- Email: [email protected]
The effects of constant and changing tempertures on the development of eggs of the freshwater snail Lymnaea auricularia (L.)
J therm 8rol Vol 6 pp 379 to 388 1981 Printed m Great Britain
0306-4565~81 040379-1050200~0 Pergamon Press Lid
THE EFFECTS OF CONSTANT AND CHANGING TEMPERATURES ON THE DEVELOPMENT OF EGGS OF THE FRESHWATER SNAIL LYI~AEA AURICULARIA (L.)
T. S a l i h , O. A1-Habbib, W. A l - N a b b i b , S. Al-Zako and T. A l l Dept. of Biology, College of Sc i e n c e , U n i v e r s i t y of Mosul, I r a q
ABSTRACT The r a t e o f d e v e l o p m e n t o f Lymnaea a u r l c u l a r i a e g g s was s t u d i e d a t v a r i o u s c o n s t a n t t e m p e r a t u r e s b e t w e e n 10 ° and 36°C. Development was a c c e l e r a t e d as t h e t e m p e r a t u r e i n c r e a s e d and a t 36°C t h e eggs f a i l e d t o d e v e l o p . S p r i n g eggs showed d i f f e r e n c e s i n t h e i r r a t e o f d e v e l o p m e n t when compared w i t h summer eggs when measured a t s i m i l a r t e m p e r a t u r e s . Both s p r i n g and summer eggs were more t h a n 90% f e r t i l e . HaCchln 8 s u c c e s s was h i g h a t t e m p e r a t u r e s b e t w e e n 10 ° and 30°C (100%- 82.9%); w h i l e a t 34°C i t was r e d u c e d t o 60.6% f o r s p r i n g e g g s . I t was above 87% a t t e m p e r a t u r e s between I0 ° and 34°C b u t i t dropped t o 62.3% a t 36°C f o r summer e g g s . I n one r e g u l a r l y c h a n g i n g t e m p e r a t u r e e x p e r i m e n t a s i g n i f i c a n t a c c e l e r a t i o n (P<.05) was f o u n d . In two o t h e r s t h e r e was no s i g n i f i c a n t d i f f e r e n c e b e t w e e n p r e d i c t e d and o b s e r v e d egg d u r a t i o n s . I n one s u d d e n l y c h a n g i n g t e m p e r a t u r e regime (1 day a t 20 ° , 1 day a t 30 ° and so on) a huge r e t a r d a t i o n o f d e v e l o p m e n t was f o u n d . In t h e o t h e r s u d d e n l y c h a n g i n g e x p e r i m e n t (1 day a t 15 ° , I day a t 25 ° ) no s i g n i f i c a n t d i f f e r e n c e was f o u n d . The e x p o s u r e o f eggs t o e x t r e m e t e m p e r a t u r e s ( 4 ° C , f r e e z i n g and 40°C) c a u s e d a r e c a r d a t l o u i n t h e r a t e o f s u b s e q u e n t d e v e l o p m e n t o f eggs a t 25°C.
KEYWORDS
Eggs; d e v e l o p m e n t ; t e m p e r a t u r e ; m o l l u s c a ; c h a n g i n g t e m p e r a t u r e s .
INTRODUCTION
A number o f Molluscan s p e c i e s a r e known t o a c t as i n t e r m e d i a t e h o s t s f o r c e r t a i n p a r a s i t i c worms. Of t h e s e ~ a u r l c u l a r i a has b e e n found t o be t h e i n t e r m e d i a t e h o s t f o r t h e l i v e r f l u k e F a s c i o l a g l g a n t l c a s w h i c h c a u s e s f a s c i o l a s l s i n s h e e p and c a t t l e i n I r a q . I n any p r o g ramme t o c o n t r o l t h e p e r s i s t e n c e and s p r e a d o f t h e d i s e a s e , i t i s of g r e a t i m p o r t a n c e t o c o n t r o l the i n t e r m e d i a t e h o s t in a d d i t i o n to c o n t r o l l i n g the p a r a s i t e i t s e l f . To do s o , i t i s n e c e s s a r y t o have knowledge o f c e r t a i n a s p e c t s o f t h e b l o l o g y o f t h i s s n a i l . Therefore, t h e main aim o f t h e p r e s e n t work i s an a t t e m p t t o g e t some i n f o r m a t i o n c o n c e r n i n g t h e e f f e c t o f t e m p e r a t u r e on b o t h t h e d e v e l o p m e n t and on h a t c h i n g o f e g g s . A good d e a l o f work has a p p e a r e d i n t h e l i t e r a t u r e c o n c e r n i n g t h e e f f e c t s o f c o n s t a n t t e m p e r a t u r e s on t h e d e v e l o p m e n t o f eggs i n v a r i o u s m o l l u s c a n s p e c i e s ( K e n d a l l , 1953; Neuma~t, 1959; Boray, 1963; S t u r r o k , 1966; Mousa and Abou E 1 - H a s s e n , 1972; S t u r r o k and S t u r r o k , 1972; S c h a l e and B e r r y , 1973; O. Al-Mabblb, 1974 and I s l a m , 1977). On t h e o t h e r h a n d , l i t t l e i s known about t h e e f f e c t s o f c h a n g i n g t e m p e r a t u r e s on t h e d e v e l o p m e n t o f eggs o f f r e s h w a t e r s n a i l s . (0. A1Habblb, 1974 and W. A1-Habblb s 1974). MATERIALS AND METHODS The s n a i l s used i n p r o d u c i n g eggs f o r t h e p r e s e n t i n v e s t i g a t i o n were c o l l e c t e d from A1-Khosar r i v e r , Mosul - I r a q . To o b t a i n egg m a s s e s , t h e t e m p e r a t u r e o f t h e w a t e r , c o n t a i n i n g t h e s n a i l , was g r a d u a l l y r a i s e d from 10 ° t o 25°C. This seems t o s t i m u l a t e t h e s n a i l s t o p r o d u c e l a r g e q u a n t i t i e s o f egg m a s s e s . A f t e r t h e p r o d u c t i o n o f t h e d e s i r e d q u a n t i t y o f egg m a s s e s , t h e s n a i l s were k e p t a t lO°C~ The egg masses were t r a n s p a r e n t and s a u s a g e s h a p e d . The egg p r o p e r i s found i n a r e l a t i v e l y l a r g e c a p s u l e embedded i n a j e l l y - l i k e mass and t h e egg c a p s u l e u s u a l l y c o n t a i n s a l a r g e amount o f a l b u m l n . The number o f egg c a p s u l e s i n e a c h egg mass ranged from 5 379
380
T SALXHet al
to 120 and in few cases up to 180 eggs were observed. The mean length and width of the egg capsules were 0.88 and 0.80 mm respectively. In all experiments, during the present work freshly laid and undeveloped eggs were used.
The d e v e l o p m e n t o f eggs was d e t e r m i n e d a t t h e c o n s t a n t t e m p e r a t u r e s 4 ° , 8 ° , 10 ° , 12 ° , 15 ° , 20 ° , 25 ° , 30 ° , 36 ° and 37°C. In e a c h e x p e r i m e n t a number o f newly l a i d eggs r a n g i n g from 30 t o 1OO were u s e d . The eggs were k e p t i n t e s t t u b e s f i l l e d w i t h d e c h l o r l n a t e d t a p w a t e r t o about 3/4 o f t h e i r volume and k e p t a t t h e d e s i r e d t e m p e r a t u r e (~ . l ° C ) . The eggs i n each e x p e r i m e n t o f t h e p r e s e n t work were examined a t l e a s t t w i c e d a i l y and t h e d u r a t i o n f o r t h e i r development and r a t e o f h a t c h i n g was r e c o r d e d . The w a t e r i n t h e t e s t t u b e s was changed d a i l y and i t s t e m p e r a t u r e was checked t w i c e a d a y . The egg d e v e l o p m e n t was a l s o i n v e s t i g a t e d u n d e r t h r e e r e g u l a r l y c h a n g i n g t e m p e r a t u r e r e g i m e s (10 ° ~ 20 ° , 1 5 ° ~ - ~ 2 5 ° and 2 0 ° ( - - ~ 3 0 ° C ) u s i n g S h e r e r growth chambers ( c e l l 2 5 5 - 5 ) . Each o f t h e s e t e m p e r a t u r e r e g i m e s was o b t a i n e d by s e t t i n g t h e e l e c t r o n i c t e m p e r a t u r e c o n t r o l l e r knob a t t h e lower t e m p e r a t u r e f o r 12 h o u r s a day and a t t h e h i g h e r t e m p e r a t u r e f o r t h e r e m a i n i n g 12 h o u r s . The c o n t r o l u n i t f o r t h e growth chamber was a r r a n g e d so as t o s w i t c h on the lower t e m p e r a t u r e c o n t r o l u n i t f o r 12 h o u r s , t h e n a u t o m a t i c a l l y s w i t c h e d i t o f f and t h e h i g h e r temp e r a t u r e c o n t r o l u n i t was s w i t c h e d on f o r a n o t h e r 12 h o u r s . This c y c l e was r e p e a t e d d a i l y in each e x p e r i m e n t u n t i l t h e d e v e l o p m e n t and h a t c h i n g o f t h e eggs was c o m p l e t e d . The i n f l u e n c e o f each o f two s e t s o f s u d d e n l y c h a n g i n g t e m p e r a t u r e s ( 1 5 ° ~ - ~ 2 5 ° and 20°(--~30°C) on t h e d e v e l o p m e n t o f t h e eggs was a l s o d e t e r m i n e d . The eggs i n each e x p e r i m e n t were t r a n s f e r r e d a b r u p t l y and k e p t a l t e r n a t e l y f o r 24 h o u r s a t t h e l o w e r t e m p e r a t u r e and t h e n f o r a n o t h e r 24 h o u r s a t the h i g h e r t e m p e r a t u r e . This was r e p e a t e d d u r i n g t h e c o u r s e o f t h e e x p e r i m e n t s u n t i l the completion of development. Three groups o f eggs were e x p o s e d t o each o f t h e f o l l o w i n g e x t r e m e t e m p e r a t u r e s : d e e p - f r e e z i n g , 4°C and 40°C, f o r d i f f e r e n t p e r i o d s o f t i m e , t h e n t h e i r s u b s e q u e n t d e v e l o p m e n t a t 25°C was i n v e s t i g a t e d .
RESULTS The mean d u r a t i o n o f the d i f f e r e n t d e v e l o p m e n t a l s t a g e s and t h a t o f h a t c h i n g o f t h e eggs d e c r e a s e d as t h e e x p e r i m e n t a l t e m p e r a t u r e was i n c r e a s e d up t o 30°C i n b o t h " s p r i n g e g g s " ( o b t a i n e d from s n a i l s c o l l e c t e d d u r i n g A p r i l ) and "summer e g g s " ( o b t a i n e d from s n a i l s c o l l e c t ed d u r i n g t h e summer) as shown i n F i g u r e s 1 and 2 and T a b l e s 1 and 2 r e s p e c t i v e l y . Q0
c
sG
AG
\
e
, 1o
, 15
i 2o
2s
i 3o
i 3B
TEMPERATURE (*C)
F i g . 1. D u r a t i o n o f d e v e l o p m e n t t o G a s t r u l a (A), l a t e t r o c h o p h o r e (B) and f o r h a t c h i n g o f s p r i n g e g g s (C) a t v a r i o u s c o n s t a n t t e m p e r a t u r e s .
Changing temperatures o n egg development of L aurwulana
381
70-
60-
50-
40>. 30-
20-
10-
8
I
I
I
!
16
24
32
40
C
TEMP
F i g . 2. D u r a t i o n of d e v e l o p m e n t t o O a s t r u l a (A), e a r l y t r o e h o p h o r e (B), l a t e t r o c h o p h o r e (C) and f o r h a t c h i n g (D) o f s u u n e r eggs a t d i f f e r ent constant temperatures.
TABLE
1
Rate of Development and Hatching at Different Constant and Changing Temperatures for Spring Eggs of L. auricularia
Duratson aC Constant Temperatures (DAYS) DevnXopmental Stage
~ s t l O n at Changln 8 temp. 10o(--) 20° Days
10°
15°
20°
25°
30°
32°
34°
;estrula
11.1
6.0
5.0
4.5
2.0
1.5
1.0
4.0
Late troohophore
20.5
15.5
11 .O
7.5
3.5
3.5
3.0
10.0
~lean d u r a t i o n to
54.9
30.3
16.0
12.4
9.0
8.5
7.5
15.6
36 °
~atching Standard error
1.846
!.05
l.O0
0.927
0.884 0.645 0.50
0.884
Sz) Z Hatch ~o. o f eggs (.)
100 56
)8.3
86.0
85.0
32.9
77.4
75
29
40
35
44
6O.6 9
82.9 35
382
T
TABLE 2
D u r a t i o n of ,Developmeut and t l a t c h l n 8 o f Summer E ~ s of Lymnaea aur'icularia at Differ,ent. Constant and Chanlin~ Temperatures O u r e t t o n Ln Days at Constant T © ~ r a t u r ~ s
r~ Scese
4o
;8stru|8
60
al
SALIH et
8°
10°
12°
15 °
20 °
25 °
30°
D u r a t i o n (Dnys) a t resu l a r l y ¢h~n~ane t e n p e r a t u r e s (L~)
('C) ]6 °
37°
2
~0
29
13
9
5
3
2
2
~erly Trochophor(
50
36
18
L2
8
~
3
4
~ate Trochophore
60
38
21
L6
lO
6
5
6
qesn d u r a t i o n t o ~atchln$
-
67,~2 31 32 23 61 L$ 39
9.39
8 3 8 ] i 2 06
-
Standard e r r o r
-
1 377 0.193 0 . 1 8 8 O 202 O.lO$ 3 223 3,268
-
(s[)
| o , o f e s S s used (u)
76
74
79
77
91
8&
79
B2
77
150 4-~ ~ ° ' 20" t - ~ 30°
,5° ,,--4 25°
20° ~
3
3
6
6
5
5
8
6
7
?
10 65
9 35
0 173
r8
D~ratLon (Days) a t l u d d e o l y ¢han81n | t e ~ r a t u r e s (°C)
0 197
74
9 17 38 O 665
66
60
9 20 27
0 915
66
T h e r e seems t o be some a c c e l e r a t i o n i n t h e d e v e l o p m e n t o f " s p r i n g eggs" above 30°C up t o 34°C, b u t t h a t a c c e l e r a t i o n i s n o t s i g n i f l c a n t . However, a t e m p e r a t u r e of 36°C a p p e a r e d t o c a u s e a f a i l u r e o f d e v e l o p m e n t i n " s p r i n g e g g s " and a r e t a r d a t i o n i n t h e d e v e l o p m e n t o f "summer e g g s " , w h i l e a t 37°C "summer e g g s " d e v e l o p e d t o t h e gastrula stage only. For b o t h g r o u p s o f eggs t h e h a t c h i n g s u c c e s s was h i g h a t v a r i o u s e x p e r i m e n t a l t e m p e r a t u r e s , i t r a n g e d from IOOX a t 10°C t o 82.9Z a t 30°C f o r " s p r i n g e g g s " (Fig. 3) and from 96.2X a t lO°C t o 76.8X a t 30°C f o r "summer e g g s "
(Fig. 4).
'° I
\
O
T
60
&o
20
|
10
2O
| '
"8
30
i
~0
TEMPERATURE ('C)
Fig. 3.
Percentage of spring e U s hatching at various constant temperatures.
Eo~ever, the hatching percent decreased to only 60.6Z at 34°C and 62.3Z at 36°C for spring and sunder eggs r e s p e c t i v e l y .
30°
Changing temperatures.on egg development of L. aunculana
383
-I00
70-
uz
c/J
-80
35-
o
0 5
Fig. 4.
I
I
I
l
!
-I
I0
15
20
25 o TEMP C
30
35
60 40
Duration of development (open c i r c l e s ) and percentage hatching ( s o l i d c l r c l e s ) of sunner eggs at d i f f e r e n t constant temperatures.
Table 1 and 2 a l s o show the mean d u r a t i o n of v a r i o u s developmental stages and of hatching of " s p r i n g eggs" a t a r e g u l a r l y changing temperature between 1 0 o ( - ~ 2 0 ° C . The 24 hour cy cl e of t h i s changing temperature regime i s shown i n F i g . 5a and t h a t of " s u m E r eggs" at the two reg. imes of r e g u l a r l y changing temperatures between 15°(--)25°C and betveen 2 0 ° O 3 0 ° C are seen i n F i g . 5b and c r e s p e c t l v e l y .
22-
2018-
0
UI61412" I08
I
I
6
12
I
18
I
24
HOURS
F i g . 5a.
Daily c y c l e of r e g u l a r l y changing temperature regimes I 0 ° ( - - ) 2 0 ° C
384
T SALIHef al 26-
24-
22oo 2O
Q.
:E UJ t-
18
16
14
_
0
6
12
18
24
HOURS
Fig. 5b. Daily c y c l e of r e g u l a r l y chenglng temperature regimes 1 5 ° 4 --) 25°C 31=
29-
27-
o(J Q. 25UJ
234 i 21--
19
.... O
I
--
6
I
12
i
-7-
24
18
HOURS
Fig. 5c. Daily c y c l e of r e g u l a r l y changing temperature regime 20°4-~30°C The r e s u l t s of the d u r a t i o n to h a t c h i n g of these groups of eggs under the r e g u l a r l y changing temperature regimes were compared with p r e d i c t e d r e s u l t s based on c o n s t a n t temperature e x p e r iments using Connollys (1980) method. The constant t e ~ e r a t u r e r e s u l t s f o r the s p r i n g eggs (Table 1) t o g e t h e r with the standard e r r ors formed the input to a w e i j h t e d r e g r e s s i o n curve f i t t i n g progrmmm vhleh was run on an Apple I I ~ c r o c o m p u t e r . This f i t t e d the data to the f o l l o ~ n g e q u a t i o n : I/D t Be + BI.T + B2.T2 + B3.T3 This a l s o gave the v a r i a n c e - c o v a r i a n c e ~ m t r i x .
....
(I)
The v a l u e s of the c o e f f i c i e n t s were:
B = .0356649903 B° i -.00597310144 B1 2 .000491434633 B3 -.00000690921892 These t o g e t h e r with the experimental r e s u l t s of the changing temperature experiments formed the input of the main computer pro&ra~me which was run on a DEC 20 computer. Three g r i d s i z e s and three step s i z e s were used (see S a l i h and Grainger (1981)). The percentage of development which
Changing temperatures on egg development of L aurlcularta
385
A I day exposure to 4°C caused a s i g n i f i c a n t r e t a r d a t i o n i n the mean d u r a t i o n of development of e~gs at 25°C (p
14-
- lO0
13-70 (n
~12,.~
U k~v
o~.o -40 II-
IO 0
I
I
I0
20
TIME
Fig. 7.
FROZEN
I0
30
(MINUTES)
The e f f e c t of f r e e z i n g time on the subsequent development of eggs at 25°C. Duration of development (open c l r c l e s ) , h a t c h ing percent ( s o l l d c l r c l e s ) .
This f i g u r e a l s o shows t h a t the percentage hatching at 25°C decreased by the f r e e z i n g time i n creased and i t reached 18.5g a f t e r f r e e z i n g the eggs f o r 25 minutes. Freezing f o r 30 minutes k l U e d a l l the eggs. F i g . 8 shows the mean d u r a t i o n of development and the percentage of hatching of eggs at 25°C a f t e r being exposed to the high temperature of 40 ° f o r v ar y i n g periods of time.
12-5 "
-100
-gS 11.5 -90
z
o I-
W
Q
- e s o~ 10.5-
"SO
9.S
|
0
S
TIME
F i g . 8.
I
I
I
10
lS
20
AT 4 0 ° C
tS 25
(HOURS)
Duration of development (open c l r c l e s ) and hatching p er cen t ( s o l i d c i r c l e s ) of eggs a t 25°C a f t e r being exposed to 40°C f o r d i f f e r e n t periods of time.
T SAuH etal
386
would be p r e d i c t e d t o t a k e p l a c e i n t h e o b s e r v e d t i m e i s c a l c u l a t e d s t a n d a r d e r r o r and m a x l m u m b l a s . T h e s e ~ a r e g i v e n i n T a b l e 3.
TABLE 3 .......
t o g e t h e r w i t h t h e maximum
P r e d l c t e d Development i n R e B u l a r l y C h a n g i n g Temperature Experiments
]
10°(--~20°
I 15°(--~25° ]20°(---~30°
Predicted ~velo~nt p (g)
60.82
75.41
99.53
Hax. SE of p
29.20
7.30
15.75
Max. bias in p
19.9
The sumner egg r e s u l t s
.185
g i v e n i n T a b l e 2 gave the f o l l o v l n g
0.47
coefficients.
B° i -.125839722
B1 B2 B3
.022948703 - .00107238839 .0000203277478
I t i s s e e n t h a t i n t h e 10 ( - - ) 2 0 ° e x p e r l m e n t 60.82Z o f t h e d e v e l o p m e n t i s p r e d i c t e d t o be c o ~ l e t e d i n t h e o b s e r v e d t i m e ( 1 5 . 6 d a y s , T a b l e 1 ) . However, t h e s t a n d a r d e r r o r i s v e r y l a r g e and p+ ( 1 . 9 8 x max s t a n d a r d e r r o r ) = 1 1 8 . 6 , and s i n c e t h i s i s g r e a t e r t h a n 100 one c a n say t h a t t h e r e i s no s i g n i f i c a n t d i f f e r e n c e (p>.OS) b e t w e e n p r e d i c t e d and o b s e r v e d . The a a x I i u a b i a s i s howe v e r a l s o l a r g e v h l e h means t h a t t h e r e i s l e s s c o n f i d e n c e i n t h e r e s u l t . I n t h e 15°4-p 25 ° e x p e r i m e n t on t h e o t h e r hand p d i f f e r s s i g n i f i c a n t l y frmn 100 (p<.OS) and s i n c e t h e b i a s i s r m a l l one c a n say t h a t t h i s c h a n g i n g t e m p e r a t u r e h a d a s i g n i f i c a n t a c c e l e r a t i n g e f f e c t on d e v e l o p m e n t . I n t h e 20 ° ¢-~ 30 ° e x p e r i m e n t no s i g n i f i c a n t e f f e c t i s f o u n d . T a b l e 2 shows t h e mean d u r a t i o n f o r d i f f e r e n t d e v e l o p m e n t a l s t a g e s and f o r h a t c h i n g i n s u ~ e r eggs d e t e r m i n e d a t two s e t s o f s u d d e n l y c h a n s l n g t e m p e r a t u r e s b e t w e e n 1 5 ° ~ ~-) 25°C and b e t w e e n
26 ° ~-~ 3o°c. I n the 1 5 ° O 25° experiment p - 121.2Z; maximum Se. of p = 12.O21; end max bias i n p - .222. Thus no s i g n i f i c a n t e f f e c t i s f o u n d . I n t h e 20 4-)30 ° e x p e r i m e n t on t h e o t h e r h a n d a v e r y l a r g e e f f e c t i s found and d e v e l o p m e n t i s s i g n i f i c a n t l y s l o w e r (p<.OS) t h a n i f i t had t a k e n p l a c e a l l t h e time a t 20 ° . I t would a p p e a r t h a t e v e n t h o u g h d e v e l o p m e n t i s s u c c e s s f u l l y c o m p l e t e d a t a c o n s t a n t t e m p e r a t u r e o f 30 ° . e x p o s u r e t o i t on s u c c e s s i v e days h a s a huge r e t a r d i n 8 e f f e c t . This should be i n v e s t i g a t e d f u r t h e r .
,6]
E x p e r i m e n t s i n t h i s n e x t p a r t o f t h e work h a v e b e e n c a r r i e d o u t u s i n g s m ~ e r eggs o n l y . Both a r e t a r d a t i o n i n d e v e l o p m e n t and a d e c r e a s e i n t h e p e r c e n t a g e o f eggs h a t c h i n g a t 25 ° o c c u r r e d a f t e r t h e eggs had b e e n e x p o s e d a t &°C f o r v a r y i n g p e r i o d s o f t i m e ( F i g . 6 ) .
.
101
-,oo
!
o
-
I
s
10 TIME
F i g . 6.
60
I
1s
20
AT 4 °C (DAYS)
D u r a t i o n o f d e v e l o p m e n t ( o p e n c i r c l e s ) and p e r c e n t a g e h a t c h i n g ( s o l l d c i r c l e s ) of eggs a t 25 ° a f t e r e x p o s u r e t o 4 ° f o r v a r y i n g p e r i o d s of time.
Changing temperatures on egg development of L aurwular~a
387
I t was found t h a t e x p o s u r e t o 40°C f o r up t o 5 h o u r s d i d n o t p r o d u c e a s i g n i f i c a n t r e t a r d i n g e f f e c t on t h e mean d u r a t i o n of d e v e l o p m e n ~ (p>O.O5). But e x p o s u r e f o r 8 h o u r s t o 40°C c a u s e d a h l g h l y s i g n i f i c a n t r e t a r d i n g e f f e c t on t h e d u r a t i o n o f d e v e l o p m e n t o f eggs (p
388
T SALIH et al
Boray, J. C. (1963). Proc. World Vet. Contr., i, 709-715. Brltz, L. and W. C. Hone (1955). Z. angew.Zool., 42, 209-234. Clarke, K. U. (1967). Bull. ent. Res., 5__7, 259-270. Connolly, J. (1979). Proc. R. It. Acad., 79B, 271-280. Grainger, J. N. R. (1959). Zool. Anz., 163--~-267-277. Kendall, S. B. (1953). J. Helminth., 27, 17-28. Mousa, A. H. and A. A. Abou EI-Hassan~972). j. EgTpt med. Ass., 55, 148-165. Neumann, D. (1959). Z. Morph. Okol Tiere, 48, 349-411. Neumann, D. (1960). Biol. Zbl., 791 585-605-.-Nojima, H. (1973). Trop. Med., 15, 23-35. Precht, H., J. Christophersen, H. Hensel, and W. Latchet (1973). Temperature and Life, Springer Verlag, Berlin. Sallh, N. and J. N. R. Grainger (1981). J. Life Sci. R.~,bl. Soc., ~, 181-185. Schalle, H . ~ D. and E. G. Berry (1973). Sterkiana, 50, 1 - 9 2 . .... Sturrock, R. F. (1966). Ann. trop. Med. Parasit.', 60~--I00-I05. Sturrock, R. F. and B. M. Sturrock (1972). Ann. trop. Med. Parasit., 66, 385-390.
0306-4565~81 040379-1050200~0 Pergamon Press Lid
THE EFFECTS OF CONSTANT AND CHANGING TEMPERATURES ON THE DEVELOPMENT OF EGGS OF THE FRESHWATER SNAIL LYI~AEA AURICULARIA (L.)
T. S a l i h , O. A1-Habbib, W. A l - N a b b i b , S. Al-Zako and T. A l l Dept. of Biology, College of Sc i e n c e , U n i v e r s i t y of Mosul, I r a q
ABSTRACT The r a t e o f d e v e l o p m e n t o f Lymnaea a u r l c u l a r i a e g g s was s t u d i e d a t v a r i o u s c o n s t a n t t e m p e r a t u r e s b e t w e e n 10 ° and 36°C. Development was a c c e l e r a t e d as t h e t e m p e r a t u r e i n c r e a s e d and a t 36°C t h e eggs f a i l e d t o d e v e l o p . S p r i n g eggs showed d i f f e r e n c e s i n t h e i r r a t e o f d e v e l o p m e n t when compared w i t h summer eggs when measured a t s i m i l a r t e m p e r a t u r e s . Both s p r i n g and summer eggs were more t h a n 90% f e r t i l e . HaCchln 8 s u c c e s s was h i g h a t t e m p e r a t u r e s b e t w e e n 10 ° and 30°C (100%- 82.9%); w h i l e a t 34°C i t was r e d u c e d t o 60.6% f o r s p r i n g e g g s . I t was above 87% a t t e m p e r a t u r e s between I0 ° and 34°C b u t i t dropped t o 62.3% a t 36°C f o r summer e g g s . I n one r e g u l a r l y c h a n g i n g t e m p e r a t u r e e x p e r i m e n t a s i g n i f i c a n t a c c e l e r a t i o n (P<.05) was f o u n d . In two o t h e r s t h e r e was no s i g n i f i c a n t d i f f e r e n c e b e t w e e n p r e d i c t e d and o b s e r v e d egg d u r a t i o n s . I n one s u d d e n l y c h a n g i n g t e m p e r a t u r e regime (1 day a t 20 ° , 1 day a t 30 ° and so on) a huge r e t a r d a t i o n o f d e v e l o p m e n t was f o u n d . In t h e o t h e r s u d d e n l y c h a n g i n g e x p e r i m e n t (1 day a t 15 ° , I day a t 25 ° ) no s i g n i f i c a n t d i f f e r e n c e was f o u n d . The e x p o s u r e o f eggs t o e x t r e m e t e m p e r a t u r e s ( 4 ° C , f r e e z i n g and 40°C) c a u s e d a r e c a r d a t l o u i n t h e r a t e o f s u b s e q u e n t d e v e l o p m e n t o f eggs a t 25°C.
KEYWORDS
Eggs; d e v e l o p m e n t ; t e m p e r a t u r e ; m o l l u s c a ; c h a n g i n g t e m p e r a t u r e s .
INTRODUCTION
A number o f Molluscan s p e c i e s a r e known t o a c t as i n t e r m e d i a t e h o s t s f o r c e r t a i n p a r a s i t i c worms. Of t h e s e ~ a u r l c u l a r i a has b e e n found t o be t h e i n t e r m e d i a t e h o s t f o r t h e l i v e r f l u k e F a s c i o l a g l g a n t l c a s w h i c h c a u s e s f a s c i o l a s l s i n s h e e p and c a t t l e i n I r a q . I n any p r o g ramme t o c o n t r o l t h e p e r s i s t e n c e and s p r e a d o f t h e d i s e a s e , i t i s of g r e a t i m p o r t a n c e t o c o n t r o l the i n t e r m e d i a t e h o s t in a d d i t i o n to c o n t r o l l i n g the p a r a s i t e i t s e l f . To do s o , i t i s n e c e s s a r y t o have knowledge o f c e r t a i n a s p e c t s o f t h e b l o l o g y o f t h i s s n a i l . Therefore, t h e main aim o f t h e p r e s e n t work i s an a t t e m p t t o g e t some i n f o r m a t i o n c o n c e r n i n g t h e e f f e c t o f t e m p e r a t u r e on b o t h t h e d e v e l o p m e n t and on h a t c h i n g o f e g g s . A good d e a l o f work has a p p e a r e d i n t h e l i t e r a t u r e c o n c e r n i n g t h e e f f e c t s o f c o n s t a n t t e m p e r a t u r e s on t h e d e v e l o p m e n t o f eggs i n v a r i o u s m o l l u s c a n s p e c i e s ( K e n d a l l , 1953; Neuma~t, 1959; Boray, 1963; S t u r r o k , 1966; Mousa and Abou E 1 - H a s s e n , 1972; S t u r r o k and S t u r r o k , 1972; S c h a l e and B e r r y , 1973; O. Al-Mabblb, 1974 and I s l a m , 1977). On t h e o t h e r h a n d , l i t t l e i s known about t h e e f f e c t s o f c h a n g i n g t e m p e r a t u r e s on t h e d e v e l o p m e n t o f eggs o f f r e s h w a t e r s n a i l s . (0. A1Habblb, 1974 and W. A1-Habblb s 1974). MATERIALS AND METHODS The s n a i l s used i n p r o d u c i n g eggs f o r t h e p r e s e n t i n v e s t i g a t i o n were c o l l e c t e d from A1-Khosar r i v e r , Mosul - I r a q . To o b t a i n egg m a s s e s , t h e t e m p e r a t u r e o f t h e w a t e r , c o n t a i n i n g t h e s n a i l , was g r a d u a l l y r a i s e d from 10 ° t o 25°C. This seems t o s t i m u l a t e t h e s n a i l s t o p r o d u c e l a r g e q u a n t i t i e s o f egg m a s s e s . A f t e r t h e p r o d u c t i o n o f t h e d e s i r e d q u a n t i t y o f egg m a s s e s , t h e s n a i l s were k e p t a t lO°C~ The egg masses were t r a n s p a r e n t and s a u s a g e s h a p e d . The egg p r o p e r i s found i n a r e l a t i v e l y l a r g e c a p s u l e embedded i n a j e l l y - l i k e mass and t h e egg c a p s u l e u s u a l l y c o n t a i n s a l a r g e amount o f a l b u m l n . The number o f egg c a p s u l e s i n e a c h egg mass ranged from 5 379
380
T SALXHet al
to 120 and in few cases up to 180 eggs were observed. The mean length and width of the egg capsules were 0.88 and 0.80 mm respectively. In all experiments, during the present work freshly laid and undeveloped eggs were used.
The d e v e l o p m e n t o f eggs was d e t e r m i n e d a t t h e c o n s t a n t t e m p e r a t u r e s 4 ° , 8 ° , 10 ° , 12 ° , 15 ° , 20 ° , 25 ° , 30 ° , 36 ° and 37°C. In e a c h e x p e r i m e n t a number o f newly l a i d eggs r a n g i n g from 30 t o 1OO were u s e d . The eggs were k e p t i n t e s t t u b e s f i l l e d w i t h d e c h l o r l n a t e d t a p w a t e r t o about 3/4 o f t h e i r volume and k e p t a t t h e d e s i r e d t e m p e r a t u r e (~ . l ° C ) . The eggs i n each e x p e r i m e n t o f t h e p r e s e n t work were examined a t l e a s t t w i c e d a i l y and t h e d u r a t i o n f o r t h e i r development and r a t e o f h a t c h i n g was r e c o r d e d . The w a t e r i n t h e t e s t t u b e s was changed d a i l y and i t s t e m p e r a t u r e was checked t w i c e a d a y . The egg d e v e l o p m e n t was a l s o i n v e s t i g a t e d u n d e r t h r e e r e g u l a r l y c h a n g i n g t e m p e r a t u r e r e g i m e s (10 ° ~ 20 ° , 1 5 ° ~ - ~ 2 5 ° and 2 0 ° ( - - ~ 3 0 ° C ) u s i n g S h e r e r growth chambers ( c e l l 2 5 5 - 5 ) . Each o f t h e s e t e m p e r a t u r e r e g i m e s was o b t a i n e d by s e t t i n g t h e e l e c t r o n i c t e m p e r a t u r e c o n t r o l l e r knob a t t h e lower t e m p e r a t u r e f o r 12 h o u r s a day and a t t h e h i g h e r t e m p e r a t u r e f o r t h e r e m a i n i n g 12 h o u r s . The c o n t r o l u n i t f o r t h e growth chamber was a r r a n g e d so as t o s w i t c h on the lower t e m p e r a t u r e c o n t r o l u n i t f o r 12 h o u r s , t h e n a u t o m a t i c a l l y s w i t c h e d i t o f f and t h e h i g h e r temp e r a t u r e c o n t r o l u n i t was s w i t c h e d on f o r a n o t h e r 12 h o u r s . This c y c l e was r e p e a t e d d a i l y in each e x p e r i m e n t u n t i l t h e d e v e l o p m e n t and h a t c h i n g o f t h e eggs was c o m p l e t e d . The i n f l u e n c e o f each o f two s e t s o f s u d d e n l y c h a n g i n g t e m p e r a t u r e s ( 1 5 ° ~ - ~ 2 5 ° and 20°(--~30°C) on t h e d e v e l o p m e n t o f t h e eggs was a l s o d e t e r m i n e d . The eggs i n each e x p e r i m e n t were t r a n s f e r r e d a b r u p t l y and k e p t a l t e r n a t e l y f o r 24 h o u r s a t t h e l o w e r t e m p e r a t u r e and t h e n f o r a n o t h e r 24 h o u r s a t the h i g h e r t e m p e r a t u r e . This was r e p e a t e d d u r i n g t h e c o u r s e o f t h e e x p e r i m e n t s u n t i l the completion of development. Three groups o f eggs were e x p o s e d t o each o f t h e f o l l o w i n g e x t r e m e t e m p e r a t u r e s : d e e p - f r e e z i n g , 4°C and 40°C, f o r d i f f e r e n t p e r i o d s o f t i m e , t h e n t h e i r s u b s e q u e n t d e v e l o p m e n t a t 25°C was i n v e s t i g a t e d .
RESULTS The mean d u r a t i o n o f the d i f f e r e n t d e v e l o p m e n t a l s t a g e s and t h a t o f h a t c h i n g o f t h e eggs d e c r e a s e d as t h e e x p e r i m e n t a l t e m p e r a t u r e was i n c r e a s e d up t o 30°C i n b o t h " s p r i n g e g g s " ( o b t a i n e d from s n a i l s c o l l e c t e d d u r i n g A p r i l ) and "summer e g g s " ( o b t a i n e d from s n a i l s c o l l e c t ed d u r i n g t h e summer) as shown i n F i g u r e s 1 and 2 and T a b l e s 1 and 2 r e s p e c t i v e l y . Q0
c
sG
AG
\
e
, 1o
, 15
i 2o
2s
i 3o
i 3B
TEMPERATURE (*C)
F i g . 1. D u r a t i o n o f d e v e l o p m e n t t o G a s t r u l a (A), l a t e t r o c h o p h o r e (B) and f o r h a t c h i n g o f s p r i n g e g g s (C) a t v a r i o u s c o n s t a n t t e m p e r a t u r e s .
Changing temperatures o n egg development of L aurwulana
381
70-
60-
50-
40>. 30-
20-
10-
8
I
I
I
!
16
24
32
40
C
TEMP
F i g . 2. D u r a t i o n of d e v e l o p m e n t t o O a s t r u l a (A), e a r l y t r o e h o p h o r e (B), l a t e t r o c h o p h o r e (C) and f o r h a t c h i n g (D) o f s u u n e r eggs a t d i f f e r ent constant temperatures.
TABLE
1
Rate of Development and Hatching at Different Constant and Changing Temperatures for Spring Eggs of L. auricularia
Duratson aC Constant Temperatures (DAYS) DevnXopmental Stage
~ s t l O n at Changln 8 temp. 10o(--) 20° Days
10°
15°
20°
25°
30°
32°
34°
;estrula
11.1
6.0
5.0
4.5
2.0
1.5
1.0
4.0
Late troohophore
20.5
15.5
11 .O
7.5
3.5
3.5
3.0
10.0
~lean d u r a t i o n to
54.9
30.3
16.0
12.4
9.0
8.5
7.5
15.6
36 °
~atching Standard error
1.846
!.05
l.O0
0.927
0.884 0.645 0.50
0.884
Sz) Z Hatch ~o. o f eggs (.)
100 56
)8.3
86.0
85.0
32.9
77.4
75
29
40
35
44
6O.6 9
82.9 35
382
T
TABLE 2
D u r a t i o n of ,Developmeut and t l a t c h l n 8 o f Summer E ~ s of Lymnaea aur'icularia at Differ,ent. Constant and Chanlin~ Temperatures O u r e t t o n Ln Days at Constant T © ~ r a t u r ~ s
r~ Scese
4o
;8stru|8
60
al
SALIH et
8°
10°
12°
15 °
20 °
25 °
30°
D u r a t i o n (Dnys) a t resu l a r l y ¢h~n~ane t e n p e r a t u r e s (L~)
('C) ]6 °
37°
2
~0
29
13
9
5
3
2
2
~erly Trochophor(
50
36
18
L2
8
~
3
4
~ate Trochophore
60
38
21
L6
lO
6
5
6
qesn d u r a t i o n t o ~atchln$
-
67,~2 31 32 23 61 L$ 39
9.39
8 3 8 ] i 2 06
-
Standard e r r o r
-
1 377 0.193 0 . 1 8 8 O 202 O.lO$ 3 223 3,268
-
(s[)
| o , o f e s S s used (u)
76
74
79
77
91
8&
79
B2
77
150 4-~ ~ ° ' 20" t - ~ 30°
,5° ,,--4 25°
20° ~
3
3
6
6
5
5
8
6
7
?
10 65
9 35
0 173
r8
D~ratLon (Days) a t l u d d e o l y ¢han81n | t e ~ r a t u r e s (°C)
0 197
74
9 17 38 O 665
66
60
9 20 27
0 915
66
T h e r e seems t o be some a c c e l e r a t i o n i n t h e d e v e l o p m e n t o f " s p r i n g eggs" above 30°C up t o 34°C, b u t t h a t a c c e l e r a t i o n i s n o t s i g n i f l c a n t . However, a t e m p e r a t u r e of 36°C a p p e a r e d t o c a u s e a f a i l u r e o f d e v e l o p m e n t i n " s p r i n g e g g s " and a r e t a r d a t i o n i n t h e d e v e l o p m e n t o f "summer e g g s " , w h i l e a t 37°C "summer e g g s " d e v e l o p e d t o t h e gastrula stage only. For b o t h g r o u p s o f eggs t h e h a t c h i n g s u c c e s s was h i g h a t v a r i o u s e x p e r i m e n t a l t e m p e r a t u r e s , i t r a n g e d from IOOX a t 10°C t o 82.9Z a t 30°C f o r " s p r i n g e g g s " (Fig. 3) and from 96.2X a t lO°C t o 76.8X a t 30°C f o r "summer e g g s "
(Fig. 4).
'° I
\
O
T
60
&o
20
|
10
2O
| '
"8
30
i
~0
TEMPERATURE ('C)
Fig. 3.
Percentage of spring e U s hatching at various constant temperatures.
Eo~ever, the hatching percent decreased to only 60.6Z at 34°C and 62.3Z at 36°C for spring and sunder eggs r e s p e c t i v e l y .
30°
Changing temperatures.on egg development of L. aunculana
383
-I00
70-
uz
c/J
-80
35-
o
0 5
Fig. 4.
I
I
I
l
!
-I
I0
15
20
25 o TEMP C
30
35
60 40
Duration of development (open c i r c l e s ) and percentage hatching ( s o l i d c l r c l e s ) of sunner eggs at d i f f e r e n t constant temperatures.
Table 1 and 2 a l s o show the mean d u r a t i o n of v a r i o u s developmental stages and of hatching of " s p r i n g eggs" a t a r e g u l a r l y changing temperature between 1 0 o ( - ~ 2 0 ° C . The 24 hour cy cl e of t h i s changing temperature regime i s shown i n F i g . 5a and t h a t of " s u m E r eggs" at the two reg. imes of r e g u l a r l y changing temperatures between 15°(--)25°C and betveen 2 0 ° O 3 0 ° C are seen i n F i g . 5b and c r e s p e c t l v e l y .
22-
2018-
0
UI61412" I08
I
I
6
12
I
18
I
24
HOURS
F i g . 5a.
Daily c y c l e of r e g u l a r l y changing temperature regimes I 0 ° ( - - ) 2 0 ° C
384
T SALIHef al 26-
24-
22oo 2O
Q.
:E UJ t-
18
16
14
_
0
6
12
18
24
HOURS
Fig. 5b. Daily c y c l e of r e g u l a r l y chenglng temperature regimes 1 5 ° 4 --) 25°C 31=
29-
27-
o(J Q. 25UJ
234 i 21--
19
.... O
I
--
6
I
12
i
-7-
24
18
HOURS
Fig. 5c. Daily c y c l e of r e g u l a r l y changing temperature regime 20°4-~30°C The r e s u l t s of the d u r a t i o n to h a t c h i n g of these groups of eggs under the r e g u l a r l y changing temperature regimes were compared with p r e d i c t e d r e s u l t s based on c o n s t a n t temperature e x p e r iments using Connollys (1980) method. The constant t e ~ e r a t u r e r e s u l t s f o r the s p r i n g eggs (Table 1) t o g e t h e r with the standard e r r ors formed the input to a w e i j h t e d r e g r e s s i o n curve f i t t i n g progrmmm vhleh was run on an Apple I I ~ c r o c o m p u t e r . This f i t t e d the data to the f o l l o ~ n g e q u a t i o n : I/D t Be + BI.T + B2.T2 + B3.T3 This a l s o gave the v a r i a n c e - c o v a r i a n c e ~ m t r i x .
....
(I)
The v a l u e s of the c o e f f i c i e n t s were:
B = .0356649903 B° i -.00597310144 B1 2 .000491434633 B3 -.00000690921892 These t o g e t h e r with the experimental r e s u l t s of the changing temperature experiments formed the input of the main computer pro&ra~me which was run on a DEC 20 computer. Three g r i d s i z e s and three step s i z e s were used (see S a l i h and Grainger (1981)). The percentage of development which
Changing temperatures on egg development of L aurlcularta
385
A I day exposure to 4°C caused a s i g n i f i c a n t r e t a r d a t i o n i n the mean d u r a t i o n of development of e~gs at 25°C (p
14-
- lO0
13-70 (n
~12,.~
U k~v
o~.o -40 II-
IO 0
I
I
I0
20
TIME
Fig. 7.
FROZEN
I0
30
(MINUTES)
The e f f e c t of f r e e z i n g time on the subsequent development of eggs at 25°C. Duration of development (open c l r c l e s ) , h a t c h ing percent ( s o l l d c l r c l e s ) .
This f i g u r e a l s o shows t h a t the percentage hatching at 25°C decreased by the f r e e z i n g time i n creased and i t reached 18.5g a f t e r f r e e z i n g the eggs f o r 25 minutes. Freezing f o r 30 minutes k l U e d a l l the eggs. F i g . 8 shows the mean d u r a t i o n of development and the percentage of hatching of eggs at 25°C a f t e r being exposed to the high temperature of 40 ° f o r v ar y i n g periods of time.
12-5 "
-100
-gS 11.5 -90
z
o I-
W
Q
- e s o~ 10.5-
"SO
9.S
|
0
S
TIME
F i g . 8.
I
I
I
10
lS
20
AT 4 0 ° C
tS 25
(HOURS)
Duration of development (open c l r c l e s ) and hatching p er cen t ( s o l i d c i r c l e s ) of eggs a t 25°C a f t e r being exposed to 40°C f o r d i f f e r e n t periods of time.
T SAuH etal
386
would be p r e d i c t e d t o t a k e p l a c e i n t h e o b s e r v e d t i m e i s c a l c u l a t e d s t a n d a r d e r r o r and m a x l m u m b l a s . T h e s e ~ a r e g i v e n i n T a b l e 3.
TABLE 3 .......
t o g e t h e r w i t h t h e maximum
P r e d l c t e d Development i n R e B u l a r l y C h a n g i n g Temperature Experiments
]
10°(--~20°
I 15°(--~25° ]20°(---~30°
Predicted ~velo~nt p (g)
60.82
75.41
99.53
Hax. SE of p
29.20
7.30
15.75
Max. bias in p
19.9
The sumner egg r e s u l t s
.185
g i v e n i n T a b l e 2 gave the f o l l o v l n g
0.47
coefficients.
B° i -.125839722
B1 B2 B3
.022948703 - .00107238839 .0000203277478
I t i s s e e n t h a t i n t h e 10 ( - - ) 2 0 ° e x p e r l m e n t 60.82Z o f t h e d e v e l o p m e n t i s p r e d i c t e d t o be c o ~ l e t e d i n t h e o b s e r v e d t i m e ( 1 5 . 6 d a y s , T a b l e 1 ) . However, t h e s t a n d a r d e r r o r i s v e r y l a r g e and p+ ( 1 . 9 8 x max s t a n d a r d e r r o r ) = 1 1 8 . 6 , and s i n c e t h i s i s g r e a t e r t h a n 100 one c a n say t h a t t h e r e i s no s i g n i f i c a n t d i f f e r e n c e (p>.OS) b e t w e e n p r e d i c t e d and o b s e r v e d . The a a x I i u a b i a s i s howe v e r a l s o l a r g e v h l e h means t h a t t h e r e i s l e s s c o n f i d e n c e i n t h e r e s u l t . I n t h e 15°4-p 25 ° e x p e r i m e n t on t h e o t h e r hand p d i f f e r s s i g n i f i c a n t l y frmn 100 (p<.OS) and s i n c e t h e b i a s i s r m a l l one c a n say t h a t t h i s c h a n g i n g t e m p e r a t u r e h a d a s i g n i f i c a n t a c c e l e r a t i n g e f f e c t on d e v e l o p m e n t . I n t h e 20 ° ¢-~ 30 ° e x p e r i m e n t no s i g n i f i c a n t e f f e c t i s f o u n d . T a b l e 2 shows t h e mean d u r a t i o n f o r d i f f e r e n t d e v e l o p m e n t a l s t a g e s and f o r h a t c h i n g i n s u ~ e r eggs d e t e r m i n e d a t two s e t s o f s u d d e n l y c h a n s l n g t e m p e r a t u r e s b e t w e e n 1 5 ° ~ ~-) 25°C and b e t w e e n
26 ° ~-~ 3o°c. I n the 1 5 ° O 25° experiment p - 121.2Z; maximum Se. of p = 12.O21; end max bias i n p - .222. Thus no s i g n i f i c a n t e f f e c t i s f o u n d . I n t h e 20 4-)30 ° e x p e r i m e n t on t h e o t h e r h a n d a v e r y l a r g e e f f e c t i s found and d e v e l o p m e n t i s s i g n i f i c a n t l y s l o w e r (p<.OS) t h a n i f i t had t a k e n p l a c e a l l t h e time a t 20 ° . I t would a p p e a r t h a t e v e n t h o u g h d e v e l o p m e n t i s s u c c e s s f u l l y c o m p l e t e d a t a c o n s t a n t t e m p e r a t u r e o f 30 ° . e x p o s u r e t o i t on s u c c e s s i v e days h a s a huge r e t a r d i n 8 e f f e c t . This should be i n v e s t i g a t e d f u r t h e r .
,6]
E x p e r i m e n t s i n t h i s n e x t p a r t o f t h e work h a v e b e e n c a r r i e d o u t u s i n g s m ~ e r eggs o n l y . Both a r e t a r d a t i o n i n d e v e l o p m e n t and a d e c r e a s e i n t h e p e r c e n t a g e o f eggs h a t c h i n g a t 25 ° o c c u r r e d a f t e r t h e eggs had b e e n e x p o s e d a t &°C f o r v a r y i n g p e r i o d s o f t i m e ( F i g . 6 ) .
.
101
-,oo
!
o
-
I
s
10 TIME
F i g . 6.
60
I
1s
20
AT 4 °C (DAYS)
D u r a t i o n o f d e v e l o p m e n t ( o p e n c i r c l e s ) and p e r c e n t a g e h a t c h i n g ( s o l l d c i r c l e s ) of eggs a t 25 ° a f t e r e x p o s u r e t o 4 ° f o r v a r y i n g p e r i o d s of time.
Changing temperatures on egg development of L aurwular~a
387
I t was found t h a t e x p o s u r e t o 40°C f o r up t o 5 h o u r s d i d n o t p r o d u c e a s i g n i f i c a n t r e t a r d i n g e f f e c t on t h e mean d u r a t i o n of d e v e l o p m e n ~ (p>O.O5). But e x p o s u r e f o r 8 h o u r s t o 40°C c a u s e d a h l g h l y s i g n i f i c a n t r e t a r d i n g e f f e c t on t h e d u r a t i o n o f d e v e l o p m e n t o f eggs (p
388
T SALIH et al
Boray, J. C. (1963). Proc. World Vet. Contr., i, 709-715. Brltz, L. and W. C. Hone (1955). Z. angew.Zool., 42, 209-234. Clarke, K. U. (1967). Bull. ent. Res., 5__7, 259-270. Connolly, J. (1979). Proc. R. It. Acad., 79B, 271-280. Grainger, J. N. R. (1959). Zool. Anz., 163--~-267-277. Kendall, S. B. (1953). J. Helminth., 27, 17-28. Mousa, A. H. and A. A. Abou EI-Hassan~972). j. EgTpt med. Ass., 55, 148-165. Neumann, D. (1959). Z. Morph. Okol Tiere, 48, 349-411. Neumann, D. (1960). Biol. Zbl., 791 585-605-.-Nojima, H. (1973). Trop. Med., 15, 23-35. Precht, H., J. Christophersen, H. Hensel, and W. Latchet (1973). Temperature and Life, Springer Verlag, Berlin. Sallh, N. and J. N. R. Grainger (1981). J. Life Sci. R.~,bl. Soc., ~, 181-185. Schalle, H . ~ D. and E. G. Berry (1973). Sterkiana, 50, 1 - 9 2 . .... Sturrock, R. F. (1966). Ann. trop. Med. Parasit.', 60~--I00-I05. Sturrock, R. F. and B. M. Sturrock (1972). Ann. trop. Med. Parasit., 66, 385-390.