Visual physiology of the Antarctic amphipod Abyssorchomene plebs

Although the visual systems of animals living in the cold, dark water of the deep sea have been investigated for some time, little is known about vision in animals inhabiting polar oceans, where temperatures are even colder and irradiance fluctuates dramatically with ice cover and season. Physiology of the compound eye of the amphipod Abyssorchomene plebs (Gammaridea: Lysianassoidea), a common Antarctic benthic scavenger, was studied electrophysiologically by electroretinography. A. plebs has a monochromatic visual system with a spectral sensitivity maximum at 487 nm, and higher sensitivity at ultraviolet wavelengths than predicted by a visual pigment template. While irradiance sensitivity determined from V/log I curves is comparable to that of mesopelagic crustaceans, temporal resolution calculated from response waveform dynamics and as determined by critical flicker fusion frequency suggest that the A. plebs eye is slower than that of crustaceans from the deep sea. A. plebs photoreceptors are physiologically adapted for a slow lifestyle in a low-light environment, where maximizing photon capture occurs at the expense of detecting fast events in the visual scene.     

INTENSITY AND CRITICAL FREQUENCY FOR VISUAL FLICKER

Using the rotating striped cylinder device previously employed for determination of the flicker response function with lower animals, corresponding measurements have been made with human observers. The curves based upon the relation between critical flash frequency and critical intensity for the signalling of the recognition of flicker have the properties of human flicker fusion data as obtained by other methods. They also have the quantitative properties of the flicker curves provided by the motor responses of insects and fishes to the seen movement of flashes. This applies to the variation found in repeated measurements as well as to the nature of the analytical function describing the connection between flash frequency and intensity. The data for human visual flicker and those for the responses of lower animals are therefore essentially homologous.     

夜行性昆虫微光视觉行为及其视觉适应机制

作为昆虫种群的重要组成部分,夜行性昆虫成功进化出了与其生存环境相适应的感觉机制,普遍认为夜行性昆虫主要依靠嗅觉和机械性感受等来探索环境,其视觉器官发生了退化或功能丧失。近年来,随着红外夜视、视网膜电位(electroretinogram, ERG)和视觉神经等生物新技术的应用,昆虫视觉生态学研究出现了突破性进展,自2002年以来陆续发现蛾类、蜜蜂和蜣螂等夜行性昆虫进化出了非凡的微光视觉(dim-light vision)能力,在夜晚(光照强度低于0.3 lx)依然可以如同在明亮的白天一样清晰、准确地感知目标物体特定的视觉特性,如明暗、颜色、形状、大小、对比度、偏振光和运动状态等,展现出视觉调控夜行性昆虫行为活动的巨大潜力。此外,这些夜行性昆虫复眼瞳孔、小眼焦距、视杆和色素颗粒等方面进化出了一些相应的形态生理特征,以提高光学灵敏度适应夜间微光环境。鉴于夜行性昆虫微光视觉行为及其视觉适应机制的研究尚处于起步阶段,仅见于少数访花昆虫或粪食性昆虫,建议加强以下几个方面的研究：(1)重大夜行性农业害虫的微光视觉及其应用的研究;(2)非典型重叠复眼的光学结构特征及其应对微光环境的适应机制研究;(3)夜行性昆虫响应微光环境的视觉适应机制研究;(4)基于夜行性昆虫微光视觉行为研发新型害虫防控技术。     

Feeding habits of alfonsino Beryx splendens

The diet of the alfonsino Beryx splendens was determined from examination of stomach contents of 287 specimens of 17 to 48 cm fork length (L_F) sampled by bottom trawl on the Chatham Rise to the east of New Zealand. Prey items were predominantly crustaceans and mesopelagic fishes. The most important prey species by mass was Sergestes spp. prawns, followed by the myctophid Lampanyctodes hectoris, and then Pasiphaea spp. prawns. Multivariate analyses indicated that small crustaceans (euphausiids and amphipods) were most important in the diet of smaller B. splendens (100–424 g, 17–26·5 cm), with larger prawn species and mesopelagic fishes most important for larger fish (425–2070 g, 27–46 cm). Moon phase and bottom temperature also explained some of the variability in diet, but the moon phase effect was difficult to explain, and the bottom temperature effect may have been confounded, to some extent, with L_F. The results indicated that B. splendens were moderately selective feeders that foraged primarily in the mesopelagic layers. The diet of New Zealand B. splendens is generally similar to those reported from other areas, i.e. dominated by mesopelagic crustaceans and fishes, and with a transition from small crustaceans to fishes with increasing predator size.     

Flicker alternating potentials in the ERGs of insects in response to two different stimuli

Summary A special pattern of the flicker is studied in insects belonging to four Orders, i. e. the differential electrical synchronised response of the eye periodically stimulated by two slightly different alternating illuminations.After having checked that the flicker in response to a regular periodical stimulation at every frequency is made up of successive equal potentials, we use two slightly different alternate flickering flashes. It is established that the alternation of two periodical stimulations of a different duration, as well as the alternation of two periodical stimulations of a different intensity, results, over a certain frequency which depends on the insect studied, in the appearance of a flicker marked with the alternation of two potentials whose difference increases at the same time as the frequency of stimulation.The dependence of this phenomenon on modulation of the light flux is described. At a given frequency of stimulation, the alternation of a high and low potential is more obvious when the modulation is lower.A particular experiment allows us to admit that the differential threshold of electrical response to two different stimulations is under 0.25%, at the frequency 100 Hz, inCalliphora erythrocephala.All the phenomena observed can be explained by a mathematical theory which considers the characteristics of the amplitude of the response to sinusoidal stimulations of various frequencies, i. e. the characteristics of the transfer function of the frequencies.     

THRESHOLD INTENSITY OF ILLUMINATION AND FLICKER FREQUENCY FOR THE EYE OF THE SUN-FISH

The sun-fish Lepomis responds to a moving system of stripes by a motion of its body. By changing the velocity of motion of the stripe system different flicker frequencies can be produced and thus the relation of flicker frequency to critical intensity of illumination can be studied. Threshold illumination varies with flicker frequency in such a way that with increasing flicker frequency the intensity of illumination must be increased to produce a threshold response in the fish. The curve of critical illumination as a function of frequency is made up of two distinct parts. For an intensity range below 0.04 millilambert and flicker frequencies below 10 per second, the rods are in function. For higher intensities and flicker frequencies above 10, the cones come into play. The maximum frequency of flicker which can be perceived by the fish''s eye is slightly above 50 per second. The flicker curve for the eye of Lepomis can easily be compared with that for the human eye. The extent of the curve for the fish is greater at low illuminations, the fish being capable of distinguishing flicker at illuminations lower than can the human eye. The transition of rod vision to cone vision occurs for the fish and for the human eye at the same intensity and flicker frequency. The maximum frequency of flicker which can be perceived is for both about the same.     

Phytophagous insect-woody sprout interactions in tropical eucalypt forest. II. Insect community structure

Abstract Sucking insects constituted 79% of all phytophagous insects collected from woody sprouts in the ground layer of a tropical eucalypt forest. Mobile insect groups such as non-psyllid Hemiptera and Orthoptera were relatively frequent in this environment compared to temperate, Eucalyptus-dominated vegetation. The high fire frequency of the tropical eucalypt forest may favour mobile insect groups. The capture of sucking insects and caterpillars peaked in dry season samples. Other patterns of abundance of phytophagous insect groups showed little consistency in their seasonal trends between host species or between vegetation types within host species. Disparities between chewing insect abundance in daytime samples and the damage chewing insects cause, may result from disproportionate consumption by large, mainly nocturnal insects, such as members of the Orthoptera. In this study, 21% of insect species were specialists on single plant species. This study suggested that insect abundance reflected the growth patterns of woody sprouts after regular burning, rather than that plant growth and development were tuned to the pressures of insect herbivory.     

Comparative study of the spectral sensitivities of mesopelagic crustaceans

The spectral sensitivities of 12 species of mesopelagic crustaceans were studied by means of electrophysiological recordings. Nine of the species are vertical migrators, while 3 are not, and 9 species possess bioluminescent organs, while 3 are not bioluminescent. All species had a single peak of spectral sensitivity with maxima between 470 nm and 500 nm. There was no apparent correlation between sensitivity maxima and daytime depth distribution, migratory behavior, or the presence or absence of bioluminescent organs. With the exception of the hyperiid amphipod Phronima sedentaria, the spectral sensitivities of these mesopelagic crustaceans demonstrate a better match for maximum sensitivity to bioluminescence than to downwelling light. Accepted: 29 June 1999     

Analysis of flicker fusion critical frequency by the iteration method

Two methods of the presentation of light stimuli for determining the flicker fusion critical frequency were compared: the classic method using a continuous increase in flicker frequency and a new iteration method in which impulses of fixed duration were presented step by step. The informative value of each method was also estimated under actual occupational conditions, where visual fatigue was estimated in users of video display terminals. Calculated values of the mean-square deviation showed that the iteration method provides a higher accuracy. This method proved to be more sensitive in studying visual fatigue.     

Mechanoreceptors in calanoid copepods: designed for high sensitivity

The mechanoreceptors of the first antennae of Pleuromamma xiphias, a mesopelagic calanoid copepod, are critical for the detection of potential threats. These receptors exceed the physiological performance of other crustacean mechanoreceptors in sensitivity to water velocities as well as in frequency response. A study of these receptors was initiated to elucidate structure–function relationships. Morphologically, the receptors resemble the arthropod scolopidial organs by the presence of a scolopale tube. However, the rigidity of the copepod receptors greatly exceeds those described for crustaceans and other arthropods. The scolopale tube completely encloses the distal dendrites and it is firmly anchored to the cuticle. Microtubules are organized in register and arise from microtubule subfibers associated with crescent-shaped rods which extend from the basal body region to the setal socket. The distal dendrites are filled with a large number of cross-linked microtubules. Termination of the distal dendrites inside the lumen of the setae is gradual with a firm anchoring to the cuticle. A likely mechanism for mechanotransduction would involve a linkage between individual microtubules and mechano-gated channels in the dendritic membrane. The rigidity probably contributes to the high frequency sensitivity, and termination of the dendrite inside the seta increases the overall sensitivity of these receptors.     

Oceanic micronektonic/macrozooplanktonic community structure and feeding in ice covered Antarctic waters during the winter (AMERIEZ 1988)

Summary Fifty-seven species of oceanic micronekton and macrozooplankton were collected under pack ice during the winter in the vicinity of the Weddell-Scotia Confluence with a modified opening-closing Tucker trawl. The majority of the 57 species did not vertically migrate and lived deeper during the winter than during the spring or fall. However, despite the short day length, several of the most common mesopelagic fish and crustaceans did migrate. Fish moved into shallower depths at night but apparently most did not continue into the near-freezing upper mixed layer, leaving that zone to the migratory crustaceans. In the upper 1000 m, the dominant species were, in order of decreasing biomass, Euphausia superba, the cnidarian Atolla wyvillei, the ctenophore Beroe sp., and the mesopelagic fish Electrona antarctica, Bathylagus antarcticus and Gymnoscopelus braueri. Thysanoessa macrura and Salpa thompsoni were biomass subdominants. The majority of the dominant species showed little seasonal differences in biomass. However, the biomass of gelatinous species varied considerably with A. wyvillei and Beroe sp. being most abundant and S. thompsoni least abundant during the winter. Incidence of food in the stomachs in several important species was low, suggesting a low impact on their Zooplankton prey. Specimens of S. thompsoni had high quantities of food in their guts but this species was uncommon so its net impact would also have been low. Euphausia superba and the three common mesopelagic fish had significantly lower stomach fullness ratings during the winter than during the fall, suggesting an overall decrease in feeding activity of dominant species during the winter.     

An assessment of pollinator visitation to Banksia spinulosa

Abstract Remote photo-monitoring of Banksia spinulosa inflorescences indicated that birds, mammals and insects were regular visitors. These included the sugar glider, brown antechinus, eastern pygmy possum, eastern spinebill, honeybee and several moth species. Eastern spine-bills were recorded at all inflorescences monitored while visitation by other animals was more sporadic. Inflorescences were visited at least once every 24 h, and visitation frequency was approximately evenly distributed during the day and night. Examination of pollen tube growth from experimental treatments indicated that pollination success was similar from both nocturnal and diurnal visitors. However, nocturnal visitors were more effective at removing pollen from newly opened flowers. The behaviour of mammals at inflorescences was such that they would transfer much more pollen to flowers than other visitors, and probably contact receptive stigmas more often. Overall, mammals were considered to be slightly more effective pollinators than the more obvious daytime visitors, eastern spinebills. Although insects visited regularly, they were thought to be less effective at pollinating flowers than vertebrate visitors. Moths carried very little pollen, and the foraging behaviour of other insects was unlikely to promote much pollination.     

The Electroretinogram of a Diurnal Gecko

Using the electroretinogram as the criterion of retinal activity the flicker fusion frequency, course of dark adaptation, and spectral sensitivity of the pure cone retina of the diurnal gecko, Phelsuma inunguis, were investigated. Both the curve relating flicker fusion frequency to stimulus intensity and that relating the amplitude of the flicker response to stimulus intensity showed a break as the intensity was increased. The dark adaptation curve was that typical of cone retinae; there was no break, adaptation was relatively rapid, and there was a total increase of sensitivity of only about 3 log units. The spectral sensitivity curve showed two maxima, a major one at about 560 mµ and another at about 460 mµ. Chromatic adaptation with red and blue lights demonstrated the presence of two independent mechanisms. Although red adaptation could not have had a direct effect on the pigment responsible for the "blue" mechanism the sensitivity of this mechanism was depressed by red adaptation. The possible relationships of the two mechanisms are discussed.     

Lower thermal tolerance in nocturnal than in diurnal ants: a challenge for nocturnal ectotherms facing global warming

1. The thermal adaptation hypothesis proposes that because thermoregulation involves a high metabolic cost, thermal limits of organisms must be locally adapted to temperatures experienced in their environments. There is evidence that tolerance to high temperatures decreases in insects inhabiting colder habitats and microclimates. However, it is not clear if thermal limits of ectotherms with contrasting temporal regimes, such as diurnal and nocturnal insects, are also adapted to temperatures associated with their circadian activities. 2. This study explores differences in heat tolerance among diurnal and nocturnal ant species in four ecosystems in Mexico: tropical montane, tropical rainforest, subtropical dry forests, and high‐elevation semi‐desert. 3. The critical thermal maximum (CT_max), i.e. the temperature at which ants lost motor control, was estimated for diurnal and nocturnal species. CT_max for 19 diurnal and 12 nocturnal ant species distributed among 45 populations was also estimated. 4. Semi‐desert and subtropical dry forest ants displayed higher tolerances to high temperatures than did ants in tropical rainforest. The lowest tolerance to high temperatures was recorded in tropical montane forest ants. In general, among all habitats, the CT_max of nocturnal ants was lower than that of diurnal ants. 5. An increase in nocturnal temperatures, combined with lower tolerance to high temperatures, may represent a substantial challenge for nocturnal ectotherms in a warming world.     

Effects of Light Adaptation on the Temporal Resolution of Deep-sea Crustaceans

The effects of light adaptation on flicker fusion frequencywere examined in the photoreceptors of 13 species of deep-seacrustaceans. Light adaptation produced a significant increasein the maximum critical flicker fusion frequency (CFF_max) in7 species—all 6 species of euphausiids in the study, and1 species of oplophorid (Group 1). This is the first exampleof an increase in temporal resolution due to light adaptationin a deep-sea species. In the other six species—2 oplophorids,1 pandalid, 1 pasiphaeid, 1 penaeid and 1 sergestid (Group 2)—lightadaptation had no effect, or resulted in a decrease in the flickerfusion frequency. The mean dark-adapted CFF_max of the Group1 species was significantly higher, and the mean response latencysignificantly lower, than those of the Group 2 species. Possibleexplanations for these differences include the activity andbioluminescence mode of preferred prey items, as well as theretention of larval/juvenile adaptations in adult eyes.     

Moon phase influences the diet of southern Ray's bream Brama australis

Diet composition of the southern Ray's bream Brama australis was examined from stomach contents of 399 specimens sampled by bottom trawl on Chatham Rise to the east of South Island, New Zealand, over 3 years. Prey items were predominantly mesopelagic fishes and crustaceans. Multivariate analysis indicated that moon phase explained more of the diet variability than any other predictor examined. It appears likely that diet composition is influenced by a combination of changes in both tidal flows and illumination. Different combinations of prey were consumed by B. australis at different times of the lunar cycle. An influence of moon phase on feeding by fishes has rarely been reported, but it is likely that moon phase influences the diets of other species that specialize in mesopelagic prey. The most important prey group by mass for B. australis was Myctophidae (primarily Lampanyctodes hectoris), followed by Stomiiformes (primarily Maurolicus australis) and shrimps (Sergestes spp). An ontogenetic shift in diet was observed, from numerical dominance by small crustaceans including amphipods and euphausiids (with some fishes) in smaller (mass <1045 g) B. australis to pelagic teleost prey (with a few larger crustaceans) in larger (>1440 g) B. australis.     

Expression of collier in the premandibular segment of myriapods: support for the traditional Atelocerata concept or a case of convergence?

Background  

A recent study on expression and function of the ortholog of the Drosophila collier (col) gene in various arthropods including insects, crustaceans and chelicerates suggested a de novo function of col in the development of the appendage-less intercalary segment of insects. However, this assumption was made on the background of the now widely-accepted Pancrustacea hypothesis that hexapods represent an in-group of the crustaceans. It was therefore assumed that the expression of col in myriapods would reflect the ancestral state like in crustaceans and chelicerates, i.e. absence from the premandibular/intercalary segment and hence no function in its formation.     

The unitary evoked potential at the frog nerve-muscle junction results from synchronous gating of fusion pores at docked vesicles

Exocytosis of a single vesicle has been proposed as the mechanism which determines quantal size by releasing a prepackaged and standard amount of acetylcholine. As first described by del Castillo and Katz (1954) the endplate potential is composed of 100 unitary events and the small variance suggests a binomial release from 100 "discrete patches of membrane". However, exocytosis of 100 vesicles selected randomly from 5000 docked vesicles would yield a variance that is 7 times greater than observed values. We propose that the presynaptic ridge with its compliment of docked vesicles functions as the "discrete patch of membrane" such that arrays of calcium activated fusion pores meter transmitter to form the unit of release. A model based on the synchronous flicker of a large number of fusion pores produces the small variance of both miniature end plate potentials and unitary end plate potentials. Release from a single locus (fusion pore) would generate the sub-MEPP. This model permits vesicle trafficking and vesicular content depletion during tetanic stimulation and explains the frequency dependency of MEPP amplitudes and changes in sub-MEPP to bell-MEPP class ratios.     

Genome size in arthropods; different roles of phylogeny,habitat and life history in insects and crustaceans

Despite the major role of genome size for physiology, ecology, and evolution, there is still mixed evidence with regard to proximate and ultimate drivers. The main causes of large genome size are proliferation of noncoding elements and/or duplication events. The relative role and interplay between these proximate causes and the evolutionary patterns shaped by phylogeny, life history traits or environment are largely unknown for the arthropods. Genome size shows a tremendous variability in this group, and it has a major impact on a range of fitness‐related parameters such as growth, metabolism, life history traits, and for many species also body size. In this study, we compared genome size in two major arthropod groups, insects and crustaceans, and related this to phylogenetic patterns and parameters affecting ambient temperature (latitude, depth, or altitude), insect developmental mode, as well as crustacean body size and habitat, for species where data were available. For the insects, the genome size is clearly phylogeny‐dependent, reflecting primarily their life history and mode of development, while for crustaceans there was a weaker association between genome size and phylogeny, suggesting life cycle strategies and habitat as more important determinants. Maximum observed latitude and depth, and their combined effect, showed positive, and possibly phylogenetic independent, correlations with genome size for crustaceans. This study illustrate the striking difference in genome sizes both between and within these two major groups of arthropods, and that while living in the cold with low developmental rates may promote large genomes in marine crustaceans, there is a multitude of proximate and ultimate drivers of genome size.     

Nectar Production of Calliandra longipedicellata (Fabaceae: Mimosoideae), an Endemic Mexican Shrub with Multiple Potential Pollinators

The nectar resource environment across which nectarivores forage may be patchy and variable. To understand the sources and consequences of such a variation, nectar production was investigated in Calliandra longipedicellata . Nectar was measured once a month throughout a 3-mo winter season in two successive years at three sites. We also conducted diurnal and nocturnal field observations to describe visitation rates of floral visitors, and a pollinator exclusion experiment to evaluate diurnal and nocturnal pollination at the three sites. In all populations, nectar secretion was primarily nocturnal, although flowers produced some nectar during the day. Sugar production per flower varied significantly at both the seasonal and population levels, although nectar production rates and a well-defined afternoon to morning production pattern were consistent across months, populations, and years. Average nectar production rates were high compared to other Calliandra species, and to most hummingbird- or hawkmoth-pollinated plants in the region. Flowers were regularly visited by hawkmoths, bats, hummingbirds and various diurnal insects, and all populations had similar rates of visitation. Nocturnal insects had the highest overall visitation rates (three times as high as those by diurnal insects). Fruit production varied among pollination treatments and populations, and significant differences were found in fruit production when flowers exposed to both diurnal and nocturnal visitation were compared to flowers exposed only to diurnal visitation. Our results and the bright-red staminal filaments of C. longipedicellata indicate lack of specialization for particular pollinators.