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Effects of temperature change on irrigation rate in Arenicola marina (L.)
Con@. Biochem. Physiol., 1972, Vol. 43A, pp. 553 to 564. Pergamon Press. Printed in Great Britain
EFFECTS OF TEMPERATURE CHANGE ON IRRIGATION RATE IN ARENICOLA MARINA (L.) MALCOLM Department
K. SEYMOUR”
of Zoology, University of Hull
(Received 22 January
1972)
Abstract-l. The effects of slow and rapid temperature fluctuations on the rate of burrow irrigation in Are&cola marina (L.) have been studied using pressure and impedance recording techniques. 2. With slow temperature change (2”C/hr) irrigation rate rises very slowly up to lO”C, faster between 10 and 14X’, more slowly up to 18°C and drops sharply above 18°C. The total number of irrigation waves, frequency of exposure of the gills and substantially the volume of water pumped vary as does the rate/temperature curve. 3. Q10 is low, rising to only 1.17 between 12.25 and 14*45”C. It is suggested that rate increase up to 18°C is a compensatory mechanism maintaining oxygen uptake for as long as possible under low-tide warm-weather conditions, and that the reversible drop in irrigation rate above 18°C is a survival mechanism for low-tide conditions. 4. Despite the characteristic rate change with gradual temperature change there is a compensatory response to quickly changed temperature which shows marked overshoot and oscillation, 5. Removal of the ventral nerve cord in a segment stops all irrigation movement in that segment. After nerve cord section in the mid trunk the rate of each half of the trunk is dictated independently by the environmental temperature of that half; it is probably the irrigation pacemaker mechanism in the cord which responds to a change in temperature by a change in rate.
INTRODUCTION As A LITTORAL fluctuations.
animal, These
&?zicolu
changes
marina is potentially
exposed
may be either slow (diurnal
to large temperature
and seasonal)
or relatively
rapid (when the burrow is covered and uncovered by the tide, when the worm moves in its burrow towards and away from the exposed sand surface or when it leaves the sand and swims up to the water surface Legendre,
1927;
Newell,
ments were from Kames for
the
year
sand surface (August)
ending
1948 ; Seymour, Bay, Millport,
22 January
varied from between
(B. L. S. Hardy,
communication).
553
used
1924;
in these
in the Armicolu
temperatures
of Nematology,
& Storrow,
Worms
3 and 7.5”C (January)
personal
* Present address : Department Harpenden, Herts.
Scotland;
1969,
(Meek
1972a).
These
Rothamsted
experi-
area of this bay,
4 in. (101 mm) to between
Fage &
below
the
12 and 17*5”C
temperatures Experimental
were Station,
554
MALCOLM K. SEYMOUR
taken in undisturbed sand and those in burrows might well be greater in summer; however they give an indication of the range of temperature to which this population is subjected. As a step towards understanding how such changes directly affect the life of Arenicolu, the effects of experimental temperature fluctuations on rate of irrigation have been studied. Irrigation activity proper is the passage of a series of waves along the dorsal side of the trunk of the worm in the U- or J-shaped burrow the worm normally occupies in muddy littoral sand (Wells, 1945). Alternate phases of thinning and thickening pass forward or backward, occluding the burrow and driving water through it in piston fashion. Each pair of gills expands as its segment thins and contracts as the segment thickens again. In creeping the same wave sequence
-
(3) ;:
(8)
,
i
1
FIG. 1. Unbroken extract from impedance records of irrigation in two worms transferred at dotted line from warm to cool sea water. Irrigation rate falls from 6.0 to 3.5 (upper record) and from 7.0 to 3.0 waves/mm (lower record). Temperature in “C, time in minutes. FIG. 2. Impedance records of irrigation in two worms a few minutes before (left) and after (right) transfer from cool to warm sea water. Irrigation rate rises from 4.0 to 8-O (upper record) and from 3.5 to 10.0 waves/mm (lower record). Figures in parentheses show how many minutes before and after transfer (at dotted line) extracts were recorded; time between extracts was occupied by non-irrigating activity. Temperature in “C, time in minutes.
TEMPRRATURE CHANGE ON IRRIGATION RATE IN AREN1CCJl.A MARINA
555
occurs, but thinning and thickening extend further ventrally and length changes may occur, resulting in movement of the worm along the burrow. (See Seymour, 1971 for discussion of wave movement in Arenicola.) In creeping, as in irrigation proper, (described by Wells, 1945,1949a, b, 19&j), contraction and expansion of the gills with the passage of each wave and movement of the water relative to the worm still take place and the two activities are practically identical from their respiratory aspect. Because of this functional and mechanical similarity, behaviour resulting in the type of record shown in Figs. 1 and 2 from worms in polystyrene tubes, which may have included both types of activity, is termed irrigation throughout this account. The term irrigation rate as used here is defined as the number of irrigation waves in a worm per min, calculated from counts of pressure or impedance records over 2-min periods wholly occupied by irrigating activity. During these investigations worms in straight polystyrene tubes showed intermittent irrigation, periods of “rest” and other activity (see Wells, 1945) alternating with it as found also by van Dam (1937). Irrigation waves usually passed taiIwards, but periods of “inverse” irrigation (tail to head) as seen by van Dam (1937) and by Kruger (1964) were also observed. Worms of similar weight (6.5 + 1 g, weighed wet) were used in the experiments and weight/rate correlation was not attempted. Irrigation rates have been recorded at different environmentaf temperatures and upon slow and rapid temperature change. Comparison of such records has provided data on the following points: (i) Change in rate with slow temperature change. (ii) Proportion of total time spent irrigating at different temperatures. (iii) Probable effects of temperature changes, and the worm’s response to them, on the life of the worm. (iv) Responses to rapid temperature change and the type of capacity adaptation they suggest. MATERIALS
AND METHODS
Specimens of Armcola marina (L.) were obtained from the Marine Laboratory at Millport, Isle of Cumbrae, Scotland and kept in shallow tanks of cooled, filtered, aerated, circulating sea-water. To monitor irrigation movements, a worm was placed in each of four straight polystyrene tubes 130 mm long and 9 mm bore which were clamped together as a unit. The tubes were sealed with polyethylene stoppers and near their ends small holes allowed free in and outflow of water. In some experiments, cyclical pressure changes in the tubes during irrigation were sensed by a Statham P23BB pressure transducer through fine polyethylene tubing attached to a nozzle cemented centrally to each tube; in others, impedance pneumographs (see Hoggarth & Trueman, 1967) detected cyclical impedance changes between a pair of diametrically opposed tinned steel wire electrodes attached centrally to each tube and just penetrating its lumen. In each, output was recorded on an inkwriting multichannel pen recorder, the Physiograph. A thermistor coupled to the Physiograph gave a continuous record of bath temperature. Experimental tanks were stirred constantly. In experiments designed to show any effect of change of temperature on irrigation
556
MALCOLMK. SEYMOUR
rate, the bath temperature was varied by i, automatically slowly replacing water at room temperature with refrigerated sea water, and ii, filling the tank with refrigerated water and allowing slow warming to room temperature. Temperatures higher than ambient were obtained with a small aquarium heater. In temperature acclimation experiments, when only the impedance recording method was used, the array of tubes containing worms was transferred rapidly from a bath at one constant temperature to one at another constant temperature.
EXPERIMENTAL
OBSERVATIONS
Vuriation in irrigation rate with gradual temperature change Specimens of Arenicola, previously kept in sea water below lO”C, were warmed and then cooled at a steady rate of 1°C every 37 min (under 2”C/hr). Mean irrigation rate plotted against temperature yields a curve as in Fig. 3a. With minor fluctuations the rate rises very slowly from 6 to lO”C, faster between 10 and 14”C, more slowly thence up to 18°C and it drops sharply above 18°C. This form of rate/temperature curve, including the steep negative slope at high temperatures, occurred in worms, both heated and cooled, which showed no subsequent illeffects; it was not an effect of irreversible heat-damage. The fluctuation in rate is illustrated also by the temperature coefficient ( QIO) calculated from rate values for 2-degree ranges (Fig. 3b). The Qr,, throughout is low, rising to only 1.17 between 12.25 and 14*45”C and thereafter falling very rapidly.
/A------‘--‘___
b
~ ‘\%,,
tamp
OC
FIG. 3. Effect of gradual temperature change (mean rate 2”C/hr) on A. marina. a. Irrigation rates in waves/mm (means of fourteen worms with one standard error above and below). b. Temperature coefficient for 2-degree ranges (between 6.25 and 20.25”C).
TEMPERATURE CHANGE ON IRRIGATION RATE IN ARENICOLA MARINA
557
Although irrigation rate increases with temperature and then falls off, the proportion of time spent irrigating at different temperatures was found to be rather constant around 55 per cent; this compares well with the 45 per cent of time over which A~enicolu in sand performed the “Normal Cyclical Pattern”, including creeping and irrigation proper (Wells, 1966). It follows from this that the total number of irrigation waves in a given period and therefore the total amount of irrigating activity, the amount of exposure of the blood-filled gills to the water, and largely the volume of water pumped past the worm must all vary in accordance with the rate/temperature curve described. If the increase in rate of irrigation were mainly an unavoidable temperature effect, of no value to the worm, a mechanism with the reciprocal effect of reducing the time spent irrigating as the rate increased might be expected to be present. No such effect is apparent. Although van Dam (1937) f ound that pumping effect of irrigation waves could vary in the same animal, long-term pressure and impedance records obtained here show little amplitude variation over experimental periods and range of temperature. Variation in irrigation rate with sudden temperature change These experiments were designed to show, in terms of irrigation rate, responses occurring within a short time of transfer from water at one temperature (Tl) to water at another temperature (T2). This sudden type of change may be quite common in nature; Grainger (1958) mentions movement through thermoclines and to or from patches of sunlight. In the case of Arenicolu, cold sea water may cover and enter a burrow where a surface temperature of 28°C may have been recorded (Kermack, 1955). Sudden increase of temperature might be encountered when a “testing” excursion is made up the burrow tailshaft into a puddle at this order of temperature. The worms were acclimated in the apparatus to Tl for at least 24 hr before the apparatus was transferred to T2 (see Figs. 1 and 2), and, 50 to 90 min later, back to Tl. Plots of irrigation rate against time are shown in Figs. 4 and 5. In an experiment (Fig. 4) using three animals transferred from 9.7 to 22.15”C a rate of 4 f 1 waves/min increased on transfer to 10 & 1.5 waves/min. Within 40 min these increases had been halved and after a further 50 min they were reduced to between 17 and 37 per cent of their initial values. At this point the apparatus was transferred back to cold water; the rates at once fell to 3 + 0.5 waves/min and after 100 min more were steady at a level close to that at the beginning of the experiment. Grainger (1958) describes two main types of response after sudden transfer from one temperature to another, and notes that they may be found in metabolic rate, heartbeat and locomotory movements. In the first there is a marked “overshoot” in the parameter being investigated. The second type shows no overshoot and a steady level at the new temperature is reached at once. The results presented in Fig. 4 show very clearly that the response in irrigation rate of Arenicola to a sudden change in temperature is of the overshoot type. The form of overshoot curve following second transfer (Fig. 4) has the form of a damped oscillation round the
558
MALCOLM K. SEYMOUR
I
0
200
100
300
FIG. 4. Irrigation rate in waves/min from impedance records, plotted against time for three worms transferred suddenly from cool sea water to which they had been acclimated for 48 hr, to warm water and back again. The worms’ responses show overshoot followed by oscillation. 5-
min
FIG. 5. Irrigation rate in waves/min from impedance records plotted against time
for two worms transferred suddenly from warm sea water in which they had been kept for 48 hr, to cool water and back again. Further information is in the text.
TEMPERATURE
CHANGE ON IRRIGATION RATE IN ARENICOLA
MARINA
559
initial rate value “leading eventually to a steady state which is typical of the new temperature” (Barnes & Barnes, 1959). Oxygen consumption of ~~Zff~~ u~~~~tr~te shows such oscillatory overshoot (Barnes & Barnes, 1959) and Fig. 1 in Grainger (1956) well shows overshoot and subsequent oscillation in the oxygen consumption of Hemimysis lamornae. Temperature change and co-ordination of irrigation
It has been established above that irrigation rate of an individual Are&cola rises or falls abruptly when the whole worm is placed in relatively warm or cool water. To investigate anterior/posterior co-ordination of irrigation behaviour the anterior and posterior halves of the trunk of a worm were surrounded independently by warmed or cooled sea water giving an 8- to lo-degree temperature differential. The resulting irrigation rate differences between halves was recorded. During half the experiments the ventral nerve cord was interrupted at the 9th chaetigerous annulus by an incision in the mid-ventral body wall. Results are schematically summarized in Fig. 6a and b. In an intact AreCola at a uniform temperature, anterior and posterior irrigation rates did not differ (they represented two counts of the same set of waves). However, if only one half of the trunk were warmed the overalE rate (i.e. of the whole trunk) rose; this effect was sometimes more marked on warming the posterior trunk than on warming the anterior trunk (Fig. 6a, 1 and 2). In other cases after warming either half of the trunk, the irrigation rate rose, or remained raised, equally (Fig. 6b, 1 and 2). Most strikingly, after transection of the ventral nerve cord half way along the trunk, at chaetigerous annulus 9 (Fig. 6a, T), the irrigation rate of each half of the worm rose or fell independently when that half was warmed or cooled; that is, each half behaved as if it were a separate worm (Fig. 6a, 3 and 4). Thus the nerve cord is responsible for co-ordinating irrigating activity and when it is bisected each half co-ordinates a wave in segments through which the cord is continuous ; a comparable effect has been demonstrated for giant nerve fibre transmission in Are&cob (Seymour, 1972b). Irrigation activity in body wall preparations ceases after removal of the ventral nerve cord, which contains the irrigation pacemaker. Since the rate of a warmed part of the trunk can determine that of a cooled part, and since this control is abolished by nerve cord transection between the parts, it is the pacemaker mechanism in the ventral nerve cord whose rate of activity is raised or lowered when warmed or cooled water surrounds the body. Conduction velocities of nerve fibres are known to vary with temperature. Also, temperature acclimation has been shown to occur in Lapis giant fibres in respect of conduction velocity, refractory period and duration of phases of the action potential (Lagerspetz & Talo, 1967). It seems, therefore, that it is at the nervous level that the primary basis of temperature dependence and acclimation is to be found. The extreme rapidity of rate change following temperature change
560
MALCOLM K. SEYMOUR
suggests that afferent impulses from cutaneous receptors may trigger the initial response. The rate of pulsation of the dorsal blood vessel of ArenicoZa (recorded with the impedance pneumograph) also varies with temperature and in one worm, cooled suddenly from 30 to 9”C, fell instantaneously from 6-5 to 3 per min. rote
-” i -7 K i Y(a)
0.
;
i
.I......I I
...a.......*......... i 3 2
4
temp.
;....... ..a....a....:
:“““”
rate
P,
,......,.,......:
a.
l-
temp.
i”.....,...........‘I
..........*....../
I
temp.
:...*....
i. I......*....*.i
i’““. ;
P.
:*..*....,*.,*..:
tsmp:... ..*.:
(b)
~-sB-s***.,.
:............
2
:. ,I,. ..*****..*.,.*......
i
.,.i...*...............*..... ........i
FIG. 6. Schematic presentation of the results of two types of experiment (a) and (b). In each the anterior (a.) and posterior (p.) halves of the trunk of &&cola were subjected independently to warm and cool sea water. The 9th chaetigerous armulus was taken as the halfway mark. Solid lines represent irrigation rate calculated from impedance records; dotted lines represent bath temperature. Both are plotted against time. Each experiment is about 1 hr long. Upward deflexion of lines indicates an abrupt rise, downward deflexion an abrupt fall in temperature or irrigation rate. Fluctuations of anterior and posterior bath temperatures cause corresponding fluctuations in anterior and posterior irrigation rates. The rates are co-ordinated in intact worms (i.e. in (b) and in (a) left of line T). After transection of the ventral nerve cord at the ninth chaetigerous annulus ((a) right of line T), the rate of each half of the worm rises or falls when that half is warmed or cooled.
TEMPERATURE CHANGE ON IRRIGATION RATE IN ARENICOLA MARINA
561
Experiments were attempted in which the worms were kept at elevated temperature (19-20°C) for 2-3 days to acclimate before being subjected to low (about SC) and then to high temperatures again (Fig. 5). In these experiments apparently abnormal spasmodic activity contrasted with the long periods of regular irrigation seen in the low to high temperature experiments, and the drop in rate on sudden cooling was small compared to the previous fluctuations at steady high temperature, with no clear overshoot. In short this result illustrated the adverse effect of sustuined exposure to high temperature. Kermack (1955) notes no abnormal behaviour of Arenicola when surface sand temperature reached 27°C and surface water 28°C at air temperature 26°C but temperatures can have been so high only temporarily at low tide. DISCUSSION
Increase in irrigation rate with temperature Metabolic processes commonly increase with increased temperature; but, as shown here, Arenicola has considerable regulatory powers. Despite this, the worm still shows an increase in irrigation at higher temperatures. A working hypothesis is postulated that this residual variation is of survival value as follows: Eliassen (1956) showed that oxygen consumption in A. marina is the same in “high tide” and “low tide” water, and Kruger (1958) also found that consumption is independent of external oxygen concentration down to 0.2 ml/l. Percentage withdrawal of oxygen from sea water, with oxygen partial pressure the same as in air and at one-twentieth of that value, is constant at 40 f 10 per cent (van Dam, 1938). It follows that at lower oxygen tension more water must be pumped for the same consumption rate at the same temperature. The effect will be enhanced as temperature rises. Van Dam (1938) showed that as oxygen tension falls in the surrounding water, at steady temperature, both volume of water pumped and irrigation rate increase at first and usually decline at very low oxygen tension. When the worm’s burrow is immersed, conditions of temperature and oxygen tension must be fairly constant; the greatest temperature fluctuations are to be expected at low water. In the warmer months as temperature rises oxygen tension must fall through increased consumption by the worm, without replenishment until the tide returns, and by its decreased solubility at elevated temperatures (see Fox, 1909). It is put forward that this increased irrigation rate up to the critical temperature of about 18°C is a survival mechanism maintaining oxygen uptake for as long as possible in warm-weather low-tide conditions. Temperature coeficient Up to about 10°C the metabolic rate is very low and steady (QrO near unity) and QrO remains low, below l-17, throughout the whole experimental temperature range. As Precht (1958) points out, “Low values of temperature coefficients are a natural mechanism to prevent the effects of too quick a change in the external temperature”. Jones (1968) describes a low plateau in &, for Patella wuZgata
562
K.
h”ftUCOLM
%WMOUR
(Gasteropoda) heartbeat over its normal environmental temperature range, i.e. that to which the animal is presumably best adapted. In Arenicola the Qis near unity below 10°C may indicate a similar adaptation. Decline in irrigation rate at h&h t~p~~t~e~
A compensation, or “capacity adaptation” exists if a vital requirement is in short supply (e.g oxygen in aquatic animals). A high metabolic rate at high temperatures would have dangerous consequences and compensatory adaptations, lowering the velocity, are favourable (Precht, 1958). In Armida at low tide in warm weather a continued increase in irrigation rate above a certain critical temperature would deplete the oxygen supply in the burrow water and increase the exposure rate of the gills as well as draw in heated, oxygen-poor surface water. This could directly damage the animal and would further increase oxygenconsuming metabolic rates. The “compensatory adaptation” of Precht, i.e. the marked, reversible drop in irrigation rate at high temperature observed here, is thus clearly to be expected. It shows that in A~~~coZa from Kames Bay 18°C is the critical temperature above which increased energy expenditure becomes uneconomic. From the foregoing hypothesis it follows that the absolute oxygen consumption of ArenicoZa should vary with temperature in the same way as irrigation rate has been shown to do. Thamdrup (1935) h as shown that this is in fact so; the following values are derived from his published figures:
Rapid t~p~atuye
Temperature (“C)
Oxygen consumption (ml OJkg per hr)
2 10 20 28
6.39 14.91 34*08 18.46
change and acc~i~tion
Oscillations such as follow initial response to rapid temperature change in are characteristically generated by a negative feedback system (Sollberger, 1965). Grainger (1956), considering an organism as a “steady-state system”, suggests that new conditions might cause temporary accumulation of deficiency of metabolic substances. So also does Prosser (1958), who considers that change in enzyme concentration and reversible alteration of enzyme protein might create an unbalanced situation. Upon correction of the imbalance an oscillation, decreasing as balance was restored, would be set up. If the feedback mechanism in Armicola is metabolic, its location must be such as to affect the irrigation wave pacemaker in the ventral nerve cord (see above). Barnes & Barnes (1959) point out that in littoral species exposed to extremes of
Arenicola
APERTURE
CHANGEON IRRIGATSON RATEIN
ARlZNlcoLA
MARINA
563
temperature metabolic processes might be expected to be coupled so as to reduce the oscillations; P. vulgata supports this expectation by showing, in heartbeat at least, no overshoot or oscillations whatever (Jones, 1968). In Awnkola, although environmental fluctuations cannot normally be so abrupt as in Pat&a, adaptation after initial overshoot is rapid and oscillations quickly disappear (see Fig. 4), representing partial temperature compensation of Precht’s Type 3 (Precht, 1958). In a short time Arenicoh can compensate its irrigation rate for changes of temperature. Nevertheless, even when temperatures vary up or down at a mean rate of only 2”C/hr, comparable to the natural rate, the residual irrigation rate fluctuation described (see Fig. 3) is found. Acknowledgements-I thank Professors P.G. ‘Espinasse and J. G. Phillips for facilities and Professor E. R. Trueman for reading and criticizing the manuscript. This work was carried out during tenure of a Research Studentship from the Science Research Council.
REFERENCES
BARNESH. & BARNESM. (1959) Oscillatory respiration in Bulonus u~p~~~y~~eDarwin. Experientia 15, 438-441. ELIASSENE. (1956) The oxygen supply during ebb of Arenicolu marina in the Danish Waddensea. Univ. Bergen hb. 12, 2-9. FAGEL. & LEGENDRE R. (1927) P&ches planctoniques B la lumiere effectuees ri.Banyuls-surMer et B Concarneau-I. Annelides polychetes. Arch Zoo2. exp. gen. 67, 23-222. Fox C. J. J. (1909) On the coef%cients of absorption of nitrogen and oxygen in distilled water and sea water, and of atmospheric carbonic acid in sea water. Trans. Faraday Sot. 5, 68-87. GRAINGERJ. N. R. (1956) Effects of changes of temperature on the respiration of certain Crustacea. Nature, Land. 178, 930-931. GRAINGERJ. N. R, (1958) First stages in the adaptation of poikilotherms to temperature change. In ~~y~~o~og~cuZ Adaptation (Edited by PnOssERC. L.), pp. 79-91. Society of General Physiologists, Was~n~on. HOCGARTHK. R. & TRUEMANE. R. (1967) Techniques for recording the activity of aquatic invertebrates. Nature, Land. 123, 1050-1051. JONESH. D. (1968) Aspects of the physiology of PatelEa vulgatu L. Ph.D. thesis, Hull. KERMACKD. M. (1955) The anatomy and physiology of the gut of the polychaete Arenicolu marina (L). Proc. 2001. Sot. Land. 125, 347-381. KR~SGER F. (1958) Zur Atmungsphysiologie von Arenicolu marina. Helgol. Wiss. Meeresunters. 6, 193-201. KRUGERF. (1964) Messungen der Pumptitigkeit von Arenicolu marina L. im Watt. Helgol. Wiss. Meeresunters. 11, 70-91. LAGERSPETZ K. Y. H. & TALO A. (1967) Temperature acclimation of the functional parameters of the giant nerve fibres in Lumbricus terrestris L.-I. Conduction velocity and the duration of the rising and falling phase of the action potential. J. exp. Biol. 47, 471+30. MEEKA, & STORROWB. (1924) On a pelagic phase of ArenicoZu rnur~~ and of Eteone arctica. Ann. Mag. nat. Hist. 14, 453--155. NEWELLG. E. (1948) A contribution to our knowledge of the life history of Arenicolu marina L.J. mar. Biol. Ass. U.K. 27, 554-580. PRECHTH. (1958) Concepts of the temperature adaptation of unchanging reaction systems in cold-blooded animals. In Physiological Adaptation (Edited by PROSSERC. L.), pp. 50-78. Society of General Physioiogists, Washington.
564
MALCOLMK. SEYMOUR
PROSSERC. L. (1958) The nature of physiological adaptation. In Physiological Adaptation (Edited by PROSSERC. L.), pp. 167-180. Society of General Physiologists, Washington. SEYMOURM. K. (1971) Burrowing behaviour in the European lugworm Arenicola marina (Polychaeta: Arenicolidae). j’. Zool. 164, 93-132. SEYMOURM. K. (1972a) Swimming in Arenicolu marina (L.). Comp. Biochem. Physiol. MA, 285-288. SEYMOURM. K. (1972b) The giant nerve fibres of Arenicola marina (L.). Comp. Biochem. Physiol. 41A, 457-464. SOLLBERGERA. (1965) Biological Rhythm Research. Elsevier, Amsterdam. THAMDRUPH. N. (1935) Bietrage zur okologie der Wattenfauna. Meddr Kommn Havunders. 10,l-25. VAN DAM L. (1937) f_?ber die Atembewegungen und das Atemvolumen von Phryganaealarven, Arenicola marina und Nereis virens, sowie iiber die Sauerstoffsausnutzung bei Anodonta cygnea, Arenicola marina und Nereis virens. Zool. Anz.118, 122-128. VAN DAM L. (1938) On the utilization of oxygen and regulation of breathing in some aquatic animals. Ph.D. thesis, Groningen. WELLS G. P. (1945) The mode of life of Arenicola marina L. J. mar. Biol. Ass. U.K. 26,
170-207. WELLS G. P. (1949a) Respiratory movements of Arenicola marina L. J. mar. Biol. Ass. U.K. 28,447-464. WELLS G. P. (1949b) The behaviour of Arenicolu marina L. in sand, and the rate of spontaneous activity cycles. J. mar. Biol. Ass. U.K. 28, 465-478. WELLS G. P. (1966) The lugworm (ArenicoZu)-a study in adaptation. NetherZandsJl Sea Res. 3, 294-313. Key Word Index-Are&cola marina (L.); temperature responses in lugworm; respiration in lugworm; burrow irrigation in lugworm.
EFFECTS OF TEMPERATURE CHANGE ON IRRIGATION RATE IN ARENICOLA MARINA (L.) MALCOLM Department
K. SEYMOUR”
of Zoology, University of Hull
(Received 22 January
1972)
Abstract-l. The effects of slow and rapid temperature fluctuations on the rate of burrow irrigation in Are&cola marina (L.) have been studied using pressure and impedance recording techniques. 2. With slow temperature change (2”C/hr) irrigation rate rises very slowly up to lO”C, faster between 10 and 14X’, more slowly up to 18°C and drops sharply above 18°C. The total number of irrigation waves, frequency of exposure of the gills and substantially the volume of water pumped vary as does the rate/temperature curve. 3. Q10 is low, rising to only 1.17 between 12.25 and 14*45”C. It is suggested that rate increase up to 18°C is a compensatory mechanism maintaining oxygen uptake for as long as possible under low-tide warm-weather conditions, and that the reversible drop in irrigation rate above 18°C is a survival mechanism for low-tide conditions. 4. Despite the characteristic rate change with gradual temperature change there is a compensatory response to quickly changed temperature which shows marked overshoot and oscillation, 5. Removal of the ventral nerve cord in a segment stops all irrigation movement in that segment. After nerve cord section in the mid trunk the rate of each half of the trunk is dictated independently by the environmental temperature of that half; it is probably the irrigation pacemaker mechanism in the cord which responds to a change in temperature by a change in rate.
INTRODUCTION As A LITTORAL fluctuations.
animal, These
&?zicolu
changes
marina is potentially
exposed
may be either slow (diurnal
to large temperature
and seasonal)
or relatively
rapid (when the burrow is covered and uncovered by the tide, when the worm moves in its burrow towards and away from the exposed sand surface or when it leaves the sand and swims up to the water surface Legendre,
1927;
Newell,
ments were from Kames for
the
year
sand surface (August)
ending
1948 ; Seymour, Bay, Millport,
22 January
varied from between
(B. L. S. Hardy,
communication).
553
used
1924;
in these
in the Armicolu
temperatures
of Nematology,
& Storrow,
Worms
3 and 7.5”C (January)
personal
* Present address : Department Harpenden, Herts.
Scotland;
1969,
(Meek
1972a).
These
Rothamsted
experi-
area of this bay,
4 in. (101 mm) to between
Fage &
below
the
12 and 17*5”C
temperatures Experimental
were Station,
554
MALCOLM K. SEYMOUR
taken in undisturbed sand and those in burrows might well be greater in summer; however they give an indication of the range of temperature to which this population is subjected. As a step towards understanding how such changes directly affect the life of Arenicolu, the effects of experimental temperature fluctuations on rate of irrigation have been studied. Irrigation activity proper is the passage of a series of waves along the dorsal side of the trunk of the worm in the U- or J-shaped burrow the worm normally occupies in muddy littoral sand (Wells, 1945). Alternate phases of thinning and thickening pass forward or backward, occluding the burrow and driving water through it in piston fashion. Each pair of gills expands as its segment thins and contracts as the segment thickens again. In creeping the same wave sequence
-
(3) ;:
(8)
,
i
1
FIG. 1. Unbroken extract from impedance records of irrigation in two worms transferred at dotted line from warm to cool sea water. Irrigation rate falls from 6.0 to 3.5 (upper record) and from 7.0 to 3.0 waves/mm (lower record). Temperature in “C, time in minutes. FIG. 2. Impedance records of irrigation in two worms a few minutes before (left) and after (right) transfer from cool to warm sea water. Irrigation rate rises from 4.0 to 8-O (upper record) and from 3.5 to 10.0 waves/mm (lower record). Figures in parentheses show how many minutes before and after transfer (at dotted line) extracts were recorded; time between extracts was occupied by non-irrigating activity. Temperature in “C, time in minutes.
TEMPRRATURE CHANGE ON IRRIGATION RATE IN AREN1CCJl.A MARINA
555
occurs, but thinning and thickening extend further ventrally and length changes may occur, resulting in movement of the worm along the burrow. (See Seymour, 1971 for discussion of wave movement in Arenicola.) In creeping, as in irrigation proper, (described by Wells, 1945,1949a, b, 19&j), contraction and expansion of the gills with the passage of each wave and movement of the water relative to the worm still take place and the two activities are practically identical from their respiratory aspect. Because of this functional and mechanical similarity, behaviour resulting in the type of record shown in Figs. 1 and 2 from worms in polystyrene tubes, which may have included both types of activity, is termed irrigation throughout this account. The term irrigation rate as used here is defined as the number of irrigation waves in a worm per min, calculated from counts of pressure or impedance records over 2-min periods wholly occupied by irrigating activity. During these investigations worms in straight polystyrene tubes showed intermittent irrigation, periods of “rest” and other activity (see Wells, 1945) alternating with it as found also by van Dam (1937). Irrigation waves usually passed taiIwards, but periods of “inverse” irrigation (tail to head) as seen by van Dam (1937) and by Kruger (1964) were also observed. Worms of similar weight (6.5 + 1 g, weighed wet) were used in the experiments and weight/rate correlation was not attempted. Irrigation rates have been recorded at different environmentaf temperatures and upon slow and rapid temperature change. Comparison of such records has provided data on the following points: (i) Change in rate with slow temperature change. (ii) Proportion of total time spent irrigating at different temperatures. (iii) Probable effects of temperature changes, and the worm’s response to them, on the life of the worm. (iv) Responses to rapid temperature change and the type of capacity adaptation they suggest. MATERIALS
AND METHODS
Specimens of Armcola marina (L.) were obtained from the Marine Laboratory at Millport, Isle of Cumbrae, Scotland and kept in shallow tanks of cooled, filtered, aerated, circulating sea-water. To monitor irrigation movements, a worm was placed in each of four straight polystyrene tubes 130 mm long and 9 mm bore which were clamped together as a unit. The tubes were sealed with polyethylene stoppers and near their ends small holes allowed free in and outflow of water. In some experiments, cyclical pressure changes in the tubes during irrigation were sensed by a Statham P23BB pressure transducer through fine polyethylene tubing attached to a nozzle cemented centrally to each tube; in others, impedance pneumographs (see Hoggarth & Trueman, 1967) detected cyclical impedance changes between a pair of diametrically opposed tinned steel wire electrodes attached centrally to each tube and just penetrating its lumen. In each, output was recorded on an inkwriting multichannel pen recorder, the Physiograph. A thermistor coupled to the Physiograph gave a continuous record of bath temperature. Experimental tanks were stirred constantly. In experiments designed to show any effect of change of temperature on irrigation
556
MALCOLMK. SEYMOUR
rate, the bath temperature was varied by i, automatically slowly replacing water at room temperature with refrigerated sea water, and ii, filling the tank with refrigerated water and allowing slow warming to room temperature. Temperatures higher than ambient were obtained with a small aquarium heater. In temperature acclimation experiments, when only the impedance recording method was used, the array of tubes containing worms was transferred rapidly from a bath at one constant temperature to one at another constant temperature.
EXPERIMENTAL
OBSERVATIONS
Vuriation in irrigation rate with gradual temperature change Specimens of Arenicola, previously kept in sea water below lO”C, were warmed and then cooled at a steady rate of 1°C every 37 min (under 2”C/hr). Mean irrigation rate plotted against temperature yields a curve as in Fig. 3a. With minor fluctuations the rate rises very slowly from 6 to lO”C, faster between 10 and 14”C, more slowly thence up to 18°C and it drops sharply above 18°C. This form of rate/temperature curve, including the steep negative slope at high temperatures, occurred in worms, both heated and cooled, which showed no subsequent illeffects; it was not an effect of irreversible heat-damage. The fluctuation in rate is illustrated also by the temperature coefficient ( QIO) calculated from rate values for 2-degree ranges (Fig. 3b). The Qr,, throughout is low, rising to only 1.17 between 12.25 and 14*45”C and thereafter falling very rapidly.
/A------‘--‘___
b
~ ‘\%,,
tamp
OC
FIG. 3. Effect of gradual temperature change (mean rate 2”C/hr) on A. marina. a. Irrigation rates in waves/mm (means of fourteen worms with one standard error above and below). b. Temperature coefficient for 2-degree ranges (between 6.25 and 20.25”C).
TEMPERATURE CHANGE ON IRRIGATION RATE IN ARENICOLA MARINA
557
Although irrigation rate increases with temperature and then falls off, the proportion of time spent irrigating at different temperatures was found to be rather constant around 55 per cent; this compares well with the 45 per cent of time over which A~enicolu in sand performed the “Normal Cyclical Pattern”, including creeping and irrigation proper (Wells, 1966). It follows from this that the total number of irrigation waves in a given period and therefore the total amount of irrigating activity, the amount of exposure of the blood-filled gills to the water, and largely the volume of water pumped past the worm must all vary in accordance with the rate/temperature curve described. If the increase in rate of irrigation were mainly an unavoidable temperature effect, of no value to the worm, a mechanism with the reciprocal effect of reducing the time spent irrigating as the rate increased might be expected to be present. No such effect is apparent. Although van Dam (1937) f ound that pumping effect of irrigation waves could vary in the same animal, long-term pressure and impedance records obtained here show little amplitude variation over experimental periods and range of temperature. Variation in irrigation rate with sudden temperature change These experiments were designed to show, in terms of irrigation rate, responses occurring within a short time of transfer from water at one temperature (Tl) to water at another temperature (T2). This sudden type of change may be quite common in nature; Grainger (1958) mentions movement through thermoclines and to or from patches of sunlight. In the case of Arenicolu, cold sea water may cover and enter a burrow where a surface temperature of 28°C may have been recorded (Kermack, 1955). Sudden increase of temperature might be encountered when a “testing” excursion is made up the burrow tailshaft into a puddle at this order of temperature. The worms were acclimated in the apparatus to Tl for at least 24 hr before the apparatus was transferred to T2 (see Figs. 1 and 2), and, 50 to 90 min later, back to Tl. Plots of irrigation rate against time are shown in Figs. 4 and 5. In an experiment (Fig. 4) using three animals transferred from 9.7 to 22.15”C a rate of 4 f 1 waves/min increased on transfer to 10 & 1.5 waves/min. Within 40 min these increases had been halved and after a further 50 min they were reduced to between 17 and 37 per cent of their initial values. At this point the apparatus was transferred back to cold water; the rates at once fell to 3 + 0.5 waves/min and after 100 min more were steady at a level close to that at the beginning of the experiment. Grainger (1958) describes two main types of response after sudden transfer from one temperature to another, and notes that they may be found in metabolic rate, heartbeat and locomotory movements. In the first there is a marked “overshoot” in the parameter being investigated. The second type shows no overshoot and a steady level at the new temperature is reached at once. The results presented in Fig. 4 show very clearly that the response in irrigation rate of Arenicola to a sudden change in temperature is of the overshoot type. The form of overshoot curve following second transfer (Fig. 4) has the form of a damped oscillation round the
558
MALCOLM K. SEYMOUR
I
0
200
100
300
FIG. 4. Irrigation rate in waves/min from impedance records, plotted against time for three worms transferred suddenly from cool sea water to which they had been acclimated for 48 hr, to warm water and back again. The worms’ responses show overshoot followed by oscillation. 5-
min
FIG. 5. Irrigation rate in waves/min from impedance records plotted against time
for two worms transferred suddenly from warm sea water in which they had been kept for 48 hr, to cool water and back again. Further information is in the text.
TEMPERATURE
CHANGE ON IRRIGATION RATE IN ARENICOLA
MARINA
559
initial rate value “leading eventually to a steady state which is typical of the new temperature” (Barnes & Barnes, 1959). Oxygen consumption of ~~Zff~~ u~~~~tr~te shows such oscillatory overshoot (Barnes & Barnes, 1959) and Fig. 1 in Grainger (1956) well shows overshoot and subsequent oscillation in the oxygen consumption of Hemimysis lamornae. Temperature change and co-ordination of irrigation
It has been established above that irrigation rate of an individual Are&cola rises or falls abruptly when the whole worm is placed in relatively warm or cool water. To investigate anterior/posterior co-ordination of irrigation behaviour the anterior and posterior halves of the trunk of a worm were surrounded independently by warmed or cooled sea water giving an 8- to lo-degree temperature differential. The resulting irrigation rate differences between halves was recorded. During half the experiments the ventral nerve cord was interrupted at the 9th chaetigerous annulus by an incision in the mid-ventral body wall. Results are schematically summarized in Fig. 6a and b. In an intact AreCola at a uniform temperature, anterior and posterior irrigation rates did not differ (they represented two counts of the same set of waves). However, if only one half of the trunk were warmed the overalE rate (i.e. of the whole trunk) rose; this effect was sometimes more marked on warming the posterior trunk than on warming the anterior trunk (Fig. 6a, 1 and 2). In other cases after warming either half of the trunk, the irrigation rate rose, or remained raised, equally (Fig. 6b, 1 and 2). Most strikingly, after transection of the ventral nerve cord half way along the trunk, at chaetigerous annulus 9 (Fig. 6a, T), the irrigation rate of each half of the worm rose or fell independently when that half was warmed or cooled; that is, each half behaved as if it were a separate worm (Fig. 6a, 3 and 4). Thus the nerve cord is responsible for co-ordinating irrigating activity and when it is bisected each half co-ordinates a wave in segments through which the cord is continuous ; a comparable effect has been demonstrated for giant nerve fibre transmission in Are&cob (Seymour, 1972b). Irrigation activity in body wall preparations ceases after removal of the ventral nerve cord, which contains the irrigation pacemaker. Since the rate of a warmed part of the trunk can determine that of a cooled part, and since this control is abolished by nerve cord transection between the parts, it is the pacemaker mechanism in the ventral nerve cord whose rate of activity is raised or lowered when warmed or cooled water surrounds the body. Conduction velocities of nerve fibres are known to vary with temperature. Also, temperature acclimation has been shown to occur in Lapis giant fibres in respect of conduction velocity, refractory period and duration of phases of the action potential (Lagerspetz & Talo, 1967). It seems, therefore, that it is at the nervous level that the primary basis of temperature dependence and acclimation is to be found. The extreme rapidity of rate change following temperature change
560
MALCOLM K. SEYMOUR
suggests that afferent impulses from cutaneous receptors may trigger the initial response. The rate of pulsation of the dorsal blood vessel of ArenicoZa (recorded with the impedance pneumograph) also varies with temperature and in one worm, cooled suddenly from 30 to 9”C, fell instantaneously from 6-5 to 3 per min. rote
-” i -7 K i Y(a)
0.
;
i
.I......I I
...a.......*......... i 3 2
4
temp.
;....... ..a....a....:
:“““”
rate
P,
,......,.,......:
a.
l-
temp.
i”.....,...........‘I
..........*....../
I
temp.
:...*....
i. I......*....*.i
i’““. ;
P.
:*..*....,*.,*..:
tsmp:... ..*.:
(b)
~-sB-s***.,.
:............
2
:. ,I,. ..*****..*.,.*......
i
.,.i...*...............*..... ........i
FIG. 6. Schematic presentation of the results of two types of experiment (a) and (b). In each the anterior (a.) and posterior (p.) halves of the trunk of &&cola were subjected independently to warm and cool sea water. The 9th chaetigerous armulus was taken as the halfway mark. Solid lines represent irrigation rate calculated from impedance records; dotted lines represent bath temperature. Both are plotted against time. Each experiment is about 1 hr long. Upward deflexion of lines indicates an abrupt rise, downward deflexion an abrupt fall in temperature or irrigation rate. Fluctuations of anterior and posterior bath temperatures cause corresponding fluctuations in anterior and posterior irrigation rates. The rates are co-ordinated in intact worms (i.e. in (b) and in (a) left of line T). After transection of the ventral nerve cord at the ninth chaetigerous annulus ((a) right of line T), the rate of each half of the worm rises or falls when that half is warmed or cooled.
TEMPERATURE CHANGE ON IRRIGATION RATE IN ARENICOLA MARINA
561
Experiments were attempted in which the worms were kept at elevated temperature (19-20°C) for 2-3 days to acclimate before being subjected to low (about SC) and then to high temperatures again (Fig. 5). In these experiments apparently abnormal spasmodic activity contrasted with the long periods of regular irrigation seen in the low to high temperature experiments, and the drop in rate on sudden cooling was small compared to the previous fluctuations at steady high temperature, with no clear overshoot. In short this result illustrated the adverse effect of sustuined exposure to high temperature. Kermack (1955) notes no abnormal behaviour of Arenicola when surface sand temperature reached 27°C and surface water 28°C at air temperature 26°C but temperatures can have been so high only temporarily at low tide. DISCUSSION
Increase in irrigation rate with temperature Metabolic processes commonly increase with increased temperature; but, as shown here, Arenicola has considerable regulatory powers. Despite this, the worm still shows an increase in irrigation at higher temperatures. A working hypothesis is postulated that this residual variation is of survival value as follows: Eliassen (1956) showed that oxygen consumption in A. marina is the same in “high tide” and “low tide” water, and Kruger (1958) also found that consumption is independent of external oxygen concentration down to 0.2 ml/l. Percentage withdrawal of oxygen from sea water, with oxygen partial pressure the same as in air and at one-twentieth of that value, is constant at 40 f 10 per cent (van Dam, 1938). It follows that at lower oxygen tension more water must be pumped for the same consumption rate at the same temperature. The effect will be enhanced as temperature rises. Van Dam (1938) showed that as oxygen tension falls in the surrounding water, at steady temperature, both volume of water pumped and irrigation rate increase at first and usually decline at very low oxygen tension. When the worm’s burrow is immersed, conditions of temperature and oxygen tension must be fairly constant; the greatest temperature fluctuations are to be expected at low water. In the warmer months as temperature rises oxygen tension must fall through increased consumption by the worm, without replenishment until the tide returns, and by its decreased solubility at elevated temperatures (see Fox, 1909). It is put forward that this increased irrigation rate up to the critical temperature of about 18°C is a survival mechanism maintaining oxygen uptake for as long as possible in warm-weather low-tide conditions. Temperature coeficient Up to about 10°C the metabolic rate is very low and steady (QrO near unity) and QrO remains low, below l-17, throughout the whole experimental temperature range. As Precht (1958) points out, “Low values of temperature coefficients are a natural mechanism to prevent the effects of too quick a change in the external temperature”. Jones (1968) describes a low plateau in &, for Patella wuZgata
562
K.
h”ftUCOLM
%WMOUR
(Gasteropoda) heartbeat over its normal environmental temperature range, i.e. that to which the animal is presumably best adapted. In Arenicola the Qis near unity below 10°C may indicate a similar adaptation. Decline in irrigation rate at h&h t~p~~t~e~
A compensation, or “capacity adaptation” exists if a vital requirement is in short supply (e.g oxygen in aquatic animals). A high metabolic rate at high temperatures would have dangerous consequences and compensatory adaptations, lowering the velocity, are favourable (Precht, 1958). In Armida at low tide in warm weather a continued increase in irrigation rate above a certain critical temperature would deplete the oxygen supply in the burrow water and increase the exposure rate of the gills as well as draw in heated, oxygen-poor surface water. This could directly damage the animal and would further increase oxygenconsuming metabolic rates. The “compensatory adaptation” of Precht, i.e. the marked, reversible drop in irrigation rate at high temperature observed here, is thus clearly to be expected. It shows that in A~~~coZa from Kames Bay 18°C is the critical temperature above which increased energy expenditure becomes uneconomic. From the foregoing hypothesis it follows that the absolute oxygen consumption of ArenicoZa should vary with temperature in the same way as irrigation rate has been shown to do. Thamdrup (1935) h as shown that this is in fact so; the following values are derived from his published figures:
Rapid t~p~atuye
Temperature (“C)
Oxygen consumption (ml OJkg per hr)
2 10 20 28
6.39 14.91 34*08 18.46
change and acc~i~tion
Oscillations such as follow initial response to rapid temperature change in are characteristically generated by a negative feedback system (Sollberger, 1965). Grainger (1956), considering an organism as a “steady-state system”, suggests that new conditions might cause temporary accumulation of deficiency of metabolic substances. So also does Prosser (1958), who considers that change in enzyme concentration and reversible alteration of enzyme protein might create an unbalanced situation. Upon correction of the imbalance an oscillation, decreasing as balance was restored, would be set up. If the feedback mechanism in Armicola is metabolic, its location must be such as to affect the irrigation wave pacemaker in the ventral nerve cord (see above). Barnes & Barnes (1959) point out that in littoral species exposed to extremes of
Arenicola
APERTURE
CHANGEON IRRIGATSON RATEIN
ARlZNlcoLA
MARINA
563
temperature metabolic processes might be expected to be coupled so as to reduce the oscillations; P. vulgata supports this expectation by showing, in heartbeat at least, no overshoot or oscillations whatever (Jones, 1968). In Awnkola, although environmental fluctuations cannot normally be so abrupt as in Pat&a, adaptation after initial overshoot is rapid and oscillations quickly disappear (see Fig. 4), representing partial temperature compensation of Precht’s Type 3 (Precht, 1958). In a short time Arenicoh can compensate its irrigation rate for changes of temperature. Nevertheless, even when temperatures vary up or down at a mean rate of only 2”C/hr, comparable to the natural rate, the residual irrigation rate fluctuation described (see Fig. 3) is found. Acknowledgements-I thank Professors P.G. ‘Espinasse and J. G. Phillips for facilities and Professor E. R. Trueman for reading and criticizing the manuscript. This work was carried out during tenure of a Research Studentship from the Science Research Council.
REFERENCES
BARNESH. & BARNESM. (1959) Oscillatory respiration in Bulonus u~p~~~y~~eDarwin. Experientia 15, 438-441. ELIASSENE. (1956) The oxygen supply during ebb of Arenicolu marina in the Danish Waddensea. Univ. Bergen hb. 12, 2-9. FAGEL. & LEGENDRE R. (1927) P&ches planctoniques B la lumiere effectuees ri.Banyuls-surMer et B Concarneau-I. Annelides polychetes. Arch Zoo2. exp. gen. 67, 23-222. Fox C. J. J. (1909) On the coef%cients of absorption of nitrogen and oxygen in distilled water and sea water, and of atmospheric carbonic acid in sea water. Trans. Faraday Sot. 5, 68-87. GRAINGERJ. N. R. (1956) Effects of changes of temperature on the respiration of certain Crustacea. Nature, Land. 178, 930-931. GRAINGERJ. N. R, (1958) First stages in the adaptation of poikilotherms to temperature change. In ~~y~~o~og~cuZ Adaptation (Edited by PnOssERC. L.), pp. 79-91. Society of General Physiologists, Was~n~on. HOCGARTHK. R. & TRUEMANE. R. (1967) Techniques for recording the activity of aquatic invertebrates. Nature, Land. 123, 1050-1051. JONESH. D. (1968) Aspects of the physiology of PatelEa vulgatu L. Ph.D. thesis, Hull. KERMACKD. M. (1955) The anatomy and physiology of the gut of the polychaete Arenicolu marina (L). Proc. 2001. Sot. Land. 125, 347-381. KR~SGER F. (1958) Zur Atmungsphysiologie von Arenicolu marina. Helgol. Wiss. Meeresunters. 6, 193-201. KRUGERF. (1964) Messungen der Pumptitigkeit von Arenicolu marina L. im Watt. Helgol. Wiss. Meeresunters. 11, 70-91. LAGERSPETZ K. Y. H. & TALO A. (1967) Temperature acclimation of the functional parameters of the giant nerve fibres in Lumbricus terrestris L.-I. Conduction velocity and the duration of the rising and falling phase of the action potential. J. exp. Biol. 47, 471+30. MEEKA, & STORROWB. (1924) On a pelagic phase of ArenicoZu rnur~~ and of Eteone arctica. Ann. Mag. nat. Hist. 14, 453--155. NEWELLG. E. (1948) A contribution to our knowledge of the life history of Arenicolu marina L.J. mar. Biol. Ass. U.K. 27, 554-580. PRECHTH. (1958) Concepts of the temperature adaptation of unchanging reaction systems in cold-blooded animals. In Physiological Adaptation (Edited by PROSSERC. L.), pp. 50-78. Society of General Physioiogists, Washington.
564
MALCOLMK. SEYMOUR
PROSSERC. L. (1958) The nature of physiological adaptation. In Physiological Adaptation (Edited by PROSSERC. L.), pp. 167-180. Society of General Physiologists, Washington. SEYMOURM. K. (1971) Burrowing behaviour in the European lugworm Arenicola marina (Polychaeta: Arenicolidae). j’. Zool. 164, 93-132. SEYMOURM. K. (1972a) Swimming in Arenicolu marina (L.). Comp. Biochem. Physiol. MA, 285-288. SEYMOURM. K. (1972b) The giant nerve fibres of Arenicola marina (L.). Comp. Biochem. Physiol. 41A, 457-464. SOLLBERGERA. (1965) Biological Rhythm Research. Elsevier, Amsterdam. THAMDRUPH. N. (1935) Bietrage zur okologie der Wattenfauna. Meddr Kommn Havunders. 10,l-25. VAN DAM L. (1937) f_?ber die Atembewegungen und das Atemvolumen von Phryganaealarven, Arenicola marina und Nereis virens, sowie iiber die Sauerstoffsausnutzung bei Anodonta cygnea, Arenicola marina und Nereis virens. Zool. Anz.118, 122-128. VAN DAM L. (1938) On the utilization of oxygen and regulation of breathing in some aquatic animals. Ph.D. thesis, Groningen. WELLS G. P. (1945) The mode of life of Arenicola marina L. J. mar. Biol. Ass. U.K. 26,
170-207. WELLS G. P. (1949a) Respiratory movements of Arenicola marina L. J. mar. Biol. Ass. U.K. 28,447-464. WELLS G. P. (1949b) The behaviour of Arenicolu marina L. in sand, and the rate of spontaneous activity cycles. J. mar. Biol. Ass. U.K. 28, 465-478. WELLS G. P. (1966) The lugworm (ArenicoZu)-a study in adaptation. NetherZandsJl Sea Res. 3, 294-313. Key Word Index-Are&cola marina (L.); temperature responses in lugworm; respiration in lugworm; burrow irrigation in lugworm.