The leg tendons of certain avian species normally calcify. The gastrocnemius, or Achilles, tendon of the domestic turkey, Meleagris gallopavo, is one such example. Its structure and biomechanical properties have been studied to model the adaptive nature of this tendon to external forces, including the means by which mineral deposition occurs and the functional role mineralization may play in this tissue. Structurally, the distal rounded, thick gastrocnemius bifurcates into two smaller proximal segments that mineralize with time. Mineral deposition occurs at or near the bifurcation, proceeding in a distal-to-proximal direction along the segments toward caudal and medial muscle insertions of the bird hip. Mineral formation appears mediated first by extracellular matrix vesicles and later by type I collagen fibrils. Biomechanical analyses indicate lower tensile strength and moduli for the thick distal gastrocnemius compared to narrow, fan-shaped proximal segments. Tendon mineralization here appears to be strain-induced, the muscle forces causing matrix deformation leading conceptually to calcium binding through the exposure of charged groups on collagen, release of sequestered calcium by proteoglycans, and increased diffusion. Functionally, the mineralized tendons limit further tendon deformation, reduce tendon strain at a given stress, and provide greater load-bearing capacity to the tissue. They also serve as important and efficient elastic energy storage reservoirs, increasing the amount of stored elastic energy by preventing flexible type I collagen regions from stretching and preserving muscle energy during locomotion of the animals.
Two models have been proposed to describe the prey transport kinematics of terrestrial vertebrates (Bramble and Wake, 1985; Reilly and Lauder, 1990). The critical difference between the models is the presence or absence of a slow open-II phase (SO-II) in the gape profile during mouth opening. Each of these models has been applied to lizards, however to date, lizard feeding kinematics have not been adequately quantified to assess the utility of these models for this clade. Neither model has been sufficiently tested due to the lack of a methodology to assess the specific differences between the models. We describe a method that uses explicit mathematical criteria to define the kinematic phases in tetrapod feeding. This "slope analysis& is used to precisely quantify and compare the transport kinematics of seven lizard species. Lizard transport kinematics were highly variable both within and across taxa. However, several common gape cycle patterns were identified. The predominant patterns were slow-fast opening (37.3%), fast opening only (22.9%) and slow opening only (21.2%). The most common pattern explicitly fits the prediction of the Reilly and Lauder model while the other two are similar to patterns observed in salamanders. Thus, lizards possess both the slow opening-fast opening pattern predicted for amniotes and the more primitive, simple opening pattern characteristic of more basal tetrapods. Plateau phases were found in only 12.8% of the profiles and only a fourth of these (3.4% of the total) explicitly fit the Bramble and Wake model (slow opening, plateau, fast opening) and two species never exhibited plateaus in their gape cycles. Thus, it is clear that the Bramble and Wake model is not supported as a generalized model for lizards or generalized tetrapods.
Postinhibitory rebound (PIR) is an intrinsic property of many neurons but the underlying mechanism is not well understood. We studied PIR and its relationship to spike adaptation in B-cells isolated from the buccal ganglia of Aplysia. These neurons exhibit PIR following inhibitory synaptic input and following direct membrane hyperpolarization. Hyperpolarizing and depolarizing voltage clamp pulses from the resting potential evoke slow changes in membrane current that persist in the form of tail currents following the pulses. A subtraction method was used to isolate slow tail currents for study. Current-voltage measurements indicate that slow outward tail currents following depolarizing pulses result from increases in membrane conductance, while inward tail currents following hyperpolarizations to −50 and −60 mV result from conductance decreases. The reversal potential of both outward and inward tail current is between −60 and −70 mV. Tail currents activated by pulses more positive than −60 mV are sensitive to the external K+ concentration and blocked by injection of Cs+ and TEA. When Ca2+ influx is prevented by bathing cells in Ca2+ free saline or by adding Co2+ or Ni2+, the tail currents are reduced but a significant fraction of the current is insensitive to these treatments. More negative conditioning pulses activate a second component of inward tail current that is weakly sensitive to K+ but more strongly effected by substitution of N-methyl glucamine or Li+ for external Na+. We conclude that both PIR and adaptation result from slow changes in a voltage dependent, non-inactivating K+ conductance that is active at voltages near the resting potential and is not tightly coupled to Ca2+ influx. In addition, a second inward current is activated by large hyperpolarizing pulses that results from an increase in Na+ and K+ conductance. This second process is likely to contribute to PIR under particular circumstances.
Black-bellied plovers (Pluvialis squatarola) have short bills and primarily peck while foraging whereas Willets (Catoptrophorus semipalmatus) have long bills and primarily probe with bills open in sediments. Intestinal digesta were collected from these species at sympatric overwintering sites in southern California near San Diego to relate sediment ingestion to bill length and feeding behavior. Plover digesta contained an estimated 29% sediment, and Willet digesta an estimated 3% sediment. Techniques based on acid insoluble ash and on the elemental markers of Al, Fe, and Ti in digesta provided similar results. High Ca concentrations in Willet digesta along with our observations suggested that the Willets in our sample fed primarily on molluscs and crustaceans. Sediment ingestion may be species-specific, not necessarily linked to bill length or probing behaviors, and may greatly affect a bird's exposure to environmental contaminants in sediment.
Although pregnant viviparous squamates are sometimes claimed to be able to resorb inviable eggs and embryos from the uterus, definitive evidence for such resorption is not available. After placing pregnant female Pseudemoia pagenstecheri into conditions under which embryonic development is terminated, we periodically harvested the gravid oviducts and examined them histologically. Females contained abnormal and degenerating eggs and embryos that had died in various stages of development. Dead embryos had undergone extensive cytolysis, dissolution, and aseptic necrosis and vitelline masses showed signs of deterioration and passage down the oviduct. The uterine mucosa lay in direct contact with the vitelline material, with no intact shell membrane intervening between them. Yolk was sometimes displaced into the exocoelom and allantoic cavity due to rupture of the extraembryonic membranes. Histological examination revealed no evidence of the uptake of yolk by the uterine epithelium or its accumulation in the subepithelial connective tissue. In many specimens, the uterine epithelium showed minuscule, apical granules. The position, appearance, and staining properties of the granules suggests them to be secretory, a manifestation of placentotrophy. Our observations indicate that P. pagenstecheri females retain dead eggs and embryos for several weeks or longer, yet do not resorb them during that period. This lizard is the second placentotrophic skink species in which resorption has been suspected, but in which abortive eggs appear to be retained or extruded instead of being resorbed by the oviducts. Researchers should not assume that squamates can digest and resorb oviductal eggs without definitive morphological evidence. J. Morphol. 256:219–234, 2003. © 2003 Wiley‐Liss, Inc.
Molecular data is ideal for exploring deep evolutionary history because of its universality, stochasticity and abundance. These features provide a means of exploring the evolutionary history of all organisms (including those that do not tend to leave fossils), independently of morphological evolution, and within a statistical framework that allows testing of evolutionary hypotheses. In particular, molecular data have an important role to play in examining hypotheses concerning the tempo and mode of evolution of animal body plans. Examples are given where molecular phylogenies have led to a re-examination of some fundamental assumptions in metazoan evolution, such as the immutability of early developmental characters, and the evolvability of bauplan characters. Molecular data is also providing a new and controversial timescale for the evolution of animal phyla, pushing the major divisions of the animal kingdom deep into the Precambrian. There have been many reasons to question the accuracy and precision of molecular date estimates, such as the failure to account for lineage-specific rate variation and unreliable estimation of rates of molecular evolution. While these criticisms have been largely countered by recent studies, one problem has remained a challenge: could temporal variation in the rate of molecular evolution, perhaps associated with "explosive" adaptive radiations, cause overestimation of diversification dates? Empirical evidence for an effect of speciation rate, morphological evolution or ecological diversification on rates of molecular evolution is examined, and the potential for rate-variable methods for molecular dating are discussed.
This symposium was organized to honor the career of Professor Milton Fingerman. Every discipline has its leaders, individuals who through insight and persistence move their field forward. Milt Fingerman is such an individual, one who has had a lasting impact on the field of crustacean endocrinology. In addition, Milt's tireless efforts have benefited the greater scientific enterprise, including the Society of Integrative and Comparative Biology and the Crustacean Society. Born in Boston, Milt attended Boston College as an undergraduate, and then went to Northwestern University for his Ph.D. His professional interest in crustaceans began during this period, when he joined the laboratory of Frank Brown and spent summers at the Marine Biological Laboratory in Woods Hole, Mass. After a two-year stint with the U.S. Army at Fort Detrick Md., Milt joined the faculty at Tulane University in 1954. Milt retired from its Department of Ecology and Evolutionary Biology in 2000, after having served as chair of the department for 13 yr. Milt also served as the Managing Editor of the American Zoologist for 15 yr, and has been an editorial board member of 8 journals and associate editor of two journals. Milt's career has been distinguished by an enormous productivity. At the time of the symposium, he had published more than 325 papers or book chapters, two books, and over 120 abstracts. His contributions to the field of crustacean endocrinology have been broad, and have covered nearly all areas of crustacean biology and physiology—color changes (Fingerman, 1966), reproduction (Fingerman, 1997), molting (Fingerman et al. , 1996), eye pigment movements (Fingerman et al. , 1959), regeneration (Fingerman et al. …
I present an overview of recent research on the isolation and characterization of members of the crustacean hyperglycemic hormone (CHH) neuropeptide family. Members of this arthropod-specific family include CHH, molt-inhibiting hormone (MIH), vitellogenesis-inhibiting hormone (VIH), and mandibular organ-inhibiting hormone (MOIH). There are two subfamilies of this neuropeptide group, based upon the presence or absence of a C-terminal CHH precursor-related peptide. There are also sequence motif differences between these subfamilies. Most of the peptides comprising this neuropeptide family are synthesized and released by the eyestalk X-organ/sinus gland complex. Recent experiments have demonstrated the presence of extra-eyestalk cells that produce CHH and the assignment of additional functions to this hormone family.
Seven subjects walked on a programmable treadmill both at constant (3.5 ± 0.0 and 5.0 ± 0.0 km/hr) and oscillating speeds (±0.5, ±1.0, ±1.5, ±2.0 km hr−1), set to sinusoidally change between the two limits in 3 sec. In each condition oxygen consumption measurements were taken. The same experimental protocols were replicated on a walkway by asking subjects to adapt their stride frequency to an audio signal corresponding to the sinusoidal stride frequency changes measured on the treadmill. Differently from what expected, only the ±2.0 km hr−1 oscillation resulted to be metabolically different from the constant speed walking, both for the treadmill and the walkway conditions. The time course of the mechanical energy of the body centre of mass could reveal that a strategy devoted to benefit from the usual energy fluctuations occurring at “constant speed,” is likely to be used to cope with speed varying sequences. From the energy curve observed at constant speed, it is possible to derive an energetically equivalent curve by cumulating acceleration portions, and deceleration ones, of a group of strides as to produce a single acceleration and a single deceleration phase, as it is observed in oscillating speed walking. Being aware of the bias introduced by using a non-inertial frame (the treadmill protocol), we are replicating the experiments with a laser beam projected on a wide radius circular path at oscillating speeds, that the subjects have to follow. The preliminary data seem to confirm the invariance of the metabolic requirements in oscillatory walking up to ±1.5 km hr−1.
. Classical studies of horseshoe crab development have provided relatively little information about the earliest stages, and the contribution of yolk cells and yolk nuclei—a deficiency due in large part to the difficulty of preparing the eggs and embryos for sectioning. Using newly developed histological resins, we show that the yolk nuclei undergo a series of changes during embryogenesis, before cellularizing and forming the midgut epithelium during the first larval stage. The digestive diverticulum forms in a 2-step process. A mesodermally derived lamina divides the yolk mass into distinct lobes, defining the boundaries of the digestive caeca. The yolk nuclei then cellularize to form the midgut epithelium.
Mitogen-activated protein (MAP) kinases constitute a large family of proteins with many functions. They are represented by a multitude of paralogous isoforms in yeast, vertebrates, and other eukaryotes. A phylogenetically conserved function of MAP kinases is to carry osmotic signals from sensory to target elements of cells. Even though this function of MAP kinases is ubiquitous and characteristic of unicellular and multicellular eukaryotes alike the contingencies between individual MAP kinases, sensor elements, and target elements have been subject to vast modification during evolution. Extensive networking of MAP kinase cascades with other signaling pathways is reflected by the large number of diverse signals that can be carried by a single MAP kinase pathway and flexible activation kinetics. It is emerging that the most important function of MAP kinase networks may not be signal amplification but integration of information about the setpoint of environmental parameters (including osmolality) with other physiological processes to control cell function. Insight into how this cellular integration of information is achieved by MAP kinase networks will shed light on the principles of cell dynamics and adaptation.
The Cactus-Microorganism-Drosophila Model System of the Sonoran Desert represents an excellent paradigm of the role of chemistry in plant-animal interactions. In this system, four species of endemic Drosophila feed and reproduce in necrotic tissue of five species of columnar cacti. Studies over the past 35 yr have characterized a myriad of interactions between the three major components of the model system. The cacti contain a variety of allelochemicals which are primarily responsible for the highly specific pattern of host plant utilization exhibited by the desert Drosophila. Plant chemistry, through its effect on the microbially produced volatile patterns, is further involved in host specificity because the flies use the volatile pattern to cue in on necroses in the appropriate species of cactus. The metabolic activities of microorganisms (bacteria and yeasts) living in the necrosis can affect the substrate chemistry in both positive and negative ways (i.e., acting to increase or to decrease the toxicity of the substrate). Finally, cactus chemistry may affect drosophilid mating behavior since larval rearing substrate has been shown to influence adult hydrocarbon epicuticular composition. In D. mojavensis, adult hydrocarbon profile has been implicated as a determinant of mate choice leading to premating isolation between geographically isolated populations that use chemically different cactus substrates. Current research is focused on the evolution and regulation of genes whose products (cytochrome P450 enzymes) are involved in the specific insect-host plant relationships which exist between the Drosophila species and the cactus species.There are many reasons why investigators choose to focus their research efforts on what are referred to as "model systems." Typically included among these would be the idea that model systems are easier to study because they are less complex than other scientific situations. At the same time, model systems should be representative of more complex, natural systems so that information that is obtained from their study is broadly applicable. For almost a century, the fruit fly, Drosophila melanogaster, has served as a model organism for the study of genetics. As a genetic paradigm, Drosophila is more tractable to scientific investigation than most organisms and has provided important insights into a wide variety of human maladies from alcohol abuse to neurological brain disorders (Bellen, 1998). Similarly, the interrelationships of the columnar cacti and the cactophilic Drosophila species of the Sonoran Desert have, for the past 35 yr, provided an excellent model system with which to study relevant questions in evolution, ecological genetics, and chemical ecology. The intent of this article is to briefly review and characterize the chemical interactions between the plants (cacti) and animals (Drosophila) of this model system, and, in addition, provide some thoughts on possible future directions for integrative approaches in this research area.
Many fishes use a powerful bite of the oral jaws to capture or tear their prey. This behavior has received less study from functional morphologists and physiologists than suction feeding, and presents an opportunity to examine motor control of fish feeding across alternative prey-capture strategies. We used electromyography to compare muscle activity patterns of the feeding bite in five teleost fishes representing at least three lineages in which biting has been independently acquired: two parrotfish (Cetoscarus bicolor and Scarus iseri), a wrasse (Cheilinus chlorourus), and two serrasalmines, a pacu (Piaractus brachypomus) and a piranha (Pygocentrus nattereri). Multivariate analysis indicated that muscle activity patterns differed significantly among species, although a four-way ANOVA designed to test for differences within a phylogenetic hierarchy revealed that the biting motor pattern was largely similar for both narrow and broad phylogenetic comparisons. A comparison of the motor patterns of biting and suction feeding species revealed that biters had significantly shorter durations of the epaxialis and sternohyoideus and significantly longer relative onset times of the epaxialis, adductor mandibulae, and sternohyoideus. Character mapping of timing variables suggested that short relative onset times are primitive for suction feeders and that this characteristic is generally retained in more advanced species. Despite these differences, all species overlap extensively in multivariate EMG space. Our results demonstrate that change in the feeding motor pattern has accompanied morphological and behavioral change in transitions from suction to biting, which suggests that the neuromotor system has not acted as a constraint on the evolution of the feeding system in fishes.
SYNOPSIS. Vibration through the substrate has likely been important to animals as a channel of communication for millions of years, but our awareness of vibration as biologically relevant information has a history of only the last 30 yr. Morphologists know that the jaw mechanism of early amphibians allowed them to perceive vibration through the substrate as their large heads lay on the ground. Although the exact mechanism of vibration production and the precise nature of the wave produced are not always understood, recent technical advances have given answers to increasingly sophisticated questions about how animals send and receive signals through the substrate. Some of us have been forced to explore the use of vibration when all other attempts to manipulate animals in the field have failed, while others began to think about vibration to explain some of the puzzling behaviors of species they were studying in other contexts. It has thus become clear that the use of vibration in animal communication is much more widespread than previously thought. We now know that vibration provides information used in predator-prey interactions, recruitment to food, mate choice, intrasexual competition and maternal/brood social interactions in a range of animals from insects to elephants.
Recent work has provided measurements of power output in avian skeletal muscles during running and flying, but little is known about the contractile properties of avian skeletal muscle. We used an in situ preparation to characterize the force–velocity properties of two hind limb muscles, the lateral gastrocnemius (LG) and peroneus longus (PL), in Wild Turkeys (Meleagris gallopavo). A servomotor measured shortening velocity for at least six different loads over the plateau region of the length–tension curve. The Hill equation was fit to the data to determine maximum shortening velocity and peak instantaneous power. Maximum unloaded shortening velocity was 13.0±1.6 L s−1 for the LG muscle and 14.8±1.0 L s−1 for the PL muscle (mean±S.E.M.). These velocities are within the range of values published for reptilian and mammalian muscles. Values recorded for maximum isometric force per cross-sectional area, 271±28 kPa for the LG and 257±30.5 kPa for the PL, and peak instantaneous power output, 341.7±36.4 W kg−1 for the LG and 319.4±42.5 W kg−1 for the PL, were also within the range of published values for vertebrate muscle. The force–velocity properties of turkey LG and PL muscle do not reveal any extreme differences in the mechanical potential between avian and other vertebrate muscle.
Marine benthic communities living in shallow-water habitats (< 100 m depth) in Antarctica possess characteristics reminiscent of Paleozoic marine communities and modern deep-sea communities. The absence of crabs and sharks, the limited diversity of teleosts and skates, the dominance of slow-moving invertebrates at higher trophic levels, and the occurrence of dense ophiuroid and crinoid populations indicate that skeleton-breaking predation is limited in Antarctica today, as it was worldwide during the Paleozoic and as it is in the deep sea today. The community structure of the antarctic benthos has its evolutionary roots in the Eocene. Data from fossil assemblages at Seymour Island, Antarctic Peninsula suggest that shallow-water communities were similar to communities at lower latitudes until they were affected by global cooling, which accelerated in the late Eocene to early Oligocene. That long-term cooling trend ultimately resulted in the polar climate and peculiar community structure found in Antarctica today. Declining temperatures beginning late In the Eocene are associated with the disappearance of crabs, sharks, and most teleosts. The sudden drop in predation pressure allowed dense ophiuroid and crinoid populations to appear and flourish. These late Eocene echinoderm populations exhibit low frequencies of sublethal damage (regenerating arms), demonstrating that there was little or no predation from skeleton-breaking fish and decapods. Current scenarios of global climate change include predictions of increased upwelling and consequent cooling in temperate and subtropical upwelling zones. Limited ecological evidence suggests that such cooling could disrupt trophic relationships and favor retrograde community structures in those local areas.
The control of cell volume in all cell types is accomplished by the regulation of two general categories of osmolytes: inorganic ions, most commonly K+ and Cl-, and small molecular weight organic compounds, usually certain amino acids and certain quaternary ammonium compounds. The difference in who regulates what does not depend phylogeny, but instead upon the type of osmotic environment that a cell expects (in an evolutionary sense) to encounter. Cells that exist in extracellular osmotic concentrations up to 300-400 mosmol/kg (mosm) rely primarily on inorganic osmolytes for volume control, while cells that exist at greater osmotic concentrations rely more on organic osmolytes for volume control. Usually, strange or unique volume regulatory mechanisms are found in cells that exist in particularly demanding osmotic conditions. In order to provide further support the foregoing generalizations, the following paper will focus on comparisons between the hypoosmotically induced mechanism of taurine efflux regulation by red blood cells of the bivalve, Noetia ponderosa, probably the best understood "invertebrate" cell type in this regard, and taurine efflux from a variety of "vertebrate" cells.
Body size, pectoralis composition, aspect ratio of the wing, and forward speed affect the use of intermittent flight in birds. During intermittent non-flapping phases, birds extend their wings and glide or flex their wings and bound. The pectoralis muscle is active during glides but not during bounds; activity in other primary flight muscles is variable. Mechanical power, altitude, and velocity vary among wingbeats in flapping phases; associated with this variation are changes in neuromuscular recruitment, wingbeat frequency, amplitude, and gait. Species of intermediate body mass (35–158 g) tend to flap-glide at slower speeds and flap-bound at faster speeds, regardless of the aspect ratio of their wings. Such behavior may reduce mechanical power output relative to continuous flapping. Smaller species (<20 g) with wings of low aspect ratio may flap-bound at all speeds, yet existing models do not predict an aerodynamic advantage for the flight style at slow speeds. The behavior of these species appears to be due to wing shape rather than pectoralis physiology. As body size increases among species, percent time spent flapping increases, and birds much larger than 300 g do not flap-bound. This pattern may be explained by adverse scaling of mass-specific power or lift per unit power output available from flight muscles. The size limit for the ability to bound intermittently may be offset somewhat by the scaling of pectoralis composition. The percentage of time spent flapping during intermittent flight also varies according to flight speed.
As the primary link between environmental change and physiological response, the neuroendocrine system is a critical part of osmoregulatory adaptations. Cortisol has been viewed as 'the' seawater-adapting hormone in fish and prolactin as 'the' fresh water adapting hormone. Recent evidence indicates that the growth hormone/insulin-like growth factor I axis is also important in seawater adaptation in several teleosts of widely differing evolutionary lineages. In salmonids, growth hormone acts in synergy with cortisol to increase seawater tolerance, at least partly through the upregulation of gill cortisol receptors. Cortisol under some conditions may promote ion uptake and interacts with prolactin during acclimation to fresh water. The osmoregulatory actions of growth hormone and prolactin are antagonistic. In some species, thyroid hormones support the action of growth hormone and cortisol in promoting seawater acclimation. Although a broad generalization that holds for all teleosts is unlikely, our current understanding indicates that growth hormone promotes acclimation to seawater, prolactin promotes acclimation to fresh water, and cortisol interacts with both of these hormones thus having a dual osmoregulatory function.
A recent total evidence analysis of the position of cetaceans (whales, dolphins and porpoises and extinct relatives) among mammals indicated that the phylogeny of these taxa remains poorly resolved. Molecular data show that 1) the order Artiodactyla (even-toed ungulates) is paraphyletic unless whales are included within it and 2) that the traditional relationships of clades within Artiodactyla are not supported. This controversy also affects the position of a wholly extinct clade, Mesonychia, which has been argued to be the group of terrestrial mammals most closely related to whales. Here I update a previous total evidence analysis by adding several hundred new informative molecular characters from the literature. Even with the addition of these characters the phylogeny remains unresolved. All most parsimonious trees, however, indicate a paraphyletic Artiodactyla with conflict existing over the exact sister taxon of Cetacea. Congruence between different equally parsimonious cladograms and the stratigraphic record as measured using the modified Manhattan Stratigraphic Measure shows that all of the competing topologies, including those with a paraphyletic Artiodactyla, are significantly congruent with the stratigraphic record. In fossil taxa cladistic optimization can be used as an alternative to "argument from design" (Lauder, 1996) to reconstruct behavior and soft tissues that do not fossilize or osteological characters that have not preserved. In certain scenarios of cetacean phylogeny, optimization indicates that taxa such as the archaic whales Ambulocetus and Pakicetus, and possibly mesonychians, are more correctly reconstructed without hair.
