cichlid fish trophic diversification. For instance, jaw protrusion distance can influence suction, attack speed, as well as bite force, and jaw protrusion angle is associated with exploiting prey from different substrates. Interestingly, premaxillary ascending process length has been shown to influence the maximum distance some cichlid fishes protrude their oral jaws, but its relationship to jaw protrusion angle is unclear. Using phylogenetic comparative methods, morphometrics, and field measurements in Malawi cichlid species, we tested the relationship between the length of the premaxillary ascending process and two components of jaw protrusion. In Malawi, the premaxilla's ascending process length ranged from 6.9 to 15.2% with respect to standard length. Maximum jaw protrusion ranged from 1.4 to 9.1% of standard length and jaw protrusion angle varied from 17° to 76°. Although jaw protrusion angle was not associated with premaxillary ascending process length, phylogenetically adjusted correlations between the ascending process and maximum jaw protrusion distance were highly significant. Evolutionary change in the premaxilla is likely critical for determining the maximum distance, but not the angle, of Malawi cichlid jaw protrusion. Examinations of this type of potential phenotypic multi-functionality will continue to illuminate the mechanisms contributing to cichlid fish diversity.

ECOMORPHOLOGICAL PATTERNS OF FEEDING IN FISH ASSEMBLAGES IN THREE SRI LANKAN RESERVOIRS

Chapter

Dec 2008

Ecomorphological correlates of diet among fish assemblages in three reservoirs of Sri Lanka were studied. Morphological characteristics and dietary habits ordinated by principal component analysis (PCA) revealed similar patterns. PCA indicated that species having greater body heights, longer gut lengths, broader eye diameters with truncate or forked caudal fins, and fewer or no barbels are predominantly herbivores or detritivores. The opposite was true for carnivorous species. Species in the three reservoirs have similar ecomorphological correlates with diet.

Rapid Evolutionary Responses in Cichlids: Genetics of Adaptation, Morphology and Taxonomic Implications

Chapter

Sep 2021

The haplochromine cichlids of Lake Victoria exhibit the fastest adaptive radiation of vertebrates known. Species identification of these lacustrine cichlids has been subject of debate for many years. Over the past 35 years, environmental perturbations have resulted in phenotypic change and possibly in hybridization, making species delimitation even more problematic. In this chapter, we document the effects of a changed environment on the ecomorphology of the zooplanktivore Haplochromis (Yssichromis) pyrrhocephalus over a 20-year period. We found that this species has extended its habitat to shallower waters and adjusted its diet to larger and more robust prey. Adaptive morphological responses to predation, to larger and tougher prey and to a hypoxic environment were found. Whether these morphological changes are the result of hybridization, phenotypic plasticity or evolutionary adaptation remains unclear. The morphological responses are sometimes so large that they transcend morphological species boundaries and even one of the limits of the genus Yssichromis. The extent of the morphological responses makes clear that nuptial colouration is indispensable for species distinction and the assessment of species richness. We review advanced molecular techniques that might make it possible to distinguish species genetically. These techniques may also reveal how adaptive responses might have played a role in the remarkable resurgence of these rapidly adapting cichlids.

Revisiting the feeding anatomy of the semi-aquatic lizard Dracaena guianensis Daudin, 1801 (Reptilia, Sauria) from the Western Brazilian Amazon

Article

Full-text available

Mar 2021

Introduction: There are about 842 reptile species known in Brazil, including 799 Squamata, being the most diverse assemblage, comprising 72 amphisbaenians, 276 lizards, and 405 snakes. Lizards have adapted to different habitats with terrestrial, fossorial, arboreal, and semi-aquatic habits. These ecological differences are reflected in skull morphology, with structures that evolved following their dietary specificity. Teiid lizard Dracaena guianensis Daudin, 1801 inhabits swamps and spends most of its time on low trees, though feeding only occurs in water. Its feeding habits are different from other family members, and its diet is mostly composed of mollusks and crustaceans. Herein, the anatomy of feeding apparatus of D. guianensis population from the Western Brazilian Amazon was dissected and documented in four exemplars for the first time. As result, it presents a dorsoventrally compressed neurocranium, dorsally oriented orbits, and heterodont dentition. Those characteristics were different from the most family members, as observed in comparisons with Ameiva ameiva (Linnaeus, 1758), which presents lateral orbits, a cranium not compressed dorsoventrally, and homodont dentition. Furthermore, in D. guianensis, it was possible to verify that muscles related to food apprehension were extremely developed, such as adductors and hyolingual muscles, which increase bite force according to the force versus cutting area in cross section; while in A. ameiva the muscles presented smaller cross sectional area and consequently, less bite force. The correlation between the anatomy of feeding apparatus and stomach contents allowed a preliminary comparison of osteological and myological characteristics to its food habits, suggesting that heterodont condition was a selective pressure directly related to durophagy.

Article

Full-text available

Oct 2019
J FISH BIOL

Lake Edward, East Africa, harbours a largely understudied assemblage of haplochromine cichlids that displays a range of adaptions to various specialised trophic niches. In this system, we discovered specimens of Haplochromis with morphologies similar to those of oral‐mollusc shellers from Lake Victoria. These morphologies are characterised by short oral jaws with stout teeth that are used either to crush molluscs or to grab the soft bodies of snails and wrench them out of their shells. A morphometric study on 47 specimens from Lake Edward revealed the presence of three new species with an oral‐shelling morphology: Haplochromis concilians sp. nov., H. erutus sp. nov. and H. planus sp. nov. All three species are formally described. Stomach‐content observations confirmed an opportunistic oral‐shelling ecology for H. concilians sp. nov. and H. erutus sp. nov. Within H. planus sp. nov., only large specimens displayed a specialised oral‐shelling morphology, but their stomachs were nearly empty, while small specimens consumed mainly Ostracoda and Hydrachnidia. Remarkably, the three species differed considerably in morphology from each other, but they each resembled oral‐sheller species from Lake Victoria.

Head Shape Modulates Diversification of a Classic Cichlid Pharyngeal Jaw Innovation

Article

Jul 2019

Functional innovations are often invoked to explain the uneven distribution of ecological diversity. Innovations may provide access to new adaptive zones by expanding available ecological opportunities and may serve as catalysts of adaptive radiation. However, diversity is often unevenly distributed within clades that share a key innovation, highlighting the possibility that the impact of the innovation is mediated by other traits. Pharyngognathy is a widely recognized innovation of the pharyngeal jaws that enhances the ability to process hard and tough prey in several major radiations of fishes, including marine wrasses and freshwater cichlids. We explored diversification of lower pharyngeal jaw shape, a key feature of pharyngognathy, and the extent to which it is influenced by head shape in Neotropical cichlids. While pharyngeal jaw shape was unaffected by either head length or head depth, its disparity declined dramatically with increasing head width. Head width also predicted the rate of pharyngeal jaw evolution such that higher rates were associated with narrow heads. Wide heads are associated with exploiting prey that require intense processing by pharyngeal jaws that have expanded surfaces for the attachment of enlarged muscles. However, we show that a wide head constrains access to adaptive peaks associated with several trophic roles. A constraint on the independent evolution of pharyngeal jaw and head shape may explain the uneven distribution of ecological diversity within a clade that shares a major functional innovation.

Relationship between jaw morphology, bite performance and diet in Serrasalmidae (Characiformes, Teleostei)

Presentation

Dec 2016

Alessia Huby

Serrasalmidae are mainly known for “piranhas” and their negative reputation of ferocious predatory fishes. A recent study demonstrated that the piranha Serrasalmus rhombeus had an extreme bite force that is even proportionally greater than that of the white shark. However, these sharp teeth fishes represent only a minority of Serrasalmidae. Other serrasalmid species (pacus and myleus) feed on plants, fruits or seeds and their bite force and feeding capacities are still uninvestigated. In the present research, in vivo bite forces were measured and compared according to jaw morphology in ten species of Serrasalmidae including six herbivorous and four carnivorous species. The Bite Force Quotient (BFQ) was calculated for each individual to compare the jaw strength across species. The results of the analysis showed that species feeding on fins and fish flesh have a significant greater bite force than species feeding on plants, fruits or seeds. This difference can be explained by the larger adductor mandibulae muscle in carnivorous species which have comparatively longer and higher skull than herbivorous species. In addition, there is a significant difference in the lower jaw morphology between piranhas and pacus and relatives. The piranha species have longer lower jaws than pacus and myleus species which have shorter and higher lower jaws. This study shows that the Serrasalmidae family regroups remarkable biters whose bite performance is mostly related to diet.

Allopatric and sympatric diversification within roach (Rutilus rutilus) of large prealpine lakes

Article

Jun 2019

Intraspecific differentiation in response to divergent natural selection between environments is a common phenomenon in some lineages of northern freshwater fishes, especially salmonids and stickleback. Understanding why these taxa diversify and undergo adaptive radiations while most other fish species in the same environments do not, remains an open question. The possibility for intraspecific diversification has rarely been evaluated for most northern freshwater fish species. Here, we assess the potential for intraspecific differentiation between and within lake populations of roach (Rutilus rutilus) – a widespread and abundant cyprinid species - in lakes in which salmonids have evolved endemic adaptive radiations. Based on more than 3,000 polymorphic RADseq markers, we detected low but significant genetic differentiation between roach populations of two ultraoligotrophic lakes and between these and populations from other lakes. This, together with differentiation in head morphology and stable isotope signatures, suggests evolutionary and ecological differentiation among some of our studied populations. Next, we tested for intralacustrine diversification of roach within Lake Brienz, the most pristine lake surveyed in this study. We found significant phenotypic evidence for ecological intralacustrine differentiation between roach caught over a muddy substrate and those caught over a rocky substrate. However, evidence for intralacustrine genetic differentiation is at best subtle and phenotypic changes may therefore be mostly plastic. Overall, our findings suggest roach can differ between ecologically distinct lakes, but the extent of intralacustrine ecological differentiation is weak, which contrasts with the strong differentiation among endemic species of whitefish in the same lakes.

The lobed-lipped species of Haplochromis (Teleostei, Cichlidae) from Lake Edward, two instead of one

Article

May 2019
J GREAT LAKES RES

Thickened lips have evolved several times within the cichlid flocks of the East African Great Lakes. This distinct and easily recognisable phenotype is a model trait to study convergent evolution. Lake Edward (Eastern Africa) contains a unique cichlid assemblage, which has remained largely understudied. Hitherto, only one cichlid species with lobed lips, Haplochromis labiatus, was known from this lake. This species has a blunt snout and rounded and mostly retrognathous jaws. However, we found specimens with lobed lips, but with acute snouts and slender and mostly prognathous jaws. These belong to a species, hitherto unknown to science: H. lobatus sp. nov. Both species occur sympatrically. We evaluated the morphological diversity within these species by investigating a total of 112 specimens using traditional and geometric morphometric approaches. Both species are formally (re)described and show a relatively large variation in their trophic morphologies, which complicates identification. Both have a small gape, stout outer teeth that strongly decrease in size laterad, and a lower jaw set anteriorly with procumbently-implanted outer teeth. Haplochromis labiatus differs from H. lobatus sp. nov. by a straight to convex vs. straight to concave head, a slightly shorter and broader lower jaw (27.7–34.3 vs. 31.2–40.7% HL; 71.4–92.4 vs. 48.5–70.5% LJL), and lobed lips that are thickened uniformly over their whole lengths vs. medially enlarged. Gut content observations revealed that both species have an insectivorous diet. While both exploit similar food sources, their morphological differences presumably prevent them from entering into direct ecological competition.

‘Homemade’: the phenotypic diversity of coral reef damselfish populations is driven by the local environment

Article

Apr 2019

Documenting phenotypic variation among populations is crucial for our understanding of micro-evolutionary processes. To date, the quantification of trophic and morphological variation among populations of coral reef fish at multiple geographical scales remains limited. This study aimed to quantify diet and body shape variation among four populations of the damselfish Dascyllus abudafur living in different environmental conditions from the central Red Sea and from Madagascar. Stomach content analyses showed that one adaptive response of D. abudafur inhabiting turbid waters is a trophic shift from almost exclusive zooplanktivory to a diet consisting of planktonic and benthic prey. Our morphometric data reveal differences in cephalic profile and body shape among populations, in agreement with this variation in trophic strategy. Isotopic diversity and body shape disparity vary among populations and we thus demonstrate that coral reef fish populations are not equal in terms of phenotypic diversity among sites and regions. Finally, our comparative analysis reveals that the main axes of body shape variation among populations are shared at both small (Red Sea sites) and large (Madagascar and Red Sea sites) spatial scales. This study raises new questions about the factors governing the direction of response to selection in this fish species.

Functional diversity in biters: the evolutionary morphology of the oral jaw system in pacus, piranhas and relatives (Teleostei: Serrasalmidae)

Article

May 2019

Serrasalmid fishes form a highly specialized group of biters that show a large trophic diversity, ranging from pacus able to crush seeds to piranhas capable of cutting flesh. Their oral jaw system has been hypothesized to be forceful, but variation in bite performance and morphology with respect to diet has not previously been investigated. We tested whether herbivorous species have higher bite forces, larger jaw muscles and more robust jaws than carnivorous species. We measured in vivo and theoretical bite forces in 27 serrasalmid species. We compared the size of the adductor mandibulae muscle, the jaw mechanical advantages, the type of jaw occlusion, and the size and shape of the lower jaw. We also examined the association between bite performance and functional morphological traits of the oral jaw system. Contrary to our predictions, carnivorous piranhas deliver stronger bites than their herbivorous counterparts. The size of the adductor mandibulae muscle varies with bite force and muscles are larger in carnivorous species. Our study highlights an underestimated level of functional morphological diversity in a fish group of exclusive biters. We provide evidence that the trophic specialization towards carnivory in piranhas results from changes in the configuration of the adductor mandibulae muscle and the lower jaw shape, which have major effects on bite performance and bite strategy.

Functional diversity in biters: the evolutionary morphology of the oral jaw system in pacus, piranhas and relatives (Teleostei: Serrasalmidae)

Article

May 2019

Rapid Divergence of Predator Functional Traits Affects Prey Composition in Aquatic Communities

Article

Jan 2019

Identifying traits that underlie variation in individual performance of consumers (i.e., trait utility) can help reveal the ecological causes of population divergence and the subsequent consequences for species interactions and community structure. Here, we document a case of rapid divergence (over the past 100 generations, or ∼150 years) in foraging traits and feeding efficiency between a lake and stream population pair of threespine stickleback. Building on predictions from functional trait models of fish feeding, we analyzed foraging experiments with a Bayesian path analysis and elucidated the traits explaining variation in foraging performance and the species composition of ingested prey. Despite extensive previous research on the divergence of foraging traits among populations and ecotypes of stickleback, our results provide novel experimental evidence of trait utility for jaw protrusion, gill raker length, and gill raker spacing when foraging on a natural zooplankton assemblage. Furthermore, we discuss how these traits might contribute to the differential effects of lake and stream stickleback on their prey communities, observed in both laboratory and mesocosm conditions. More generally, our results illustrate how the rapid divergence of functional foraging traits of consumers can impact the biomass, species composition, and trophic structure of prey communities.

Feeding structures in the ray-finned fish Eurynotus crenatus (Actinopterygii: Eurynotiformes): implications for trophic diversification among Carboniferous actinopterygians

Article

Dec 2018

The Permo-Carboniferous eurynotiforms show conspicuous modifications to postcranial and cranial morphology relative to primitive actinopterygian conditions, and represent an important early example of functional experimentation within ray-finned fishes. Although eurynotiforms are represented by abundant articulated fossil material, the internal anatomy of the group is not well known. Microcomputed tomography (μCT) of Eurynotus crenatus from the early Carboniferous (Viséan) Wardie Shales Member of the Gullane Formation of Wardie, Scotland provides detailed information on the jaws, palate and dentition. The lower jaw is deep and bears a well-developed convex dental plate on the prearticular/coronoids. The dentary bears a dorsally directed posterior process and lacks any obvious marginal dentition. The prearticular bears a low coronoid process. Apart from the first and second dermopalatines, and a likely accessory vomer, bones of the palate are tightly sutured or fused. The upper dental plate comprises a longitudinal, concave horizontal dental surface that occludes with the convex lower toothplate, and a more vertical region consisting of anastomosing ridges. The parasphenoid has a narrow anterior corpus and a broad posterior stalk that bears a pronounced midline notch. The smooth, irregularly punctated surfaces of the dental plates are formed by closely packed teeth with conjoined crowns, providing clues to the evolution of the more monolithic toothplates of Amphicentrum from the peg-like teeth reported in the earliest and most anatomically generalised eurynotiforms. The feeding apparatus shows many qualitative and quantitative features consistent with the processing of hard prey items. Eurynotus and its relatives show the first clear example of jaw and dental structures consistent with durophagy among actinopterygians. The origin of the group in the early Carboniferous is suggestive of diversification into newly available ecological roles in the aftermath of the end-Devonian extinction.

Intrinsic Constraints on the Diversification of Neotropical Cichlid Adductor Mandibulae Size: ADDUCTOR MANDIBULAE SIZE IN CICHLINAE

Article

Feb 2018

The diversification of functional traits may be constrained by intrinsic factors, such as structural, mechanical, developmental, or physiological limitations. We explored the biomechanical and constructional constraints on the size of the major jaw closing muscles, the adductor mandibulae complex (AM), in a diverse clade of freshwater fish - the Neotropical cichlids. Using phylogenetic comparative methods, we contrasted patterns of size variation and diversification rates of three AM divisions with variables describing head size and biomechanical coefficients describing force and velocity transmission. We found that all three AM muscles examined were impacted by constructional constraints, namely, (1) the space available in the head (head length and width—all AMs), (2) competition with the eye (AM1 and AM2), (3) competition for space among the three major AM divisions (e.g., AM1 vs. AM3), and (4) potentially the shape of the lower jaw (AM2). Only AM2 size was significantly associated with lower jaw biomechanical coefficients, but opposite predictions based on force transmission (i.e., no compensation for low mechanical advantage). Diversification rates of the mass of the divisions of the AM were also not connected to the diversification rates of their biomechanical coefficients. Previously suggested compensation in AM mass for reduced force transmission among ram-feeding predators appears to be driven by overall body plan changes (lengthening of the head in elongate bodies) and only indirectly to biomechanical trade-offs. Strong constructional constraints on AM size likely limit potentially functional morphospace occupation, and highlight the highly integrated nature of ram-suction feeding functional adaptations in Neotropical cichlids. Anat Rec, 301:216–226, 2018. © 2018 Wiley Periodicals, Inc.

Ecomorphological trajectories of reef fish sister species (Pomacentridae) from both sides of the Isthmus of Panama

Article

Full-text available

Jun 2018
ZOOMORPHOLOGY

Rosalia Aguilar-Medrano

The vicariance model of biogeography focuses on allopatric speciation through fragmentation from an ancestral biota via a barrier that interrupts gene flow between populations. The evolutionary processes that occur over time in sister species on each side of the vicariance event influence their traits by a compromise between divergence and conservatism. The eastern Pacific and the Caribbean Sea were separated by the Isthmus of Panama ~3–6 Mya and allopatric speciation occurred on either side of the isthmus. Differences in ecological conditions on each side of the Isthmus of Panama separating the sister species may have shaped their niches and morphologies over evolutionary time. The objectives of this study were to: (1) analyze the variation in niche, morphology, and size in each pair of sister damselfish species on both sides of the Isthmus of Panama, (2) determine whether these variables show specific patterns on each side of the isthmus, and (3) determine whether these variables are correlated through evolution. The results showed no relationship between morphology and niche, but size was related to both niche and morphology. Sister damselfish species on either side of the Isthmus of Panama differ in terms of niche, morphology, and size. Nevertheless, they also show similarities, indicating environmental constraints and conservatism. This study describes a model in which adaptation or divergence and conservatism shaped the evolution of sister damselfish species on both sides of the Isthmus of Panama. These mechanisms are fundamental to population biology, and they act in opposite directions.

Durophagous biting in sea otters (Enhydra lutris) differs kinematically from raptorial biting of other marine mammals

Article

Full-text available

Oct 2017
J EXP BIOL

Sea otters represent an interesting model for studies of mammalian feeding evolution. Although they are marine mammals, sea otters returned to the sea relatively recently and feed at the surface. Therefore, they represent a transitional stage of aquatic adaptation. Currently no feeding performance studies of sea otters have been conducted. The main objective of this study was to characterize the feeding kinematic profile in sea otters. It was hypothesized that sea otters would exhibit a terrestrial feeding behavior and that they forcefully crush hard prey at large gapes. As a result, biting kinematics would be congruent with biting behavior reported for their terrestrial ancestors, thus providing additional evidence that raptorial biting is a conserved behavior even in recently aquatic mammals. Sea otters consistently used a durophagous raptorial biting mode characterized by large gapes, large gape angles, and lack of lateral gape occlusion. The shorter skulls and mandibles of sea otters, along with increased mechanical advantages of the masseter and increased bite force, form a repertoire of functional traits for durophagy. Here we consider durophagy to be a specialized raptorial biting feeding mode. A comparison of feeding kinematics of wild vs captive sea otters showed no significant differences in lateral kinematic profiles and only minor differences in three frontal kinematic profiles, which included a slower maximum opening gape velocity, a slower maximum gape opening velocity, and a slower maximum closing gape velocity in captive sea otters. Data indicate functional innovations for producing large bite forces at wide gape and gape angles.

Diversity Methods of the Strike Teleostei in Connection with Morphology Their Jaw Apparatus (Review)

Article

Jul 2023

The paper provides a review features of the strike Teleostei methods – suction, ram and bite, in different representatives at the definitive stage of development with characteristic morphology traits their feeding apparatus at qualitative level. In the paper we describe new traits of construction jaw apparatus some Teleostei species, those testifie in favour application them several methods of the strike separately or at a time during feeding.

Diversity of Feeding Methods in Teleosts (Teleostei) in the Context of the Morphology of Their Jaw Apparatus (Review)

Article

Aug 2023

Differential growth of the adductor muscles, eyeball, and brain in the chick Gallus gallus with comments on the fossil record of stem‐group birds

Article

Jul 2023

The avian head is unique among living reptiles in its combination of relatively large brain and eyes, coupled with relatively small adductor jaw muscles. These derived proportions lend themselves to a trade‐off hypothesis, wherein adductor size was reduced over evolutionary time as a means (or as a consequence) of neurosensory expansion. In this study, we examine this evolutionary hypothesis through the lens of development by describing the jaw‐adductor anatomy of developing chickens, Gallus gallus, and comparing the volumetric expansion of these developing muscles with growth trajectories of the brain and eye. Under the trade‐off hypothesis, we predicted that the jaw muscles would grow with negative allometry relative to brain and eyes, and that osteological signatures of a relatively large adductor system, as found in most nonavian dinosaurs, would be differentially expressed in younger chicks. Results did not meet these expectations, at least not generally, with muscle growth exhibiting positive allometry relative to that of brain and eye. We propose three, nonmutually exclusive explanations: (1) these systems do not compete for space, (2) these systems competed for space in the evolutionary past, and growth of the jaw muscles was truncated early in development (paedomorphosis), and (3) trade‐offs in developmental investment in these systems are limited temporally to the perinatal period. These explanations are considered in light of the fossil record, and most notably the skull of the stem bird Ichthyornis, which exhibits an interesting combination of plesiomorphically large adductor chamber and apomorphically large brain.

Typology of the Suspensorium Structure of Teleost Fishes in Regard to Their Feeding (Review)

Article

Aug 2022

From a pair to a dozen: the piscivorous species of Haplochromis (Cichlidae) from the Lake Edward system

Article

Full-text available

Apr 2022

Piscivory is a common trophic niche among cichlids of the East African Great Lakes, including Lakes Edward and George. From these two lakes, we examined the taxonomic diversity of cichlid species with a piscivorous morphology. Prior to this study, two piscivorous species were formally described, Haplochromis squamipinnis and H. mentatus. We redescribe both species and describe an additional ten new species of Haplochromis with a piscivorous morphology: H. latifrons sp. nov., H. rex sp. nov., H. simba sp. nov., H. glaucus sp. nov., H. aquila sp. nov., H. kimondo sp. nov., H. falcatus sp. nov., H. curvidens sp. nov., H. pardus sp. nov., and H. quasimodo sp. nov. All twelve species differ in dominant male colour pattern (unknown for H. latifrons sp. nov. and H. curvidens sp. nov.) and morphological traits. The species can be divided into two morphological groups: the macrodontic piscivores and the microdontic piscivores. This division potentially reflects an ecological differentiation in habitat use, hunting technique, prey species, and prey size. We conclude that some 12–20% of the species from the cichlid assemblage of Lake Edward have a piscivorous morphology.

Seeökosysteme V: Synökologie (Teil 1)

Chapter

Nov 2021

de Nach Beiträgen zu Autökologie und Populationsökologie werden die Seeökosysteme aus der Sicht der Synökologie betrachtet. Die Gemeinschaften der Arten werden zunächst als Gemeinschaften 1. Ordnung, Gilden von Konkurrenten, mit dem Schwerpunkt des Vorkommens in der Litoralzone und in Flachseen behandelt. Die Charakteristika der Flachseen und deren Bistabilität werden dargestellt an Beispielen von Makrophyten dominierten Klarwasserseen und von planktischen Algen dominierten Trübwasserseen. Die Gemeinschaften der Makrophyten werden beschrieben nach taxonomischer Zusammensetzung, aus Sicht der Pflanzensoziologie, nach den Wuchsformen, als Primärproduzenten, als Futterquelle für Konsumenten, als Habitat und Schutzraum für litorale Organismen. Die Gemeinschaft des Zoobenthos wird dargestellt nach Artenzusammensetzung, Tiefenverteilung, Trophie, besiedelten Substraten, als funktionelle Gruppen und nach trophischen Positionen. Das Meiozoobenthos wird dem Makrozoobenthos gegenübergestellt. Die Gemeinschaft der Fische wird für typische Seen beschrieben nach taxonomischer Zusammensetzung, nach funktionellen Gruppen, den Typen der Nahrungsaufnahme und den trophischen Positionen, insbesondere für die sympatrisch lebenden Arten der Coregonen. Die verschiedenen Nahrungsnutzungen der Fische als Zooplanktivore, Herbivore und die Nutzung litoraler, profundaler und pelagischer Quellen sowie die Verschiebung des Nahrungsspektrums im Verlauf der ontogentischen Entwicklung werden dargestellt. Die Rolle der Vögel für Seeökosysteme wird an Beispielen gezeigt. Abstract en In this chapter the community ecology in lake ecosystems is considered, following previous contributions on autecology and population ecology. The communities of species are looked upon at the levels of 1st order, guilds of competing species with indirect interactions, and 2nd order at the level of direct interactions in food webs. Shallow lakes and litoral zones are characterized versus deep lakes. The bistability of shallow lakes is shown by shifts between clearwater lakes or turbid lakes, dominated by macrophytes or by phytoplankton. The communities of macrophytes are desribed by taxonomic composition, as phytosoziological associations, by growth forms, as primary producers, as food sources, and as habitats and protective shelters for littoral organisms. The zoobenthos communities are considered by their taxonomic composition, depth distributions, lake trophy, substrates, as functional groups and by the trophic positions of species. Meiozoobenthos and macrozoobenthos are compared by different examples. Fish communities are characterized by species composition, as functional groups, types of feeding and trophic positions of species. The forms of sympatric Coregonus species are considered as ecospecies. The different food types of fish species are shown for zooplanktivores, herbivores, and use of littoral, profundal and pelagic sources, and the shift of food types during fish ontogeny. The ecological role of birds for lake ecosystems is demonstrated by different examples.

Constraints on the Ecomorphological Convergence of Zooplanktivorous Butterflyfishes

Article

Full-text available

May 2021

Synopsis Whether distantly related organisms evolve similar strategies to meet the demands of a shared ecological niche depends on their evolutionary history and the nature of form–function relationships. In fishes, the visual identification and consumption of microscopic zooplankters, selective zooplanktivory, is a distinct type of foraging often associated with a suite of morphological specializations. Previous work has identified inconsistencies in the trajectory and magnitude of morphological change following transitions to selective zooplanktivory, alluding to the diversity and importance of ancestral effects. Here we investigate whether transitions to selective zooplanktivory have influenced the morphological evolution of marine butterflyfishes (family Chaetodontidae), a group of small-prey specialists well known for several types of high-precision benthivory. Using Bayesian ancestral state estimation, we inferred the recent evolution of zooplanktivory among benthivorous ancestors that hunted small invertebrates and browsed by picking or scraping coral polyps. Traits related to the capture of prey appear to be functionally versatile, with little morphological distinction between species with benthivorous and planktivorous foraging modes. In contrast, multiple traits related to prey detection or swimming performance are evolving toward novel, zooplanktivore-specific optima. Despite a relatively short evolutionary history, general morphological indistinctiveness, and evidence of constraint on the evolution of body size, convergent evolution has closed a near significant amount of the morphological distance between zooplanktivorous species. Overall, our findings describe the extent to which the functional demands associated with selective zooplanktivory have led to generalizable morphological features among butterflyfishes and highlight the importance of ancestral effects in shaping patterns of morphological convergence.

Diversity in rest-activity patterns among Lake Malawi cichlid fishes suggests a novel axis of habitat partitioning

Article

Full-text available

Mar 2021

Animals display remarkable diversity in rest and activity patterns that are regulated by endogenous foraging strategies, social behaviors, and predator avoidance. Alteration in the circadian timing of activity or the duration of rest-wake cycles provide a central mechanism for animals to exploit novel niches. The diversity of the 3000+ cichlid species throughout the world provides a unique opportunity to examine variation in locomotor activity and rest. Lake Malawi alone is home to over 500 species of cichlids that display divergent behaviors and inhabit well-defined niches throughout the lake. These species are presumed to be diurnal, though this has never been tested systematically. Here, we measure locomotor activity across the circadian cycle in 11 Lake Malawi cichlid species. We document surprising variability in the circadian time of locomotor activity and the duration of rest. In particular, we identify a single species, Tropheops sp. “red cheek” that is nocturnal. Nocturnal behavior was maintained when fish were provided shelter, but not under constant darkness, suggesting it results from acute response to light rather than an endogenous circadian rhythm. Finally, we show that nocturnality is associated with increased eye size after correcting for evolutionary history, suggesting a link between visual processing and nighttime activity. Together, these findings identify diversity of locomotor behavior in Lake Malawi cichlids and provide a system for investigating the molecular and neural basis underlying variation in nocturnal activity.

The Evolutionary Continuum of Functional Homodonty to Heterodonty in the Dentition of Halichoeres Wrasses

Article

Full-text available

Sep 2020
INTEGR COMP BIOL

Vertebrate dentitions are often collapsed into a few discrete categories, obscuring both potentially important functional differences between them and insight into their evolution. The terms homodonty and heterodonty typically conflate tooth morphology with tooth function, and require context-dependent subcategories to take on any specific meaning. Qualifiers like incipient, transient, or phylogenetic homodonty attempt to provide a more rigorous definition but instead highlight the difficulties in categorizing dentitions. To address these issues, we recently proposed a method for quantifying the function of dental batteries based on the estimated stress of each tooth (inferred using surface area) standardized for jaw out-lever (inferred using tooth position). This method reveals a homodonty-heterodonty functional continuum where small and large teeth work together to transmit forces to a prey item. Morphological homodonty or heterodonty refers to morphology, whereas functional homodonty or heterodonty refers to transmission of stress. In this study, we use Halichoeres wrasses to explore how functional continuum can be used in phylogenetic analyses by generating two continuous metrics from the functional homodonty-heterodonty continuum. Here we show that functionally heterodont teeth have evolved at least three times in Halichoeres wrasses. There are more functionally heterodont teeth on upper jaws than on lower jaws, but functionally heterodont teeth on the lower jaws bear significantly more stress. These nuances, which have functional consequences, would be missed by binning entire dentitions into discrete categories. This analysis points out areas worth taking a closer look at from a mechanical and developmental point of view with respect to the distribution and type of heterodonty seen in different jaws and different areas of jaws. These data, on a small group of wrasses, suggest continuous dental variables can be a rich source of insight into the evolution of fish feeding mechanisms across a wider variety of species.

A new species and biology of the Late Cretaceous 'blunt-snouted' bony fish, Thryptodus (Actinopterygii: Tselfatiiformes), from the United States

Article

Apr 2019

Kenshu Shimada

Thryptodus zitteli Loomis (Actinopterygii: Tselfatiiformes) is an enigmatic Late Cretaceous bony fish with a massive blunt rostrum that lived in the Western Interior Seaway of North America. Here, a second species of Thryptodus, T. loomisi sp. nov., is described on the basis of two skulls and some isolated rostra from the Britton Formation (Cenomanian–lower Turonian) of Texas, USA. In addition, the type species, T. zitteli, is redescribed and a nearly complete skeleton of the species from the Austin Chalk of Texas is examined to further decipher the biology of Thryptodus. Thryptodus primarily lived in offshore environments and reached up to about 1.8 m in total length. With a massive head, the fossil fish had a dorsal fin that spanned much of the body length, elongate pectoral, pelvic, and anal fins, and a small forked caudal fin, suggesting that Thryptodus was a sluggish swimmer. The function of the peculiar blunt rostrum in Thryptodus remains uncertain. Likewise, the exact diet of Thryptodus remains unknown. However, the skull construct suggests that Thryptodus had powerful lower jaws and hyoid-based suction feeding.

Actinopterygians: Head, Jaws and Muscles: Anatomical, Functional, and Developmental Diversity in Chordate Evolution

Chapter

Jan 2019

This chapter is targeted to a broad scientific audience such as students and non-specialists who would like to explore and understand the diversity of the head, jaws and cranial muscles encountered within the large class of ray-finned fishes (Actinopterygii). Actinopterygians are a wide group of bony fishes including more than 30,000 species, which means that it is obviously not possible to carry out a case-by-case assessment or to condense the subject in a few pages. Therefore, we have described the role of the musculoskeletal elements of the head occurring during breathing and feeding in a ray-finned fish representative of the group, as well as we have demonstrated that the actinopterygian skull is truly distinctive among vertebrates. We have also tried to explain the main information concerning the diversification and evolution of the jaws and muscles of the five extant actinopterygian lineages with more specificities on teleostean fishes which are the most diverse and advanced clade.

Consideraciones ecomorfológicas del mecanismo de captura de presas en Xiphias gladius (Linnaeus, 1758)

Article

Jan 2009

This paper analyzes the prey capture mechanism of the swordfish (Xiphias gladius), assuming a RAM feeding mechanism and a wide dietary trophic spectrum. The complete cephalic región is studied, and the osteology and miology associated with the prey capture mechanism are described. A four-bar linkage model was applied to assess the efficiency of the mouth opening and a biokinetic model to evalúate the mouth closure efficiency. The majority of the neurocranial structures are displaced towards the posterior región, with a high degree of ossification and a prevalence of joints with beveled edges and sutures. The vertical bar of the suspensorium, which supports the opercular series and lower jaw are noteworthy. The premaxilla and maxilla are closely jointed, without any possibility of relative movement, although a primordial ligament remains. The configuration of the lever system of the adductor mandibulae muscle determines the biokinetic system, whose forcé transmission efficiency is around 30%) for the external fascicles (A2 +A3á) and 15% for the inner fascicle (A3ß). The kinetic transmission coefficient (K = q r-1 ) is 9.75, whereas the forcé transmission coefficient (f = q r-1 ) is 0.102. The morphofunctional design that allows the capture of fast-swimming prey is analyzed and discussed; the high kinematic transmission coefficient coincides with the valúes found for piscivorous fishes.

EVIDENCE FOR MULTIPLE ORIGINS AND SYMPATRIC DIVERGENCE OF TROPHIC ECOTYPES OF SMELT (OSMERUS) IN NORTHEASTERN NORTH AMERICA

Article

Full-text available

Jun 1993
EVOLUTION

The rainbow smelt, Osmerus mordax (Mitchill), is an osmerid fish that exhibits extensive life-history diversity throughout watersheds of northeastern North America. There are both ∗∗∗sea-run (anadromous) and lake-resident (lacustrine) populations and the latter have diversified further into "dwarf-" and "normal-sized" life-history types. Anadromous and lacustrine smelt may inhabit the same watershed and there are several instances where dwarf and normal populations reside within the same lake. We assayed variation among smelt for morphological traits linked to feeding performance in fishes to see if trophic ecology might promote life-history diversity in Osmerus. We also examined mitochondrial DNA (mtDNA) restriction site variation among forms to assess their evolutionary interrelationships. Dwarf smelt had significantly more gill rakers, larger eyes, but shorter upper jaws than normal lake and anadromous smelt. The populations clustered into two trophic "morphotypes"; an anadromous/normal lake group of populations and a group consisting only of dwarf smelt. The mtDNAs of 444 smelt from 16 populations were digested with 12 restriction enzymes revealing 93 composite mtDNA genotypes that clustered (UPGMA) into two major phylogenetic groups differing by 0.78% in sequence. Both genetic groups were present in dwarf and normal smelt as well as in anadromous fish. Further, geographic proximity, rather than trophic morphotype, appeared to be the major determinant of genetic affinities among populations. In two lakes, however, dwarf and normal smelt populations had significantly different mtDNA genotype frequency distributions indicating that the forms are reproductively isolated within both lakes. A clustering analysis of population affinities suggested that the divergence of sympatric dwarf and normal populations had occurred independently in the two lakes. We concluded (1) that trophic ecology is an important factor promoting differentiation in smelt life histories; (2) that smelt ecotypes are polyphyletic and there have been multiple, independent divergences of Osmerus life-history types throughout northeastern North America; and (3) that the biological and mtDNA differences between coexisting dwarf and normal lake smelt argue strongly that their genetic isolation may have developed sympatrically.

Towards a Constructional Morphology of Cichlid Fishes (Teleostei, Perciformes)

Abstract

No full-text available

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