Magnus Lindström

Eye function of Mysidacea (Crustacea) in the northern Baltic Sea.

Eye spectral sensitivity, [S(lambda)], was measured in seven northern Baltic mysid species using an electroretinogram technique. Their S(lambda) curves were compared with the spectral distribution of underwater light at their normal habitats. In the littoral species Neomysis integer, Praunus flexuosus and Praunus inermis, the S(lambda) maxima, [S(lambda)(max)], were in the wavelength-bands of 525-535, 505-515 and 520-530 nm respectively. The neoimmigrant species Hemimysis anomala had a S(lambda)(max) around 500 nm and high sensitivity at 393 nm, possibly indicating UV-sensitivity. S(lambda) of the pelagic species Mysis mixta and Mysis relicta sp. II was at about 505-520 nm. M. relicta sp. I from Pojoviken Bay and fresh water humic Lake Pääjärvi had S(lambda)(max) at approximately 550 nm and 570 nm respectively. This is in accordance with a similar long-wavelength shift in light transmittance of the respective waters. The eyes of the latter population were also damaged by strong light. The pontocaspian neoimmigrant H. anomala is clearly adapted to waters transmitting more blue light.

Eye function of Mysis relicta Lovén (Crustacea) from two photic environments. Spectral sensitivity and light tolerance

Abstract Spectral sensitivities, S(λ), and light tolerances of the eyes of two geographically isolated populations of the opossum shrimp Mysis relicta Loven were studied by recording the electroretinogram. Measurements of the downward irradiance of light in the different water localities revealed a correlation between the spectral sensitivity peak of the mysid eye and the light-transmission properties of the water. Eyes of animals from the “red-transmitting” Lake Paajarvi (transmission maximum 600–700 nm) had a S(λ)max at ≈ 570 nm. The sensitivity of dark-adapted eyes was markedly suppressed by moderate light exposures. Three days of recovery in darkness restored eye sensitivity. Eyes of animals from Pojoviken bay (part of the Baltic Sea, transmission maximum in 565–585 nm) had a S(λ)max of ≈ 550 nm, and upon bright light exposures the sensitivity of the eyes recovered to the sensitivity of the dark-adapted state in ≈ 24 h. These results have a bearing on the adaptional and evolutionary forces acting on the mysid eye, and on the occurrence of sibling species in the Tvarminne area. The importance of spectral sensitivity and light tolerance on vertical migration as well as the impact of light on photoreceptor membrane disruption are briefly discussed.

Exposure to contaminants exacerbates oxidative stress in amphipod Monoporeia affinis subjected to fluctuating hypoxia.

Fitness and survival of an organism depend on its ability to mount a successful stress response when challenged by exposure to damaging agents. We hypothesized that co-exposure to contaminants may exacerbate oxidative stress in hypoxia-challenged benthic animals compromising their ability to recover upon reoxygenation. This was tested using the amphipod Monoporeia affinis exposed to hypoxia followed by reoxygenation in sediments collected in polluted and pristine areas. In both sediment types, oxygen radical absorbance capacity (ORAC) and antioxidant enzyme activities [superoxide dismutase (SOD) and catalase (CAT)] increased during hypoxia, suggesting that M. affinis has a strategy of preparation for oxidative stress that facilitates recovery after a hypoxic episode. Exposure to contaminants altered this anticipatory response as indicated by higher baselines of ORAC and SOD during hypoxia and no response upon reoxygenation. This coincided with significantly elevated oxidative damage evidenced by a marked reduction in glutathione redox status (ratio of reduced GSH/oxidized GSSG) and an increase in lipid peroxidation (TBARS levels). Moreover, RNA:DNA ratio, a proxy for protein synthetic activity, decreased in concert with increased TBARS, indicating a linkage between oxidative damage and fitness. Finally, inhibited acetylcholinesterase (AChE) activity in animals exposed to contaminated sediments suggested a neurotoxic impact, whereas significant correlations between AChE and oxidative biomarkers may indicate connections with redox state regulation. The oxidative responses in pristine sediments suggested a typical scenario of ROS production and removal, with no apparent oxidative damage. By contrast, co-exposure to contaminants caused greater increase in antioxidants, lipid peroxidation, and slowed recovery from hypoxia as indicated by CAT, GSH/GSSG, TBARS and AChE responses. These results support the hypothesized potential of xenobiotics to hamper ability of animals to cope with fluctuating hypoxia. They also emphasize the importance of understanding interactions between antioxidant responses to different stressors and physiological mechanisms of oxidative damage.

Spectral and visual sensitivities of Cirolana borealis Lilljeborg, a deep-water isopod (Crustacea : Flabellifera)

Abstract The electroretinogram (ERG) of the dark-adapted compound eye of Cirolana borealis Lilljeborg has a corneal negative on response. The latency period varies between 140 and 8 ms and depends on stimulus intensity. The spectral sensitivity, measured over the range 406–673 nm, has its maximum around 495–528 nm, corresponding to a visual pigment of 514 nm, according to Dartnalls nomogram urves. Only one pigment appears to be present. The ERG visual threshold sensitivity for an extended light source and defined as a 5 μV response at 495 nm, is 2.1 · 10 8 qu·cm −2 ·s −1 ( n =17). One eye was 10 times more sensitive than the others. The electrophysiological results confirm that the eye of Circolana is of the scotopic type and thus is well adapted to perceive light of low intensities.

Eye Adaptation to Different Light Environments in Two Populations of Mysis relicta: A Comparative Study of Carotenoids and Retinoids

Abstract The content of carotenoids and retinoids was compared in the eyes of two Finnish populations of the opossum shrimp, Mysis relicta, which have been reproductively isolated for at least 9000 years: one from the deep, dark, Lake Pääjärvi, the other from the Baltic Sea (Pojoviken Bay). The eyes of the lake population (LP) are highly susceptible to light damage, while those of the sea population (SP) are more resistant. Carotenoids are known to act as antioxidants protecting cells against free radicals and reactive oxygen species; retinoids, on the contrary, may be phototoxic in certain conditions. Analyzed by spectrophotometry and HPLC, the carotenoid content was broadly similar in the eyes of the two populations as regards both total amount and relative proportions of more than 20 components. Noteworthy differences were found in only three of the major components, among these astaxanthin, which was two times higher in SP compared with LP. The most interesting finding was the 1.6-fold higher content of retinoids in LP compared with SP, with retinol as the dominant component (40% of total) in both populations. Retinol is a precursor of the visual-pigment chromophore retinal. The result is consistent with the idea that animals inhabiting extremely dim light environments, where very little photoregeneration of metarhodopsin to rhodopsin can occur, need a large store of chromophore (or precursors) for effective “dark” regeneration of visual pigment. We suggest that almost all the rhodopsin is then in the native state and massive pigment activation following exposure to stronger light may trigger photoreceptor damage. If such animals are handled without due light protection, e.g., when transferred to a new habitat or collected for biological experiments, their vision will be severely impaired.

Visual pigment, dark adaptation and rhodopsin renewal in the eye of Pontoporeia affinis (Crustacea, Amphipoda)

The benthic amphipod Pontoporeia affinis lives in the Baltic sea and in northern European lakes in an environment where very little light is available for vision. The eyes, consisting of 40–50 ommatidia, are correspondingly modified. Microspectrophotometric recordings on isolated eyes show the presence of at least two kinds of screening pigments in the ommatidia with maxima at 540–580 nm and 460–500 nm. Difference spectra obtained from the rhabdoms after exposure to red and blue light, respectively, give evidence of a single rhodopsin with its maximum at 548 nm and a 500-nm metarhodopsin. In ERG recordings sensitivity in the dark-adapted state, after saturating exposures to blue and to red light, stabilizes at levels determined by the rhodopsin concentration. No change is observed during 10–14 h after the beginning of dark adaptation. However, using animals pre-exposed with a strong red light and then kept in darkness, it is found that after a delay of 20–40 h sensitivity of the dark-adapted eye begins to increase and finally, after 5–6 days reaches a level corresponding to 100% rhodopsin. Thus, a slow renewal of rhodopsin appears to occur in darkness, where a photoisomerization of metarhodopsin is excluded.

Factors affecting the horizontal migration of the amphipod Pontoporeia affinis Lindström. I. Pacording method and response to water currents

Abstract Pontoporeia affinis Lindstrom was subjected to slow horizontal water currents in narrow aquaria 3 m long and its swimming activity recorded by pairs of photocells. A relationship was established between the number of animals and activity level. By dividing the aquaria with intersecting walls during the day, when the animals hid in the sediment, the activity recorded in separate sections during subsequent nights revealed that Pontoporeia migrates upstream. This migration probably takes place only at the very beginning of the light period or just before it. The experimental method is explained in detail.

Lake and Sea Populations of Mysis relicta (Crustacea,Mysida) with Different Visual-Pigment Absorbance Spectra Use the Same A1 Chromophore

Glacial-relict species of the genus Mysis (opossum shrimps) inhabiting both fresh-water lakes and brackish sea waters in northern Europe show a consistent lake/sea dichotomy in eye spectral sensitivity. The absorbance peak (λmax) recorded by microspectrophotometry in isolated rhabdoms is invariably 20–30 nm red-shifted in “lake” compared with “sea” populations. The dichotomy holds across species, major opsin lineages and light environments. Chromophore exchange from A1 to A2 (retinal → 3,4-didehydroretinal) is a well-known mechanism for red-shifting visual pigments depending on environmental conditions or stages of life history, present not only in fishes and amphibians, but in some crustaceans as well. We tested the hypothesis that the lake/sea dichotomy in Mysis is due to the use of different chromophores, focussing on two populations of M. relicta from, respectively, a Finnish lake and the Baltic Sea. They are genetically very similar, having been separated for less than 10 kyr, and their rhabdoms show a typical lake/sea difference in λmax (554 nm vs. 529 nm). Gene sequencing has revealed no differences translating into amino acid substitutions in the transmembrane parts of their opsins. We determined the chromophore identity (A1 or A2) in the eyes of these two populations by HPLC, using as standards pure chromophores A1 and A2 as well as extracts from bovine (A1) and goldfish (A2) retinas. We found that the visual-pigment chromophore in both populations is A1 exclusively. Thus the spectral difference between these two populations of M. relicta is not due to the use of different chromophores. We argue that this conclusion is likely to hold for all populations of M. relicta as well as its European sibling species.

Factors affecting the horizontal migration of the amphipod Pontoporeia affinis Lindström. II. Effects of temperature, salinity and substratum

Abstract Pontoporeia affinis Lindstrom was subjected to temperature gradients, increased salinity and different substrata in narrow aquaria 3 m long and its swimming activity was recorded by pairs of photocells. By dividing the aquaria with intersecting walls during the day, when the animals hid in the sediment, the activity recorded in separate sections during subsequent nights revealed that Pontoporeia migrates towards the warmer end of the aquarium. Preference for soft substrata dominates temperature preference. Increased salinity activates swimming activity even during the day. Partly using a new IR video-recording method, increased temperature was found to decrease swimming activity. The new method is described in detail.

Effects of bleached kraft mill effluents on the swimming activity of Monoporeia affinis (crustacea, amphipoda) lindström

The crustacean Monoporeia affinis Lindstrom was exposed to two different concentrations of bleached kraft mill effluent (BKME) containing, originally, 8.3 mg/g organic chlorine determined as adsorbable organic halogen (AOX). The swimming activity of the animals was recorded by pairs of infra-red sensitive photocells attached to 5.6 1 aquaria having a seawater inflow rate of 12 ml/min. The test sequence included a control phase, an exposure phase and a recovery phase. During the exposure phase the total swimming activity decreased in three of the four test aquaria containing effluent, indicating that the animals had retreated into the sediment. Total activity increased during the recovery phase and, in the case of the lower organic chlorine concentration, activity almost achieved the original control-phase level. Statistical differences in swimming activity changes during experiment were evaluated using ANOVA. Experimental methods are explained in detail.