Thermal effect on the diel activity rhythm of scorpions from mesic and xeric habitats

Journal of Arid Environments (1979) 2, 339-346

Thermal effect on the diel activity rhythm of scorpions from mesic and xeric habitats M. R. Warburg & A. Ben Horin* Rhythmic activity was studied in four scorpion species: Scorpio maurus fuscus H. & E., Nebo hierochonticus E. Sim., Buthotus judaicus E. Sim. and Leiurus quinquestriatus H. & E. All species occur in the Mediterranean region: the first two are restricted to the oak-woodland, whereas the last two are found in xeric habitats extending into the arid region. The rhythmic activity of the mesic species indicates diurnal and crepuscular patterns, whereas the xeric species are mostly nocturnal. Increased temperature affected their activity by causing a drop indicating thermal adaptation.

Introduction Scorpions are generally considered to be nocturnal animals (Cloudsley-Thompson, 1956 1963). Some desert scorpions are known to be active mostly during the early hours of the evening. Thus both Vejovis mesaensis and V. confusus disappeared at 03.00 h (Hadley & Williams, 1968). Similar observations have been reported for Diplocentrus spitzeri (Crawford & Krehoff, 1975), and for Paruroctonus boreus (Tourtiotte, 1974). The latter leaves its burrow immediately after darkness and is active during the first two hours after sunset. On the other hand, some tropical species may be crepuscular: Toye (1970) found that Pandinus imperator has a diurnal pattern of behaviour and so does P. gregoryi (C. Constantinou in, Cloudsley-Thompson, 1978), both reaching a peak in activity during late afternoon and early evening. Actograph experiments have so far been conducted on 15 species (see Table I in CloudsleyThompson, 1978). Most experimental procedures did not involve controlling temperature conditions. In the present study we attempt to analyze the temperature effect on the diel rhythm and compare it in four scorpion species from different habitats.

Materials and Methods Rhythmic activity was studied in the laboratory under controlled temperature and during a 12 h light-dark cycle. The actograph used here is based on the apparatus described by Palmer (1973). It consists of a perspex box measuring 5 x 6 x 20 cm and rotating at its mid-point on a pivot. At one side an electrical contact closes a circuit, thus signalling any change in the situation of the box resulting from the scorpion's movements inside, and recording the change on a Model 712 Telrad Recorder. The recording paper moved at a • Department of Biology, Israel Institute of Technology (Technion), Haifa, Israel. 0140-1963/79/040339

+08

$02.0010

© 1979 Academic Press Inc. (London) Limited

M. R. WARBURG & A. BEN HORIN

340

speed of 1 em/min, thus a record of the 24 h experimental period was obtained. The actograph apparatus was placed inside a Struers Refritherm where temperature was controlled at ± 0·5 °C. Animals could be observed through a side window. Humidity could not be controlled inside the apparatus but relative humidity measurements (using Honeywell Lithium Chloride elements) have shown it to range between 50 and 70 per cent r.h. The activity was studied at four temperatures-20, 25, 28 and 35°C. Four scorpion species were studied: Scorpio maurus fuscus H. & E., Nebo hierochonticus E. Sim., Buthotus judaicus E. Sim, and Leiurus quinquestriatus H. & E.

7 6 5 4 3

L. IlUlnllUIsfr/ofus (n: 3)

(0)

L. Ilu/nllullsfriofus (n:3)

( b)

4 3

2 I

2 I

B judoicul (n: 5) B judo/cus (n=S)

3

2 I

N hillrochonficus (n: 3)

i

1800

I

24.00

i 1800

i

06.00

I 24.00

I

0600

L. lluinllulIsfrlofus (n =4)

4

L.

(d)

Iluinllu~sfriofus (n=2)

3 2 I

N hi~rochon"cus (n: 2)

B [udatcus (n=3)

3 2 I

N hilfochonficus (n: 2)

3

s. maurus fuscus

i

18.00

I

24.00

i 06.00

(n: 3)

2 I

I 2400

I 0600

I 12.00

SCORPION RHYTHMS

341

Results The rhythmical activity of S. m. fuscus has shown a high activity during the afternoon hours (12.00--18.00 h) and during the first half of the night (18.00--24.00 hHFigs 1, 2). With temperature rising to 28 and 35°C, the activity during the afternoon period dropped drastically (Figs 3, 5(a)). This pattern does not show when total activity was calculated (Table 1), nor when the activity in the 'illuminated' versus 'in darkness' periods were compared (Table 3). It appears that total activity was indeed affected by increasing temperatures and it actually dropped at 28 and 35°C after a rise at the optimal temperature of 25 -c (Fig. 6). In N. hierochonticus, activity was always high during the early part of the night 18.00-24.00 h and during the morning hours 06.00--12.00 hr (Figs 1,2). It was lowest during the second half of the night (00.00--06.00 h) (see Figs 3, 5(a)). The activity during the afternoon dropped considerably with increasing temperatures (28, 35 "C), Total activity was highest at 20°C (Table I), and appeared to be concentrated mostly during the illuminated period (Table 3). The total activity during the darkness period appeared to be about constant. Temperature affected activity of N. hierochonticus by causing a drop in activity with temperature up to 28°C, but at 35 "C an increase in activity was noticeable (Fig. 6, Table 1). A similar pattern in total activity was noticeable also in B. judaicus (Table I, Fig. 4(b)). This is a nocturnal animal which is active mostly during darkness hours (Fig. 5(b), Table 3), especially during the early hours of the night (18.00-21.00, see Figs I, 2). Temperature does not seem to affect this pattern of activity (Figs 3(d), 4, 6). Finally, L. quinquestriatus is active during daytime at 20°C, but not at al1 other temperatures studied (Figs 1, 2) where it shows a definite nocturnal activity pattern (Fig. 4, Table 3). Temperatures affected its activity by causing a decline in total activity (Table I, Figs 5(b), 6).

Table 1. Total activity (average number of runs) for each scorpion species at different temperatures (number of runs in brackets)

Temperature

CC)

20 25 28 35 Total

Scorpion species S.m·fuscus

39'8 (5) 69'1 (4) 56·9 (3) 30·0 (2) 50'5 (14)

N. hierochonticus

40·6 24'6 13·0 28·5

(3) (5)

(2) (2)

27·2 (12)

B.judaicus

L. quinquestriatus

20'0 (3) 41'0 (8) 24·3 (3) 16'3 (3) 30·0 (17)

55'0 (3) 36'1 (3) 39·4 (4) 5'5 (2) 36·8 (12)

The significance of the difference in total activity between S. m. [uscus and N. hierochonticus is P < 0·01 and between S. m. fuscus and B. [udaicus is P < 0·05.All other differences are not significant.

Table 2. The statistical significance (P) of the difference in activity between any pair of scorpion species (chi square)

Temperature eC) Scorpion species S. m. [uscus vs N. hierochonticus S. m. fuscus vs B. judaicus S. m. [uscus vs L. quinquestriatus N. hierochonticus vs B. judaicus

N. hierochonticus vs L. quinquestriatus B. judaicus vs L. quinquestriatus

20

25

28

35

n.s,

<0'001 <0'01 <0'01 <0'05 n.s, n.s,

<0·001 <0'001 n.s, n.s, <0·001 n.s,

<0'05 <0'001 n.s, <0·001 <0'05

<0·05 n,s.

<0'01 n.s, <0·001

n.s,

M. R. WARBURG & A. BEN HORIN

342

Table 3. Activity (average number oj runs) during a 12-12 h 'illuminated' and 'in darkness' cycle at jour temperatures

Temperature

Scorpion species

(0C)

20

18.00-06.00 h

P

S. m fuscus

5 3 3 3

22·4 29·6 4·0 29'0

17-4 11·0 16·0 26·0

<0'01 <0'01 n.s,

S. m.juscus

4 5 8 3

41-6 13'6 8·5 9'4

27'5 11·0 32·5 26'7

3 2 3 4

13'6 8·6 5·0

43·3 13·0 15·7 34·4

<0'001 <0-001

2 2 3 2

10·0 15·0 6·0 1·5

20·0 13·5 10-3 4·0

n.s, n.s. n.s, n.s.

i

N. hierochonticus B.judaicus L. quinquestriatus

S. m.fuseus

28

N. hierochonticus B.judaicus L. quinquestriatus

S. mi fuscus

35

'In darkness'

06.00-18.00 h

N. hierochonticus B. judaicus L. quinquestriatus

25

'Illuminated'

n

N. hierochonticus B.judaicus L. quinquestriatus

4 3 2

n.s,

<0'05 n.s,

<0-001 <0'01

n.s,

<0'001

L. qulnqussfriofus (n=12)

I

on

c: ~

B judoicus (n =17)

3 2

'0 I

.'" 0 c

. ~ >

<[

N hlsrochonfil:us (n =12)

3 2 I

s. mourus

12.00

18.00

24.00

tuscus (n: 14)

06.00

12.00

Time (h)

Figure 2. Total average activity of four scorpion species.

Discussion The results obtained in this study indicate a significant difference in most experiments between the activity patterns of the four species (Table 2). Two of the species differed significantly in their behaviour at all temperatures studied (S. m. fuscus as compared to

SCORPION RHYTHMS

343

B. judaicus). All other combinations of species pairs differed significantly in their activity pattern at only two temperatures. We shall consider those points which seem to us to be of interest in view of what is already known about the dispersal of these species and the microclimate within their habitat (Warburg & Ben-Horin, 1978). Considering the first two species, S. m. juscus and N. hierochonticus, both inhabiting the oak-woodland: we found no significant difference in their activity at 20°C. This could imply that some other factor permits their coexistence in spite of the overlap in activity pattern which may cause some competition. The difference in activity patterns between B. judaicus and N. hierochonticus at the high temperatures is of interest. Both species are found together in the Mediterranean region where their behaviour pattern does not differ significantly. We know, however, that the buthid species prefers stone terraces and rocks, whereas the diplocentrid species is found under very large stones with deep soil where it can dig its burrows. Furthermore, the large pedipalps of N. hierochonticus enable it to feed upon pillbugs (Armadillo ojficinalis) which are abundant there. Finally, the species B. judaicus and L. quinquestriatus occur together in xeric habitats. Their behaviour differs significantly both at low (20°C) and high (35 "C) temperatures, but not at intermediate temperatures.

28

28

(0)

24

24

U; <:

~

'l5 0

.,e

(e)

20

20

16

16

12

12

8

8

4

4

'"

~ ~

2

~

~...

<

24

21-24 20

(b)

20 16

(d)

fill S

maarus tuscus

~ N. hitlrochonlicus

16 12 12

8

8

4

4

21-24

Figure 3. Activity of S. m.fuscus and N. hierochonticus (calculated for 3 h periods), (a) at 20 DC, (b) at 25°C, (c) at 28 DC, (d) at 35 -c. 23

M. R. WARBURG & A. BEN HORIN

344

S. m. [uscus and N. hierochonticus showed both nocturnal and diurnal activity patterns. It has previously been found that S. maurus (palmatus?) has a peak of activity between 18.00 and 21.00 (Cloudsley-Thompson, 1956). The other two species (B. judaicus and L. quinquestriatus) were largely nocturnal. This is apparent at the optimal temperatures of 20 and 25°C. The nocturnal behaviour of L. quinquestriatus has previously been described by Cloudsley-Thompson (1963). The first two species inhabit mesic habitats in Mediterranean oak-woodland with high vegetation cover and a mild microclimate (Warburg & Ben-Horin, 1978). Of the other two species, B. judaicus is found in xeric habitats in the Mediterranean region, although it is found also in other habitats, while L. quinquestriatus is a desert species which extends its distribution into xeric habitats of the Mediterranean region. Both show a remarkable decline in activity at high temperatures (35°C). This is similar to a behaviour pattern previously observed in another desert poikilotherm, the isopod Venezillo arizonicus(Warburg, 1964). It is an adaptation to high temperatures, and is described here for the first time in scorpions.

28 (b)

(0)

24 20 20 16

16

12

. c

2 '0

.'" . .,; c

12

8

8

4

4

f

>

2-

>.

24

«

20

~u

21-24

21-24 (c)

20

(d)

16

DB judaicus ~ L. qUinqu.slrialus

16 12 12 8 4

8 4

06-09 03-06 09-12 Time (h)

Figure 4. Activity of B. judaicus and L. quinquestriatus (calculated for 3 h periods), (a) at 20°C, (b) at 25 "C, (c) at 28°C, (d) at 35 -c.

SCORPION RHYTHMS 35

345

(a)

30

'V

S. ",OlJrIJSIlJsclJs

o N hierochonliCIJS

25

~~ ::\1 o/'~/ Y\~~ /;\ ?/: ~ ~

35

~

30

2. "> :;: u

«

12-18 18-2400-0606-12 12-18 18-2400-0606-12 12-18 18-24 00-06 06-12 12-\8 18-2400-0606-12 ( b)

25

A

B. jlJdoiclJS

° L. qlJinqlJeslriollJS

1:{ 2

/

'> t,V _

•

~

g

~ ?".__ I /~ I". \

1 d 12-IS IS-24 00-0606-12 12-IS IS-24 00-0606-12 12-18 18-2400-0606-12 12-1818-2400-0606-12 Time ( h)

Figure 5. (a) Activity of S.m. [uscus and N. hierochonticus calculated for 6 hr periods. (b) Activity of B. judaicus and L. quinquestriatus calculated for 6 h periods.

70 en e

S. m. tuscus

N lIierocllonliclJs

8 jlJdoiclJs

L. qlJinqlJeslriollJs

60

...e

50

d

40

0

c

..«'" Q)

~ >

30 20 10 20

30

40

I 2'0 30

40

II 2~ 30 40 I 20

30

40

T (Oc)

Figure 6. Temperature effect on activity of four scorpion species.

References Cloudsley-Thompson, J. L. (1956). Studies in diurnal rhythms-VI. Bioclimatic observations in Tunisia and their significance in relation to the physiology of the fauna, especially woodlice, centipedes, scorpions and beetles. Annals and Magazine of Natural History (12) 9: 305-329.

346

M. R. WARBURG & A. BEN HORIN

Cloudsley-Thompson, J. L. (1963). Some aspects of the physiology of Buthotus minax (Scorpiones: Buthidae) with remarks on other African scorpions. Entomologist's Monthly Magazine 98: 243-246. Cloudsley-Thompson, J. L. (1978). Biological clocks in Arachnida. Bulletin of the British Arachnological Society, 4: 184-191. Crawford, C. S. & Krehoff, R. C. (1975). Diel activity in sympatric populations of the scorpions Centruroides sculpturatus (Buthidae) and Diplocentrus spitzeri (Diplocentridae). Journal of Arachnology, 2: 195-204. Hadley, N. F. & Williams, S. C. (1968). Surface activities of some North American scorpions in relation to feeding. Ecology, 49: 726-734. Palmer, J. D. (1973). Tidal rhythms: the clock control of the rhythmic physiology of marine organisms. Biological Reviews, 43: 377-418. Tourtlotte, G. I. (1974). Studies on the biology and ecology ofthe northern scorpion, Paruroctonus boreus (Girard). Great Basin Naturalist, 34: 167-179. Toye, S. A. (1970). Some aspects of the biology of two common species of Nigerian scorpions. Journal of Zoology, London, 162: 1-9. Warburg, M. R. (1964). The response of isopods towards temperature, humidity and light. Animal Behaviour, 12: 175-186. Warburg, M. R. & Ben-Horin, A. (1978). Temperature and humidity effects on scorpion distribution in northern Israel. Symposia of the Zoological Society of London, 42: 161-169.