A functional morphospace for the skull of labrid fishes: patterns of diversity in a complex biomechanical system

The Labridae (including wrasses, the Odacidae and the Scaridae) is a species‐rich group of perciform fishes whose members are prominent inhabitants of warm‐temperate and tropical reefs worldwide. We analyse functionally relevant morphometrics for the feeding apparatus of 130 labrid species found on the Great Barrier Reef and use these data to explore the morphological and mechanical basis of trophic diversity found in this assemblage. Morphological measurements were made that characterize the functional and mechanical properties of the oral jaws that are used in prey capture and handling, the hyoid apparatus that is used in expanding the buccal cavity during suction feeding, and the pharyngeal jaw apparatus that is used in breaking through the defences of shelled prey, winnowing edible matter from sand and other debris, and pulverizing the algae, detritus and rock mixture eaten by scarids (parrotfishes). A Principal Components Analysis on the correlation matrix of a reduced set of ten variables revealed complete separation of scarids from wrasses on the basis of the former having a small mouth with limited jaw protrusion, high mechanical advantage in jaw closing, and a small sternohyoideus muscle and high kinematic transmission in the hyoid four‐bar linkage. Some scarids also exhibit a novel four‐bar linkage conformation in the oral jaw apparatus. Within wrasses a striking lack of strong associations was found among the mechanical elements of the feeding apparatus. These weak associations resulted in a highly diverse system in which functional properties occur in many different combinations and reflect variation in feeding ecology. Among putatively monophyletic groups of labrids, the cheilines showed the highest functional diversity and scarids were moderately diverse, in spite of their reputation for being trophically monomorphic and specialized. We hypothesize that the functional and ecological diversity of labrids is due in part to a history of decoupled evolution of major components of the feeding system (i.e. oral jaws, hyoid and pharyngeal jaw apparatus) as well as among the muscular and skeletal elements of each component. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82 , 1–25.     

Heterozygosity and extra-pair paternity: biased tests result from the use of shared markers

Recent studies of extra-pair paternity have found support for the idea that heterozygous males have an advantage in siring offspring. Most studies use DNA microsatellite loci to determine paternity and then use the same loci to estimate individual heterozygosity. However, because the likelihood of detecting extra-pair offspring depends on the combinations of parental alleles, it is possible that biases arise from particular allele combinations. This might produce false support for the influence of heterozygosity on mating behaviour. We used a simulation model to assess how large this bias might be. We found two sources of bias. First, we found a bias in the null hypothesis of a simple statistical test commonly used to test several predictions of the heterozygosity hypothesis. The use of randomization tests could eliminate this bias. Second, we found that using the same loci for both paternity and heterozygosity can cause an increase in results supporting the heterozygosity hypothesis when no effect of heterozygosity actually exists. This bias is reduced through the use of more markers with higher levels of polymorphism and heterozygosity, but can be eliminated entirely by using a separate set of markers to determine paternity and assess heterozygosity. The two sources of bias reduce evidence favouring the heterozygosity hypothesis, but do not negate all of the studies that support it. We suggest that further studies of heterozygosity and extra-pair paternity are important and likely to be informative, but our recommendations should be incorporated by researchers to improve the reliability of their conclusions.     

Diversification of coordination patterns during feeding behaviour in cheiline wrasses

Successful fish feeding often requires the coordination of several complex motor and sensory systems to ensure that food is accurately detected, approached, acquired, and consumed. In the present study, we address feeding behaviour as a coordinated set of multiple, facultatively independent, anatomical systems. We sought to determine whether the patterns of interaction between trophic, locomotor, and oculomotor systems are associated with changes in morphology and ecology within a closely-related, but trophically divergent, group of fishes. We present a quantitative kinematic analysis of skull motion, locomotor behaviour, and oculomotor responses during feeding to assess coordination in three functional systems directly involved in feeding. We use coordination profiles to depict the feeding behaviours of three carnivorous coral reef fishes of the tribe Cheilinini in the family Labridae (the wrasses): Cheilinus fasciatus (a slow-swimming predator of benthic invertebrates), Epibulus insidiator (a slow-stalking predator with extraordinary jaw protrusion), and Oxycheilinus digrammus (a fast-attack predator). Differences were detected in several variables relating to jaw, body, fin, and eye movements. Overall patterns of coordination were more similar between E. insidiator and O. digrammus , which are capable of capturing elusive prey, than between C. fasciatus and E. insidiator , which are the two most closely-related species among the three. Evidence for the evolution of coordination patterns among cheiline fishes suggests that the sensory-motor systems involved in processing stimuli and coordinating a physical response during feeding have changed considerably, even among closely-related species.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 289–308.     

Functional Morphology of Aquatic Flight in Fishes: Kinematics, Electromyography, and Mechanical Modeling of Labriform Locomotion

Labriform locomotion is the primary swimming mode for many fishesthat use the pectoral fins to generate thrust across a broadrange of speeds. A review of the literature on hydrodynamics,kinematics, and morphology of pectoral fin mechanisms in fishesreveals that we lack several kinds of morphological and kinematicdata that are critical for understanding thrust generation inthis mode, particularly at higher velocities. Several needsinclude detailed three-dimensional kinematic data on speciesthat are pectoral fin swimmers across a broad range of speeds,data on the motor patterns of pectoral fin muscles, and thedevelopment of a mechanical model of pectoral fin functionalmorphology. New data are presented here on pectoral fin locomotionin Gomphosus varius, a labrid fish that uses the pectoral finsat speeds of 1 –6 total body lengths per second. Three-dimensionalkinematic data for the pectoral fins of G. varius show thata typical "drag-based" mechanism is not used in this species.Instead, the thrust mechanics of this fish are dominated bylift forces and acceleration reaction forces. The fin is twistedlike a propeller during the fin stroke, so that angles of attackare variable along the fin length. Electromyographic data onsix fin muscles indicate the sequence of muscle activity thatproduces antagonistic fin abduction and adduction and controlsthe leading edge of the fin. EMG activity in abductors and adductorsis synchronous with the start of abduction and adduction, respectively,so that muscle mechanics actuate the fin with positive work.A mechanical model of the pectoral fin is proposed in whichfin morphometrics and computer simulations allow predictionsof fin kinematics in three dimensions. The transmission of forceand motion to the leading edge of the fin depends on the mechanicaladvantage of fin ray levers. An integrative program of researchis suggested that will synthesize data on morphology, physiology,kinematics, and hydrodynamics to understand the mechanics ofpectoral fin swimming.