Metabolic acclimation to temperature in a terrestrial snail

030%9629/80.0901-0135SO200/0

Camp. Biochem Physiol.. Vol 67A. pp 135 10 139 0 Pergamon Press Ltd 19X0 Printed m Great Britain

METABOLIC

ACCLIMATION TO TEMPERATURE TERRESTRIAL SNAIL KENNETH

Division

of Biological

B.

and

ARMITAGE

Sciences, The University (Received

DAVID

of Kansas,

13 December

IN A

STINSON

Lawrence.

KS 66045 U.S.A

1979)

Abstract--- 1. Oxygen consumption (I&,,,)was higher at each successive temperature from 7; = 5535°C in all acclimation groups of Smiotrema leai (Pilsbry) (Gastropoda: Pulmonata). 2. The M:T curve of fed snails acclimated (TJ at 5’C was translated with respect to all other acclimation groups (T, = 15, 25, 5-25C). 3. The M:T curves of starved snails evidenced various patterns of translation, clockwise rotation with translation, and counterclockwise rotation with translation among the various T, groups. 4. There was a pattern of increased metabolism of starved animals with respect to fed snails from low to high T,. 5. Qlo was highest at low T, in all 7; groups. Qlo between z = 7; for the three constant 7; ranged from 1.5 to 1.7 indicating a Precht Type 3 compensation. 6. Low Qro at high T, at all 7; suggests rapid metabolic compensation. 7. The pattern of acclimation suggests snails are either warm- or cold-acclimated. 8. A comparison of M:T curves of laboratory-acclimated snails with field acclimatized suggests feeding interacts with temperature in the temperature compensation process.

INTRODUCTION Temperature change markedly processes. Many poikilotherms

affects physiological living in environments

with daily or seasonally fluctuating temperatures compensate metabolically for temperature changes (Bullock, 1955). Patterns of acclimatization provide poikilotherms with some degree of independence from changes in environmental temperature. Seasonal changes in the metabolic response to temperature generally are attributed to thermal acclimation, but other factors, such as activity and starvation (Newell & Bayne, 1973), can affect the metabolic response. Because temperature may profoundly affect the mobilization and use of energy by a species, it is of interest to determine the relationship between the seasonal and daily temperature regimes a species encounters and its thermal responses. Possibly, metabolic compensation is evolutionarily conservative such that patterns of metabolic compensation could reflect phylogenetic history rather than local temperature environment. Gastropods occupy a wide variety of habitats. Land snails may evidence seasonal acclimatization in their metabolism-temperature (M:T) relations (Barnhart & Armitage, 1979) but apparently lack the temperature insensitive zone characteristic of many intertidal gastropods (Newell & Roy, 1973; McMahon & RussellHunter, 1977). Presumably, acclimatization of the M:T curve is a response to thermal acclimation. Some rate functions in terrestrial gastropods show thermal acclimation in some species (Roy, 1963; Rising & Armitage, 1969) but not in others (Mason, 1971; Riddle, 1977). The small pulmonate land snail Stenotrem leai (Pilsbry) evidences seasonal changes in its M:T relations (Barnhart & Armitage, 1979). This study tests the hypothesis that seasonal acclimatization in M:T relations is primarily thermal acclimation.

MATERIALS AND METHODS Snails were collected from a perennial artesian marsh in Atchison County 2.4 km south of Muscotah, Kansas, in mid October, 1977. They were returned to the laboratory where they were cleaned and maintained in small plastic terraria placed in a growth chamber maintained at 15°C and a photoperiod of 12L: 12D for 2 months. Each terrarium was stocked with lettuce, moist paper toweling, and a container of water in order to provide food and to maintain high humidity. Four groups of 140 snails each were acclimated for 21 days before measurements of oxygen consumption began. Three groups were maintained at ambient (=acclimation, T,) temperatures of 5°C 15°C and 25°C. The fourth group was maintained at temperatures which cycled from 5°C at night to 25°C by day. Each acclimation group was divided into two subgroups of 70 snails each. One subgroup was provided with food and water; the other received only water. i;, determinations were measured with a Gilson Differential Respirometer. All snails were carefully cleaned to remove any algae or other debris. All determinations were made on groups of 10 snails in 8 ml flasks to which 0.3 ml of 54/, KOH and a filter-paper wick were added to the center well as a CO2 absorbent. Ten randomly selected snails from each subgroup were placed in each of seven flasks. The two subgroups from each 7; group were run simultaneously. Four flasks prepared in the same manner as the experimental flasks except for snails served as controls. After the flasks were attached to the respirometer, the snails were maintained for 1 hr at 15°C for adjustment to the conditions in the flasks. Routine metabolism (r’,,) was measured at seven exposure temperatures (T,) in the following sequence: 15, 5, 20, 25, 10, 30, 35°C. Five determinations were made at 10 min intervals at each T.. Snails remained extended from the shell during respirometry, but activity was not quantified. Following respirometry, each group of snails was weighed to obtain whole wet weight and then placed in a drying oven at 60°C. Subsequently snails were weighed to obtain whole dry weight, placed in 5Y,, HCI to remove the shell, dried. and weighed to obtain tissue dry weight. Shell 135

KENNETH B. ARMWAGEand DAVID S~INSON

136 Table

1. Influence

K

of acclimation temperature, oxygen consumption Means ?; = 5°C

(‘C)

exposure temperature, of active Stenotrema

and starvation

on the routine

leai

Vo, (m1.min.g wet tissue) + SE 7; = 15°C T, = 25°C

I-, = 5-1O’C

5

F S

0.946 + 0.029 0.823 k 0.084

0.780 + 0.052 0.832 + 0.034

0.614 + 0.016 0.566 + 0.013

0.618 + 0.017 0.834 + 0.060

10

F S

1.512 +_ 0.023 1.375 + 0.065

1.101 + 0.081 1.076 + 0.075

0.834 k 0.029 0.881 f 0.022

0.941 + 0.039 1.286 + 0.061

15

F S

2.173 k 0.048 1.818 * 0.133

1.561 f 0.073 1.367 f 0.041

1.559 k 0.061 1.604 k 0.039

1.907 i 0.064 2.246 + 0.109

20

F S

2.537 + 0.076 2.176 f 0.082

1.949 + 0.120 1.979 f 0.101

2.169 f 0.071 2.221 f 0.027

2.223 + 0.074 2.595 f 0.201

25

F S

3.376 f 0.340 3.068 f 0.081

2.403 f 0.159 2.487 f 0.148

2.447 k 0.071 2.704 k 0.087

2.876 + 0.117 3.094 + 0.272

30

F S

3.885 f 0.072 3.567 + 0.149

3.022 f 0.203 3.085 f 0.129

2.897 f 0.059 3.156 f 0.067

3.317 * 0.079 3.412 k 0.285

35

F S

4.554 f 0.088 4.264 f 0.154

3.605 f 0.337 3.936 f 0.170

3.520 k 0.067 3.366 + 0.182

3.775 i_ 0.079 3.404 + 0.203

N = 7, the number of experimental groups of T, = acclimation temperature; F = fed: S = starved.

weight was determined by difference between whole weight and tissue dry weight and was subtracted from whole wet weight to obtain tissue wet weight. ko, was expressed at STP as ~1 O2 min ‘g wet tissue following the procedure of Barnhart & Armitage (1979). Basic statistics were calculated using the BMDP2D computer programs (Dixon, 1975). RESULTS Among fed animals, voJ ranged from 0.57 ~1 Oz. min ‘g wet tissue at z = 5°C and T, = 25°C to 4.55 ~1 O2 .rnin. g wet tissue at T, = 35°C and TL = 5°C (Table 1). vob, was higher at each successive 7: from 5 to 35°C in all acclimation groups. The pat-

10

snails

each;

T. = exposure

temperature,

tern was the same for starved animals. At T, = 5”C, all ri,, of starved animals were lower than those of fed animals. At T, = 15”C, the value of starved and fed animals were generally similar (Table 1, Fig. 1). However, at T, = 25°C pob, of starved animals exceeded that of fed animals except at Tc = 5” and 35°C. At T, = 5-25X, li,* of starved animals was higher at all T, except 35°C. Thus, there is a pattern of increased metabolism of starved animals with respect to fed snails from low to high T, (Fig. 1). Among fed animals, the M:T curve of T, = 5°C animals is translated (Prosser, 1973:376) with respect to all other acclimation groups (Fig. 2). The M:T curve of 7” = 15°C animals is nearly identical to that

4.0 -

l

-

TA=5”

FED

l

-

TA=25’ FED TA:ZY STARVED TA ~5-25~ FED TA =5-25’ STARVED

. & ------

5”

IO”

15’

20”

25”

30”

35O

ENVIRONMENTAL Fig. 1. The effect of exposure

temperature

5”

IO”

TEMPERATURE

on oxygen

consumption

15”

20”

25”

30”

35’

(T,) of fed and starved

snails.

137

Metabolic acclimation in snails

15” ENVIRONMENTAL Fig. 2. The effect of temperature

acclimation

TEMPERATURE

on oxygen consumption

of the 7; = 25’C at higher T,, but is translated with respect to the 7; = 25°C at low Tc,.The M:T curve of the snails acclimated to changing temperatures, 7; = 5-25°C is similar to that of the 7; = 25°C at low 7;, but is translated with respect to the 7; = 15°C and 7; = 25’C curves at all Te 3 15’C. The acclimation patterns of starved snails differ from those of fed animals (Fig. 2) The M:T curve of T, = 5°C is translated with respect to the M:T curve of T, = 25°C except at Tc = 20°C. The value for IT; = 5°C snails at r = 20°C seems unusually low and represents a downward inflection of the M:T curve. A similar deflection occurred at Tc = 2O’C in the M:T curve of fed animals at 7; = 5’C. Possibly this deflection represents experimental error for if the M:T curves for 7; = 5C snails are smoothed, the values at T< = 20-C clearly would be higher. Thus, translation seems likely rather than some complex physiological response centered on T, = 2O’C.

20°

25O

30°

35O

(TE)

of fed and starved

Stmotr.ema

hi.

The convergence of the M:T curves for animals acclimated at 7; = 5’ and 15’C at T< = 5C suggests a combination of translation with counterclockwise rotation (Prosser, 1973:376). By contrast, the M:T curves of the snails acclimated at 7; = 25” and 5525°C converge at 35°C. This pattern suggests clockwise rotation with translation. Clearly, the pattern of acclimation depends on which sets of curves are compared. The lack of a consistent pattern of acclimation among the M:T curves of starved snails compared to fed snails suggests that feeding (or its lack) interacts with temperature to produce the observed M:T curve. This suggestion is consistent with the demonstration that several intrinsic and extrinsic factors determine the shape of M:T curves (Newell & Roy, 1973; Newell et a/., 1976). All snails acclimated to high temperatures had high Q at low 7;, especially at l&l5 C (Fig. 3). Snails ac%mated to low 7; had maximal QIo at low 7;,

4.0

35

I

I

I

-

Tn =Y

FED

‘\

.o I

5-10

I

IO-15

I

15-20

1

20-25

I

25-30

I

30-35

ENVIRONMENTAL Fig. 3. The effect of acclimation

temperature

I

5-10

I

I

IO-15

15-20

TEMPERATURE

and environmental starved snails.

I

20-25

25-30

30-35

(TE)

temperature

on the QIO of fed and

KENNETHB. ARMITAGE and DAWD STINXJN

138

especially at 5510°C. Generally, Qr,, of low 7; animals were lower at low 7; and higher at high T, than those of high Ti snails (Fig. 3). Q,a between 7; = ?; for the three acclimation temperatures ranged from 1.5 to 1.7 indicating that acclimation resulted in partial or Type 3 compensation (Precht, 1958).

DISCUSSION M:T relations were modified by temperature acclimation in Sfenotrema leai as reported for slugs (Segal, 1961; Roy, 1963; Rising & Armitage, 1969). Our results contrast with those reported for the desert snail Rhahdotus .schiedeunus and for Helix uspersa (Riddle, 1977). There is considerable variation in the acclimatory responses of molluscs. The freshwater Lrmrzuea stuyrwlk evidences acclimation to resistance adaptations but not to capacity adaptations (Harrison, 1977) whereas Physa hawnii evidenced clockwise rotation with translation following acclimation (Daniels & Armitage, 1969). Reverse acclimation occurred in the freshwater limpet Laeuapex fuscus (McMahon, 1973). The marine Bul[ia digitalis also did not evidence temperature acclimation but did have a broad temperature-insensitive zone in the M:T curve (Brown & da Silva, 1979). The M:T curve of the amphibious Pomacea paludosa did not show a temperature-insensitive zone whereas that of Marisa cornuarietis did (Frieburg & Hazelwood, 1977). Temperature-insensitive zones are lacking in both laboratory-acclimated (Figs 1 & 2) and fieldacclimatized S. leai (Barnhart & Armitage, 1979). This pattern of variation in the acclimatory responses of gastropods suggests that the responses are adaptive to the environmental conditions prevailing in the species’ habitats rather than being determined by phylogeny. The simplest explanation of the adaptive value of translation is that activity is maintained at low T, when animals are acclimated at low 7; and energy is conserved at high T, when animals are acclimated at high 7;. This interpretation is supported by the pattern of low Qr,, at high 7; which is independent of 7; (Fig. 3). This regulation of metabolism at high T, may be best explained as rapid metabolic compensation (Riddle, 1977) which is not as complete as in those species with temperature-insensitive zones in their M:T curves. The high QIo at low Tc is characteristic of animals living at low habitat temperatures (Rao & Bullock, 1954) and is consistent with the hypothesis that temperature adaptation permits activity to be maintained at low Tc. Additionally. the high Qlo at low T, enables the snails to rapidly increase activity when environmental temperatures are warming. This response would be especially important during fall and spring when temperatures commonly fall to low values at night and rise during the day. The pattern of translation of animals acclimated at various 7; suggests that these snails do not acclimate along a continuous temperature curve but acclimate to either low( =cold) or high( = warm) temperatures. The M:T curve of T, = 15 C snails is essentially identical to that of the 7; = 25’C snails at high Tc,,but is translated upward at low T, (Fig. 2, fed). Presumably there is a threshold temperature or transition tem-

perature zone above which animals are warmacclimated and below which they are cold-acclimated. Animals near the threshold temperature or transition zone might be expected to have characteristics of both warm- and cold-acclimation. The M:T curve of the ?; = 15°C animals is consistent with this model. A similar pattern occurred in field acclimatized Daphnia amhigua (Armitage & Lei, 1979). The M:T curve of snails acclimated to T, = 5525’C is similar to the M:T curve of K = 25’C animals at low T, and lies intermediate to the warm- and cold-acclimated curves at high T, (Fig. 2, fed). The response of the 7; = 5525°C snails suggests that they are responding to both a warm and a cold temperature cue, but the overall counter-clockwise rotation and translation of the M:T curve of the 7; = 5-25°C animals with respect to the 7; = 25’C snails indicates that the cold temperature cue predominates. The dominant effect of the cold temperature cue raises the possibility that natural selection has resulted in a response pattern which favors activity over energy conservation, The pattern of increased metabolism of starved animals with respect to fed animals from low to high 7; suggests that activity strategies may be related to energy availability. Metabolism may increase in starved snails and the degree of response is related to feeding habits (Calow, 1974). Prolonged exposure to low temperature could indicate winter dormancy and an absence of food; therefore, at 7; = 5’C, starved animals would be expected to reduce metabolism in comparison with fed animals. At higher temperatures, however, the snails could starve to death and the temperature cues could indicate high activity and food availability. Thus, at high 7; starved snails would increase metabolism in comparison with fed snails as the starved snails seek food. This interpretation of the effects of starvation on metabolism requires that either increased activity is reflected in the routine metabolism measured in the respirometers or that there was differential activity on the part of fed and starved snails in the respirometers. Because activity was not quantified, it is not possible to eliminate differential activity as the cause of some of the differences between fed and starved snails. Interestingly, cycling from low to high temperatures had a much greater effect on the increased metabolism of starved animals than did the constant high 7; = 25°C. Perhaps this response is another example of a possible complex interaction between the effects of temperature and level of feeding on the M:T relationship. The M:T curves of S. leai resulting from temperature acclimation in the laboratory differ from those of acclimatized animals whose oxygen consumption was measured shortly after the snails were collected. The M:T curves of field animals converged at 10 and 15 C (Barnhart & Armitage, 1979). There was no clear translation of M:T curves. rather the seasonal changes (fall: winter: spring: summer) were described as a progression from linearity in the fall to increasing curvilinearity by counterclockwise rotation at low temperatures and clockwise rotation at high temperatures. The convergence of the M:T curves of the field animals at low 7; is similar to the M:T curves of laboratory animals starved and acclimated at 7; = 5, 5-25’C (Fig. 2). This similarity suggests that feeding is part of acclimatization of field animals.

Metabolic acclinnation in snails This study demonstrates that feeding and temperature acclimation are part of the acclimatization process of Stenotrema leai. The quantitative roles of these factors and the contributions of other environmental factors and their interactions are yet to be clarified.

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139

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MASON