Evolutionary implications of swimming behaviour in meiobenthic copepods

Body morphology is said to be the all important factor in determining swimming prowess in copepods. Fusion and differentiation of the body (tagmosis) is coupled with advance into the pelagic realm of the Gymnoplea and is thought, by the provision of a rigid thoracic tagma, to promote swimming efficiency. Thus pelagic copepods are believed to be secondarily derived from bottom dwelling predecessors. Experimental evidence is presented to show that the majority of bottom dwelling harpacticoid families, including the most primitive and the most advanced, have representatives that undergo active sustained swimming movements. Such a widespread occurrence is indicative of a conservative evolutionary trait. This primitive behaviour is linked to precopulatory association which takes place necessarily in the water column; it is a feature retained by representatives of all copepod orders. The implication of cephalic appendage vibration (feeding currents) is the essential feature in the swimming success of the Gymnoplea; planktonic efficiency in these is suggested to have evolved coincident with, rather than because of increased tagmosis.     

Center of mass motion in swimming fish: effects of speed and locomotor mode during undulatory propulsion

Studies of center of mass (COM) motion are fundamental to understanding the dynamics of animal movement, and have been carried out extensively for terrestrial and aerial locomotion. But despite a large amount of literature describing different body movement patterns in fishes, analyses of how the center of mass moves during undulatory propulsion are not available. These data would be valuable for understanding the dynamics of different body movement patterns and the effect of differing body shapes on locomotor force production. In the present study, we analyzed the magnitude and frequency components of COM motion in three dimensions (x: surge, y: sway, z: heave) in three fish species (eel, bluegill sunfish, and clown knifefish) swimming with four locomotor modes at three speeds using high-speed video, and used an image cross-correlation technique to estimate COM motion, thus enabling untethered and unrestrained locomotion. Anguilliform swimming by eels shows reduced COM surge oscillation magnitude relative to carangiform swimming, but not compared to knifefish using a gymnotiform locomotor style. Labriform swimming (bluegill at 0.5 body lengths/s) displays reduced COM sway oscillation relative to swimming in a carangiform style at higher speeds. Oscillation frequency of the COM in the surge direction occurs at twice the tail beat frequency for carangiform and anguilliform swimming, but at the same frequency as the tail beat for gymnotiform locomotion in clown knifefish. Scaling analysis of COM heave oscillation for terrestrial locomotion suggests that COM heave motion scales with positive allometry, and that fish have relatively low COM oscillations for their body size.     

Thermal dependence of swimming endurance in juvenile brown trout

The maximum swimming stamina of hatchery reared juvenile brown trout Salmo trutta , swimming against a fixed-velocity water flow of 36·6 cm s^-1 (6·97 L s^-1), was achieved at 16·1° C, and a 90% performance level occurred over a breadth of 7·7° C (12·2–19·9° C). The wide range of temperatures at which swimming performance is close to the maximal capacity could be a consequence of the implications for survival of this function.     

Size-related effects and the influence of metabolic traits and morphology on swimming performance in fish

Energy metabolism fuels swimming and other biological processes. We compared the swimming performance and energy metabolism within and across eight freshwater fish species. Using swim tunnel respirometers, we measured the standard metabolic rate (SMR) and maximum metabolic rate (MMR) and calculated the critical swimming speed (U_crit). We accounted for body size, metabolic traits, and some morphometric ratios in an effort to understand the extent and underlying causes of variation. Body mass was largely the best predictor of swimming capacity and metabolic traits within species. Moreover, we found that predictive models using total length or SMR, in addition to body mass, significantly increased the explained variation of U_crit and MMR in certain fish species. These predictive models also underlined that, once body mass has been accounted for, U_crit can be independently affected by total length or MMR. This study exemplifies the utility of multiple regression models to assess within-species variability. At interspecific level, our results showed that variation in U_crit can partly be explained by the variation in the interrelated traits of MMR, fineness, and muscle ratios. Among the species studied, bleak Alburnus alburnus performed best in terms of swimming performance and efficiency. By contrast, pumpkinseed Lepomis gibbosus showed very poor swimming performance, but attained lower mass-specific cost of transport (MCOT) than some rheophilic species, possibly reflecting a cost reduction strategy to compensate for hydrodynamic disadvantages. In conclusion, this study provides insight into the key factors influencing the swimming performance of fish at both intra- and interspecific levels.     

条背萤幼虫水生适应性形态与游泳行为研究

研究了条背萤Luciolasubstriata幼虫的形态特征及其对游泳行为的适应。形态及扫描电镜观察发现,条背萤幼虫存在二态现象。1～2龄幼虫虫体扁平,多毛。有7对呼吸鳃,分别位于腹部第1～7节。3～6龄幼虫虫体扁平呈船形,无呼吸鳃,靠气管呼吸。二者均具有扁平桨状的足、燕尾状尾节及位于尾节末端的圆柱形粘附器官。条背萤幼虫游动时身体腹面朝上,呈仰泳姿态,足向后划水。3～6龄幼虫仰泳时足共有8种摆动姿势。幼虫仰泳时足摆动1个周期所需时间为(0.611±0.16)s。腹部末端可上下左右摆动,当幼虫向前游动时,尾部上下摆动1个周期所需时间为(1.795±0.44)s。幼虫的游泳速度为(0.85±0.16)mh。仰泳中的幼虫改变方向时,头部和尾部同时向身体的一侧弯曲,当头部与尾部呈近90°时,幼虫用力将尾部伸直,此时水产生一个反作用力继续推动幼虫转向,幼虫转向的范围为0～90°。条背萤2种类型幼虫呼吸系统的不同决定着幼虫外部形态的差异及游泳行为的不同,而导致这种呼吸系统、形态及运动行为不同的原因很可能是条背萤对环境的适应性进化。     

Effect of mobility on femur midshaft external shape and robusticity

This study investigates differences in femur midshaft shape, robusticity, and sexual dimorphism derived from external measurements between a broad range of prehistoric and historic North American populations with different subsistence strategies and inferred levels of mobility. The sample was divided into six groups to test whether observed femur midshaft variables follow the patterns predicted based on archaeologically and historically determined subsistence and mobility data. The results suggest significant variation in femur midshaft shape and robusticity in all populations, and that inferred mobility levels do not correspond consistently with femur midshaft structure in either males or females. Results do, however, support the prediction that sexual dimorphism is generally greater in more mobile populations.     

The structural mechanics and evolution of aquaflying birds

Mass‐specific bone strength was examined in the forelimb and hindlimb of 64 species of birds to determine if aquaflying birds (which utilize the wings for propulsion underwater) differ in their skeletal strength compared with other avian taxa. Long bone strengths were estimated from cross‐sectional measurements. Compared with the expectation from geometric similarity, humeral section modulus in volant birds scales nearly isometrically, while femoral strength scales with significant positive allometry. Penguin mass‐specific humeral strength is greatly elevated, but the average humeral strength in species that are propelled by the wings in both air and water do not differ from the values calculated in non‐diving taxa. However, amphibious flyers have gracile femora. Comparative analyses using independent contrasts were utilized to examine the impact of phylogenetic signal. The residual measured for the penguin–procellariiform humeral strength contrast was larger in magnitude (residual of 2.14) than at any other node in the phylogeny. The data strongly indicate that the transition from an amphibious flight condition to a fully aquatic condition involves greater changes in mechanical factors than the transition from purely aerial locomotion to amphibious wing use. There remains the possibility that a historical effect, such as ancestral body size, has impacted the mechanical scaling of penguins. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 687–698.     

Unloaded shape identification of human cornea by variational shape optimization

Abstract

The present study proposes a computational method to identify the unloaded corneal shape based on the prescribed surface profile of the cornea acquired from in vivo measurements. Variational shape optimization of the unloaded corneal shape was formulated to satisfy that the corneal shape at the mechanical equilibrium state in the physiological situation corresponded to the prescribed surface profile. The shape variation was calculated using the Lagrange multiplier method with a finite element solution. Numerical solution showed that the optimized corneal shape was in excellent agreement with the prescribed surface profile of the cornea without μm-scale surface irregularities.     

Hooked setae: tests of the anchor hypothesis

Abstract. We tested the hypothesis that hooked setae function as anchors in three species of tubiculous polychaetes ( Eudistylia vancouveri, Schizobranchia insignis , and Owenia fusiformis ). All maintained position within their tubes when exposed to high pressures (up to 100–200 kPa) applied from the posterior direction (where it would tend to cause the tips of hooks to embed in the tube wall). When pressure was applied in the opposite direction, where hooks would not tend to embed in the tube wall, the worms were expelled from their tubes at lower pressures (30–100 kPa). The ability of these worms to maintain their position within their tubes was independent of body size. On the basis of these findings we made three predictions. First, worms that use their hooked setae as anchors should have those hooks located on the body in greatest number and size on the segments associated with greatest worm diameter. Second, as worms increase in size, setal armory should increase in a predictable way. The force that can be applied to extract worms from their tubes by suction feeding fish or wave action would increase as the area subject to suction increases (proportional to the cross sectional area of the tube). Therefore, we predict that setal armory should also increase as a squared function. Third, hooks or uncini should show patterns of wear or loss and/or the worms' bodies should show scars or wounds where the setae are most used (e.g., where worm diameter is at its maximum). All of these predictions were supported by the data and indicate that hooked setae function as anchors for tubiculous polychaetes. This is important for understanding the biology of these animals and has implications for using hooked setae as characters in phylogenetic analyses.     

Cranial shape in fruit,nectar, and exudate feeders: Implications for interpreting the fossil record

At least 29 species of fossil primates have been referred to fruit, nectar, and/or exudate feeding dietary niches. Many studies have detailed the morphological correlates of fruit feeding in comparison to insectivory and folivory. In contrast, few studies have sought to differentiate the morphological correlates of fruit feeding from those of nectar and exudate feeding. This study investigates the differences between fruit, nectar, and exudate feeders using 22 cranial and dentary shape variables representing 28 species of living marsupials, bats, and primates. Discriminant function analysis is used to investigate the differences between these dietary categories using both the complete data set and a reduced data set composed of variables that might reasonably be available from fragmentary fossil material. The success rates of post-hoc classifications are 94 and 88%, respectively. These results demonstrate that it is possible to discriminate among fruit, nectar, and exudate feeders among fossil taxa with a reasonable degree of certainty using the data and techniques outlined here. Nectar feeders exhibit a unique combination of features that are associated with reduced masticatory strength and their role as pollination agents. Exudate feeder skulls and dentaries exhibit a combination of features that reflect the high stresses encountered by the anterior dentition through bark gouging behavior. Fruit feeders are morphologically diverse, exhibiting cranial and mandibular shape values that overlap with both nectar and exudate feeders. It is suggested that this diversity reflects the variety of physical properties represented among fruits, and the tendency for individual frugivore species to specialize on particular fruits. Am J Phys Anthropol 102:187–202, 1997 © 1997 Wiley-Liss, Inc.     

Comparisons of swimming performance in rainbow trout using constant acceleration and critical swimming speed tests

Maximum swimming performance of seasonally acclimated rainbow trout Oncorhynchus mykiss was compared among short-duration constant acceleration tests ( U _max) and with the well established, but longer duration critical swimming speed ( U _crit) test. The present results show that U _max was insensitive to a range of acceleration rates that differed by more than three-fold. Thus, test duration could be reduced from 58 to 18 min without affecting the estimate of U _max. The value of U _max, however, was up to 57% higher than U _crit. Only the slowest acceleration rate tested (an increase of 1 cm s⁻¹ every min) had a significantly lower U _max, and this was up to 19% higher than U _crit. Even so, the potential saving in the test duration was small (70 v. 90 min) when compared with a ramp- U _crit test (a standard U _crit test but with the water velocity initially ramped to c . 50% of the estimated U _crit). Therefore, swim tests that are appreciably shorter in duration than a ramp- U _crit test result in U _max being appreciably greater than U _crit. An additional discovery was that the ramp- U _crit performance of cold-acclimated rainbow trout was independent of the recovery period between tests. These results may prove useful in making comparisons among different swim test protocols and in designing swim tests that assess fish health and toxicological impacts.     

Biomechanics of swimming in the pufferfish Diodon holocanthus: propulsive momentum enhancement is an adaptation for thrust production in an undulatory median and paired-fin swimmer

A form of large-amplitude elongated-body theory appropriate for the analysis of undulatory fins attached to a rigid body of elliptical section suggests a benefit due to momentum enhancement relative to the fins on their own. This theoretical prediction is experimentally confirmed for the first time. Theoretical momentum enhancement factors for Diodon holocanthus (2.2 and 2.7 for the median and pectoral fins, respectively) compared well to inferred thrust values determined from particle-image velocimetry (PIV) wake measurements (2.2-2.4 and 2.7-2.9). Caudal fin mean theoretical thrust was not significantly different from measured (PIV) values (n = 24, P > 0.05), implying no momentum enhancement. Pectoral-fin thrust was half that of the median and caudal fins due to high fin-jet angles, low circulation and momentum. Average total fin thrust and fish drag were not significantly different (n = 24, P > 0.05). Vortex rings generated by the fins were elliptical, with size dependent on fin chord and stroke amplitude. Hydrodynamic advantages (thrust enhancement at no cost to hydrodynamic efficiency, reduction of side forces minimizing energy wasting yawing motions and body drag) are probably common among rigid-bodied organisms propelled by undulatory fins. A trade-off between momentum enhancement and the rate of momentum generation (thrust force) sets a practical limit to the former. For small fins whilst momentum enhancement is high, absolute thrust is low. In addition, previously suggested limitations on thrust enhancement set by reductions in propulsive force associated with progressive reductions in fin wavelength are found to be biologically unrealistic.     

Functional types of diving beetle (Coleoptera: Hygrobiidae and Dytiscidae), as identified by comparative swimming behaviour

The swimming behaviour of ten species of diving beetles was studied with a video image analysing system, with the aim of testing the interpretation of their size and shape as functional characters reflecting adaptations to different swimming strategies. Velocity, sinuosity of the trajectory, and the relation between the two were studied in an unobstructed aquarium and, for the four largest species, in an aquarium with vertical sticks. Species predicted to be poor swimmers had the lowest average and maximum velocities. A globular species considered to have high manoeuvrability swam in highly sinuous trajectories, and could maintain this sinuosity at a wide range of velocities. One of the larger species, considered to be adapted to high speed swimming, also swam in highly sinuous trajectories, but only at slow velocities; its swimming pattern was considered to be the product of behavioural rather than morphological constraints. For two of the largest species, there was a significant decrease in sinuosity at higher velocities, whilst another was found to have a good compromise between velocity and manoeuvrability. In the aquarium with obstacles all the species reduced their maximum velocity, while the effect on sinuosity varied between species. Although the space limitation of the aquarium and the lack of motivation could have prevented some species from reaching their maximal velocities, a good agreement was found between the predicted and the actual swimming characteristics.     

Evolutionary patterns of shape and functional diversification in the skull and jaw musculature of triggerfishes (Teleostei: Balistidae)

The robust skull and highly subdivided adductor mandibulae muscles of triggerfishes provide an excellent system within which to analyze the evolutionary processes underlying phenotypic diversification. We surveyed the anatomical diversity of balistid jaws using Procrustes‐based geometric morphometric analyses and a phylomorphospace approach to quantifying morphological transformation through evolution. We hypothesized that metrics of interspecific cranial shape would reveal patterns of phylogenetic diversification that are congruent with functional and ecological transformation. Morphological landmarks outlining skull and adductor mandibulae muscle shape were collected from 27 triggerfish species. Procrustes‐transformed skull shape configurations revealed significant phylogenetic and size‐influenced structure. Phylomorphospace plots of cranial shape diversity reveal groupings of shape between different species of triggerfish that are mostly consistent with phylogenetic relatedness. Repeated instances of convergence upon similar cranial shape by genetically disparate taxa are likely due to the functional demands of shared specialized dietary habits. This study shows that the diversification of triggerfish skulls occurs via modifications of cranial silhouette and the positioning of subdivided jaw adductor muscles. Using the morphometric data collected here as input to a biomechanical model of triggerfish jaw function, we find that subdivided jaw adductors, in conjunction with a unique cranial skeleton, have direct biomechanical consequences that are not always congruent with phylomorphospace patterns in the triggerfish lineage. The integration of geometric morphometrics with biomechanical modeling in a phylogenetic context provides novel insight into the evolutionary patterns and ecological role of muscle subdivisions in triggerfishes. J. Morphol. 277:737–752, 2016. © 2016 Wiley Periodicals, Inc.     

The inheritance of shovel shape in maxillary central incisors

The aim of this study is to investigate the inheritance of the shovel shape of maxillary permanent central incisors. The material collected on Hailuoto Island, off the western coast of Finland, consists of 319 dental casts. The genealogical data are from the parish register. The genetic method is based on the incidence of the trait in the sibships as compared to that in the whole population sample. The results suggest that the trait is hereditary, and transmitted by a single intermediate autosomal gene, although more complex models of inheritance are also acceptable.     

The effect of progressive hypoxia on swimming activity and schooling in Atlantic herring

Schools of herring exposed to progressive hypoxia show a peak in velocity during severe hypoxia, at 15–34% oxygen saturation, followed by a decrease in swimming speed until school disruption occurred. The observed increase in swimming speed during severe hypoxia reveals a graded response, since the lower the fish's swimming speed prior to severe hypoxia ( U ₉₅₋₅₀, the speed at oxygen saturations between 95 and 50%), the greater the relative increase in swimming speed. The oxygen saturations at which both peak velocity and school disruption occurred were lower for fish with lowest U ₉₅₋₅₀, suggesting that the fish with the slowest speed U ₉₅₋₅₀ reach their critical P_O2 (at which there is respiratory distress) last, i.e. at lower oxygen saturation. At a functional level, it is suggested that herring encountering hypoxia increase their speed in order to find more favourable conditions, and the magnitude of this increase is modulated by their respiratory distress. It is also hypothesised that the observed increase in speed may be related to an increase in the rate of position shifting within the school. Since the oxygen saturation at which the response to hypoxia occurs and the magnitude of the response are related to the fish's preferred speed prior to severe hypoxia, it is suggested that such a preferred speed should be measured in experiments testing the effect of hypoxia on fish behaviour.     

Endurance swimming of diploid and triploid Atlantic salmon

When groups of diploid (mean ±  s . e . fork length, L _F) 33·0 ± 1·4 cm and triploid (35·3 ± 0·5 cm) Atlantic salmon Salmo salar were forced to swim at controlled speeds in a carefully monitored 10 m diameter 'annular' tank no significant difference was found between the maximum sustained swimming speeds ( U _ms, maintainable for 200 min) where the fish swam at the limit of their aerobic capability. Diploids achieved 2·99 body lengths per second (bl s⁻¹)(0·96 m s⁻¹) and triploids sustained 2·91 bl s⁻¹(1·02 m s⁻¹). The selection of fish for the trials was based on their ability to swim with a moving pattern projected from a gantry rotating at the radius of the tank and the selection procedure did not prove to be significant by ploidy. A significant difference was found between the anaerobic capabilities of the fish measured as endurance times at their prolonged swimming speeds. During the course of the experimentation the voluntary swimming speed selected by the fish increased and the schooling behaviour improved. The effect of the curvature of the tank on the fish speeds was calculated (removing the curved effect of the tank increased the speed in either ploidy by 5·5%). Implications of the endurance times and speeds are discussed with reference to the aquaculture of triploid Atlantic salmon.     

Constraints on the wing morphology of pterosaurs

Animals that fly must be able to do so over a huge range of aerodynamic conditions, determined by weather, wind speed and the nature of their environment. No single parameter can be used to determine-let alone measure-optimum flight performance as it relates to wing shape. Reconstructing the wings of the extinct pterosaurs has therefore proved especially problematic: these Mesozoic flying reptiles had a soft-tissue membranous flight surface that is rarely preserved in the fossil record. Here, we review basic mechanical and aerodynamic constraints that influenced the wing shape of pterosaurs, and, building on this, present a series of theoretical modelling results. These results allow us to predict the most likely wing shapes that could have been employed by these ancient reptiles, and further show that a combination of anterior sweep and a reflexed proximal wing section provides an aerodynamically balanced and efficient theoretical pterosaur wing shape, with clear benefits for their flight stability.     

Ontogenetic differentiation of swimming performance in Gilthead seabream (Sparus aurata, Linnaeus 1758) during metamorphosis

The critical swimming speed (U_crit) of gilthead seabream (Sparus aurata, Linnaeus 1875) was studied in two ontogenetic phases, early (13.7-18.7 mm total length, TL) and late metamorphosis (20.4-34.3 mm TL, after the full development of fin meristics and during squamation ontogeny), under four exercise temperatures (15, 20, 25 and 28 °C). Both the exercise temperature and the ontogenetic stage had a significant effect on the relative U_crit (RU_crit) of S. aurata, with the fish of early metamorphosis phase (E group) presenting significantly higher RU_crit than those of the late metamorphosis stage (L group). This ontogenetic shift in swimming performance was accompanied by significant ontogenetic shifts of body shape and of muscle anatomy. Compared to the L group, S. aurata of the E group were characterized by a streamline body shape and significantly higher relative contribution of the slow-red muscle to the cross-sectional area of the body (31.0 ± 1.3% vs 12.0 ± 1.2% in the L group).     

Geometric morphometrics and paleoneurology: brain shape evolution in the genus Homo

Paleoneurology concerns the study and analysis of fossil endocasts. Together with cranial capacity and discrete anatomical features, shape can be analysed to consider the spatial relationships between structures and to investigate the endocranial structural system. A sample of endocasts from fossil specimens of the genus Homo has been analysed using traditional metrics and 2D geometric morphometrics based on lateral projections of endocranial shape. The maximum and frontal widths show a size-related pattern of variation shared by all the taxa considered. Furthermore, as cranial capacity increases in the non-modern morphotypes there is a general endocranial vertical stretching (mainly centred at the anterior ascending circumvolution) with flattening and relative shortening of the parietal areas. This pattern could have involved some structural stress between brain development and vault bones at the parietal midsagittal profile in the heavy encephalised Neandertals. In contrast, modern humans show a species-specific neomorphic hypertrophy of the parietal volumes, leading to a dorsal growth and ventral flexion (convolution) and consequent globularity of the whole structure. Brain tensors such as the falx cerebri have been hypothesised to represent one of the main physical constraints on morphogenetic trajectories, with additional influences from cranial base structures. The neurofunctional inferences discussed here stress the role of the parietal areas in the visuo-spatial coordination and integration, which can be involved in higher cerebral functions and related to conceptual thinking.