Unequal saccades generated by velocity interactions in the peripheral oculomotor system

Experiments with precision eye movement recordings show binocularly unequal saccades to be present under several stimulus conditions having as a common theme ongoing low velocities at the times of the saccades. Simulations using a model of eye muscles and eyeball dynamics reproduce these unequal saccades in quantitative agreement with the experimental findings. The model uses equal innervation for the saccades, and demonstrates a peripheral interaction between the muscle forces and the eye velocities to be the cause of the large inequality of the simulated binocular saccades. Thus, the simulations provide evidence that Hering's law continues to describe the innervation patterns to corresponding muscles producing these binocularly unequal saccades found in the experimental situation.     

A novel fork head gene mediates early steps during Xenopus lens formation.

Xlens1 is a novel Xenopus member of the fork head gene family, named for its nearly restricted expression in the anterior ectodermal placode, presumptive lens ectoderm (PLE), and anterior epithelium of the differentiated lens. The temporal and spatial restriction of its expression suggests that: (1) Xlens1 is transcribed initially at neural plate stages in response to putative signals from the anterior neural plate that transform lens-competent ectoderm to lens-biased ectoderm; (2) further steps in the process of lens-forming bias restrict Xlens1 expression to the presumptive lens ectoderm (PLE) during later neural plate stages; (3) interactions with the optic vesicle maintain Xlens1 expression in the lens placode; and (4) Xlens1 expression is downregulated as committed lens cells undergo terminal differentiation. Induction assays demonstrate that pax6 induces Xlens1 expression, but unlike pax6, Xlens1 cannot induce the expression of the lens differentiation marker beta-crystallin. In the whole embryo, overexpression of Xlens1 in the lens ectoderm causes it to thicken and maintain gene expression characteristics of the PLE. Also, this overexpression suppresses differentiation in the lens ectoderm, suggesting that Xlens1 functions to maintain specified lens ectoderm in an undifferentiated state. Misexpression of Xlens1 in other regions causes hypertrophy of restricted tissues but only occasionally leads ectopic sites of gamma-crystallin protein expression in select anterior head regions. These results indicate that Xlens1 expression alone does not specify lens ectoderm. Lens specification and differentiation likely depends on a combination of other gene products and an appropriate level of Xlens1 activity.     

Fishers' knowledge and seahorse conservation in Brazil

From a conservationist perspective, seahorses are threatened fishes. Concomitantly, from a socioeconomic perspective, they represent a source of income to many fishing communities in developing countries. An integration between these two views requires, among other things, the recognition that seahorse fishers have knowledge and abilities that can assist the implementation of conservation strategies and of management plans for seahorses and their habitats. This paper documents the knowledge held by Brazilian fishers on the biology and ecology of the longsnout seahorse Hippocampus reidi. Its aims were to explore collaborative approaches to seahorse conservation and management in Brazil; to assess fishers' perception of seahorse biology and ecology, in the context evaluating potential management options; to increase fishers' involvement with seahorse conservation in Brazil. Data were obtained through questionnaires and interviews made during field surveys conducted in fishing villages located in the States of Piauí, Ceará, Paraíba, Maranhão, Pernambuco and Pará. We consider the following aspects as positive for the conservation of seahorses and their habitats in Brazil: fishers were willing to dialogue with researchers; although captures and/or trade of brooding seahorses occurred, most interviewees recognized the importance of reproduction to the maintenance of seahorses in the wild (and therefore of their source of income), and expressed concern over population declines; fishers associated the presence of a ventral pouch with reproduction in seahorses (regardless of them knowing which sex bears the pouch), and this may facilitate the construction of collaborative management options designed to eliminate captures of brooding specimens; fishers recognized microhabitats of importance to the maintenance of seahorse wild populations; fishers who kept seahorses in captivity tended to recognize the condtions as poor, and as being a cause of seahorse mortality.     

Ontogenetic changes in the auditory sensitivity of damselfishes (pomacentridae)

Psychophysical experiments demonstrated that the hearing abilities of two damselfish species change during ontogeny. Auditory thresholds of four size-groups of juvenile bicolor damselfish. Pomacentrus partitus, and for comparative purposes, three different sized juveniles belonging to a closely related species, P. variablis, were determined through classical conditioning experiments conducted in a standing wave tube. Young juveniles (10–27 days post-metamorphosis) exhibited poor hearing, with detection limens ranging from 54 dB (at 300 Hz) to 15 dB (at 1500 Hz) higher than known adult thresholds. Thresholds decreased exponentially with increasing age, while rapidly approaching adult levels. Youngest juveniles exhibited flat, untuned audiograms, with the appearance of a best frequency and a pattern of increasing acuity progressing in a manner similar to that observed in mammals and birds.     

Methylated analogues of prostaglandin E2 and the gastric mucosal barrier

15(R)-methyl PGE₂ methyl ester (15MPG) and 16,16-dimethyl PGE₂ methyl ester (16DMPG) were assessed for their effect on gastric mucosal permeability to Na⁺ and H⁺ in dogs prepared by antrectomy and vagally-denervated fundic pouches. 15MPG did not increase mucosal permeability to either ion when given topically (18.75 – 300 μg) or parenterally (30 μg), and did not affect permeability increases induced by topical 5mM sodium taurocholate in acid solution. 16DMPG caused significant increases in net Na⁺ gain when given topically (18.75 – 75 μg) but did not affect net H⁺ loss from the pouch lumen. Attempts to use higher doses of 16DMPG were abandoned because of bleeding from the pouch, and perforation in one animal. It is conceivable that 16DMPG could cause adverse effects on the gastric mucosal barrier if used to suppress gastric secretion therapeutically. 15MPG does not share this potentially harmful property and remains worthy of further study as an inhibitor of gastric secretion with therapeutic promise.     

A mathematical model of water flux through aortic tissue

Water flux in porcine aortic segments produced by the sudden application of a hydrostatic pressure gradient has been described in a recent paper by Harrison and Massaro (1976). A mathematical model is developed here to explain the results obtained when pressure is applied to either covered or uncovered samples. The model predicts that the rate of exudation in both instances should be substantially identical for a period of time ∼ 0.2τ, where τ is the consolidation time. The consolidation time is proportional to the hydraulic resistance to liquid flow, and inversely proportional to the compressive stiffness of the artery. The existence of a time-dependent water flux in an arteryin vivo during periodic pressurization is predicted by the mathematical model if the resistance to water flow at the endothelium is not excessive. The pore pressure within the bulk of the media is predicted to pulsate in a highly unexpected fashion. These predictions follow naturally from the fact that the consolidation phenomenon in large arteries, as determined by the compression tests of Harrison and Massaro, is of long duration, much longer than the period of a heartbeat. Pressure gradientsin vivo in interstitial fluid are then confined to a very small fraction of the total arterial wall thickness. A potential for plasma “sloshing” across the endothelial junctions exists. The convective flux of water across an endothelial layer may therefore be of a pulsatile character in normal arteriesin vivo.     

Allopatric distribution of juvenile red-legged banana prawns (Penaeus indicus H. Milne Edwards, 1837) and juvenile white banana prawns (Penaeus merguiensis De Man, 1888), and inferred extensive migration, in the Joseph Bonaparte Gulf, northwest Australia

During October to December 1997, we trawled estuarine habitats in the Joseph Bonaparte Gulf (JBG) to determine the distribution of juvenile red-legged banana prawns, Penaeus indicus (H. Milne Edwards, 1837) and white banana prawns, Penaeus merguiensis (de Man, 1888). We made 229 beam-trawls at 185 sites, mostly over a 100-m path (3-min duration). A Global Positioning System (GPS) receiver was used to verify our location. During October to December 1998, we intensively resampled three of the rivers that were sampled in 1997 to confirm the gulf-wide distribution of P. indicus and P. merguiensis and to investigate the microhabitat use of P. indicus. We chose previously sampled and new sites in Forsyth Creek (eastern JBG), the Lyne River (Cambridge Gulf), and the Berkeley River (western JBG). We made 249 trawls at 21 sites, mostly over 100 m.Juvenile banana prawns were abundant in eastern JBG, Cambridge Gulf and western JBG. They were not abundant in southern JBG, although fewer trawls were made there, due to its inaccessibility. In eastern JBG and Cambridge Gulf, over 96% and 73% (respectively) of juvenile banana prawns were P. indicus and they were more abundant there than in the western JBG. Conversely, in the western JBG over 93% of the juvenile banana prawns were P. merguiensis and they were more abundant than in the eastern JBG and Cambridge Gulf. The Lyne River in the northwestern Cambridge Gulf seems to be the transition zone; both P. indicus and P. merguiensis are equally abundant.P. indicus are most abundant on the mangrove-lined muddy banks of waterways within mangrove forests, similar habitats to P. merguiensis. Within these habitats, they were most abundant in gutters and small creeks, rather than rivers and large creeks. Few P. indicus or P. merguiensis were caught in 100 m² trawls undertaken midriver (on the channel bottom and on emergent banks), although these habitats may be only 100 m from the mangrove-lined habitats. In all creek and river habitats, both species are most catchable at low tide (irrespective of daylight or darkness) when they move out of the mangrove forests and accumulate in the remnant water bodies.The offshore fishery for P. indicus is in northwestern JBG in waters 50-80 m deep, about 300 and 200 km, respectively, from where juveniles are abundant in their extensive inshore habitats in east JBG and in Cambridge Gulf, demonstrating a geographical separation of the juvenile and adult phases. Postlarval P. indicus, spawned offshore, must use tides and currents to travel south and east to reach nursery habitats. Emigrant subadults must migrate north and west, across relatively shallow inshore sand substrates (30-40 m deep) to reach their offshore habitats.