Tamara M. Frank

Visual Spectral Sensitivities of Bioluminescent Deep-Sea Crustaceans

The spectral sensitivities of eight species of deep-sea decapod shrimps (Family Oplophoridae) were determined from shipboard measurements of electroretinograms of dark-captured specimens. Notostomus gibbosus and N. elegans are maximally sensitive at 490 nm, and chromatic adaptation experiments indicate that a single visual pigment is present. Peak sensitivities of Acanthephyra smithi and A. curtirostris are at 510 nm, a longer wavelength than expected for such deep-sea dwellers. The four photophore-bearing species, Systellaspis debilis, Janicella spinacauda, Oplophorus spinosus, and O. gracilirostris have sensitivity maxima at 400 and 500 nm, and chromatic adaptation experiments indicate the presence of two visual pigments. This unusual short wavelength sensitivity may provide the basis for congener recognition based on the spectral bandwidth of luminescence.

Giant Deep-Sea Protist Produces Bilaterian-like Traces

One of the strongest paleontological arguments in favor of the origin of bilaterally symmetrical animals (Bilateria) prior to their obvious and explosive appearance in the fossil record in the early Cambrian, 542 million years ago, is the occurrence of trace fossils shaped like elongated sinuous grooves or furrows in the Precambrian. Being restricted to the seafloor surface, these traces are relatively rare and of limited diversity, and they do not show any evidence of the use of hard appendages. They are commonly attributed to the activity of the early nonskeletonized bilaterians or, alternatively, large cnidarians such as sea anemones or sea pens. Here we describe macroscopic groove-like traces produced by a living giant protist and show that these traces bear a remarkable resemblance to the Precambrian trace fossils, including those as old as 1.8 billion years. This is the first evidence that organisms other than multicellular animals can produce such traces, and it prompts re-evaluation of the significance of Precambrian trace fossils as evidence of the early diversification of Bilateria. Our observations also render indirect support to the highly controversial interpretation of the enigmatic Ediacaran biota of the late Precambrian as giant protists.

Comparative study of the spectral sensitivities of mesopelagic crustaceans

Abstract 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.In a previous companion paper, we presented the details of our algorithms for performing nonlocal density functional theory (DFT) calculations in complex 2D and 3D geometries. We discussed scaling and parallelization, but did not discuss other issues of performance. In this paper, we detail the precision of our methods with respect to changes in the mesh spacing. This is a complex issue because given a Cartesian mesh, changes in mesh spacing will result in changes in surface geometry. We discuss these issue using a series of rigid solvated polymer models including square rod polymers, cylindrical polymers, and bead-chain polymers. By comparing the results of the various models, it becomes clear that surface curvature or roughness plays an important role in determining the strength of structural solvation forces between interacting solvated polymers. The results in this paper serve as benchmarks for future application of these algorithms to complex fluid systems.

Spectral Composition of Bioluminescence of Epipelagic Organisms from the Sargasso Sea

The spectral characteristics of single identified epipelagic sources of bioluminescence from the western Sargasso Sea were measured with an optical multichannel analyzer (OMA) system during the April, 1985, Biowatt cruise. The emission spectra of specimens representing 45 species from 8 phyla were measured. Peak bioluminescence emissions typically occurred between 440 and 500 nm, in the blue region of the visible spectrum. Three exceptions involved emission in the green, yellow, and red spectral regions. Intraspectific variability in spectra, was noted in several species. One shrimp species exhibited two modes of light emission, each with different emission spectra. Other cases involved dynamic color shifts of 10 to 14 nm; the source of the spectral variability is unknown, but may involve optical filtering or differences in the color of luminescence from multiple sites of light emission. Measurements from independent samples of unsorted plankton revealed different spectral distributions. This suggests that the spectral emissions of bioluminescence in the upper water column will vary, based on species assemblage.

UV Light in the Deep‐Sea: In Situ Measurements of Downwelling Irradiance in Relation to the Visual Threshold Sensitivity of UV‐Sensitive Crustaceans

Several species of deep‐sea crustaceans possess unusually high spectral sensitivity to UV light, measured elec‐trophysiologically. In addition, behavioral experiments indicate that these species are equally sensitive to near‐UV and blue‐green light. These results raised questions about the functional significance of this short wavelength sensitivity, since it is commonly believed that UV light is virtually absent in the deep‐sea. Using submersible based technology, we conducted measurements of downwelling irradiance at two wavelengths ‐ 380 and 480 nm. These measurements indicate that the irradiance of 380 nm light at 500–600 m, the daytime depth range of the crustaceans with a U V sensitivity peak, is high enough to be detected by these species. In addition, measurements of the spectrum of the downwelling light field conducted at dusk demonstrate that spectral changes visible at the surface are not visible at 150 m. These results are discussed with respect to hypotheses on the functional significance of ...

Comparative Study of Temporal Resolution in the Visual Systems of Mesopelagic Crustaceans

The temporal characteristics of the visual systems of eight species of mesopelagic crustaceans were studied using the electroretinogram (ERG). Experiments were conducted on shipboard, using dark-captured specimens collected off the south coast of Cuba. As one would expect based on the relative intensity differences in their light environments, the deepest living species, Systellaspis debilis and Sergia filictum, have low maximum critical flicker fusion frequencies (CFFs) of 21-25 Hz, whereas the shallower living species Oplophorus gracilirostris and Janicella spinacauda have higher maximum CFFs (31-32 Hz). One of the shallowest living species, Funchalia villosa, has an unusually low maximum CFF (24 Hz), which may be a function of working with a dark-adapted eye. Two of the bilobed euphausiid species, Nematobrachion flexipes and N. sexspinosus, have very high maximum CFFs (44-57 Hz), comparable to those of surface-dwelling crabs, even though they live between 400 and 600 m. The maximum CFF of Stylocheiron maximum, a shallower living bilobed euphausiid, is only 36 Hz, indicating that maximum CFF among the euphausiids cannot be correlated with depth of occurrence. The unusually high flicker fusion frequency of the deeper living euphausiids may be correlated to their preference for bioluminescent prey.

Evidence for Behavioral Sensitivity to Near-UV Light in the Deep-Sea Crustacean Systellaspis debilis

The role of UV light in the deep-sea environment has been discounted in the past, due to the assumptions that (1) there is insufficient UV light available for vision and, therefore (2) deep-sea organisms would not be sensitive to these wavelengths. A recent study that employed electrophysiological techniques on dark-captured deep-sea crustaceans demonstrated that several species of deep-sea crustaceans possess very high sensitivity to near-UV light. The current study was undertaken to determine if near-UV light would also elicit a behavioral response from these species. The species studied was Systellaspis debilis, an oplophorid shrimp whose daytime depth ranges from 600 to 700 m. A method for tethering shrimp was developed which allowed them to freely orient in response to changes in the ambient light field. Behavioral responses to changes in ambient light included changes in body tilt with respect to the horizontal plane, changes in swimming speed, and movement of the feeding appendages. These experiments, the first of their kind on a deep-sea organism, demonstrate that behaviorally, S. debilis is equally sensitive to very low intensities of blue-green and near-UV light.

Comparative Study of Behavioral-Sensitivity Thresholds to Near-UV and Blue-Green Light in Deep-Sea Crustaceans

The behavioral sensitivities of five species of deep-sea crustaceans (order Decapoda: Acanthephyra curtirostris, A. smithi, Notostomus gibbosus, Janicella spinacauda and Oplophorus gracilirostris) to near-UV and blue-green light were studied during a research cruise off the coast of Hawaii in 1993. Two of the five species have electrophysiologically-measured spectral sensitivity peaks at 400 and 500 nm, while the remaining three species have a single sensitivity peak at 490 to 500 nm. In the current study, behavioral mean threshold sensitivities (defined as the lowest irradiance change to which the shrimp would give a behavioral response) were determined for tethered specimens of each species at two wavelengths, 400 and 500 nm. The mean behavioral threshold sensitivities of the two species with putative dual visual-pigment systems were approximately the same to near-UV and blue-green light, while the other three species were significantly less sensitive to near-UV vs blue-green light. Results from these experiments indicate that (1) behavioral information obtained from tethered shrimp accurately reflects their spectral sensitivity, and (2) the sensitivity of the putative dichromats to near-UV light is sufficiently low to detect calculated levels of near-UV light remaining in the down-welling field at their daytime depth of 600 m. Possible functions of this high sensitivity to short wavelength light are discussed.

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

Abstract The effects of light adaptation on flicker fusion frequency were examined in the photoreceptors of 13 species of deep-sea crustaceans. Light adaptation produced a significant increase in the maximum critical flicker fusion frequency (CFFmax) in 7 species—all 6 species of euphausiids in the study, and 1 species of oplophorid (Group 1). This is the first example of an increase in temporal resolution due to light adaptation in a deep-sea species. In the other six species—2 oplophorids, 1 pandalid, 1 pasiphaeid, 1 penaeid and 1 sergestid (Group 2)—light adaptation had no effect, or resulted in a decrease in the flicker fusion frequency. The mean dark-adapted CFFmax of the Group 1 species was significantly higher, and the mean response latency significantly lower, than those of the Group 2 species. Possible explanations for these differences include the activity and bioluminescence mode of preferred prey items, as well as the retention of larval/juvenile adaptations in adult eyes.

A novel vertebrate eye using both refractive and reflective optics.

Sunlight is attenuated rapidly in the ocean, resulting in little visually useful light reaching deeper than approximately 1000 m in even the clearest water. To maximize sensitivity to the relatively brighter downwelling sunlight, to view the silhouette of animals above them, and to increase the binocular overlap of their eyes, many mesopelagic animals have developed upward-pointing tubular eyes. However, these sacrifice the ability to detect bioluminescent and reflective objects in other directions. Thus, some mesopelagic fish with tubular eyes extend their visual fields laterally and/or ventrally by lensless ocular diverticula, which are thought to provide unfocused images, allowing only simple detection of objects, with little spatial resolution. Here, we show that a medial mirror within the ventrally facing ocular diverticulum of the spookfish, Dolichopteryx longipes, consisting of a multilayer stack derived from a retinal tapetum, is used to reflect light onto a lateral retina. The reflective plates are not orientated parallel to the surface of the mirror. Instead, plate angles change progressively around the mirror, and computer modeling indicates that this provides a well-focused image. This is the first report of an ocular image being formed in a vertebrate eye by a mirror.