Tight junctions (TJs) are an integral component of models illustrating ion transport mechanisms across fish epithelia; however, little is known about TJ proteins in fishes. Using immunohistochemical methods and Western blot analysis, we examined the localization and expression of occludin, a transmembrane TJ protein, in goldfish tissues. In goldfish gills, discontinuous occludin immunostaining was detected along the edges of secondary gill lamellae and within parts of the interlamellar region that line the lateral walls of the central venous sinus. In the goldfish intestine, occludin immunolocalized in a TJ-specific distribution pattern to apical regions of columnar epithelial cells lining the intestinal lumen. In the goldfish kidney, occludin was differentially expressed in discrete regions of the nephron. Occludin immunostaining was strongest in the distal segment of the nephron, moderate in the collecting duct and absent in the proximal segment. To investigate a potential role for occludin in the maintenance of the hydromineral balance of fishes, we subjected goldfish to 1, 2 and 4 weeks of food deprivation,...]]>
Parental care is a widespread and ecologically relevant adaptation known to enhance the developmental environment of offspring. Parental behaviors, however, may entail both costs and benefits for developing offspring. In Children's pythons (Antaresia childreni), we monitored both maternal egg-brooding behavior and intra-clutch oxygen partial pressure (PO2) in real-time to assess the effects of various brooding behaviors on PO2 in the clutch micro-environment at three stages of development. Furthermore, at the same developmental stages, we measured O2 consumption rates (VO2) of eggs at varying PO2 to determine their critical oxygen tension (i.e. the minimal PO2 that supports normal respiratory gas exchange) and to predict the impact that naturally brooded intra-clutch PO2 has on embryonic metabolism. At all three stages of development, a tightly coiled brooding posture created an intra-clutch PO2 that was significantly lower than the surrounding nest environment. Maternal postural adjustments alleviated this hypoxia, and the magnitude of such corrections increased with developmental stage. Mean intra-clutch PO2 decreased with stage of development, probably because of increasing egg VO2. Additionally, embryo critical oxygen...]]>
We employ numerical simulation to investigate the hydrodynamics of carangiform locomotion as the relative magnitude of viscous and inertial forces, i.e. the Reynolds number (Re), and the tail-beat frequency, i.e. the Strouhal number (St), are systematically varied. The model fish is a three-dimensional (3D) mackerel-like flexible body undulating with prescribed experimental kinematics of carangiform type. Simulations are carried out for three Re spanning the transitional and inertial flow regimes, Re=300 and 4000 (viscous flow), and (inviscid flow). For each Re there is a critical Strouhal number, St*, at which the net mean force becomes zero, making constant-speed self-propulsion possible. St* is a decreasing function of Re and approaches the range of St at which most carangiform swimmers swim in nature (St~0.25) only as Re approaches infinity. The propulsive efficiency at St* is an increasing function of Re while the power required for swimming is decreasing with Re. For all Re, however, the swimming power is shown to be significantly greater than that required to tow the...]]>
Jawless fishes (Agnatha; lampreys and hagfishes) most closely resemble the earliest stage in vertebrate evolution and lamprey-like animals already existed in the Lower Cambrian [about 540 million years ago (MYA)]. Agnathans are thought to have separated from the main vertebrate lineage at least 500 MYA. Hagfishes have primitive eyes, but the eyes of adult lampreys are well-developed. The southern hemisphere lamprey, Geotria australis, possesses five types of opsin genes, three of which are clearly orthologous to the opsin genes of jawed vertebrates. This suggests that the last common ancestor of all vertebrate lineages possessed a complex colour vision system. In the eyes of many bony fishes and tetrapods, well-focused colour images are created by multifocal crystalline lenses that compensate for longitudinal chromatic aberration. To trace the evolutionary origins of multifocal lenses, we studied the optical properties of the lenses in four species of lamprey (Geotria australis, Mordacia praecox, Lampetra fluviatilis and Petromyzon marinus), with representatives from all three of the extant lamprey families. Multifocal lenses...]]>
Hypoxic pulmonary vasoconstriction (HPV) is an adaptive response that diverts pulmonary blood flow from poorly ventilated and hypoxic areas of the lung to better ventilated parts, matching blood perfusion to ventilation. HPV is an ancient and highly conserved response expressed in the respiratory organs of all vertebrates. However, the underlying mechanism and the role of the endothelium remain elusive. Isolated intrapulmonary arteries (internal diameter <346 µm) from the American alligator Alligator mississippiensis were mounted in microvascular myographs for isometric tension recording. Resting vessels and vessels contracted with either serotonin (5-HT) or endothelin-1 (ET-1) were exposed to sustained (45 min) hypoxia (PO2<5 mmHg). In ET-1-contracted vessels, hypoxia induced a monophasic, sustained and fully reversible constriction, which was independent of the endothelium. In relaxed or in 5-HT-contracted vessels, hypoxia did not cause constriction. The effects of ET-1, ETA and ETB as well as the general ET-receptor antagonist were studied. ET-1 caused a contraction of the pulmonary arteries through stimulation of ETA-receptors. ETA and ETB immunoreactive staining revealed the location...]]>
The landing–take-off asymmetry of running was thought to derive from, or at least to be consistent with, the physiological property of muscle to resist stretching (after landing) with a force greater than it can develop during shortening (before take-off). In old age, muscular force is reduced, but the deficit in force is less during stretching than during shortening. The greater loss in concentric versus eccentric strength with aging led us to hypothesize that older versus younger adults would increase the landing–take-off asymmetry in running. To test this hypothesis, we measured the within-step changes in mechanical energy of the centre of mass of the body in old and young subjects. The difference between the peaks in kinetic energy attained during the fall and during the lift of the centre of mass is greater in the old subjects. The difference between the time to lift and accelerate the centre of mass (positive work) and to absorb the same amount of energy during the downward displacement...]]>
We investigated photoacclimation in the symbiotic Mediterranean coral Cladocora caespitosa by exposing it to three light levels (30, 80 and 250 µmol m–2 s–1), which are in the range of those recorded for this species. The coral response to a change in both light and temperature was also assessed, by subjecting coral to two treatments corresponding to winter (14°C and 30 µmol m–2 s–1) and summer (23°C and 250 µmol m–2 s–1) conditions, as measured in the Ligurian Sea. Photosynthesis, measured using both respirometry and pulse amplitude modulated (PAM) fluorometry, revealed a linear relationship only at low light levels. At higher irradiance, relative electron transport rate (rETR) approached saturation more slowly than rates of oxygen production. At constant temperature, a change in light did not induce any change in zooxanthellae (zoox) and chlorophyll (Chla+c2) concentrations (mean 3.7x106 zoox cm–2 and 14.1 µg cm–2, respectively); however, chlorophyll concentrations significantly increased under low light and temperature, probably in order to maintain a sufficient level of autotrophy. Maximal gross photosynthesis (Pgmax)...]]>
Apart from regulating insect development, juvenile hormones (JHs) play an
important role in insect reproduction, where they initiate vitellogenin
synthesis and regulate the uptake of yolk by the ovary. JH synthesis is a
tightly regulated process controlled by neurons and peptidergic neurosecretory
cells. One of the known stimulatory regulators of JH biosynthesis is
glutamate, and its N-methyl-
The nutrient amino acid transporter (NAT) subfamily is the largest subdivision of the sodium neurotransmitter symporter family (SNF; also known as SLC6; HUGO). There are seven members of the NAT population in the African malaria mosquito Anopheles gambiae, two of which, AgNAT6 and AgNAT8, preferably transport indole- and phenyl-branched substrates, respectively. The relative expression and distribution of these aromatic NATs were examined with transporter-specific antibodies in Xenopus oocytes and mosquito larval alimentary canal, representing heterologous and tissue expression systems, respectively. NAT-specific aromatic-substrate-induced currents strongly corresponded with specific accumulation of both transporters in the plasma membrane of oocytes. Immunolabeling revealed elevated expressions of both transporters in specific regions of the larval alimentary canal, including salivary glands, cardia, gastric caeca, posterior midgut and Malpighian tubules. Differences in relative expression densities and spatial distribution of the transporters were prominent in virtually all of these regions, suggesting unique profiles of the aromatic amino acid absorption. For the first time reversal of the location of a transporter between apical and basal membranes...]]>
We studied the mechanical properties of deep red aerobic muscle of yellowfin tuna (Thunnus albacares), using both in vivo and in vitro methods. In fish swimming in a water tunnel at 1–3 L s–1 (where L is fork length), muscle length changes were recorded by sonomicrometry, and activation timing was quantified by electromyography. In some fish a tendon buckle was also implanted on the caudal tendon to measure instantaneous muscle forces transmitted to the tail. Between measurement sites at 0.45 to 0.65 L, the wave of muscle shortening progressed along the body at a relatively high velocity of 1.7 L per tail beat period, and a significant phase shift (31±4°) occurred between muscle shortening and local midline curvature, both suggesting red muscle power is directed posteriorly, rather than causing local body bending, which is a hallmark of thunniform swimming. Muscle activation at 0.53 L was initiated at about 50° of the tail beat period and ceased at about 160°, where 90° is peak muscle length...]]>
Separate studies of terrestrial and aquatic locomotion are abundant, but research addressing locomotion in transitional environments (e.g. mud) is scant. The African lungfish (Protopterus annectens) moves in a gradation of water to mud conditions during seasonal droughts, and breathes air. Thus, the lungfish was an ideal organism for our study to determine the effects of a wide range of viscosities on lateral undulatory swimming and to simulate some of the muddy conditions early tetrapods may have encountered. Regardless of viscosity, several aspects of lungfish swimming were similar to those of other swimming vertebrates including: posteriorly propagated muscle activity that was unilateral and alternated between the left and right sides at each longitudinal location, and posterior increases in the amount of bending, the amplitude of muscle activity and the timing differences between muscle activity and bending. With increased viscosity (1–1000 cSt), significant increases occurred in the amount of lateral bending of the vertebral column and the amplitude of muscle activity, particularly in the most anterior sites,...]]>
Addiction is a complex psychiatric disorder considered to be a disease of the brain's natural reward reinforcement system. Repeated stimulation of the `reward' pathway leads to adaptive changes in gene expression and synaptic organization that reinforce drug taking and underlie long-term changes in behaviour. The primitive nature of reward reinforcement pathways and the near universal ability of abused drugs to target the same system allow drug-associated reward and reinforcement to be studied in non-mammalian species. Zebrafish have proved to be a valuable model system for the study of vertebrate development and disease. Here we demonstrate that adult zebrafish show a dose-dependent acute conditioned place preference (CPP) reinforcement response to ethanol or nicotine. Repeated exposure of adult zebrafish to either nicotine or ethanol leads to a robust CPP response that persists following 3 weeks of abstinence and in the face of adverse stimuli, a behavioural indicator of the establishment of dependence. Microarray analysis using whole brain samples from drug-treated and control zebrafish identified 1362 genes that...]]>
A honeybee's waggle dance is an intriguing example of multisensory convergence, central processing and symbolic information transfer. It conveys to bees and human observers the position of a relatively small area at the endpoint of an average vector in a two-dimensional system of coordinates. This vector is often computed from a collection of waggle phases from the same or different dancers. The question remains, however, of how informative a small sample of waggle phases can be to the bees, and how the spatial information encoded in the dance is actually mapped to the followers' searches in the field. Certainly, it is the variability of a dancer's performance that initially defines the level of uncertainty that followers must cope with if they were to successfully decode information in the dance. Understanding how a dancer's behaviour is mapped to that of its followers initially relies on the analysis of both the accuracy and precision with which the dancer encodes spatial information in the dance. Here...]]>
Insect ecdysis is a precisely coordinated series of behavioral and hormonal events that occur at the end of each molt. A great deal is known about the hormonal events that underlie this process, although less is known about the neuronal circuitry involved. In this study we identified two populations of neurons that are required for larval and adult ecdyses in the fruit fly, Drosophila melanogaster (Meigen). These neurons were identified by using the upstream region of two genes that code for atypical soluble guanylyl cyclases to drive tetanus toxin in the neurons that express these cyclases to block their synaptic activity. Expression of tetanus toxin in neurons that express Gyc-89Da blocked adult eclosion whereas expression of tetanus toxin in neurons that express Gyc-89Db prevented the initiation of the first larval ecdysis. Expression of tetanus toxin in the Gyc-89Da neurons also resulted in about 50% lethality just prior to pupariation; however, this was probably due to suffocation in the food as lethality was prevented...]]>
Brown ghost knifefish, Apteronotus leptorhynchus, are a species of weakly electric fish that produce a continuous electric organ discharge (EOD) that is used in navigation, prey capture and communication. Stereotyped modulations of EOD frequency and amplitude are common in social situations and are thought to serve as communication signals. Of these modulations, the most commonly studied is the chirp. This study presents a quantitative analysis of chirp production in pairs of free-swimming, physically interacting male and female A. leptorhynchus. Under these conditions, we found that in addition to chirps, the fish commonly produce a second signal type, a type of frequency rise called abrupt frequency rises, AFRs. By quantifying the behaviours associated with signal production, we find that Type 2 chirps tend to be produced when the fish are apart, following periods of low aggression, whereas AFRs tend to be produced when the fish are aggressively attacking one another in close proximity. This study is the first to our knowledge that quantitatively describes both...]]>
In finches husking time is non-linearly related to the ratio of seed hardness to maximal bite force. Fringillids produce larger bite force and husk relatively hard seeds faster than estrildids of similar size. This is at least partly explained by their relatively larger jaw muscle mass and a difference in husking technique. However, the effect of differences in skull geometry on bite force is unclear. In this study differences in skull morphology that may contribute to the difference in bite force between fringillids and estrildids are analyzed. The shape of the skull was described by the 3D coordinates of a set of landmarks and, after eliminating size, the effect of differences in the shape of the skull on bite force was determined using a static force model. EMG recordings of jaw muscles during seed cracking were used to validate assumptions about the muscle activation patterns used for the static bite force model. The analysis shows that most of the variation in skull...]]>
Otophysine fish possess Weberian ossicles, which connect the swimbladder to the inner ear and improve hearing ability. There is a high diversity in the morphology of the swimbladder and Weberian apparatus in catfishes, which might affect hearing. We have examined these structures in representatives of six families with large, single bladders (Ariidae, Auchenipteridae, Heptapteridae, Malapteruridae, Mochokidae, Pseudopimelodidae) and five subfamilies from two families (Callichthyidae, Loricariidae) having small, paired, encapsulated bladders. We tested their hearing abilities utilizing the non-invasive auditory evoked potential recording technique. Species with single, non-encapsulated, free airbladders possess one, three or four ossicles, whereas species with encapsulated bladders possess one or two. The relative sizes of the bladders and ossicles were significantly smaller in the latter group. All species were able to detect sound stimuli between 50 Hz and 5 kHz. Interspecific differences in hearing sensitivity varied at most by 24 dB below 1 kHz, whilst this variation increased to more than 50 dB at higher frequencies. Catfishes with free bladders had lower...]]>
The barrier to water loss from the skin of birds and mammals is localized in the stratum corneum (SC), the outer layer of the epidermis. The SC consists of corneocytes, each surrounded by a protein envelope, and a lipid compartment, formed by an extracellular matrix of lipids and by lipids covalently bound to the protein envelope. In mammals, covalently bound lipids in the SC consist of -hydroxyceramides attached to the outer surface of corneocytes. Evidence suggests that covalently bound lipids in the SC might be crucial for the establishment of a competent permeability barrier. In this study we assessed the composition of covalently bound lipids of the avian SC and their relationship to cutaneous water loss (CWL) in two populations of house sparrows, one living in the deserts of Saudi Arabia and the other in mesic Ohio. Previously, we showed that CWL of adult desert sparrows was 25% lower than that of mesic birds. In the present study we characterize covalently bound lipids...]]>
Developing animals may face a cost–benefit tradeoff during growth mediated through hormones such as glucocorticoids, as the hormone is essential for development but can have detrimental consequences. To investigate potential tradeoffs caused by brief, moderate elevations of corticosterone in avian young, we artificially elevated the hormone levels in two ways: feeding corticosterone-containing worms and applying corticosterone dermal patches. The former experiment tested the effects of an acute corticosterone elevation (25 min) on begging behavior, whereas the latter explored the effects of artificially elevated corticosterone for 24 to 48 h on growth. Corticosterone altered both begging behavior and growth of white-crowned sparrow nestlings. It increased latency to beg immediately after the treatment and suppressed growth as early as 24 h after the patch application. These experiments also showed that the effects depended on the age or types of development (e.g. gaining mass or growing feathers) that the nestlings were going through.
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