Comprehensive passage (COMPASS) model: a model of downstream migration and survival of juvenile salmonids through a hydropower system

Migratory fish populations are impacted worldwide by river impoundments. Efforts to restore populations will benefit from a clear understanding of survival and migration process over a wide-range of river conditions. We developed a model that estimates travel time and survival of migrating juvenile salmonids (Oncorhynchus spp.) through the impounded Snake and Columbia rivers in the northwestern United States. The model allows users to examine the effects of river management scenarios, such as manipulations of river flow and spill, on salmonid survival. It has four major components: dam passage and survival, reservoir survival, fish travel time, and hydrological processes. The probability that fish pass through specific routes at a dam and route-specific survival probabilities were based on hydroacoustic, radio telemetry, PIT tag, and acoustic tag data. We related reservoir mortality rate (per day and per km) to river flow, water temperature, and percentage of fish passing through spillways and then fit the relationships to PIT-tag survival data. We related fish migration rate to water velocity, percentage of fish passing through spillways, and date in the season. We applied the model to two threatened “Evolutionarily Significant Units” (as defined under the US Endangered Species Act): Snake River spring/summer Chinook salmon (O. tshawytscha Walbaum) and Snake River steelhead (O. mykiss Walbaum). A sensitivity analysis demonstrated that for both species survival through the hydropower system was responsive to water temperature, river flow, and spill proportion. The two species, however, exhibited different patterns in their response. Such information is crucial for managers to effectively restore migratory fish populations in regulated rivers. Guest editors: R. L. Welcomme & G. Marmulla Hydropower, Flood Control and Water Abstraction: Implications for Fish and Fisheries     

Advancing provision of multi-species fish passage: Behaviour of adult European eel (Anguilla anguilla) and brown trout (Salmo trutta) in response to accelerating flow

The behavioural response of downstream moving European eel (Anguilla anguilla) and brown trout (Salmo trutta) to velocity gradients created by orifice weirs placed in a flume were studied. The aim was to identify interspecific variation and test two hypotheses: (1) a more abrupt velocity gradient would induce a higher avoidance response and over a greater distance, and (2) fish would acclimate to the velocity gradient by incrementally sampling conditions closer to the orifice until successful passage occurred. European eel moved along the channel floor and walls, responding after physical contact with the weir. Brown trout moved downstream head first and switched orientation at the velocity gradient without contacting the structure. Brown trout spent longer than European eel immediately upstream of a channel floor orifice, although time to pass was similar; but less time at a mid-column orifice despite taking longer to pass. The mid-column orifice delayed both species longer. European eel passed orifices head first on initial encounter with no rejections, whereas brown trout passed tail first. Positions where brown trout first switched orientation and closest point to the orifice reached during initial approach occurred closer to a channel floor than mid-column treatment. Brown trout did not appear to acclimate to the velocity gradient by sampling successively closer to the orifice. Interspecific variation in behaviour remains a key challenge in developing multi-species fish passes.     

Mean flow and turbulence characteristics of a full-scale spiral corrugated culvert with implications for fish passage

A micro-acoustic Doppler velocimeter (ADV) was used to measure three-dimensional mean velocity and turbulence characteristics in a full-scale culvert with spiral corrugations. The culvert was set up in a test bed constructed to examine juvenile salmon passage success in various culvert types. The test culvert was 12.2 m long and 1.83 m in diameter and set at a 1.14% slope. The corrugations were 2.54 cm deep by 7.62 cm peak to peak with a 5° right-handed pitch. Cross-sectional grids of ADV measurements were taken at discharges of 0.028, 0.043, 0.071, 0.099, 0.113, 0.227, and 0.453 m³/s at nine locations. In the uniform flow region, the centerline velocity profiles were consistent with fully rough turbulent flows and the friction factor was independent of Reynolds number and was very close to theoretical results. Secondary flow induced by the spiral corrugations caused asymmetries in the velocity and turbulence distributions creating a reduced velocity zone (RVZ) on the right side of the culvert as seen looking upstream, which small fish could utilize to aid their upstream passage. Velocity and axial components of turbulence in the RVZ were found to be much less than in mid-channel or on the left of the culvert, and the difference became greater at increased flow rates. In addition, cross-stream and vertical velocity components within the RVZ were small relative to the downstream axial component, while lateral and vertical turbulence intensities were comparable to the axial component. Observations from a concurrent fish passage study showed that more juvenile fish migrate through the right side of the culvert within the RVZ.     

Using a baited camera to assess relative abundance of juvenile Pacific cod: Field and laboratory trials

Juvenile fishes are sometimes difficult to survey because they occur in a variety of structurally complex habitats that are not readily sampled with traditional trawl or seine gear. Laboratory experiments and field sampling were conducted to determine whether a baited-camera system could be used effectively to survey age-0 gadids. Pacific cod (Gadus macrocephalus Tilesius), saffron cod (Eleginus gracilis Tilesius), and walleye pollock (Theragra chalcogramma Pallas) all responded to bait bags presented in the laboratory, with increased general activity and approaches to the bait. Pacific cod responded most strongly, and remained in close proximity to the bait bag. In nearshore habitats of Kodiak, Alaska, age-0 gadids (mostly Pacific cod) were quickly attracted to a baited-camera system. Arrival rates stabilized within 15-min, and several metrics for Pacific cod abundance taken from the video records were closely correlated with the numbers collected in seine hauls. Highest correlations occurred with the total number of fish arriving in camera view during 15-min sets (NFA₁₅) and with the overall maximum number of fish observed at one time during the sets (MaxN_O). The time for first arrival of fish in view (TFA) was not correlated significantly with the numbers of fish in seine collections. NFA₁₅ was also useful for age-1+ saffron cod. Occasionally, the presence of large fish had a negative effect on assessments of age-0 fish, but the impact was important only when the large fish were present continuously. The baited-camera system performed equally well in seagrass, kelp and open habitats, and can be used to rapidly assess the relative abundance of Pacific cod and selected other species in a wide range of habitats in shallow and deep water.     

Patterns and some mechanisms of downstream migration of juvenile salmonids (with reference to the Utkholok and Kalkaveyem rivers in northwestern Kamchatka)

Principal patterns of the downstream migration of juvenile salmonids (Salmonidae) were discovered on the basis of data of three years of observations. It was found that the time of the beginning, the duration, and the scope of the downstream migration in each particular year are determined by a complex of environmental factors. The crucial abiotic factors are the temperature, the water level of the river, and the illumination. The biotic factors comprise the complex trophic factor. The abiotic environmental factors play the leading role in the realization of the downstream migration at the early ontogenetic stages. The role of the biotic environmental factors increases at the late ontogenetic stages. It was demonstrated that the juveniles that perform downstream migrations are a heterogeneous group consisting of fish of different species and specimens at different ontogenetic stages, of various sizes and ages, and those ready for the transition to the marine environment to variable degrees. The analysis of the patterns of the downstream migration allowed us to describe some mechanisms that control the realization of this process.     

Assessment of a retrofitted downstream fish bypass system for wild Atlantic salmon (<Emphasis Type="Italic">Salmo salar</Emphasis>) smolts and kelts at a hydroelectric facility on the Exploits River,Newfoundland, Canada

In 2002 and 2003, the Bishops Falls hydroelectric generating facility on the Exploits River, insular Newfoundland, Canada, underwent extensive refurbishing including replacement of turbines and installation of a ‘retrofitted’ bypass and fish handling system. The effectiveness of this new bypass system has been assessed during the annual downstream run of wild Atlantic salmon smolt and kelt in 2003 and 2004. In 2003, 195 smolt were radio tagged and released between June 9 and July 2, in the forebay of the hydro plant (19 releases) and one upstream (in-river) release. Fish guidance efficiency (FGE) of the system overall was 63% (123 of 195 fish) with 36 fish passing through the turbines, and six known mortalities. In 2004, between June 9 and July 2, a total of 358 smolt and 103 kelt were released in the forebay in 45 and 13 releases (n = 8 per release), respectively. The FGE of the system for smolt was 71.7% (257 of 358 fish) and for kelt was 92.3% (95 of 103 fish). In 2004, 96 tagged smolt passed through the turbines and 43 (44.8%) were detected at a downstream station confirming they had survived turbine passage, suggesting an overall survival of smolt passage of the Bishops Falls hydro facility in the order of 85%. A total of seven kelts (6.8%) passed through the turbines and were not detected 1.5 km downstream suggesting they did not survive turbine passage. Smolt spent on average 39.8 h in the forebay before exiting in 2003 and forebay residency averaged 26 h in 2004. In both years, most smolt selected their passage route, actively or passively, within the first 10 h with secondary peaks at 25–30 h and 50–55 h, corresponding to evening passage in the second and third night, after release. Few smolt were bypassed or entrained into turbines during daylight hours. In both years turbine passed smolt spent more time in the forebay suggesting the longer fish reside in the forebay the greater the likelihood of turbine entrainment. Kelt were either bypassed or turbine entrained relatively quickly, within 2 h of release, and virtually all kelts were bypassed/turbine entrained during the hours of 18:00 and 01:00. These data on fish behaviour and residency in the forebay will assist further refinement of operations of the bypass facility to optimize survival.     

Expression, purification, and in vitro characterization of recombinant salmon insulin-like growth factor-II

The insulin-like growth factors, IGF-I and IGF-II, are single chain polypeptides, which are structurally related to proinsulin and promote proliferation and differentiation of cells in many vertebrate species. Previous attempts to produce recombinant salmon IGF-II (rsIGF-II) were compromised by low expression levels and co-purification of incorrectly cleaved protein with the authentic recombinant product. In this study, a gene containing the coding region for Atlantic salmon (Salmo salar) IGF-II was cloned into a modified pET32a expression vector and transformed into Escherichia coli BL21 trxB (DE3) cells. Upon growth and induction (with IPTG) of the transformant, recombinant salmon IGF-II (rsIGF-II) was expressed as an insoluble, 28kDa thioredoxin.sIGF-II fusion protein linked by a protease cleavage motif (trx.FAHY.sIGF-II) in inclusion bodies. The inclusion bodies were subsequently solubilized and the fusion protein was purified by Ni-affinity chromatography. Recombinant IGF-II (7.8kDa) was then released from the fusion partner using H64A subtilisin BPN' protease and purified by reversed-phase HPLC. Homogeneity of the final recombinant product was confirmed by N-terminal amino acid sequencing, ion-spray mass spectrometry, SDS-polyacrylamide gel electrophoresis, and analytical reversed-phase HPLC. The biological activity of rsIGF-II was demonstrated in cultured rat L6 myoblasts and was found to be approximately 9- and 5-fold less potent than recombinant human IGF-I and recombinant salmon IGF-I, respectively, a result similar to that demonstrated previously with other recombinant fish IGF-II's in non-homologous cell lines.     

Chemical composition and theoretical nutritional evaluation of the produced fractions from enzymic hydrolysis of salmon frames with Protamex™

An amount of 200 kg fresh salmon frames were enzymic hydrolysed with the commercial protease mixture Protamex™, which is known to produce non-bitter hydrolysates. After the enzymic procedure the frames were separated by centrifugation into five fractions: an aqueous fraction rich in peptides, an insoluble fraction, an emulsion fraction, salmon oil and a bone fraction. Approximately 48% of total crude protein present in the salmon frames were found in the aqueous fraction, in which the lipid content was reduced to <0.1% in dry samples after ultramembrane filtration (UF fraction). The UF fraction was low in tryptophan, leucine and phenylalanine+tyrosine, but high in taurine. Nearly 19% of total crude protein present in the salmon frames were found in the insoluble fraction. This fraction was high in most of the indispensable amino acids. Approximately 77% of total lipids present in the salmon frames were isolated as salmon oil, which was high in both eicosapentaenic acid (EPA) and docosahexaenic acid (DHA). The bone fraction contained 62% of total ash present in the salmon frames and was high in the minerals Ca, P and Mg and also in the trace elements Cu, Fe, I, Mn, Se and Zn. All of the produced fractions were low in the undesirable substances As, Cd, Hg and Pb. For future studies the UF fraction and salmon oil might be interesting as health promoting agents, the insoluble fraction as dietary protein supplement and the bone fraction as dietary mineral supplement.     

Numerical flow simulation of pool-type fishways: new ways with well-known tools

Fish passage structures are built to restore the connectivity of rivers and allow the migration of aquatic fauna. In order to assess the functioning of a pool-type fishway, it is necessary, inter alia, to possess detailed knowledge of its flow structure, since observations of fishways, and in particular of the visible water surface, can only provide a rough idea of the actual conditions inside the pools. Numerical simulation has been used for many years to support engineering sciences. Especially, the modeling of flow processes in hydraulic machines can, on the one hand, help avoid major problems during the design stage of fish passage structures and, on the other, improve the structure’s hydraulic performance. To this end, two diploma theses within the framework of a research project of the local energy supplier Energie Baden-Württemberg AG (EnBW) employed modeling tools for 3D flow simulation, primarily for pool-slot fishways (PSF), and for traditional vertical slot fishways (VSF). Guest editors: R. L. Welcomme & G. Marmulla Hydropower, Flood Control and Water Abstraction: Implications for Fish and Fisheries     

The Visually Mediated Escape Response in Fish: Predicting Prey Responsiveness and the Locomotor Behaviour of Predators and Prey

The outcome of predator-prey encounters is determined by a number of factors related to the locomotor and sensory performance of the animals. Escape responses can be triggered visually, i.e. by the magnifying retinal image of an approaching object (i.e. a predator), called the looming effect, and calculated as the rate of change of the angle subtended by the predator frontal profile as seen by the prey. A threshold of looming angle (ALT, the Apparent Looming Threshold) determines the reaction distance of a startled fish, which is proportional to the attack speed of the predator and its apparent frontal profile. Optimal tactics for predator attacks as well as consideration on their functional morphology are discussed in relation to ALT. Predator optimal attack speeds depend on predator morphology as well as the prey ALT. Predictions on the scaling of ALT suggest that ALT may increase (i.e. implying a decrease in reaction distance) with prey size in cases in which predator attack speeds are high (i.e. > 4 L/s in a 1-m long predator), while it may be relatively independent of prey size when predators attack at lower speeds. The issue of scaling of ALT is discussed using examples from field and laboratory studies. While the timing of the escape is a crucial issue for avoiding being preyed upon, the direction of escape manoeuvres may also determine the success of the escape. A simple theoretical framework for optimal escape trajectories is presented here and compared with existing data on escape trajectories of fish reacting to startling stimuli.     

Ion homeostasis and interrenal stress responses in juvenile Pacific herring, Clupea pallasi, exposed to the water-soluble fraction of crude oil

Juvenile Pacific herring, Clupea pallasi, were exposed both acutely (96 h) and chronically (9 weeks) to three concentrations of the water-soluble fraction (WSF) of North Slope crude oil. Mean (± S.E.) total PAH (TPAH) concentrations at the beginning of the acute exposure experiment were: 9.7 ± 6.5, 37.9 ± 8.6 and 99.3 ± 5.6 μg/L. TPAH concentrations declined with time and the composition of the WSF shifted toward larger and more substituted PAHs. Significant induction of hepatic cytochrome P450 content, ethoxyresorufin O-deethylase and glutathione-S-transferase activities in WSF-exposed fish indicated that hydrocarbons were biologically available to herring. Significant but temporary, elevations in plasma cortisol (4.9-fold and 8.5-fold increase over controls in the 40 and 100 μg/L groups, respectively), lactate (2.2-fold and 3.1-fold over controls in the 40 and 100 μg/L groups) and glucose (1.3-fold, 1.4-fold and 1.6-fold over controls in the 10, 40 and 100 μg/L groups) occurred in fish exposed acutely to WSF. All values returned to baseline levels by 96 h. Similar responses were seen with the first of several sequential WSF pulses in the chronic exposure study. Subsequent WSF pulses resulted in muted cortisol responses and fewer significant elevations in both plasma lactate and glucose concentrations. Hematocrit, leucocrit, hemoglobin concentration and liver glycogen content were not affected by acute or chronic WSF exposure. Plasma [Cl⁻], [Na⁺] and [K⁺] were significantly higher in the 100 μg/L WSF-exposed group by 96 h compared to control fish, and continued to be elevated through the entire chronic exposure period. Unlike the measured stress parameters, ionoregulatory dysfunction was not modulated by WSF pulses. The results of this study suggest that chronic exposure to WSF affects at least two important physiological systems in herring: the ability of fish to maintain ion homeostasis and the interrenally-mediated organismal stress response.     

Response of dugongs to boat traffic: The risk of disturbance and displacement

Disturbance from boats has been documented for many species of marine mammals, especially cetaceans, but has never been quantified for dugongs. Dugongs depend on seagrass for food. This food mostly occurs in shallow coastal areas where boat traffic is high. Thus there is potential for boats to alienate dugongs from critical habitat areas. Using an overhead video observation system (‘blimp-cam’), we observed the behaviour of focal dugongs during controlled boat pass experiments and while no boats were present. The percentage of time focal dugongs spent feeding and travelling was unaffected by boat presence, the number of boat passes and whether a pass included a stop and restart (pass continuity). The duration, distance and direction of a focal dugong's subsurface behaviour were unaffected by number, continuity or distance of boat passes. However, focal dugongs were less likely to continue feeding if the boat passed within 50 m, than if the boat passed at a greater distance. Mass movements of dugong feeding herds in response to experimental and opportunistically observed boats were timed on 42 occasions but only lasted an average of 122 s. These movements occurred in response to boats passing at a range of speeds, and at distances of less than 50 m to over 500 m. The levels of boat traffic we observed may reduce dugongs' feeding time budget by a maximum of 0.8-6%. Thus at present boats appear unlikely to be having a substantive effect on the energy intake of dugong populations at our study site on the Moreton Banks near Brisbane, Australia. However, boat traffic is likely to increase in this fast growing region, raising concern about the future impact of boats on this and other dugong populations.     

A description of ammonium content of output waters from trout farms in relation to stocking density and flow rates

Daily levels of ammonium content in the outflow water of an intensive trout farm and of a mountain pond stocked with rainbow trout were monitored. Output water was sampled for 30 days and analysed every 30 min by an automatic ion selective electrode system (Applikon ADI 2013); input water was also monitored. The ammonium output level was influenced more by atmospheric events than nitrogen excretion by fish. Observed data confirmed an overall ammonium excretion model previously estimated in both laboratory and field conditions. The high water flow, that characterises the intensive trout farm where the observations were made induced a high dilution of metabolites. Consequently, if the peaks of ammonium output did not reach values of 0.35–0.40 mg l⁻¹ the environmental impact was limited and not easily detected. Our results allow us to affirm that the optimal level of water flow rate for effective zeolite-operated filtration is around 10.3 l t⁻¹ s⁻¹.     

Behavioural responses of juvenile Steller sea lions to abdominal surgery: Developing an assessment of post-operative pain

Marking and tracking of marine mammals is required to gain a better understanding of life history traits; however, some marking procedures used are likely painful. Recent technological advances include intra-abdominally implanted archival telemetry devices for the life-long monitoring of individual animals. No research to date has assessed any aspect of post-operative pain in marine mammals. This study specifically evaluated behavioural responses in nine juvenile Steller sea lions to the abdominal surgery required for insertion of telemetry devices. Behaviours predicted to reflect post-operative pain, including posture and body movements, were assessed during 3-day pre-, 3-day post-, and days 10–12 post-surgery. The proportion of time sea lions spent on land standing increased from 0.00 to 0.07 and then decreased to 0.04, for pre-, post-, and late post-surgery respectively. Similarly, the proportion of land time spent with the back arched increased from 0.01 to 0.57, and then decreased to 0.33. The time sea lions spent on land with pressure on their ventral side while sitting or lying down declined from 1.0 pre-surgery to 0.17 post-surgery, and increased to 0.20 late post-surgery. The time sea lions spent in locomotion on land and in the water decreased from 0.05 in pre-surgery to 0.01 post-surgery, and returned to 0.06 by late post-surgery. These results suggest that behaviours such as back arch, standing, time spent with pressure on the ventral side, and locomotion may be useful in the assessment of pain following abdominal surgery in sea lions. The presence of these behaviours and their persistence for up to 12 days after surgery suggest that more work is required to further develop safe and effective analgesic methods for this procedure.     

Isolation and characterization of acidic glycosphingolipids from the gill of the Pacific Salmon (Oncorhynchus keta): A novel hybrid-type ganglioside with isoglobo- and neolacto-Series

Monosialosyl gangliosides and sulfoglycolipids in the gill of pacific salmon, Oncorhynchus keta, have been prepared by solvent extraction and DEAE-Sephadex column chromatography. Acidic glycolipid bands (M1-M13) detected by thin layer chromatography were separated by Iatrobeads column chromatography and 13 components were characterized by TLC, compositional analysis, methylation analysis, chemical and enzymatic degradation, liquid secondary ion mass spectrometry and (1)H nuclear magnetic resonance spectroscopy. In addition to the acidic glycolipids with known structures (SM4s, SM3, GM3, LM1, GM1b and V(3)alphaFuc,IV(3)betaGalNAc-GM1a), two fractions (M11 and M13) of unknown monosialosyl gangliosides with TLC mobility slower than GM1a were isolated and characterized as having the following structure with a hybrid of isoglobo- and neolacto-series. [formula: see text] Analysis of fatty acid indicated predominance of C24:1 fatty acid in the upper band (M11) and shorter chain saturated fatty acids in the lower band (M13). The tissue concentrations of M11 and M13 were 1.15 and 0.96 mumol/kg wet weight, respectively.     

Reduction of predation risk under the cover of darkness: Avoidance responses of mayfly larvae to a benthic fish

Summary Mayfly larvae of Paraleptophlebia heteronea (McDunnough) had two antipredator responses to a nocturnal fish predator (Rhinichthys cataractae (Valenciennes)): flight into the drift and retreat into interstitial crevices. Drift rates of Paraleptophlebia abruptly increased by 30 fold when fish were actively foraging in the laboratory streams but, even before fish were removed, drift began returning to control levels because larvae settled to the substrate and moved to areas of low risk beneath stones. This drifting response was used as an immediate escape behavior which likely decreases risk of capture from predators which forage actively at night. Surprisingly, drift most often occurred before contact between predator and prey, and we suggest that in darkness this mayfly may use hydrodynamic pressure waves for predator detection, rather than chemical cues, since fish forage in an upstream direction. Although drifting may represent a cost to mayfly larvae in terms of relocation to a new foraging area with unknown food resources, the immediate mortality risk probably out-weighs the importance of staying within a profitable food patch because larvae can survive starvation for at least 2 d. In addition to drifting, mayflies retreated from upper, exposed substrate surfaces to concealed interstitial crevices immediately after a predator encounter, or subsequent to resettlement on the substrate after predator-induced drift. A latency period was associated with this response and mayflies remained in these concealed locations for at least 3 h after dace foraging ceased. Because this mayfly feeds at night and food levels are significantly lower in field refugia under stones, relative to exposed stone surfaces, predator avoidance activity may limit foraging time and, ultimately, reduce the food intake of this stream mayfly.     

Oxygen consumption and blood flow distribution in perfused skeletal muscle of chinook salmon

An isolated, perfused salmon tail preparation showed oxyconformance at low oxygen delivery rates. Addition of pig red blood cells to the perfusing solution at a haematocrit of 5 or 10% allowed the tail tissues to oxyregulate. Below ca. 60 ml O₂ kg⁻¹ h⁻¹ of oxygen delivery (DO₂), VO₂ was delivery dependent. Above this value additional oxygen delivery did not increase VO₂ of resting muscle above ca. 35 ml O₂ kg⁻¹ h⁻¹. Following electrical stimulation, VO₂ increased to ca. 65 ml O₂ kg⁻¹ h⁻¹, with a critical DO₂ of ca. 150 ml O₂ kg⁻¹ h⁻¹. Dorsal aortic pressure fell to 69% of the pre-stimulation value after 5 min of stimulation and to 54% after 10 min. Microspheres were used to determine blood flow distribution (BFD) to red (RM) and white muscle (WM) within the perfused myotome. Mass specific BFD ratio at rest was found to be 4.03 ± 0.49 (RM:WM). After 5 min of electrical stimulation the ratio did not change. Perfusion with saline containing the tetrazolium salt 3-(4,5-Dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) revealed significantly more mitochondrial activity in RM. Formazan production from MTT was directly proportional to time of perfusion in both red and WM. The mitochondrial activity ratio (RM:WM) did not change over 90 min of perfusion.     

Responses of blowfly motion-sensitive neurons to reconstructed optic flow along outdoor flight paths

The retinal image flow a blowfly experiences in its daily life on the wing is determined by both the structure of the environment and the animal’s own movements. To understand the design of visual processing mechanisms, there is thus a need to analyse the performance of neurons under natural operating conditions. To this end, we recorded flight paths of flies outdoors and reconstructed what they had seen, by moving a panoramic camera along exactly the same paths. The reconstructed image sequences were later replayed on a fast, panoramic flight simulator to identified, motion sensitive neurons of the so-called horizontal system (HS) in the lobula plate of the blowfly, which are assumed to extract self-motion parameters from optic flow. We show that under real life conditions HS-cells not only encode information about self-rotation, but are also sensitive to translational optic flow and, thus, indirectly signal information about the depth structure of the environment. These properties do not require an elaboration of the known model of these neurons, because the natural optic flow sequences generate—at least qualitatively—the same depth-related response properties when used as input to a computational HS-cell model and to real neurons.     

Response of bee-flies to the shape and pattern of model flowers: implications for floral evolution in a Mediterranean herb

1. The functional significance of floral traits in Linum pubescens (Linaceae), a Mediterranean annual that is pollinated almost exclusively by the bee-fly Usia bicolor (Bombyliidae), was investigated. The flies feed on both pollen and nectar, and use the flowers as mating rendezvous sites in the afternoon.
2. Choice experiments with model flowers were used to determine the response of U. bicolor to visual cues, such as shape, size, colour and pattern.
3. Bee-flies strongly preferred models with a dissected outline over models with a simple outline. They also preferred pink models over other colours, and larger models over smaller models.
5. Flies landing on models with converging lines ('nectar guides') tended to follow the lines to the point where they meet in the centre of the model, while flies landing on plain models showed undirected behaviour, often moving to the edge of the model.
6. Flies were strongly attracted to flowers of L. pubescens which had a fly glued on to one of the petals, as well as flowers with a dark spot painted onto one of the petals. In addition, models with a dark spot were strongly preferred over plain models during the afternoon when flies exhibit mating behaviour. This evidence suggests that the dark centre of the L. pubescens flower may function as an attractant to mate-seeking bee-flies.