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1.
Summary The superposition eye of the cockchafer, Melolontha melolontha, exhibits the typical features of many nocturnal and crepuscular scarabaeid beetles: the dioptric apparatus of each ommatidium consists of a thick corneal lens with a strong inner convexity attached to a crystalline cone, that is surrounded by two primary and 9–11 secondary pigment cells. The clear zone contains the unpigmented extensions of the secondary pigment cells, which surround the cell bodies of seven retinula (receptor) cells per ommatidium and a retinular tract formed by them. The seven-lobed fused rhabdoms are composed by the rhabdomeres of the receptor cells 1–7. The rhabdoms are optically separated from each other by a tracheal sheath around the retinulae. The orientation of the microvilli diverges in a fan-like fashion within each rhabdomere. The proximally situated retinula cell 8 does not form a rhabdomere. This standard form of ommatidium stands in contrast to another type of ommatidium found in the dorsal rim area of the eye. The dorsal rim ommatidia are characterized by the following anatomical specializations: (1) The corneal lenses are not clear but contain light-scattering, bubble-like inclusions. (2) The rhabdom length is increased approximately by a factor of two. (3) The rhabdoms have unlobed shapes. (4) Within each rhabdomere the microvilli are parallel to each other. The microvilli of receptor 1 are oriented 90° to those of receptors 2–7. (5) The tracheal sheaths around the retinulae are missing. These findings indicate that the photoreceptors of the dorsal rim area are strongly polarization sensitive and have large visual fields. In the dorsal rim ommatidia of other insects, functionally similar anatomical specializations have been found. In these species, the dorsal rim area of the eye was demonstrated to be the eye region that is responsible for the detection of polarized light. We suggest that the dorsal rim area of the cockchafer eye subserves the same function and that the beetles use the polarization pattern of the sky for orientation during their migrations. 相似文献
2.
Polarization sensitivity in arthropod photoreceptors is crucially dependent on the arrangement of the microvilli within the rhabdom. Here, we present an electron-microscopical study in which the degree of microvillar alignment and changes in the cross-sectional areas of the rhabdoms along their length were studied in the compound eye of the desert ant, Cataglyphis bicolor. Serial cross-sections through the retina were taken and the orientation of the microvilli was determined in the photoreceptors of individually identified ommatidia. The reconstructions of microvillar alignment were made in the three anatomically and functionally distinct regions of the Cataglyphis compound eye: the dorsal rim area (DRA), the dorsal area (DA), and the ventral area (VA). The following morphological findings are consistent with polarization sensitivities measured previously by intracellular recordings. (1) The microvilli of the DRA photoreceptors are aligned in parallel along the entire length of the cell from the distal tip of the rhabdom down to its proximal end, near the basement membrane. The microvilli of the retinular cells R1 and R5 are always parallel to each other and perfectly perpendicular, with only minor deviation, to the microvillar orientation of the remaining receptor cells. (2) In the DA and VA regions of the eye, the microvillar tufts of the small receptors R1, R3, R5, R7, and R9 change their direction repetitively every 1-4 7m for up to 90°. In contrast, the large receptor cells R2, R4, R6, and R8 maintain their microvillar orientation rigidly. (3) In the DRA ommatidia, the cross-sectional areas of the rhabdomeres do not change along the length of the rhabdom, but substantial changes occur in the DA and VA ommatidia. 相似文献
3.
Specialized ommatidia of the polarization-sensitive dorsal rim area in the eye of monarch butterflies have non-functional reflecting tapeta 总被引:1,自引:0,他引:1
Many insects exploit sky light polarization for navigation or cruising-course control. The detection of polarized sky light
is mediated by the ommatidia of a small specialized part of the compound eye: the dorsal rim area (DRA). We describe the morphology
and fine structure of the DRA in monarch butterflies (Danaus plexippus). The DRA consists of approximately 100 ommatidia forming a narrow ribbon along the dorsal eye margin. Each ommatidium contains
two types of photoreceptor with mutually orthogonal microvilli orientations occurring in a 2:6 ratio. Within each rhabdomere,
the microvilli are well aligned. Rhabdom structure and orientation remain constant at all retinal levels, but the rhabdom
profiles, as seen in tangential sections through the DRA, change their orientations in a fan-like fashion from the frontal
to the caudal end of the DRA. Whereas these properties (two microvillar orientations per rhabdom, microvillar alignment along
rhabdomeres, ommatidial fan array) are typical for insect DRAs in general, we also report and discuss here a novel feature.
The ommatidia of monarch butterflies are equipped with reflecting tapeta, which are directly connected to the proximal ends
of the rhabdoms. Although tapeta are also present in the DRA, they are separated from the rhabdoms by a space of approximately
55 μm effectively inactivating them. This reduces self-screening effects, keeping polarization sensitivity of all photoreceptors
of the DRA ommatidia both high and approximately equal. 相似文献
4.
Sonja Kleinlogel N. Justin Marshall 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2009,195(12):1153-1162
The ommatidia of crustacean eyes typically contain two classes of photoreceptors with orthogonally oriented microvilli. These
receptors provide the basis for two-channel polarisation vision in the blue–green spectrum. The retinae of gonodactyloid stomatopod
crustaceans possess a great variety of structural specialisations for elaborate polarisation vision. One type of specialisation
is found in the small, distally placed R8 cells within the two most ventral rows of the mid-band. These ultraviolet-sensitive
photoreceptors produce parallel microvilli, a feature suggestive for polarisation-sensitive photoreceptors. Here, we show
by means of intracellular recordings combined with dye-injections that in the gonodactyloid species Odontodactylus scyllarus, the R8 cells of mid-band rows 5 and 6 are sensitive to linear polarised ultraviolet light. We show that mid-band row 5 R8
cells respond maximally to light with an e-vector oriented parallel to the mid-band, whereas mid-band row 6 R8 cells respond maximally to light with an e-vector oriented
perpendicular to the mid-band. This orthogonal arrangement of ultraviolet-sensitive receptor cells could support ultraviolet
polarisation vision. R8 cells of rows 5 and 6 are known to act as quarter-wave retarders around 500 nm and thus are the first
photoreceptor type described with a potential dual role in polarisation vision. 相似文献
5.
Roger D. Santer Eileen A. Hebets 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2009,195(4):393-399
The ability of animals to learn and remember underpins many behavioural actions and can be crucial for survival in certain
contexts, for example in finding and recognising a habitual refuge. The sensory cues that an animal learns in such situations
are to an extent determined by its own sensory specialisations. Whip spiders (Arachnida, Amblypygi) are nocturnal and possess
uniquely specialised sensory systems that include elongated ‘antenniform’ forelegs specialised for use as chemo- and mechanosensory
feelers. We tested the tactile learning abilities of the whip spider Phrynus marginemaculatus in a maze learning task with two tactile cues of different texture—one associated with an accessible refuge, and the other
with an inaccessible refuge. Over ten training trials, whip spiders got faster and more accurate at finding the accessible
refuge. During a subsequent test trial where both refuges were inaccessible, whip spiders searched for significantly longer
at the tactile cue previously associated with the accessible refuge. Using high-speed cinematography, we describe three distinct
antenniform leg movements used by whip spiders during tactile examination. We discuss the potential importance of tactile
learning in whip spider behaviour and a possible role for their unique giant sensory neurons in accessing tactile information. 相似文献
6.
M. Blum T. Labhart 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2000,186(2):119-128
We made intracellular recordings from the photoreceptors of the polarisation-sensitive dorsal rim area of the cricket compound
eye combined with dye marking. By measuring visual field sizes and optical axes in different parts of the dorsal rim area,
we assessed the optical properties of the ommatidia. Due to the large angular sensitivities (median about 20°) and the high
sampling frequency (about 1 per degree), the visual fields overlap extensively, such that a given portion of the sky is viewed
simultaneously by a large number of ommatidia. By comparing the dye markings in the retina and in the optic lobe, the axon
projections of the retinula cells were examined. Receptors R1, R2, R5 and R6 project to the lamina, whereas R7 projects to
the medulla. The microvilli orientation of the two projection types differ by 90° indicating the two analyser channels that
give antagonistic input to polarisation-sensitive interneurons. Using the retinal marking pattern as an indicator for the
quality of the intracellular recordings, the polarisation sensitivity of the photoreceptors was re-examined. The polarisation
sensitivity of recordings from dye-coupled cells was much lower (median: 4.5) than that of recordings in which only one cell
was marked (median: 9.8), indicating that artefactual electrical coupling between photoreceptors can significantly deteriorate
polarisation sensitivity. The physiological value of polarisation sensitivity in the cricket dorsal rim area is thus typically
about 10.
Accepted: 4 November 1999 相似文献
7.
Mizuki Uemura Andrej Megli
Myron P. Zalucki Andrea Battisti Gregor Belui
《Biology letters》2021,17(2)
Processionary caterpillars of Thaumetopoea pityocampa (in Europe) and Ochrogaster lunifer (in Australia) (Lepidoptera: Notodontidae) form single files of larvae crawling head-to-tail when moving to feeding and pupation sites. We investigated if the processions are guided by polarization vision. The heading orientation of processions could be manipulated with linear polarizing filters held above the leading caterpillar. Exposure to changes in the angle of polarization around the caterpillars resulted in corresponding changes in heading angles. Anatomical analysis indicated specializations for polarization vision of stemma I in both species. Stemma I has a rhabdom with orthogonal and aligned microvilli, and an opaque and rugged surface, which are optimizations for skylight polarization vision, similar to the dorsal rim of adult insects. Stemmata II-VI have a smooth and shiny surface and lobed rhabdoms with non-orthogonal and non-aligned microvilli; they are thus optimized for general vision with minimal polarization sensitivity. Behavioural and anatomical evidence reveal that polarized light cues are important for larval orientation and can be robustly detected with a simple visual system. 相似文献
8.
Margit Schweigkofler T. Bartolomaeus Luitfried von Salvini-Plawen 《Zoomorphology》1998,118(2):117-128
The hooded hooks of Capitella capitata are aligned in a transverse row inside each neuro- and notopodial rim of the last thoracic and all abdominal setigers. Each
seta consists of a rostrum, a capitium, the spines of which surmount the rostrum, and a long, sigmoid shaft or manubrium,
towards which rostrum and capitial spines are curved. A thin hood, complete except for a subapical opening and a short, subrostral
cleft, encloses the apical portions of the seta. Generally, the tip of the rostrum extends beyond the hood. The hood consists
of an outer and an inner lamella, between which is a compartment loosely filled with fibrillar material. Hooded hooks are
generated at the dorsal edge of the neuropodial rim and at the ventral edge of the notopodial rim during the entire life of
C. capitata. Chaetogenesis starts in a small compartment surrounded by the basal chaetoblast and four follicle cells. Initially a group
of microvilli emanating from the chaetoblast preforms the rostrum. Next, stout microvilli appear adrostrally, each preforming
a spine of the capitium. When both structures have been formed, the longitudinal axis of the anlage shifts, because the actin
filaments inside the microvilli reorientate and initiate formation of the manubrium. During this initial phase of chaetogenesis
the anlage sinks into the chaetoblast, until the latter finally enwraps the anlage, except the tip of the rostrum. The chaetoblast
now generates microvilli that face the new setal structures and preform the hood. During further development the microvilli
separate into two layers, an inner and an outer one. The inner layer of microvilli merges with the manubrium prior to the
outer layer. Addition of setal material occurs between the bases of the microvilli and elongates the manubrium until it extends
beyond the epidermal surface. The microvilli, which have continuously been withdrawn from the seta during chaetogenesis, remain
in the basal section. Specific morphogenetic and structural correspondence between the hooked setae of species of Maldanomorpha,
Psammodrilida and Oweniida, the uncini of species of the Sabellida, Terebellida and Pogonophora, and the hooded hooks of species
of Capitellidae justify the hypothesis that all these setae are homologous. This hypothesis implies the existence of a monophyletic
group consisting of all polychaetous Annelida with such setae.
Accepted: 16 December 1997 相似文献
9.
G. C. Grigg L. A. Beard T. Moulton M. T. Queirol Melo L. E. Taplin 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(6):445-452
The broad-snouted caiman Caiman latirostris, of South America mostly frequents freshwater but occurs also in estuaries. Nothing of substance is known of its osmoregulatory
physiology but, in the light of accumulating evidence that alligatorids lack specialised adaptations for life in hyperosmotic
waters, we anticipated its physiology would be more similar to that of Alligator mississippiensis than the euryhaline Crocodylus porosus, which has both lingual salt glands and a more complex renal:cloacal system. This proved to be the case. Caiman captured
in estuaries of the Ilha do Cardoso in southern Brazil were effective hypo-osmotic osmoregulators in salinities of 0–24 ppt
(seawater = 35 ppt). Plasma osmolarity, sodium and chloride were similar to those in other crocodilians and not influenced
by salinity. Plasma urea was low and did not vary with salinity. We found no evidence of lingual or other salt glands. Urinary
electrolyte concentrations varied considerably with salinity and in ways reminiscent of A. mississippiensis but very different from C. porosus.
Ca. latirostris dehydrated in seawater more rapidly than C. porosus and had substantially higher integumental permeability to water. Caiman did not drink seawater but rehydrated rapidly when
returned to freshwater (FW). We found small caiman (<500 g) only in very low salinities (<3 ppt) and larger caiman closer
to the sea. We postulate that medium to large Ca. latirostris can take advantage of the feeding opportunities presented by the estuarine mangal despite lacking the physiological specialisations
of crocodylids. Two individuals which we re-sighted by chance had travelled at least 600 m in 2–3 days, showing that every
caiman we captured or saw was within easy reach of FW. Most likely their habitation of the estuary and its mangal is achieved
through a combination of low surface area:volume ratio, relatively impermeable skin, and periodic access to FW.
Accepted: 11 May 1998 相似文献
10.
Ultrastructure and orientation of ommatidia in the dorsal rim area of the locust compound eye 总被引:1,自引:0,他引:1
In many insect species, a dorsal rim area (DRA) in the compound eye is adapted to analyze the sky polarization pattern for compass orientation. In the desert locust Schistocerca gregaria, these specializations are particularly striking. The DRA of the locust consists of about 400 ommatidia. The facets have an irregular shape, and pore canals are often present in the corneae. Screening pigment is missing in the region of the dioptric apparatus suggesting large receptive fields. The rhabdoms are shorter, but about four times larger in cross-section than the rhabdoms of ordinary ommatida. Eight retinula cells contribute to the rhabdom. The microvilli of retinula cell 7 and of cells 1, 2, 5, 6, 8 are highly aligned throughout the rhabdom and form two blocks of orthogonal orientation. The microvilli in the minute rhabdomeres of retinula cells 3 and 4, in contrast, show no particular alignment. As in other insect species, microvillar orientations are arranged in a fan-like pattern across the DRA. Photoreceptor axons project to distinct areas in the dorsal lamina and medulla. The morphological specializations in the DRA of the locust eye most likely maximize the polarization sensitivity and suggest that the locust uses this eye region for analysis of the sky polarization pattern. 相似文献
11.
Ajay Narendra Ali Alkaladi Chloé A. Raderschall Simon K. A. Robson Willi A. Ribi 《PloS one》2013,8(10)
The Australian intertidal ant, Polyrhachis sokolova lives in mudflat habitats and nests at the base of mangroves. They are solitary foraging ants that rely on visual cues. The ants are active during low tides at both day and night and thus experience a wide range of light intensities. We here ask the extent to which the compound eyes of P. sokolova reflect the fact that they operate during both day and night. The ants have typical apposition compound eyes with 596 ommatidia per eye and an interommatidial angle of 6.0°. We find the ants have developed large lenses (33 µm in diameter) and wide rhabdoms (5 µm in diameter) to make their eyes highly sensitive to low light conditions. To be active at bright light conditions, the ants have developed an extreme pupillary mechanism during which the primary pigment cells constrict the crystalline cone to form a narrow tract of 0.5 µm wide and 16 µm long. This pupillary mechanism protects the photoreceptors from bright light, making the eyes less sensitive during the day. The dorsal rim area of their compound eye has specialised photoreceptors that could aid in detecting the orientation of the pattern of polarised skylight, which would assist the animals to determine compass directions required while navigating between nest and food sources. 相似文献
12.
Physiological characterization of the compound eye in monarch butterflies with focus on the dorsal rim area 总被引:4,自引:0,他引:4
Julia Stalleicken Thomas Labhart Henrik Mouritsen 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2006,192(3):321-331
The spectral, angular and polarization sensitivities of photoreceptors in the compound eye of the monarch butterfly (Danaus plexippus) are examined using electrophysiological methods. Intracellular recordings reveal a spectrally homogenous population of UV
receptors with optical axes directed upwards and ≥10° to the contralateral side. Based on optical considerations and on the
opsin expression pattern (Sauman et al. 2005), we conclude that these UV receptors belong to the anatomically specialized dorsal rim area (DRA) of the eye. Photoreceptors
in the main retina with optical axes <10° contralateral or ipsilateral have maximal sensitivities in the UV (λmax≤340 nm), the blue (λmax=435 nm) or in the long-wave range (green, λmax=540 nm). The polarization sensitivity (PS) of the UV receptors in the DRA is much higher (PS=9.4) than in the UV cells (PS=2.9)
or green cells (PS=2.8) of the main retina. The physiological properties of the photoreceptors in the DRA and in the main
retina fit closely with the anatomy and the opsin expression patterns described in these eye regions. The data are discussed
in the light of present knowledge about polarized skylight navigation in Lepidopterans. 相似文献
13.
Recent molecular analyses consistently resolve the “spoon worms” (Echiura) as a subgroup of the Annelida, but their closest
relatives among annelids still remain unclear. Since the adult morphology of echiurans yields limited insight into their ancestry,
we focused on characters of their larval anatomy to contribute to this discussion. Electron microscopical studies of the larval
protonephridia (so-called head kidneys) of the echiuran species Thalassema
thalassemum revealed distinct correspondences to character states in serpulid polychaetes, although a close relationship between Echiura
and Serpulidae is not supported by any phylogenetic analysis. The larval head kidneys of T. thalassemum consist of only two cells, a terminal cell and a duct cell. The terminal cell forms a tuft of six cilia projecting into the
lumen of the terminal cell. The cilia are devoid of circumciliary microvilli. A filter structure is formed by two to three
layers of elongate microvilli that surround the lumen of the terminal cell in a tubular manner. A thin layer of extracellular
matrix (ECM) encloses the outer microvilli of the tubular structure. The tips of the microvilli project into the lumen of
the adjacent duct cell but are not directly connected to it. However, mechanic coupling is facilitated by the surrounding
ECM and abundant hemidesmosomes. The distal end of the multiciliary duct cell forms the external opening of the nephridium;
a specialized nephropore cell is absent. Apart from the multiciliarity of the duct cell, details of the head kidneys in T. thalassemum reveal no support for the current assumption that Echiura is closely related to Capitellida and/or Terebelliformia. Available
data for other echiuran species, however, suggest that the head kidneys of T. thalassemum show a derived state within Echiura. 相似文献
14.
F. Zufall M. Schmitt R. Menzel 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1989,164(5):597-608
Summary Retinula cells in the compound eye of the cricket (Gryllus bimaculatus) were recorded intracellularly and stained with Lucifer yellow. Two different methods were used to determine the spectral sensitivity of these cells: a) the spectral scanning method, and b) the conventional flash method. Three spectral types, with S()-curves close to the rhodopsin-absorption functions, were found with
max at 332 nm (UV), 445 nm (blue) and 515 nm (green), respectively.Blue receptors were only recorded in the anatomically specialized dorsal rim area (DRA), and UV and green receptors in the dorsal region of the pigmented part of the eye, whereby green receptors were only found in the ventral eye. On the basis of these results, model calculations are presented for di- and trichromatic colour vision in the cricket.The fluorescence markings revealed green receptors whose axons project with short visual fibres to the lamina, and a UV receptor with a long visual fibre which projects through the lamina to the medulla. The blue receptors send their axons either to the lamina and medulla (long visual fibres) or only to the lamina (short visual fibres).The temporal dynamics of the three receptor types were examined. The blue receptors lack a phasic component of the receptor potential, and the time from stimulus on-set to peak potential is strongly increased compared to the UV and green receptors. Light adaptation reduces the latency to less than half of the dark adapted state.Spectral adaptation experiments revealed an unidirectional coupling between UV and green receptors, and it was found that polarization sensitivity (PS) in blue cells was much higher (PS= 6.5±1.5) than that of UV (PS=1.76±0.05) and green (2.26±0.57) receptors. The functional aspects of the three receptor types are discussed with respect to the presented physiological and morphological data.Abbreviations
DA
dorsal area
-
DRA
dorsal rim area
-
PS
polarization sensitivity 相似文献
15.
A new species of the genus Paracobitis, Paracobitis nanpanjiangensis is described from tributaries of the Nanpanjiang River drainage in China. It is distinguished from its congeners, except
P. oligolepis and P. wujiangensis, by body scaleless or with rudimentary scales (caudal peduncle with several deeply embedded scales). It can be differentiated
from P. wujiangensis by the complete lateral line (vs. incomplete), lower dorsal crest reaching the vertical of origin of anal fin (vs. shorter
and higher dorsal crest not reaching the base of anal fin). It is distinguished from P. oligolepis by the following characters: branched dorsal fin with 81/2 (a few 91/2) rays (vs. 91/2), interspaces between bars in front
of dorsal fin conspicuously thinner than those behind (vs. vermiform markings), dorsal head without vermiform markings or
obscure (vs. clearly vermiform markings on dorsal head), vertebrae 4 + 36–38 (vs. 4 + 39–41). 相似文献
16.
Zélia Velez Peter C. Hubbard Kevin Welham Joerg D. Hardege Eduardo N. Barata Adelino V. M. Canário 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2009,195(7):691-698
Olfactory sensitivity to bile salts is wide-spread in teleosts; however, which bile salts are released in sufficient quantities
to be detected is unclear. The current study identified bile salts in the intestinal and bile fluids of Solea senegalensis by mass spectrometry–liquid chromatography and assessed their olfactory potency by the electro-olfactogram. The main bile
salts identified in the bile were taurocholic acid (342 mM) and taurolithocholic acid (271 mM) plus a third, unidentified,
bile salt of 532.3 Da. These three were also present in the intestinal fluid (taurocholic acid, 4.13 mM; taurolithocholic
acid, 0.4 mM). In sole-conditioned water, only taurocholic acid (0.31 μM) was released in sufficient quantities to be measured
(release rate: 24 nmol kg−1 min−1). Sole had high olfactory sensitivity to taurocholic acid but not to taurolithocholic acid. Furthermore, olfactory sensitivity
was higher in the upper (right) olfactory epithelium than the lower (left). These two bile acids contribute about 40% of the
olfactory potency of intestinal fluid and account for the difference in potency at the two epithelia. Taurocholic acid (but
not taurolithocholic acid), and possibly other types of bile acid not tested, could be used as chemical signals and the upper
olfactory epithelium is specialised for their detection. 相似文献
17.
Akihisa Torii Antony S. Harold Takakazu Ozawa Yukio Iwatsuki 《Ichthyological Research》2003,50(2):129-139
This study redescribes Bregmaceros mcclellandi Thompson, 1840, based on one specimen (74.4 mm SL) from the Bay of Bengal and 66 specimens (30.0–84.7 mm SL) from Mumbai
(Bombay), India, because the type specimens have apparently been lost. The present specimens are characterized by having black
dorsal, pectoral, and caudal fins and show the following morphology: caudal fin slightly forked; body chromatophores present
mainly at the dorsal part; no scales on cheek; vertebrae 52–55 (13–15 + 38–41); dorsal rays 52–59; anal rays 54–60; pectoral
rays 18–20; caudal rays 27–31 (principal rays 14); transverse scales 14–15. In the 66 Mumbai specimens, it was confirmed that
the distinctive black fin pigmentation developed sequentially with growth, with complete pigmentation first on the anterior
lobe of the dorsal fin, then simultaneously on the posterior lobe of the dorsal fin, the caudal fin, and the pectoral fin,
and last, on the anal fin. This species is known only from the Arabian Sea, Bay of Bengal, and Gulf of Thailand. A review
of 16 nominal Bregmaceros species indicates that, besides B. mcclellandi, the distinctive dark fin pigmentation is found in B. atripinnis (Tickell), B. atlanticus Goode and Bean, B. japonicus Tanaka, and B. lanceolatus Shen. B. atripinnis is considered a junior synonym of B. mcclellandi, and the others are clearly distinct from B. mcclellandi. Comments are made on some of the characters to more fully characterize the species and for reference in future revisionary
and phylogenetic studies.
Received: June 17, 2002 / Revised: December 2, 2002 / Accepted: December 24, 2002 相似文献
18.
In solution NMR spectroscopy the residual dipolar coupling (RDC) is invaluable in improving both the precision and accuracy
of NMR structures during their structural refinement. The RDC also provides a potential to determine protein structure de novo. These procedures are only effective when an accurate estimate of the alignment tensor has already been made. Here we present
a top–down approach, starting from the secondary structure elements and finishing at the residue level, for RDC data analysis
in order to obtain a better estimate of the alignment tensor. Using only the RDCs from N–H bonds of residues in α-helices
and CA–CO bonds in β-strands, we are able to determine the offset and the approximate amplitude of the RDC modulation-curve
for each secondary structure element, which are subsequently used as targets for global minimization. The alignment order
parameters and the orientation of the major principal axis of individual helix or strand, with respect to the alignment frame,
can be determined in each of the eight quadrants of a sphere. The following minimization against RDC of all residues within
the helix or strand segment can be carried out with fixed alignment order parameters to improve the accuracy of the orientation.
For a helical protein Bax, the three components A
xx
, A
yy
and A
zz
, of the alignment order can be determined with this method in average to within 2.3% deviation from the values calculated
with the available atomic coordinates. Similarly for β-sheet protein Ubiquitin they agree in average to within 8.5%. The larger
discrepancy in β-strand parameters comes from both the diversity of the β-sheet structure and the lower precision of CA–CO
RDCs. This top-down approach is a robust method for alignment tensor estimation and also holds a promise for providing a protein
topological fold using limited sets of RDCs. 相似文献
19.
The leiognathid genus Nuchequula can be defined by the following combination of characters: mouth protruding downward; a narrow band of small, slender, villiform
teeth in both jaws; teeth on upper jaw strongly recurved; the lateral line almost complete; a dark blotch on the nape. Although
the genus was first established as a subgenus of Eubleekeria, it is here raised to generic level on the basis of the aforementioned morphological characters and recent molecular biological
evidence. The genus comprises six valid species: N. blochii (Valenciennes 1835), distributed in India and Thailand; N. flavaxilla sp. nov., occurring only at Panay I., Philippines; N. gerreoides (Bleeker 1851), widely distributed in the Indo-West Pacific, from the Persian Gulf to Cape York, Australia, and north to
Taiwan; N. glenysae sp. nov., from northern Australia and Ambon, Indonesia; N. longicornis sp. nov., from the Gulf of Thailand and Indonesia; and N. nuchalis (Temminck and Schlegel 1845), occurring in southern China including Taiwan, and southern Japan. Diagnostic characters of
the species belonging to the genus are as follows: N. blochii—breast scaled, cheek naked, and a conspicuous black blotch distally on spinous dorsal fin; N. flavaxilla sp. nov.—breast naked, dorsolateral body surface fully scaled, preorbital spine bicuspid and not expanded distally, and second
dorsal and anal fin spines conspicuously elongated; N. gerreoides—breast naked, anterior part of dorsolateral surface of body almost completely scaled, and second dorsal and anal fin spines
not conspicuously elongated; N. glenysae sp. nov.—breast completely scaled, cheek scaled, and unique complicated sensory canals present on the suborbital area, extending
to the nape; N. longicornis sp. nov.—breast naked, dorsolateral body surface fully scaled, preorbital spine bicuspid or tricuspid and extended distally,
and second dorsal fin spines only conspicuously elongated; N. nuchalis—breast naked, anterior part of dorsolateral surface of body widely naked, and a conspicuous dark blotch distally on spinous
dorsal fin. 相似文献
20.
We have examined the fine structure of dorsal rim ommatidia in the compound eye of the three odonate species Sympetrum striolatum, Aeshna cyanea and Ischnura elegans. These ommatidia exhibit several specializations: (1) the rhabdoms are very short, (2) there is no rhabdomeric twist, and (3) the rhabdoms contain only two, orthogonally-arranged microvillar orientations. The dorsal rim ommatidia of several other insect species are known to be anatomically specialized in a similar way and to be responsible for polarization vision. We suggest that the dorsal rim area of the odonate compound eye plays a similar role in polarization vision. Since the Odonata are a primitive group of insects, the use of polarized skylight for navigation may have developed early in insect phylogeny. 相似文献