Exposure to Bright Light Has Little Effect on Eye Sensitivity and Ultrastructure of Saduria entomon(Crustacea; Isopoda; Valvifera)(Physiology)

11 Pages·1991·7.8 MB·English

by  Magnus Lindstrom

ZOOLOGICAL SCIENCE 8: 653-663 (1991) 1991 Zoological Societj ofJapan
Exposure to Bright Light Has Little Effect on Eye Sensitivity
and Ultrastructure of Saduria entomon
(Crustacea; Isopoda; Valvifera)
Magnus Lindstrom1 Wilhelm Fortelius1 and V. Benno Meyer-Rochow2
,
]Tviirminne Zoological Station, University ofHelsinki, SF-10900 HANKO, Finland and
'School ofScience and Technology, Department ofBiological Sciences,
University of Waikato, Private Bag, Hamilton, New Zealand
—
ABSTRACT Specimens of the isopod Saduria entomon were caught during late winter nights in
Finland and divided intothree groups: onewasnot at allexposed toany light and served asthecontrol;
a second was exposed to midday sunlight of 9.1X1020qu/m2s for 30min: the third was exposed to
artificial white light of4.2X 1020qu m:s during the day for30min. The visual sensitivity thresholds as
well as V log I curves of 15 exposed animals from 30min to 456h postexposure were recorded at
random intervals and compared with values obtained from nine control animals. Only a very minor
reduction ofsensitivity in exposed animals was noticed. Parallel ultrastructural studies confirmed that
light-induced structural derangements of visual membranes, known to occur in other species, were
minimal, with an enlargement of microvilli to twice their normal diameter being the most obvious.
Spectral sensitivity curves recorded from nine control animals reverased one single peak to light of550
nm wavelength, close to maximum transmission of the water in which the animals occur. The res—ults
show that apparently not all crustaceans possess eyes that are easily damag—ed by bright light and in
view of the light-induced sensitivity loss reported in Mysis relicta (13) highlight the danger of
attemptingtopredicthowphotoreceptorsofanotherspecieswouldrespond,evenifthespeciesoccurred
in the same habitat.
published, in this journal, a thorough analysis of
INTRODUCTION
light-inducedsensitivitylossandsubsequent recov-
In several species of crustaceans it was noticed ery in the opossum shrimp Mysis relicta [13], we
that exposure to even moderate levels of bright- decided to follow up that study with an investiga-
ness could suppress visual sensitivity for several tion into the effects of bright light on the visual
days, if not longer [1.2. 3. 4]. Anatomical studies propertieas and ultrastructure of the eye of Sadur-
in parallel with the physiological observations have ia entomon, an isopod species that frequentl\
revealed the light-induced photoreceptor damage shares the same habitat with Mysis relicta. The
or breakdown, once triggered, continued to pro- results from this investigation clearly show that
ceed in the dark long after the initial exposure to even in species inhabiting seemingly identical en-
light [4-9], and. at least in Jasus edwardsii [4] and vironments, a reliable prediction on how the
Boreomysis megalops [10]. had a direct impact on photoreceptors would respond to an exposure of
the behaviour. bright light in other species m difficult, if not
Crustaceans that normally inhabit environments impossible.
oflow ambient light levels [2, 7. 9j. or are primari-
ly noctural [4. g] seem to be especially at risk \ MATKRIALS AM) METHODS
further aggravating factor appears to be higher
than usual temperature [11. 12]. Having earlier
Electrophysiology
Accepted March 15, 1991 I xperimental animals <>t various sizi
Received were collected in traps at 5 20m depth from the
X
654 M. LlNDSTROM, W. FORTELIUS AND B. MEYER-ROCHOW
Eastern Baltic Sea off Tvarminne Zoological Sta- Wratten 87 gelatin filters and sometimes a heat
tion and brought to the surface during winter filteraswell, whichwereinsertedintheraypathof
nights in complete absence of artificial lights. All white light coming from a microscope lamp. The
handling was done with the aid of"Find-R-Scope" incident light, perpendicular to the eye surface,
infra-red viewers. Captured animals were main- was centered around the hole through which the
tained in the laboratory forseveralweeksat5-6°C recording electrode was lowered 40-50/um into
under totally dark conditions and served as con- the eye. The light spot made by the stimulating
trols. Some of the animals were exposed to the flash was large enough to cover the entire eye.
midday sun at an intensity of9.1X1020qu/m2s for Always the same region of the eye was aimed for
30min from 12.50 to 13.20hr in water of 6°C. A when inserting the electrode. Following prepara-
wide beakerplaced in awhiteplastictroughserved tions, which, on average, did not take longer than
as the holding receptacle during exposure. The 10min, the test animals were given 30min in total
outside temperature happened to be the same as darkness to recuperate from the operation. The
the water temperature. Animals treated in this system for stimulation consisted of an extended
W
way are referred to as "sunexposed animals". source (Osram 6B, 15 microscope lamp, po-
Animals exposed to artificial, white light, 4.2 weredbyaconstantvoltagedevice) andallrecord-
1020qu/m2s in intensity, are referred to as "light- ings were made in the AC-setting. Fourteen
exposed". The set-up during the 30min exposure narrow band spectral interference filters, covering
toartificial lightconsistedofa 1000mlglassbeaker wavelengths from406to 673 nm, were available to
(diameter 100mm) filled with 600ml of water. test spectral sensitivity. Flash duration was 0.5
The beaker was insulated from stray light with a sec.
styroxcollar at the heightofthewaterlevel. Light At the completion of the recording the eye and
spectrum andintensityweremeasuredwithaQSM position ofthe electrode were examinedunderthe
2500 quantum spectrometerunder identical condi- microscope; head and body of the experimental
tions through the bottom of the beaker (without animals were then preserved in alcohol.
animals). This means the there was an extra glass
bottom between sensor and the light source. The Electron microscopy
light source consisted of two Argaphoto-BM-200 For ultrastructural observations by transmission
V/500W photolamps 50cm overthe bottomofthe electron microscopy a number ofeyes from anim-
beaker. The lamps were cooled by two electric als representing controls as well as those that had
fans and the temperature ofthe watersurrounding been exposed to sun or artificial lights for 30min
the animals was thermostatically controlled and and then allowed to recuperate in the dark for 30
reached a maximum of 8°C. min, 24hr, and 41 hr, were carefully removed
Following the exposures to either artificial or from the heads and cut free from surrounding
sun light, the animals were immediately returned tissue in a procedure that did not take longer than
totheirdarkenvironments, butkeptseparatefrom 2min. Theeyeswereprefixedfor 12hrinsodium-
non-exposed control animals. Tests of post- cacodylate-buffered2 1/2% glutaraldehyde, trans-
exposure visual sensitivity commenced as early as ferred to buffer, and postifixed three weeks later
30min and continued for up to 456hr thereafter. for 2hr in sodium-cacodylate-buffered 2% Os04.
Forty-one animals altogether were examined elec- Dehydration was achieved in the usual way and
trophysiologically, but only about 2/3 lasted followed by embedding in Epon. Sections for
throughout the experiment and could be evalu- electron microscopy were cut with a Reichert
ated. OMU2 ultramicrotome, stained in uranylacetate
Experimental procedures closely followed those and lead citrate for a few min each, and examined
reported previously [2, 13]. During preparation, under a Philips 400 TEM.
using infra-red image converters mounted on a
Wild-5 stereomicroscope, eachanimalwasillumin-
ated by light that had passed through 2 Kodak
Eye Sensitivity and Structure of Isopoda 655
RESULTS wavelengths. There was little variation in the
seven specimens studied, hence the small standard
deviations at all wavelengths tested (Fig. I). Max-
Electrophysic)k)gy imum sensitivity is situated close to the region o(
ERG-waveforms of two main shapes were re- maximum transmittance of the water in this area
corded, although by far the most common one was (approx. 565 nm [3]). which suggests that the
a rapid initial cornea-negative "on-response" fol- animals may be considered well-adapted to the
lowed by a slightly slower return to the baseline. local photic environment.
This kind ofresponse wasvirtually identical to that Taking a response of 50//V as threshold level,
of the eye of the isopod Cirolana borealis [2]. we compared absolute sensitivities to white light in
Another type of response that seemed to come animals of different lengths and different degrees
from eyes in which the electrode and made less of dark-adaptation (Fig. 2). No statistically signi-
optimal contact, i.e. either did not penetrate the ficant correlation with size (and, therefore, pre-
corneal hole well or had been pushed into the eye sumably age) ofthe animal was found (R=0.045).
toofar. displayed aposititve overshoot immediate- Animals that had been exposed to artificial light
ly following the initial negative deflection. Where
responsesofthis type were used forthe analysis, as
10000
with all other responses too, only the amplitude of
the initial negative deflection wasconsidered. This
made comparisons between animals consistent.
All eyes responded to increasing light intensities
with an increase in amplitude. The highest peak
amplitude recorded was 3050juV in a fully dark-
adapted animal, but in the majority ofeyes tested
peak amplitudes were in the vicinity of 1000/^V.
Spectral sensitivity, measured from the eyes of
seven control specimens, peaksat550 nm and then
falls off towards both shorter and longer
'6 " 5 4 3 2 1
log density
3-5 i S2 <-S2 -»-S7 oS8 «S32 «S36 +S37 »S41a *S41b
-yM Fig. 2. A comparison of the eye's sensitivity with the
30 _ >^ animal'ssize (monitored astelson length) revealson
*
correlation
J" \
6
I 20 -
in \
T 5 5
10 \ - <*o
r I
I
:00 500nm eoc 15 20
Telsonlength(mm)
Fig. I. Spectral sensitivity curve of Saduria Ottoman,
based on recordings from se\en different animals 'Control • 5hda 24hda •48nda °72hda
Standard deviation for each wavelength tested is \\i, ; \ log I i response stimulus intensity)dataol
indicated b\ vertical bars. The sinde maximum (550 ninecontrol animals not exposed to light prior tothe
nm) is situated in the region of maximum light recordings, plotted on log-log axes ITin
transmission of the watercolumn (approx. 565 nm) sensitivities cluster around a log I ol 5 and pli-
Abscissa: the wave-length plotted upon a linear tudesaround 1000ftV. Differentsymbol sent
scale of frequenc\ different animaK
656 M. LlNDSTROM, W. FORTELIUS AND B. MeYER-RoCHOW
before, did, however, display a trend of reduced artificial light, fall within the limits set by the five
sensitivity, which prompted further examination. curves shown in Figure5, representing the ex-
V/logI curvesofninecontrol animalsareshown treme dark-adaptation times0.5 hr and approx. 70
A
in Figure 3. Taking most and least sensitive hr. further 4 V/log I curves, representing
curves, they are distributed across a sensitivity light-exposed animals tested between 22 and28hr
band roughly 1 log unit wide and display some post-exposure and another 4 from 41-48hr post-
variation in maximum amplitude, but basically exposure animals have been recorded (not shown)
they are very similar in shape. V/log I curves of andfallexactlywithintheclusterofcurveshownin
seven animals tested from 3 hr to 456hr of dark- Figures4 and 5.
adaptation following a 30min exposure to sun- In the study ofthe mysid compound eye [13], it
light, form a cluster with little variation between was found that a useful indication ofthe degree of
one another (Fig. 4). Likewise, the V/logI curves light-inducedsensitivityreductionwasprovidedby
of all thirteen animals exposed for 30min to an examination of the 50-100/uV response span
1 000
^v
100
5 4 3 2 1
logdensity log density
*S253hda ^S2724hda <>S2828hda S2944hda nS60.5hda <>S180.5hda *S1672hda S2070hda
+-S3048hda -S38288hda °S39456hda xS2275hda
Fig. 4. V/log I data ofseven animals obtained at indi- Fig. 5. V/log I data of five animals obtained at indi-
cated times of dark adaptation (da) following a 30 cated times of dark-adaptation (da) following a 30
min exposure to midday sunlight of 9.1xl020qu/ min exposure to artificial light of 4.2xl020qu/m2s
m2s intensity. Irrespective of whether testing was during the day. Irrespective ofwhether testingwas
carried out three hours postexposure (animal S25) carried out 0.5hr (animal S6) or75hr (animal S22)
or 456hr postexposure (animal S39), the difference postexposure, the difference between these, the
betweentheseandthecontrolcurvesofFig. 3isvery curves generated by sun-exposed animals, and the
small. controls is very minor.
5r
Fig. 6. Responses of 50juV and 100//V and
* \ their corresponding stimulus intensities (on
i,
III the ordinate) in relation to postexposure
time plotted on the abscissa. Note the
slightly elevated sensitivities of the non-
exposed control group but the rather uni-
form span of the 50-100//V bar on all
24 48 72-Nr 456 animals tested.
Dark-adaptionafterexposure(h)
Control 4Exposed <j>Sun-exposed
Eye Sensitivity and Structure of [sopoda 657
and its associated neutral density range (Fig. 6).
Foreach group the mean log density value causing Histology
a 50//V response was calculated. Both exposure Dissection oi the eye. because o\ the very hard
groups differed on a statistically significant level cuticle surrounding it. proved difficult, but ade-
from the control group (t-test, control versus light- quately fixed material from eyes oi 1 1 animals was
exposed. t=3.21; p=0.(X)8 and control versus analayzed byelectron microscopy. An overview of
sun-exposed t=2.75; p=0.018). No significant gross ommatidiae organisation is shown in Figure
differences showed up between sun and artificial 19. There were few screening pigment granules
light exposed animals. In contrast to the Mysis surrounding the crystalline cones and. it agree-
data [13], the length of the 50-100^V bar is ment with Nilsson [18], no changes were found in
virtually identical in controls, sun- and light- light and in darkness. Transversely sectioned
exposed animals and only the position ofthe bar in rhabdoms of animals, whether or not exposed to
relation to associated neutral densities varies light, displayed a variety of sizes and shapes and
slightly between the groups. This suggests that all were often 5-lobed with diameters between oppo-
animals, irrespective of their previous exposure site lobes ofaround 30//m (Figs. 8, 9, 11). Screen-
history, apparently possess well-functioning eyes, ing pigment granules were moderate in number
albeit with slightly different thresholds. and occupied peripheral positions in dark-adapted
Another parameter looked at was the difference animals. The numberofcontributing retinula cells
between the neutral densities responsible for giv- was normally five, although two smaller additional
ing rise to 50fA/ and 100/uV responses (Fig. 7). ones were usually present and sometimes were
As in the mysid study [13], this parameter de- seen to have a small rhabdomere as well. Rhab-
scribes the slope of the V/log I curves. Thus, the doms stained uniformly and even in eyes of anim-
significantly high value of this parameter for the als exposed to sunlight and artificial lights the
sun-exposed group as compared with the control majoirty of the rhabdoms retained their integrity
group (t=-5.31; p=0.0003) and the light- and staining characteristics known from the con-
exposed group (t=—2.25; p=0.04) demonstrates trols. Central regions of abnormal microvilli iso-
a shallower slope for the V/log I curve of the lated from apparently undamaged and relatively
sun-exposed group. No statistically significant unaltered rhabdom by an electron-translucent gap
difference between control and artificial light did develop in some eyes 24hr postexposure to
group was revealed. sunlight (Fig. 9).
Irregularities and a loosening of the microvillar
compound occurred in some ommatidia of the
light-exposed, 24 hr post-exposure eye (Fig. L0).
However, in all eyes examined 24 hr and 41 hr
-. post-exposure, screening pigment granules in the
1 0.75-
dark-adapted peripheral positions and the overall
picture of retinula cells and rhabdoms was that ot
2- : :c near-normality (Fig. 11). Since the mictOViUi are
c
the structures not only most at risk from photo
? 025 induced structural damage, but also represent the
site of phOtO-transduction and are. thus, a good
24 43 72 288 456 structural indicator of "function", a closer look at
Dark-adactionafterexposure(h) their organization seemed an essential require*
ntrol •Exposed .Sunexposed ment for this investigation.
Fig. 7. Log-density difference between stimuli giving In animals that had been m the dark for at least
rise to 50/tV and 100ft\ responses plotted Bgainsl tWO weeks prior to fixation, microvilli exhibited an
control-, sun-, and artificial light exposed animals, extremely regular lattice of parallel oriented.
atbessctiesdsaat postexposure times indicated on the blind-ending tubes, measuring 65-75 nm in dia-
658 M. LlNDSTROM, W. FORTELIUS AND B. MEYER-ROCHOW
j 1* • *.*.
Fig. 8. 5. entomonrhabdoms(Rh)comeinvariousshapes,buttypicallymeasureapproximately30jumacross. They
are made up of five major and two minor retinula cells (numbered 1-7). In this dark-adapted control animal
screening pigment granules are located peripherally. The scale is 10jum.
Fig. 9. Somerhabdomslikethisofa30minsun-exposedanimalfixed24hrpostexposureinthedark,displaycentral
lesions. Most ofthe rhabdom and itsconstituent microvilli, however, are intact andscreeningpigmentgranules
are generally in the dark-adapted position. The scale is 5/um.
Fig. 10. A certain degree of loosening of the microvillar arrangement and serrations at the edges ofthe rhabdom
were found in material exposed for 30min to artificial light and then fixed 24hr after recuperation in the dark.
Eye Sensitivity and Structure of Isopoda 659
meter (Figs. 12. 13). The regular and dense pack-
DISCUSSION
ing of the microvilli resulted in hexagonal profiles
ofthe latterwhen sectioned transversely (Fig. 12). In view of the many publications describing
As with microvilli ofother crustaceans, their cyto- light-induced sensitivity loss and ultrastructural
plasmic interior was in communication with the damage in crustacean photoreceptors, summarised
retinulacell plasma, althought bundlesofmicrovil- in [13], the result that in Saduria entotnon expo-
li seemed to arise from the same anchor point sure tosun and artificial lights had very little effect,
similar to the situationsdescribed from lobster [14] comes as a surprise. S. entotnon can hardly be
and crayfish [15]. termed an animal that habituallyor frequently gets
A 30min exposure to artificial light resulted in exposed to sunlight. On the contrary; it spends
few signs of microvillar disruption 30 min post- most of its time in or near the bottom mud of the
exposure (Fig. 14). Rhabdom microvilli were still Baltic Sea and is clearly nocturnal throughout the
regular, though suggestions of swellings in year [24]. It is, however, extremely tolerant to
amongst them were apparent. The edges of the changing salinities [16] and copes with a wide
rhabdom exhibited signs of light-adaptation in the range of oxygen concentrations and temperatures
form of vesicles budding off towards the retinula as well [25]. At present we can not offer an
cell and screening pigment granules were in the exhaustive explanation as to why the eyes oisome
light-adapted position (Fig. 15). Twenty-four isopods like the deepwater species Cirolana
hours post-exposure a considerable proportion of borealis and Bathynomyus giganteus apparently
microvilli had become enlarged (Fig. 16), afeature lose all sensitivity [2, 9] and react with a disintegra-
also seen in the eye of Mysis relicta as a consequ- tion of the rhabdom to an exposure of bright light
ence of bright light exposure [13]. [6, 9] while others including the Antarctic Clypto-
Although a greatervariety ofmicrovillardimen- notus antarcticus [17] and Saduria entotnon (this
sions and orientations than in the dark-adapted paper) suffer little structural and/or functional
control rhabdoms was obvious in eyes exposed to effect.
bright light, the overall impression was that of Saduria has a fairly thick, multilayered cornea
relatively undisturbed rhabdoms. The swelling of (approx. 30-40//m; this paper) and so has Glypto-
the microvillar diameters to at least twice the size notus (approx. 70//m [17]) but we do not believe
ofthose ofthe dark-adapted controls was the most that corneal thickness and ultiastructurc alone are
obvious change. Forty one hours post-exposure the reason for the greater light tolerance in these
microvillar diameters had become reduced, but two species, for Cirolana borealis which reacts
still had not reached the pre-exposure dark- sensitively to bright light exposure [2. 6] also has
adapted control dimensions (Fig. 17). rather thick corneal lenses (20-55//m: [18]), and
Animals exposed to the somewhat brighter sun- the same dichotomy is observed in the amphipods
light for 30 min exhibited similar trends, but on a Orchomene plebs and O. sp. cf. rossi [7. 1 1|. The
lesser scale. For example, signs of rhabdom dam- duration of the initial exposure to light was twice
age, confined to the central portion of some rhab- as long in Mysis relieta 13]. but the intensity Ol the
[
doms. were indeed seen 24 hr post-exposure (1 ig. light used was much lower than that used in this
9). But microvillar diameters 30 min postexposure Study. This. too. points to a more fundanienl.il
were virtually unchaneged from dark-adapted con- difference in the eye physiolog) ol the two species.
trols as well as 24 hr post-exposure eyes (Fig. 18) An interesting structural parallel t«> M. relicta
[l<| niter the enlarged microvillusdiametersin the
eye Ol Saduria, following exposure to bright light
The scale is 15 peak.
Fig. 11. Approximate!) twodaysfollowing 30mmofexposure tosunlight, rhabdomsol animalssubsequent!)
the dark like this example are apparent!) normal and, apart from a small remnant of the central 1- si
earlier, quite indistinguishable from control animals The scale is 10//m
660 M. LlNDSTROM, W. FORTELIUS AND B. MEYER-ROCHOW
13
// W
I
*\i
?
:
Fig. 12. Rhabdom microvilli ofdark-adapted, control animals display a regular array ofhexagonally-packed tubes
measuring 65-75nm in diatmeter. The scale is 0.5fxm.
Fig. 13. Whenlongitudinally-sectioned,themicrovilliofrhabdomsofdark-adaptedcontrolanimalsdisplayaparalle
alignment, a uniform diameter of 70nm and anchor-points at the edge of the cytoplasm shared by a group of
Eye Sensitivity and Structure of [sopoda 661
But while in M. rclicta the loosening oi the micro-
villus compound led to a worseningstate culminat-
ing in a severe derangement of microvilli, the
Saduria eye possessed sufficient "self-healing"
powers to go back to normal. The minor nature of
the structural damage was completely mirrored by
the ERGs, recorded pre- and post-exposure.
While therewasastatisticallysignificant difference
in the thresholds and the way the V/log I curves
began to rise within the first 50//V (between 50
and 100 uV amplitudes), the effect was very minor
t
when compared with the dramatic sensitivity loss
and flattening ofV/log I curves in M. relicta under
very similar experimental conditions [13]. In fact,
the higher sensitivities in the dark-adapted con-
trols showed an overall, greater scatter than those
recorded post-exposure. This indicates to us that
the unnaturally longperiod the controls have spent
in totaldarkness might have increased the amounts
ofphoto-pigment to abnormally high levels, which
then raises the question, whether the small micro-
villus diameters observed in the dark-adapted con-
—
trols can be considered normal or abnormally
small. In any case, there can be absolutely no
doubt ofthe ability ofthe exposed eyes to function
normally over a wide range, covering more than 4
log units, of photic stimulation even following the
exposure to bright light.
Fig. 19. Schematic representation of longitudinal sec-
tion of ommatidial unit in the eye of Saduria en-
tomon (after Nilsson [IX]). A-axon; CC=crystal-
line cone; CE=conc cell extension; CI. corneal
layers; DP=distal pigment; E=eyc capsule mem-
brane; FM=fenestrated membrane; (» glial cell;
RC=retinula cell; RH=rhabdom; RP reflecting
pigment.
microvilli. The scale is 0.5,um.
FlG. 14. Afterthirty minutesin the dark followinga 3')mm exposure toartificial lights, microvillaidiametersare still
apparentlyunchanged fromcontrols, but acertaindegreeofdisruption ofthe regularorder isbecomingapparent
The scale is li 5//m.
FlG. 15. Same treatment as in Fig. 14. but the focus is on the edge of the rhabdom where typical sums ol
light-exposure like budding vesicles, screening pigment grams (arrow), are apparent. The scale is 0.6/um
Fig. 16. In all three animals in which rhabdoms uere examined one da\ follwing exposure to artificial light fol 50
mm. the microvillai organization for the greater part remained intact, but microvillar dimensions I),id i I
with diameters now being 2-3 times as wide as the controls. The scale is0.5 //m
Fig. 17. Even 4] hr following exposure to artificial light, microvillus diameters are not back to the control values
The scale is 0.5 //m
Fig. IS. A touch oflight-induced irregularities in the organization and dimensionsof microvilli is al» n 50
min sun-exposed rhabdoms Rut at 24 hr postexposure (this micrograph), the rhabdom is ban I liffi r<
the control. The scale is 0.5 //m.
662 M. LlNDSTROM, W. FORTELIUS AND B. MEYER-ROCHOW
The spectral sensitivity curve with its single 23-37.
maximum in the green part of the spectrum 4 Meyer-Rochow, V. B. andTiang, K. M. (1984) The
appears to reflect a high degree of evolutionary eye ofJasus edwardsii (Crustacea, Decapoda, Pali-
adaptation to the light transmission properties of nuridae): electrophysiology, histology, and be-
haviour. Zoologica, 45: 1-85.
Tvarminne offshore waters, which exhibit a max-
5 Loew, E. R. (1976) Light, and photoreceptor de-
imum at around 565 nm [3]. Spectral sensitivity generation in the Norway lobster, Nephrops norve-
apparently does not undergo any change with size gicus (L.). Proc. R. Soc. London, 193B: 31-44.
(and, therefore, presumably age) of the animals, 6 Nilsson, H. L. and Lindstrom, M. (1983) Retinal
which agrees with recent studies by Ziedins and damage and sensitivity loss of a light-sensitive
Meyer-Rochow [19] on Petrolisthes elongatus and crustacean compound eye {Cirolana borealis): elec-
Forward and Cronin [20] on intertidal crabs. Sea- tBirooln.,m1i0c7r:os2c77o-p2y92a.nd electrophysiology. J. Exp.
sonal changes, however, documented in the 7 Meyer-Rochow, V. B. (1981) The eye of
crayfish by Nosaki [21] and Suzuki et al. [22] as Orchomene sp. cf. O. rossi, an amphipod living
well as variations between geographically isolated undertheRossIceShelf(Antarctica). Proc. R. Soc.
populations, reported for example in Mysis relicta London, 212B: 93-111.
by Lindstrom and Nilsson [3] cannot be ruled out. 8 Shelton, P. M. J., Gaten, E. and Chapman, C. J.
Whatthisstudyhasmade abundanlyclearisthat g(i1c9u8s5)(LL.)ig(hCtruasntdacreeat)in.alPrdoacm.aRg.eSionc.NeLpohnrdoopns,n2o2r6vBe:-
generalizations are dangerous. Even crustacean 218-236.
species co-inhabiting the same environment may 9 Chamberlain, S. L., Meyer-Rochow, V. B. and
display very differnt responses to the exposure of Dossert,W. P. (1986) Morphologyoftheeyeofthe
bright light. In the words of Nilsson [23], who giant deep-sea isopod Bathynomus giganteus. J.
Morphol., 189: 145-156.
presented three examples of crustaceans with
"apparentlythe 'wrong' type ofeye", oneisforced 10 A(1t9t8r5a)maCdhaaln,gJe.sGi.n,beFohsasvai,ouJr. aHn.daenydeNmiolrspshono,loHg.yLo.f
to accept "how easy it is to underestimate the Boreomysis megalops Sars (Crustacea: Mysidacea)
competence of evolution". following exposure to short periods ofartificial and
natural daylight. J. Exp. Mar. Biol. Ecol., 85: 135-
148.
ACKNOWLEDGMENTS
11 Meyer-Rochow,V. B. andTiang,K. M. (1979) The
The authors are indebted to the Finnish Academy of effects of light and temperature on the structural
organisation of the eye of the Antarctic amphipod
Sciences and the Walter and Andree de Nottbeck's
Orchomene plebs (Crustacea). Proc. R. Soc. Lon-
Foundation for the support rendered to wards this pro-
don, 206B: 353-368.
ject and Tvarminne Zoological Station for providing
workingfacilities. V. B. Meyer-Rochow,further,wishes 12 Meyer-Rochow, V. B. and Tiang, K. M. (1982)
tothankthe Alexanderv. HumboldtFoundation(Bonn, Comparison between temperature-induced changes
Germany) and Prof. Y. Morita (Hamamatsu Medical and effects caused by dark/light adaptation in the
University, Japan) for their roles in the success of this eyes of two species of Antarctic crustaceans. Cell
Tissue Res. 221: 625-632.
project.
13 Lindstrom, M., Nilsson, H. L. andMeyer-Rochow,
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