Aquatic prey capture in ray-finned fishes: a century of progress and new directions

The head of ray-finned fishes is structurally complex and is composed of numerous bony, muscular, and ligamentous elements capable of intricate movement. Nearly two centuries of research have been devoted to understanding the function of this cranial musculoskeletal system during prey capture in the dense and viscous aquatic medium. Most fishes generate some amount of inertial suction to capture prey in water. In this overview we trace the history of functional morphological analyses of suction feeding in ray-finned fishes, with a particular focus on the mechanisms by which suction is generated, and present new data using a novel flow imaging technique that enables quantification of the water flow field into the mouth. We begin with a brief overview of studies of cranial anatomy and then summarize progress on understanding function as new information was brought to light by the application of various forms of technology, including high-speed cinematography and video, pressure, impedance, and bone strain measurement. We also provide data from a new technique, digital particle image velocimetry (DPIV) that allows us to quantify patterns of flow into the mouth. We believe that there are three general areas in which future progress needs to occur. First, quantitative three-dimensional studies of buccal and opercular cavity dimensions during prey capture are needed; sonomicrometry and endoscopy are techniques likely to yield these data. Second, a thorough quantitative analysis of the flow field into the mouth during prey capture is necessary to understand the effect of head movement on water in the vicinity of the prey; three-dimensional DPIV analyses will help to provide these data. Third, a more precise understanding of the fitness effects of structural and functional variables in the head coupled with rigorous statistical analyses will allow us to better understand the evolutionary consequences of intra- and interspecific variation in cranial morphology and function.     

The macroevolutionary consequences of phenotypic integration: from development to deep time

Phenotypic integration is a pervasive characteristic of organisms. Numerous analyses have demonstrated that patterns of phenotypic integration are conserved across large clades, but that significant variation also exists. For example, heterochronic shifts related to different mammalian reproductive strategies are reflected in postcranial skeletal integration and in coordination of bone ossification. Phenotypic integration and modularity have been hypothesized to shape morphological evolution, and we extended simulations to confirm that trait integration can influence both the trajectory and magnitude of response to selection. We further demonstrate that phenotypic integration can produce both more and less disparate organisms than would be expected under random walk models by repartitioning variance in preferred directions. This effect can also be expected to favour homoplasy and convergent evolution. New empirical analyses of the carnivoran cranium show that rates of evolution, in contrast, are not strongly influenced by phenotypic integration and show little relationship to morphological disparity, suggesting that phenotypic integration may shape the direction of evolutionary change, but not necessarily the speed of it. Nonetheless, phenotypic integration is problematic for morphological clocks and should be incorporated more widely into models that seek to accurately reconstruct both trait and organismal evolution.     

The ocellate river stingray (Potamotrygon motoro) exploits vortices of sediment to bury into the substrate

Particle image velocimetry and video analysis were employed to determine the pectoral-fin mechanism used by the stingray Potamotrygon motoro to bury into sand. Rapid oscillations of the body and folding motions of the posterior portion of the pectoral fin suspended sediment beneath the pectoral disc and directed vortices of sediment onto the dorsal surface, where they dissipated and the sediment settled. Body coverage was increased by increased fin displacement and speed and also by the occasional collision of vortices that redirected sediment flow towards the head and tail.     

A fluid dynamics approach to bioreactor design for cell and tissue culture

The problem of controlling cylindrical tank bioreactor conditions for cell and tissue culture purposes has been considered from a flow dynamics perspective. Simple laminar flows in the vortex breakdown region are proposed as being a suitable alternative to turbulent spinner flask flows and horizontally oriented rotational flows. Vortex breakdown flows have been measured using three-dimensional Stereoscopic particle image velocimetry, and non-dimensionalized velocity and stress distributions are presented. Regions of locally high principal stress occur in the vicinity of the impeller and the lower sidewall. Topological changes in the vortex breakdown region caused by an increase in Reynolds number are reflected in a redistribution of the peak stress regions. The inclusion of submerged scaffold models adds complexity to the flow, although vortex breakdown may still occur. Relatively large stresses occur along the edge of disks jutting into the boundary of the vortex breakdown region.     

Galectins in teleost fish: Zebrafish (Danio rerio) as a model species to address their biological roles in development and innate immunity

Cell surface glycans, such as glycocoproteins and glycolipids, encode information that modulates interactions between cells, or between cells and the extracellular matrix, by specifically regulating the binding to cell surface-associated or soluble carbohydrate-binding receptors, such as lectins. Rapid modifications of exposed carbohydrate moieties by glycosidases and glycosyltransferases, and the equally dynamic patterns of expression of their receptors during early development, suggest that both play important roles during embryogenesis. Among a variety of biological roles, galectins have been proposed to mediate developmental processes, such as embryo implantation and myogenesis. However, the high functional redundancy of the galectin repertoire in mammals has hindered the rigorous characterization of their specific roles by gene knockout approaches in murine models. In recent years, the use of teleost fish as alternative models for addressing developmental questions in mammals has expanded dramatically, and we propose their use for the elucidation of biological roles of galectins in embryogenesis and innate immunity. All three major galectin types, proto, chimera, and tandem-repeat, are present in teleost fish, and phylogenetic topologies confirm the expected clustering with their mammalian orthologues. As a model organism, the zebrafish (Danio rerio) may help to overcome limitations imposed by the murine models because it offers substantial advantages: external fertilization, transparent embryos that develop rapidly in vitro, a diverse toolbox of established methods to manipulate early gene expression, a growing collection of mutations that affect early embryonic development, availability of cell lines, and most importantly, an apparently less diversified galectin repertoire. Published in 2004.     

Analysis of the effect of disturbed flow on monocytic adhesion to endothelial cells

The preferential adhesion of monocytes to vascular endothelial cells (ECs) at regions near branches and curvatures of the arterial tree, where flow is disturbed, suggests that hemodynamic conditions play significant roles in monocyte adhesion. The present study aims to elucidate the effects of disturbed flow on monocyte adhesion to ECs and the adhesive properties of ECs. We applied, for the first time, the micron-resolution particle image velocimetry (μPIV) technique to analyze the characteristics of the disturbed flow produced in our vertical-step flow (VSF) chamber. The results demonstrated the existence of a higher near-wall concentration and a longer residence time of the monocytic analog THP-1 cells near the step and the reattachment point. THP-1 cells showed prominent adhesion to ECs pretreated with TNF in the regions near the step and the reattachment point, but they showed virtually no adhesion to un-stimulated ECs. Pre-incubation of the TNF-treated ECs with antibodies against intercellular adhesion molecule-1 (ICAM-1), vascular adhesion molecule-1 (VCAM-1), and E-selectin inhibited the THP-1 adhesion; the maximal inhibition was observed with a combination of these antibodies. Pre-exposure of ECs to disturbed flow in VSF for 24 h led to significant increases in their surface expressions of ICAM-1 and E-selectin, but not VCAM-1, and in the adhesion of THP-1 cells. Our findings demonstrate the importance of complex flow environment in modulating the adhesive properties of vascular endothelium and consequently monocyte adhesion in regions of prevalence of atherosclerotic lesions.     

Contrast adaptation to time constraints on development of two pre-dispersal predators of dandelion (<Emphasis Type="Italic">Taraxacum officinale</Emphasis>) seed

Pre-dispersal seed predators of quickly maturing inflorescences of Asteraceae are constrained by shortage of development time. At seed dispersal, they should pupate or, if still immature, relocate into another inflorescence. To investigate how dominant coleopteran predators of dandelion seed, Glocianus punctiger (Curculionidae) and Olibrus bicolor (Phalacridae), cope with time limitation we combined observation (development and temperature of dandelion capitulum, thermal constants of predator development, age structure of larval populations at seed dispersal) and analogy (“rate isomorphy” in predator development, comparing “model” coleopteran species with similar temperature requirements). Development of a dandelion capitulum takes 21 days. The time available to G. punctiger (140–190 day degrees, development threshold 6.3°C) is sufficient to complete development and pupate after seed dispersal. By contrast, only 30–50 day degrees are available to O. bicolor (threshold 13.5°C) and this is not enough to complete development and consequently immature larvae should move to other capitula to continue feeding until pupation. These contrast strategies which are determined by this thermal adaptation, are accompanied by differences in larval morphology. The “cold adapted” G. punctiger has an apodous larva not capable of migrating between capitula while the “warm adapted” O. bicolor has a mobile campodeiform larva capable of migration.