The pupil response of a teleost fish, Porichthys notatus: description and comparison to other species.

The pupil response of Porichthys notatus to different intensities of illumination is described and compared to that of P. myriaster, Cephaloscyllium ventroisum, and a human. While the fully dark adapted pupil is round, at the highest light intensities it consists of only two small, almost independent, apertures with a total area 4.9% of that observed in the fully dilated animal. The response is at least partially consensual and occurs, albeit at a much reduced rate, in isolated eyes. P. notatus also displays retinomotor movements comparable to those seen in most teleosts, suggesting that, contrary to most previous assumptions, pupillary responses and retinomotor migrations are not mutually exclusive.

Shewanella woodyi sp. nov., an exclusively respiratory luminous bacterium isolated from the Alboran Sea.

Thirty-four strains of nonfermentative, respiratory, luminous bacteria were isolated from samples of squid ink and seawater from depths of 200 to 300 m in the Alboran Sea. Although these strains had a few properties similar to properties of Shewanella (Alteromonas) hanedai, they did not cluster phenotypically with any previously described bacterium. The nucleotide sequence of a 740-bp segment of luxA was not homologous with other known luxA sequences but clustered with the luxA sequences of Shewanella hanedai, Vibrio logei, Vibrio fischeri, and Photobacterium species. The 16S RNA gene from two strains was sequenced and was found to be most closely related to the S. hanedai 16S RNA gene. Based on the differences observed, we describe the new isolates as members of new species, Shewanella woodyi sp. nov. Strain ATCC 51908 (= MS32) is the type strain of this new species.

Not All Ctenophores Are Bioluminescent: Pleurobrachia.

The traditional view has been that all species of the phylum Ctenophora are capable of producing light. Our inability to elicit luminescence from members of the well-known genus Pleurobrachia, as well as a lack of published documentation, led to an effort to determine whether this genus is truly bioluminescent. Physical and chemical assays of several species from the family Pleurobrachiidae produced no evidence of bioluminescence capability, although all other species of ctenophores tested gave positive results. Some of the historical misperception that Pleurobrachia can produce light might be attributable to confusion with similar luminous genera.

Cephalopod Predation Facilitated by Dinoflagellate Luminescence.

Predation by nocturnal cephalopods on nonluminous prey was examined in the presence of dinoflagellate bioluminescence. Sepia officinalis Linnaeus and Euprymna scolopes Berry were tested for predation efficiency in darkness illuminated by the luminescent dinoflagellate Pyrocystis fusiformis Murry. Prey were mysids, Holmesimysis sculpta (Tattersall); grass shrimp, Palaemonetes pugio Holthuis; and mosquito fish, Gambusia affinis Baird and Girard. Tests were conducted in aquaria containing 0-20 cells ml-1 of P. fusiformis. Predation increased as numbers of luminescent dinoflagellates increased. Controls were predation tests in the presence of P. fusiformis during nonluminescent photophase or in the absence of dinoflagellates. Movements of squid and prey readily stimulated luminescence. Behavior and correlated luminescence in infrared-illuminated aquaria were recorded by image-intensified and infrared video cameras. Sepia strikes on prey were common under luminescent conditions--85% occurred in less than 10 min; but strikes in darkness were rare. E. scolopes attacked more frequently than Sepia, and almost 90% obtained prey under luminescent conditions. This study demonstrates the ability of squid to use dinoflagellate bioluminescence to locate and capture nonluminous prey. The burglar alarm theory of the adaptive significance of dinoflagellate bioluminescence is supported.

Slow Photic and Chemical Induction of Bioluminescence in the Midwater Shrimp, Sergestes similis Hansen.

The initial luminescent response to photic stimulation of dark-maintained specimens of the midwater shrimp, Sergestes similis Hansen, differed from the conventional counterillumination response. Animals were initially unresponsive to light; bioluminescence was only induced after a latency of 3 min. Maximum intensity was reached after approximately 25 min. During the induction process, light emission from the anterior light organs was frequently observed prior to output from the posterior organ. Once luminescence was induced, responses exhibited the typical fast kinetics of the counterillumination response and changes in light organ output occurred synchronously. Visual input was necessary to maintain this state. Dark readaptation of counterilluminating animals resulted in a return to the slow response kinetics characteristic of untested animals. Because eyestalk ablation or crushing caused immediate production of luminescence in previously untested animals, the slow induction did not involve the ability of the light organs to produce light. Serotonin was effective in stimulating bioluminescence in intact animals; the induction of light emission proceeded at a rate similar to that for photic stimulation. Other putative neurotransmitters, including norepinephrine, acetylcholine, GABA, and L-glutamic acid, did not stimulate bioluminescence. Isolated light organs exhibited high background levels of light emission, which were unchanged by serotonin treatment. However, serotonin was effective in stimulating luminescence in animals with ablated eyestalks. These results suggest a dual control system involved in the induction and maintenance of bioluminescence in S. similis.

Bioluminescence Maintenance in Juvenile Porichthys notatus.

Bioluminescence in the midshipman fish, Porichthys notatus from the Santa Barbara coastal region, was quantified from onset through the first two years of life. Maximum light emission was 2.5 x 109 photons s-1 upon leaving the nest and reached 2.0 x 1010 photons s-1 within the first year. These intensities may be sufficient for counterillumination in moon or starlight over most of the depth range of the fish. The bioluminescence of juveniles recently detached from the nest was depleted by multiple topical applications of a dilute noradrenalin solution. A luciferin-free diet also exhausted luminescence in 10-18 months. Bioluminescence was restored within 24 h after feeding depleted fish with dried specimens of the bioluminescent marine ostracod Vargula hilgendorfii, and light emission capacity was correlated with the amount consumed. Predation by second year fish (18 months) upon juvenile P. notatus (3 months) or upon live V. tsujii also restored luminescence. After restoration, luminescence gradually disappeared within several months. Consumption of luciferin-containing organisms by already competent fish did not increase light intensity. Juvenile P. notatus from the Santa Barbara coastal region require exogenous luciferin to remain luminescent.

Ultrastructure and Neuronal Control of Luminous Cells in the Copepod Gaussia princeps.

The physiology of light production in copepods is largely unknown. The mesopelagic copepod Gaussia princeps possesses luminous glands, each consisting of a single large cell discharging through a cuticular pore. Slow flashes external to the cuticle are triggered from excised abdomens by electrical stimulation of the ventral nerve cord. Each luminous cell contains UV fluorescent secretory vesicles distally, which are secreted through a valved cuticular pore. Each luminous cell, except for the most proximal portion, is surrounded by a cellular sheath, which appears to form the distal valve. Luminous cells have a stem containing small, electron-lucent precursors to secretory vesicles proximal to the fluorescent vesicles. Nerve terminals, filled with large synaptic vesicles, are associated with the unsheathed proximal cell membrane. Gap junctions interconnect the nerve terminals, and possibly serve to accelerate conduction to the luminous cell to achieve a synchronous effector output.

Patterns of Stimulated Bioluminescence in Two Pyrosomes (Tunicata: Pyrosomatidae).

Pyrosomes are colonial tunicates that, in contrast with typical luminescent plankton, generate brilliant, sustained bioluminescence. They are unusual in numbering among the few marine organisms reported to luminesce in response to light. Each zooid within a colony detects light and emits bioluminescence in response. To investigate the luminescence responsivity of Pyrosoma atlanticum and Pyrosomella verticillata, photic, electrical, and mechanical stimuli were used. Photic stimulation of 1.5 x 109 photons{middot}s-1{middot}cm-2, at wavelengths between 350 and 600 nm, induced bioluminescence, with the maximum response induced at 475 nm. The photic-excitation half-response constant was 1.1 x 107 photons{middot}s-1{middot}cm-2 at 475 nm for P. atlanticum; P. verticillata had a significantly higher half-response constant of 9.3 x 107 photons{middot}s-1{middot}cm-2. Individual zooids within a colony, however, appeared to have different half-response constants. Stimulus strength influenced recruitment of zooids and, in turn, luminescent duration and quantum emission. Image intensification revealed saltatory propagation of luminescence across the colony, owing to photic triggering among zooids. Repetitive, regular mechanical or electrical stimulation elicited rhythmic flashing characterized by alternating periods of high and low light intensities.

The visual pigments of four deep-sea crustacean species.

The visual pigments of four mesopelagic crustacean species were studied at sea by means of microspectrophotometry. The absorbance maxima obtained for the visual pigments and their metarhodopsins, respectively, were: 493 nm and 481 nm (Systellaspis debilis), 485 nm and 480 nm (Acanthephyra curtirostris), 491 nm and 482 nm (A. smithi), and 495 nm and 487 nm (Sergestes tenuiremis). The spectral characteristics of the rhodopsins and metarhodopsins permit high photosensitivity and facilitate photoregeneration in a nearly monochromatic environment. Photic regeneration of rhodopsins from the deep-sea environment was demonstrated, and data were obtained which are consistent with the occurrence of dark regeneration. Specific optical density of the observed visual pigments was calculated for two species.

Eye size of pelagic crustaceans as a function of habitat depth and possession of photophores.

Eye diameter, interommatidial angle, and rhabdom dimensions were measured for a variety of crustacean species differing in habitat depth and bioluminescence ability. Eyes are smaller and eye growth rates are lower at greater depths for species in five of the six families examined, and photophore-bearing species tend to have larger eyes than relatives which lack photophores. Rhabdoms are smaller and interommatidial angles are larger in small eyes, factors which, with reduced aperture size, are generally associated with decreased visual sensitivity and acuity. This suggests that the eyes of many deep-sea crustaceans are poorly suited to a dimly lit environment; however, the small eyes of deep-sea crustaceans may still perceive luminescent sources from appropriate distances because of the much higher contrast at depth between luminescent sources and background light. Smaller eyes also impose a lower energetic burden and are potentially less visible to predators than are large eyes.

A multichannel microspectrophotometer for visual pigment investigations.

The microspectrophotometer described replaces the photomultiplier of conventional scanning systems with a multichannel detector. By eliminating scanning-related artifacts, particularly those associated with mechanical vibrations, this system makes possible ship-based microspectrophotometric studies of visual pigments of marine organisms too fragile for live transport to shore-based laboratories. The performance of the multichannel microspectrophotometer is compared with that of conventional scanning systems and absorbance spectra taken at sea on isolated rhabdoms from Euphausia pacifica are presented. Difference spectra gave a lambda max for rhodopsin of 483 nm and a lambda max for metarhodopsin of 489 nm.

Structure of dactyl sensilla in the kelp crab, Pugettia producta.

In the kelp crab, Pugettia producta, flat plate setae cover all but the ventral surfaces of the walking leg dactyls. Dendrites enter the setal shaft located inside the plate superstructure, and extend to a region of the setal tip that contains a system of minute pores resembling the pore systems found in chemosensory sensilla of insects. Presumably, much of the chemosensitivity of the dactyls in the kelp crab is mediated by the plate setae. In the interior of the dactyl, supporting cells and the neurons innervating plate setae, other types of setae, and other presumptive sensilla form scolopidia. Large scolopidia, containing as many as 12 dendrites, appear to innervate some of the plate setae and also large ventral rodlike setae that might be chemosensory. Two of the dendrites of large scolopidia usually have more densely packed microtubules, longer ciliary axonemes, slightly larger rootlets, and dark A fibers with arms, characteristics indicative of mechanosensory function. Some dactyl setae, therefore, could be both mechanosensory and chemosensory. Small scolopidia containing two or three dendrites that exhibit mechanosensory characteristics appear to innervate small, rodlike setae, which presumably are strictly mechanosensory. The two types of structures located on the epicuticular cap, elliptical structures resembling campaniform sensilla and small cones in pits resembling CAP organs, appear to be dually innervated and presumably are mechanosensory, although other functions are possible. The internal positions of the scolopidia, together with the support afforded by an extracellular dendritic sheath, by the scolopale, and by desmosomelike and septate junctions, may serve to protect internal portions of setal dendrites, some of which appear to remain functional in nonmolting adults that have abraded setae.

Far red bioluminescence from two deep-sea fishes.

Spectral measurements of red bioluminescence were obtained from the deep-sea stomiatoid fishes Aristostomias scintillans (Gilbert) and Malacosteus niger (Ayres). Red luminescence from suborbital light organs extends to the near infrared, with peak emission at approximately 705 nanometers in the far red. These fishes also have postorbital light organs that emit blue luminescence with maxima between 470 and 480 nanometers. The red bioluminescence may be due to an energy transfer system and wavelength-selective filtering.

Chemical induction of feeding in California spiny lobster,Panulirus interruptus (Randall): : Responses to molecular weight fractions of abalone.

Molecular weight fractions of abalone muscle were tested for the ability to induce appetitive feeding and locomotor behavior in the spiny lobster,Panulirus interruptus. Fractions of <1000, 1000-10,000 and >10,000 daltons were isolated by ultrafiltrations and gel chromatography from a seawater extract of abalone muscle. The two lower-molecular-weight fractions (<1000, 1000-10,000) were the least stimulatory of the three fractions tested, and both were ineffective as feeding stimulants. Solutions combining any two of the three isolated fractions produced behavioral activity equal to that caused by whole extract; thus, no single fraction was essential to the stimulatory capacity of abalone. The >1000-dalton fraction was also highly stimulatory, meaning that large and not small molecules were essential in initiating feeding. Finally, a 75% ethanol-insoluble component of the <10,000 fraction was effective, while the ethanol-soluble portion was not. Since the insoluble material consisted predominantly of peptides and polypeptides, it is probable that these molecules act as principal stimulants in abalone muscle.

Effects of abrasion and Na+ on dactyl-mediated chemoreception in mature kelp crabs, Pugettia producta (Randall).

Extracellular recordings from the mixed sensory nerves innervating the abraded dactylopodites of the kelp crab, Pugettia producta (Randall), indicate that at least some chemoreceptors and mechanoreceptors remain functional. The chemoreceptors of the abraded dactyls are sensitive to both the concentration and chemical nature of the stimulants. The responses of the chemoreceptors, but not of the mechanoreceptors, are reduced when choline is substituted for sodium in the stimulant solutions. Only chemoreception is blocked by the topical application of tetrodotoxin (TTX) to the dactyls; partial reversal of the blockage occurs with time. The differential blockage of receptor activity by low Na+ and TTX is consistent with the idea that spike initiation occurs more distally in the dendrites of the chemosensory neurons than in the mechanosensory neurons. The relevance of this to the ability of at least some abraded dactyl setae to remain functional in a long-lived, nonmolting crab is considered.

Cryptic bioluminescence in a midwater shrimp.

The mesopelagic shrimp Sergestes similis emits ventrally directed bioluminescence that closely matches the intensity of downward-directed illumination and is able to rapidly modify its light output to match changes in background intensity. Masking experiments show that the photoreceptors involved are the compound eyes or adjacent tissues. Light emission originates from modified portions of the hepatopancreas and is similar to oceanic light in angular distribution and spectral characteristics. Normally oriented animals respond minimally to upward-directed light.

Gap junctions suggest epithelial conduction within the comb plates of the ctenophore Pleurobrachia bachei.

Intercellular gap junctions occur between the ciliated cells that make up the comb plates of the ctenophore Pleurobrachia. Similar junctions are found within the ciliated grooves which run from the apical organ to the first plate of each comb row, as well as throughout the endoderm of the meridional canals. Gap junctions were not found in the ectodermal tissue between the comb rows. The distribution of junctions suggests that excitation conduction within the ciliated grooves, comb plates and meridional canal endoderm may be epithelial.

The caudal luminous organs of lanternfishes: general innervation and ultrastructure.

Neuroanatomical, light and electron microscopic investigations of the caudal luminous organs of two lanternfish species, Stenobrachius leucopsarus and Parvilux ingens, were conducted in a search for morphological correlates underlying their luminescent behavior and control mechanisms. Complex neural pathways involving the spinal nerves and the sympathetic nerve chain of the caudal peduncle are associated with profuse segmental innervation to both the supracaudal and infracaudal organs. Neural composition of these segmental subunits indicates that pre-ganglionic (spinal) as well as post-ganglionic (sympathetic) fibers are involved in the neural control of luminescence of these organs. Neuro-photocyte units, in which multiple nerve branches are sandwiched between two lamellar photocytes and establish large surface areas of close appposition, as well as gap junctions apparently interconnecting all photocytes throughout the luminous organs, may account for the very rapid and simultaneous displays of spontaneous or electrically driven luminescence. The organization of the caudal luminous organs is compared with that of lanternfish photophores. Relatively few granular and agranular synaptic vesicles are present in some nerve processes of the photocyte units, suggesting that adrenergic neurotransmission as well as electrotonic spread of excitation may be involved at the neuro-photocyte junctions.