Can members of the south-western Gila robusta species complex be distinguished by morphological features?

The goal for this project was to re-examine key morphological characters hypothesized to differentiate Gila intermedia, Gila robusta and Gila nigra and outline methods better suited for making species designations based on morphology. Using a combination of meristic counts, morphological measurements and geometric morphometrics, morphological dissimilarities were quantified among these three putative species. Traditional meristic counts and morphological measurements (i.e. distances between landmarks) were not useful for species identification. Geometric morphometrics, however, identified differences among species, while also suggesting an effect of geographic location on morphological variation. Using canonical variate analysis for the 441 fish sampled in this study, geometric morphometrics accurately predicted true group membership 100% of the time for G. nigra, 97% of the time for G. intermedia and 91% of the time for G. robusta. These results suggest that geometric morphometric analysis is necessary to identify morphological differences among the three species. Geometric morphometric analysis used in this study can be adopted by management officials as a tool to classify unidentified individuals.

Sustained periodic terrestrial locomotion in air-breathing fishes.

While emergent behaviours have long been reported for air-breathing osteichthyians, only recently have researchers undertaken quantitative analyses of terrestrial locomotion. This review summarizes studies of sustained periodic terrestrial movements by air-breathing fishes and quantifies the contributions of the paired appendages and the axial body to forward propulsion. Elongate fishes with axial-based locomotion, e.g. the ropefish Erpetoichthys calabaricus, generate an anterior-to-posterior wave of undulation that travels down the axial musculoskeletal system and pushes the body against the substratum at multiple points. In contrast, appendage-based locomotors, e.g. the barred mudskipper Periophthalmus argentilineatus, produce no axial bending during sustained locomotion, but instead use repeated protraction-retraction cycles of the pectoral fins to elevate the centre of mass and propel the entire body anteriorly. Fishes that use an axial-appendage-based mechanism, e.g. walking catfishes Clarias spp., produce side-to-side, whole-body bending in co-ordination with protraction-retraction cycles of the pectoral fins. Once the body is maximally bent to one side, the tail is pressed against the substratum and drawn back through the mid-sagittal plane, which elevates the centre of mass and rotates it about a fulcrum formed by the pectoral fin and the ground. Although appendage-based terrestrial locomotion appears to be rare in osteichthyians, many different species appear to have converged upon functionally similar axial-based and axial-appendage-based movements. Based on common forms observed across divergent taxa, it appears that dorsoventral compression of the body, elongation of the axial skeleton or the presence of robust pectoral fins can facilitate effective terrestrial movement by air-breathing fishes.

Do we all walk the walk? A comparison of walking behaviors across tetrapods.

A walking gait has been identified in a range of vertebrate species with different body plans, habitats, and life histories. With increased application of this broad umbrella term, it has become necessary to assess the physical characteristics, analytical approaches, definitions, and diction used to describe walks. To do this, we reviewed studies of slow speed locomotion across a range of vertebrates to refine the parameters used to define walking, evaluate analytical techniques, and propose approaches to maximize consistency across subdisciplines. We summarize nine key parameters used to characterize walking behaviors in mammals, birds, reptiles, amphibians, and fishes. After identifying consistent patterns across groups, we propose a comprehensive definition for a walking gait. A walk is a form of locomotion where the majority of the forward propulsion of the animal comes from forces generated by the appendages interacting with the ground. During a walk, an appendage must be out of phase with the opposing limb in the same girdle and there is always at least one limb acting as ground-support (no suspension phase). Additionally, walking occurs at dimensionless speeds <1 v* and the duty factor of the limbs is always >0.5. Relative to other gaits used by the same species, the stance duration of a walk is long, the cycle frequency is low, and the cycle distance is small. Unfortunately, some of these biomechanical parameters, while effectively describing walks, may also characterize other, non-walking gaits. Inconsistent methodology likely contributes to difficulties in comparing data across many groups of animals; consistent application of data collection and analytical techniques in research methodology can improve these comparisons. Finally, we note that the kinetics of quadrupedal movements are still poorly understood and much work remains to be done to understand the movements of small, exothermic tetrapods.

Scale Thickness Predicts Skin Puncture-Force Resistance in Three Pleuronectiform Fishes.

In fishes, the skin and scales provide a physical barrier to the external environment and must withstand direct physical insult from biotic and abiotic features of the habitat. Flatfishes likely rely heavily on their scales for physical defense because they rest directly on the substrate. Using a flatfish model, we asked: what are the effects of scale type and scale morphology on puncture force resistance? We also asked: are there morphological and functional differences between the eyed and blind sides in flatfishes and do the morphological and functional properties of scales vary with organism size? Using a large size range of three species of Pleuronectid flatfish (Isopsetta isolepis, n = 10; Parophrys vetulus, n = 10; and Platichthys stellatus, n = 12), we measured the force required to puncture the integument using a sample of skin+scales taken from the eyed and blind side of each individual. We also measured the diameter, area, and thickness of the scales of each individual. Scaling relationships (body length vs. variable of interest) were derived for each species and compared with a priori expectations of geometric similarity. We found no relationship between scale type and puncture resistance and no differences in morphological parameters or puncture resistance between the eyed and blind side within a given species. These flatfish species do vary in their ability to withstand puncture forces; however, once scale thickness is taken into account, species differences disappear. Thus, the ability of a flatfish to withstand mechanical insult from puncture-forces varies depending on the thickness of the scale.

El Grosor de la escala Predice la Resistencia a la Punción de la Piel en Tres Peces Pleuronectiformes (Scale Thickness Predicts Skin Puncture-Force Resistance in Three Pleuronectiform Fishes) En los peces, la piel y las escamas proporcionan una barrera física al ambiente externo y deben resistir la injuria física directa de las características bióticas y abióticas del hábitat. Los peces planos probablemente dependen mucho de sus escamas para la defensa física porque descansan directamente sobre el sustrato. Usando un modelo de peces planos, preguntamos: ¿cuáles son los efectos del tipo y la morfología de la escama en la resistencia a la fuerza de punción? También preguntamos: ¿hay diferencias morfológicas y funcionales entre los lados ciego y ocular en los peces planos y si las propiedades morfológicas y funcionales de las escamas varían con el tamaño del organismo? Usando un amplio rango de tamaño de tres especies de peces planos Pleuronectidos (Isopsetta isolepis, n = 10; Parophrys vetulus, n = 10; y Platichthys stellatus, n = 12), medimos la fuerza requerida para perforar el integumento utilizando una muestra de escamas de la piel tomada del lado ocular y ciego de cada individuo. También medimos el diámetro, el área y el grosor de las escamas de cada individuo. Se derivaron relaciones escalares (longitud corporal vs. variable de interés) para cada especie y se compararon con las expectativas a priori de similitud geométrica. No encontramos ninguna relación entre el tipo de escama y la resistencia a la punción, y no hay diferencias en los parámetros morfológicos o la resistencia a la punción entre el lado ciego y ocular dentro de una especie dada. Estas especies de peces planos varían en su capacidad para soportar las fuerzas de punción; sin embargo, una vez que se toma en cuenta el grosor de la escama, las diferencias entre especies desaparecen. Por lo tanto, la capacidad de un pez plano para soportar la injuria mecánica de las fuerzas de punción varía según el grosor de la escama. Translated to Spanish by C.A. Alfonso (calfonsoc@vt.edu).

Espessura da Escama Prevê a Resistência à Força de Punção Cutânea em Três Peixes Pleuronectiformes (Scale Thickness Predicts Skin Puncture-Force Resistance in Three Pleuronectiform Fishes) A pele e as escamas dos peixes fornecem uma barreira física ao ambiente externo, devendo aguentar injúrias provenientes dos aspectos bióticos e abióticos do seu habitat. Os linguados provavelmente dependem muito de suas escamas para defesa porque eles estão em contato direto com o substrato. Usando um modelo de linguado, perguntamos quais os efeitos do tipo de escama e da morfologia da mesma na resistência à punção. Nós também perguntamos se existem diferenças morfológicas e funcionais entre os lados dos olhos e os lados cegos em linguados e se as propriedades morfológicas e funcionais das escamas variam com o tamanho do organismo. Usando uma extensa faixa de tamanho de três espécies de linguados pleuronectídeos (Isopsetta isolepis, n = 10; Parophrys vetulus, n = 10; e Platichthys stellatus, n = 12), medimos a força necessária para perfurar o tegumento em uma amostra de pele+escamas tirada de ambos os lados de cada indivíduo. Também medimos o diâmetro, área e espessura das escamas deles. As relações de escalonamento (comprimento do corpo vs. variável de interesse) foram derivadas para cada espécie e comparadas às expectativas de similaridade geométrica determinadas a priori. Não encontramos relação entre o tipo de escama e a resistência à perfuração e não houve diferenças nos parâmetros morfológicos ou na resistência à perfuração entre o lado dos olhos e o lado cego em uma dada espécie. Essas espécies de linguado variam em sua capacidade de aguentar forças de punção; no entanto, uma vez que a espessura da escama é levada em conta, as diferenças entre as espécies desaparecem. Assim, a capacidade de um linguado de suportar injúrias mecânicas causadas por perfuração varia dependendo da espessura da escama. Translated to Portuguese by G. Sobral (gabisobral@gmail.com).

Benthic walking, bounding, and maneuvering in flatfishes (Pleuronectiformes: Pleuronectidae): New vertebrate gaits.

Video-based observations of voluntary movements reveal that six species of pleuronectid flatfishes use sequential portions of long-based dorsal and anal fins as "feet" (hereafter, fin-feet) to move on the substrate. All six species used a gait that we term "walking," which produced constant forward movement, and several of these species also used a second gait that we call "bounding" for intermittent movements over the substrate. We selected Pacific Sand Sole, Psettichthys melanostictus, and English Sole, Parophrys vetulus, for kinematic analyses of these two gaits. Psettichthys melanostictus consistently used walking for benthic locomotion; Parophrys vetulus primarily used a bounding gait. During forward walking, a fin ray swings up off the substrate, protracts and converges with neighboring fin rays to contribute to a fin-foot. The fin-foot pushes down on the substrate and rotates posteriorly by sequential recruitment of fin rays, a pattern known as a metachronal wave. As one fin-foot passes off the posterior end of the fin, a new fin-foot forms anteriorly. During bounding, undulations of the body and tail assist one or two waves of fin-feet, producing rapid but intermittent forward acceleration of the body. Flatfishes also use fin-feet to maneuver on the substrate. The Starry Flounder, Platichthys stellatus, performs near zero displacement rotation by running waves of fin-feet in opposing directions along the dorsal and anal fins. Although other teleosts use specialized pectoral fin rays for bottom walking (e.g., Sea Robins: Triglidae), the duplication of structures and patterns of movement in the median fins of flatfishes more closely resembles metachronal motions of millipede feet or the parapodia of polychaete worms. Sequential use of median fin rays in flatfishes resembles that of other teleosts that swim with elongate median fins, including Amiiformes, Gymnotiformes, and some Tetraodontiformes, but flatfishes offer a novel form of substrate locomotion based on dorsal and anal fins.

Mudskipper pectoral fin kinematics in aquatic and terrestrial environments.

Mudskippers use pectoral fins for their primary mode of locomotion on land and pectoral fins in conjunction with the axial musculature and caudal fin to move in water. We hypothesized that distinct pectoral fin movements enable effective locomotion in each environment. Additionally, we made three functional predictions about fin movements during locomotion on land versus water: the pectoral fin is depressed more on land than in water; the pectoral fin will have greater changes in fin area between propulsive and recovery phases in water versus land; anterior and posterior excursions will be greater on land than in water. Locomotion was recorded in each environment using a high-speed digital-imaging system and kinematic variables were calculated from digitized landmark points. Variables were analyzed using principal components analysis and matched pairs t-tests. Mudskippers produce distinct kinematic patterns across environments (P < 0.003), although only some of our predictions were supported. The magnitude of fin depression is the same across habitats. However, depression occurs during the propulsive phase on land (by -0.60 cm), whereas during the propulsive phase in water the fin is elevated (by +0.13 cm). We were unable to support the hypothesis that fin orientation differs between environments. Lastly, anterior extension of the fin is greater on land (1.8 cm, versus 1.3 cm in water), creating a larger stride length in this environment. We posit that the mudskipper pectoral fin may facilitate stability in water and thrust production on land, and suggest that the robust fin morphology of the goby lineage may predispose species within this group to terrestrial locomotion.