At the 2002 SICB meeting in Anaheim, we brought together some of the leaders in terrestrial and marine phylogeography for a day-long symposium. This symposium combined presentations from ten scientists whose question-driven research focuses on testing hypotheses about patterns and processes in biogeography in both vertebrate and invertebrate animals and including marine, terrestrial, and freshwater systems. The papers gathered here cover the breadth of the presentations. By explicitly seeking to combine marine and terrestrial workers into a single symposium we hoped that the different patterns and processes that predominate in major biomes and the different assumptions made by the workers in those areas would be highlighted.

I contrast mitochondrial DNA genealogies based on 612 bp of the cytochrome b gene across four co-distributed species of frogs in Northeastern Brazil. They are Hyla albomarginata, Hyla branneri, Proceratophrys boiei, and Scinax nebulosus. Samples were collected from the core or edge of six rainforest remnants in the states of Pernambuco and Alagoas. Three fragments are located within the humid Atlantic Forest morphoclimatic domain (municipalities of Cabo de Santo Agostinho, Ibateguara, and Jaqueira), two are located in the transition zone between the Atlantic Forest domain and the semi-arid Caatinga (Caruaru and Timbaúba), and one is found within the Caatinga (Brejo da Madre de Deus). Results show that local patterns and levels of genetic diversity are influenced by taxon-specific habitat requirements. Populations of the montane, closed-canopy species P. boiei show strong geographical structure, reflecting barriers to gene flow that predate human-driven habitat destruction. Species occurring along forest edges, such as H. albomarginata and S. nebulosus, show genetic patterns similar to those of P. boiei, but lower levels of genetic divergence. The more generalist Hyla branneri shows no geographic pattern. The data are in agreement with distribution and fossil data gathered for other groups of organisms, suggesting that mesic forests occupied the currently arid Caatinga in the recent past.

Patterns of distribution and processes of differentiation have often been contrasted between terrestrial and marine biotas. The islands of Oceania offer an excellent setting to explore this contrast, because the geographic setting for terrestrial and shallow-water, benthic, marine organisms are the same: the myriad islands strewn across the vast Pacific. The size of species ranges and the geographic distribution of endemism are two biogeographic attributes that are thought to differ markedly between terrestrial and marine biotas in the Pacific. While terrestrial species are frequently confined to single islands or archipelagoes throughout Oceania, marine species tend to have wide to very wide distributions, and are rarely restricted to single island groups except for the most isolated archipelagoes. We explore the conditions under which species can reach an island by dispersal and differentiate. Genetic differentiation can occur either through founder speciation or vicariance; these processes are requisite ends of a continuum. We show that founder speciation is most likely when few propagules enter the dispersal medium and survive well while they travel far. We argue that conditions favorable to founder speciation are common in marine as well as terrestrial systems, and that terrestrial-type, archipelagic-level endemism is likely common in marine taxa. We give examples of marine groups that show archipelagic level endemism on most Pacific island groups as well as of terrestrial species that are widespread. Thus both the patterns and processes of insular diversification are variable, and overlap more between land and sea than previously considered.

Evolutionary innovations that require or provide increased per-capita energy budgets and competitive performance should appear at times and in places where resources are abundant and accessible and where predators and competitors impose intense selection. By contrast, innovations without functional benefits should become established in productive environments under conditions of weak selection from enemies. I confirmed these predictions in comparative studies of two types of innovation in gastropod shells. The labral tooth, a structure facilitating predation, appeared in 45 Cenozoic clades of marine gastropods, with the highest concentrations originating during the early Miocene, late Miocene, and Pliocene, all times and sites of high planktonic productivity, large expanses of warm shallow water, and diverse predator-rich biotas. Left-handed coiling, a condition with no obvious survival benefits, arose 19 times independently in right-handed clades. Most left-handed clades, including eight arising in regions outside the tropics, evolved in productive regions where the larva and/or the adult is shielded from intense predation. The times and places of origin of new traits in clades thus offer insights into the geography of evolutionary opportunity.

Simultaneous studies of both nuclear and mitochondrial markers were undertaken in two widespread Indo-West Pacific (IWP) marine invertebrates to compare and contrast the ability of these markers to resolve genetic structure. In particular, we were interested in the resolution of a genetic break between the Indian and Pacific Oceans due to historical isolation. Sequence variation from the nuclear gene encoding myosin heavy chain (MyHC) and the mitochondrial gene cytochrome oxidase I (COI) were examined for the snapping shrimp Alpheus lottini from wide-ranging populations throughout the Indian and Pacific Oceans. A previously identified genetic break between oceans based on COI sequences appears to have been an artifact caused by the inadvertent inclusion of pseudogene sequences; our new COI data provide evidence only of a break between IWP and East Pacific populations. Distribution of a single nucleotide polymorphism in MyHC, on the other hand, shows evidence of a cline between Indian and Pacific Oceans. New allozyme and mtDNA sequence data were also obtained for the starfish Linckia laevigata. Allozyme data show a clear genetic break between Indian Ocean populations and Pacific (including western Australian) populations, whereas the distribution of mtDNA haplotypes shows a region of overlap in the central IWP. Comparisons of our data for both Alpheus and Linckia with data from other population genetic studies in the IWP suggest that nuclear markers (allozymes, sequence data and morphological characters) may in some instances reveal historical patterns of genetic population structure whereas mtDNA variation better reflects present day patterns of gene flow.

Historical biogeography and comparative phylogeography have much in common. Both seek to discover common historical patterns in the elements of biotas, although typically at different tiers of evolutionary history. Comparative phylogeography is based on phylogeographic analyses of multiple taxa, usually widespread species. By comparing the phylogeographic structures of numerous widespread sympatric species, one can infer whether the current fauna has been historically stable, as evidenced by the relative frequency of geographically congruent reciprocally monophyletic groups. Alternatively, if species distributions are ephemeral over evolutionary time, a mixture of phylogeographic structures is expected. Coalescence analyses contribute information about history irrespective of whether haplotype phylogenies are structured or not. In the aridlands of North America, several isolating events are evident in the phylogeographic patterns of birds, mammals and herps. A mid-peninsular seaway in Baja California, dated at ca. one million years before present, had a pervasive effect, with 13 of 16 assayed species showing a concordant split. Hence, this community appears to have been a stable assemblage of species over the past one million years. In contrast, the avifauna of the Sonoran-Chihuahuan deserts consists of two species with a concordant split and three other species that are undifferentiated across both deserts. Hence, the species in this area have had different histories. The Baja biota appears to resemble its ancestral configuration to a greater degree than the Sonoran-Chihuahuan one. A deeper evolutionary event separated taxa in Baja California from the eastern deserts, showing that the aridlands fauna was affected by events at different times resulting in overlain tiers of history.

Quantitative flow visualization has many roots and has taken several approaches. The advent of digital image processing has made it possible to practically extract useful information from every kind of flow image. In a direct approach, the image intensity or color (wavelength or frequency) can be used as an indication of concentration, density and temperature fields or gradients of these scalar fields in the flow (Merzkirch, 1987). For whole-field velocity measurement, the method of choice by experimental fluid mechanicians has been the technique of Particle Image Velocimetry (DPIV). This paper presents a novel approach to extend the DPIV technique from a planar method to a full three-dimensional volume mapping technique useful in both engineering and biological applications.

Boxfishes (Teleostei: Ostraciidae) are rigid-body, multi-propulsor swimmers that exhibit unusually small amplitude recoil movements during rectilinear locomotion. Mechanisms producing the smooth swimming trajectories of these fishes are unknown, however. Therefore, we have studied the roles the bony carapaces of these fishes play in generating this dynamic stability. Features of the carapaces of four morphologically distinct species of boxfishes were measured, and anatomically-exact stereolithographic models of the boxfishes were constructed. Flow patterns around each model were investigated using three methods: 1) digital particle image velocimetry (DPIV), 2) pressure distribution measurements, and 3) force balance measurements. Significant differences in both cross-sectional and longitudinal carapace morphology were detected among the four species. However, results from the three interrelated approaches indicate that flow patterns around the various carapaces are remarkably similar. DPIV results revealed that the keels of all boxfishes generate strong longitudinal vortices that vary in strength and position with angle of attack. In areas where attached, concentrated vorticity was detected using DPIV, low pressure also was detected at the carapace surface using pressure sensors. Predictions of the effects of both observed vortical flow patterns and pressure distributions on the carapace were consistent with actual forces and moments measured using the force balance. Most notably, the three complementary experimental approaches consistently indicate that the ventral keels of all boxfishes, and in some species the dorsal keels as well, effectively generate self-correcting forces for pitching motions—a characteristic that is advantageous for the highly variable velocity fields in which these fishes reside.

A continuously swimming mullet modulates its thrust production by changing slip-the ratio between its swimming speed U and the speed V with which the body wave travels down its body. This variation in thrust is reflected in the wake of the fish. We obtained 2-dimensional impressions of the wake behind a mullet swimming at a slip of 0.7 equivalent to active swimming, at a slip of 0.9 close to free-wheeling, and at a slip of 1.1 when the fish is braking. Independent of the slip, vortices are shed at the tail when the tail tip reaches its maximum lateral excursion. The manner in which the wake changes as it decays depends on the degree of slip: At a slip well below unity, the wake decays without any qualitative changes in shape, the medio-frontal cross section of the mature wake consists of a double row of alternating vortices separated by an undulating jet, and the angle between the jet flow and the mean path of motion is close to 45°; at a slip above unity, the vortices stretch out laterally and the mature wake resembles a single row of oval vortices with two vortex cores, and the jet between the vortices is almost perpendicular to the mean path of motion; the wake at slip of 0.9 exhibits a pattern intermediate between the wakes at slips 0.7 and 0.9 with slightly elongate vortices and a jet angle of 61°.

Animal generated water movements are visualized and quantified using two-dimensional particle image velocimetry (PIV). The resulting vector flow fields allow for the study of the distribution of velocity, vorticity and vortices. Structural and temporal aspects of animal-induced flows covering a range of Reynolds (Re) numbers between less than 1 to more than 10⁴ are presented.

Maps of flow induced by continuous foraging and intermittent escape responses of tethered nauplius and copepodid stages of the marine copepod Temora longicornis offer insight in viscosity-dominated flow regimes. Fast escape responses of the equally sized largest nauplius stage and the smallest copepodid stage are compared. The nauplius moves by generating a viscous flow pattern with high velocities and vorticity; the copepodid moves by using inertial effects to produce a vortex ring with a rearward jet through the center.

Larvae and small adult fish (zebra danio) use a burst-and-coast-swimming mode at Re numbers up to 6,000, shedding a vortex ring with the associated jet at the tail during the burst phase. Flow patterns during the coasting phase differ between the small larvae and larger adults due to the changes in importance of viscosity.

A 12 cm long mullet swimming in a continuous mode generates a chain of vortex rings with a backward undulating jet through the centers of the rings at Re numbers of 4 × 10⁴ in inertia-dominated regimes.

Our empirical results provide realistic insight in the scale effects determining the morphology of the interactions between animals and water.

The great anatomical diversification of paired fins within the Actinopterygii (ray-finned fishes) can be understood as a suite of evolutionary transformations in design. At a broad taxonomic scale, two clear trends exist in the morphology of the anteriorly situated pectoral fins. In comparing basal to more derived clades, there are general patterns of (i) reorientation of the pectoral fin base from a nearly horizontal to more vertical inclination, and (ii) migration of the pectoral fin from a ventral to mid-dorsal body position. As yet, the functional significance of these historical trends in pectoral fin design remains largely untested by experiment. In this paper we test the proposal that variation in pectoral fin structure has an important influence on the magnitude and orientation of fluid forces generated during maneuvering locomotion. Using digital particle image velocimetry for quantitative wake visualization, we measure swimming forces in ray-finned fishes exhibiting the plesiomorphic and apomorphic pectoral fin anatomy. Our experiments focus on rainbow trout (Oncorhynchus mykiss), a lower teleost with pectoral fins positioned ventrally and with nearly horizontally inclined fin bases, and bluegill sunfish (Lepomis macrochirus), a relatively derived perciform fish with more vertically oriented pectoral fins positioned mid-dorsally on the body. In support of hypotheses arising from our prior wake studies and previously untested models in the literature, we find that the pectoral fins of sunfish generate significantly higher forces for turning and direct braking forces closer to the center of mass of the body than the pectoral fins of trout. These results provide insight into the hydrodynamic importance of major evolutionary transformations in pectoral fin morphology within the Actinopterygii.

The median fins of fishes consist of the dorsal, anal, and caudal fins and have long been thought to play an important role in generating locomotor force during both steady swimming and maneuvering. But the orientations and magnitudes of these forces, the mechanisms by which they are generated, and how fish modulate median fin forces have remained largely unknown until the recent advent of Digital Particle Image Velocimetry (DPIV) which allows empirical analysis of force magnitude and direction. Experimental hydrodynamic studies of median fin function in fishes are of special utility when conducted in a comparative phylogenetic context, and we have examined fin function in four ray-finned fish clades (sturgeon, trout, sunfish, and mackerel) with the goal of testing classical hypotheses of fin function and evolution. In this paper we summarize two recent technical developments in DPIV methodology, and discuss key recent findings relevant to median fin function. High-resolution DPIV using a recursive local-correlation algorithm allows quantification of small vortices, while stereo-DPIV permits simultaneous measurement of x, y, and z flow velocity components within a single planar light sheet. Analyses of median fin wakes reveal that lateral forces are high relative to thrust force, and that mechanical performance of median fins (i.e., thrust as a proportion of total force) averages 0.35, a surprisingly low value. Large lateral forces which could arise as an unavoidable consequence of thrust generation using an undulatory propulsor may also enhance stability and maneuverability. Analysis of hydrodynamic function of the soft dorsal fin in bluegill sunfish shows that a thrust wake is generated that accounts for 12% of total thrust and that the thrust generation by the caudal fin may be enhanced by interception of the dorsal fin wake. Integration of experimental studies of fin wakes, computational approaches, and mechanical models of fin function promise understanding of instantaneous forces on fish fins during the propulsive cycle as well as exploration of a broader locomotor design space and its hydrodynamic consequences.

A recurring question in the study of fish biomechanics and energetics is the mechanical power required for tail-swimming at the high speeds seen among aquatic vertebrates. The quest for answers has been driven by conceptual advances in fluid dynamics, starting with ideas on the boundary layer and drag initiated by Prandtl, and in measurement techniques starting with force balances focussing on drag and thrust. Drag (=thrust) from measurements on physical models, carcasses, kinematics as inputs to hydromechanical models, and physiological power sources vary from less than that expected for an equivalent rigid reference to over an order of magnitude greater. Estimates of drag and thrust using recent advances largely made possible by increased computing power have not resolved the discrepancy. Sources of drag and thrust are not separable in axial undulatory self propulsion, are open to interpretation and Froude efficiency is zero. Wakes are not easily interpreted, especially for thrust evaluation. We suggest the best measures of swimming performance are velocity and power consumption for which 2D inviscid simulations can give realistic predictions. Steady swimming power is several times that required for towing an equivalent flat plate at the same speed.

Vorticity control is employed by marine animals to enhance performance in maneuvering and propulsion. Studies on fish-like robots and experimental apparatus modelling rigid and flexible fins provide some of the basic mechanisms employed for controlling vorticity.

The shape and motion of the pectoral fins vary considerably among fishes that swim in the labriform mode. Pectoral fin motion in fishes is highly variable, but one conspicuous axis of this variation is the rowing-flapping axis. At one extreme of this axis, paddle-shaped fins row back and forth in a plane that is parallel to fish motion, while at the other extreme, wing-shaped fins flap up and down in a plane that is perpendicular to fish motion. We have used two fish, the threespine stickleback (Gasterosteus aculeatus) and the bird wrasse (Gomphosus varius), that fall near the extremes of the rowing-flapping axis to study the dynamic, energetic, and ecological and evolutionary consequences of this kinematic variation. Our work confirms some traditionally held assumptions about rowing and flapping dynamics and energetics but reject others. A computer simulation experiment of virtual rowing and flapping appendages makes several predictions about differences in maneuvering performance and swimming energetics between rowing and flapping, which, in turn, make predictions about the behavior and ecological distribution of fishes that vary along the rowing-flapping axis. Both laboratory and field studies of labrid swimming ability and distribution support these predictions.

Flapping flight and swimming in many organisms is accompanied by significant bending of flexible wings and fins. The instantaneous shape of wings and fins has, in turn, a profound effect on the fluid dynamic forces they can generate, with non-monotonic relationships between the pattern of deformation waves passing along the wing and the thrust developed. Many of these deformations arise, in part, from the passive mechanics of oscillating a flexible air- or hydrofoil. At the same time, however, their instantaneous shape may well emerge from details of the fluid loading. This issue—the extent to which there is feedback between the instantaneous wing shape and the fluid dynamic loading—is core to understanding flight control. We ask to what extent surface shape of wings and fins is controlled by structural mechanics versus fluid dynamic loading. To address this issue, we use a combination of computational and analytic methods to explore how bending stresses arising from inertial-elastic mechanisms compare to those stresses that arise from fluid pressure forces. Our analyses suggest that for certain combinations of wing stiffness, wing motions, and fluid density, fluid pressure stresses play a relatively minor role in determining wing shape. Nearly all of these combinations correspond to wings moving in air. The exciting feature provided by this analysis is that, for high Reynolds number motions where linear potential flow equations provide reasonable estimates of lift and thrust, we can finally examine how wing structure affects flight performance. Armed with this approach, we then show how modest levels of passive elasticity can affect thrust for a given level of energy input in the form of an inertial oscillation of a compliant foil.

Characterized by complex geometry and complicated dynamic process, biological fluid dynamics in swimming and flying is usually of large scale vortex flows with four-dimensional nature, namely, spatial three-dimensional and one-dimensional in time. Conventional theories for understanding power and energetics in swimming and flying rely exclusively on the consistent potential flow formulation in qualitatively analyzing the physics as well as the observations and measurements in visualizing the flows so as to support the theories. In the present paper we address a new paradigm of the so-called, simulation-based biological fluid dynamics that can digitize and visualize swimming and flying by using computational mechanical modeling of the biological fluid dynamics through faithful reconstruction of morphology and realistic representation of kinematics of an individual object. We demonstrate an integrated computational system as a baseline for the simulation-based biological fluid dynamics, which involves four subsystems of the morphological modeling, the kinematic modeling, the computational fluid dynamic modeling, and the post-processing for visualization. Applications of a realistic model of insect flapping flight and an extensive study on the Micro Air Vehicle are then presented and discussed.

Simple models are presented of the energetics of annual migration and of central place foraging, taking account of the speed and energy cost of the journeys. They are applied to insects, fish, birds and mammals of a wide range of sizes, which travel by flapping or soaring flight, by swimming or by running. It is shown that annual migrations of several thousand kilometres are unlikely to be beneficial except for marine mammals and flying birds. Marine mammals and large flying birds are the animals most likely to be able to benefit from foraging over very large distances. Observed migration and foraging ranges generally lie within the limits predicted by the models.

Cephalopods are uniquely suited to field energetic studies. Their hollow mantles that pump water for respiration and jetting also can accommodate differential transducer-transmitters. These transmitters indicate pressure-flow power output, which can be calibrated against oxygen consumption by swim-tunnel respirometry. Radio-acoustic positioning telemetry (RAPT) records pressure-flow power and animal movements with meter accuracy in nature. Despite inherent inefficiencies, jetting is the primary mode of locomotion for both primitive nautilus and powerful, migratory oceanic squids. In between, large-finned squid and cuttlefish mix jetting with fin undulation in complex gaits that increase locomotor efficiency. Our studies show that the complex nervous systems cephalopods evolved to control mixed gaits are also sensitive to flow and density fields in nature and that they use these to further reduce locomotion costs. Buoyed up by evacuated shells, nautilus and cuttlefish live in boundary layers and navigate cheaply through them like balloonists. Large-finned, negatively buoyant squid soar like eagles in rising currents, but lose control in currents above one body length per second. Many muscular squids have life histories linked to current systems. Neutrally buoyant ammoniacal cephalopods in the mesopelagic are a limiting case in need of study. The small density differential between seawater and isotonic ammonium chloride trebles their volume, making them blimp-like with very low power densities. Some species live entirely in this restricted habitat, but most become ammoniacal late in ontogeny, as they approach semelparous reproduction. Ammonium retained for buoyancy as carbon is terminally mobilized from muscle protein for gametes and energy, compensates for lost muscle power.

Porpoising is the popular name for the high-speed surface piercing motion of dolphins and other species, in which long, ballistic jumps are alternated with sections of swimming close to the surface. The first analysis of this behavior (Au and Weihs, 1980) showed that above a certain “crossover” speed this behavior is energetically advantageous, as the reduction in drag due to movement in the air becomes greater than the added cost of leaping.

Since that publication several studies documented porpoising behavior at high speeds. The observations indicated that the behavior was more complex than previously assumed. The leaps were interspersed with relatively long swimming bouts, of about twice the leap length. In the present paper, the possibility of dolphins using a combination of leaping and burst and coast swimming is examined. A three-phase model is proposed, in which the dolphin leaps out of the water at a speed U_f, which is the final speed obtained at the end of the burst phase of burst and coast swimming. The leap is at constant speed and so the animal returns to the water at U_f, goes to a shallow depth and starts horizontal coasting while losing speed, till it reaches U_i. At that point it starts active swimming, accelerating to U_f. It then starts the next leap. Ranges of speeds for which this three-stage swimming is advantageous are calculated as a function of animal and physical parameters.

Notation

C—Constant defined in ^{equation (12)}

C_D—Coasting drag coefficient

D—Drag

g—Gravitational acceleration

H—Height of jump

J—Energy required for jump

k—Ratio of swim length to jump length

l—Distance

L—Total distance (^{eq. 28})

m—Added mass

M—Animal mass

M₁—Total mass

r—Coefficient defined in ^{eq. (22)}

R—Ratio of energies, for three-phase swimming

R₂—Ratio of energies, for burst and coast swimming

t—Time

T—Thrust

U—Speed

V—Body volume

W—Weight

α—Emergence (=return) angle

β—Swim / coast drag penalty ratio

γ—Surface effects drag ratio

ρ—Density of seawater and cetacean.

Subscripts

a—air

av—Average

b—Burst phase

c—Coast phase

e—Reference (maximal) thrust

f—Final, at end of burst

i—Initial, at start of burst

j—Jump phase

n—Nominal reference thrust

o—Optimal

s—Surface swimming

w—Water