Zoological Museum, University of Oslo, Sarsgt. 1, Oslo 5,. Norway. mon in all kinds ... hammer et al., this volume) include the studies by. Lillehammer 1975, 1976 ...
Annts Limnol
20 (1-2) 1984 : 91-94
Studies on egg development in the Fennoscandian Isoperla species (Plecoptera)
1
S.J. S a l t v e i t A. Lillehammer
1
Three species of Isoperla occur in Fennoscandia. The most common is /. grammatica, although it has not been recorded above the subalpine vegetation belt. /. difformis has a similar distribution, but is less common. /. obscura occurs mainly at high latitudes and altitudes, although it is also abundant in large rivers. Eggs were reared at temperatures of 4, 8, 12, 16, 20 and 24° C. /. difformis did not hatch at 4° C. /. grammatica at 4 and 8° C while /. obscura did not hatch at 16° C and above. Egg mortality was high in /. difformis at 24° C. Incubation period decreased with increase in temperature and varied between 28 and 68 days in /. grammatica and between 15 and 83 days in /. difformis. For /. grammatica and /. difformis, the relationship between the egg incubation period and the water temperature was linear on logarithmic scales. For /. obscura, no such relationship was found and the mean incubation period at all temperatures was 305 ± 57 (S.D.) days. Explanations are presented to explain these differences in egg incubation characteristics. Etudes sur le développement des œufs des espèces finnoscandinaves à'Isoperla
(Plecoptera).
Trois espèces à.'Isoperla vivent en Finnoscandinavie. La plus commune est /. grammatica. bien qu'elle ne se rencontre pas au-dessus de l'étage subalpin. /. difformis présente une même distribution mais est moins commune. /. obscura se trouve surtout à des latitudes et altitudes élevées bien qu'elle soit aussi abondante dans les grandes rivières. Des oeufs furent placés à des températures de 4, 8, 12, 16, 20 et 24° C. /. difformis n'éclôt pas à 4 ° C, /. grammatica à 4 et 8° C et il en est de même d7. obscura à 16° C. La mortalité des œufs d'/. difformis est élevée à 24° C. La durée d'incubation décroit quand la température augmente et varie entre 28 et 68 jours pour /. grammatica et entre 15 et 83 jours pour /. difformis. Pour ces deux espèces, la relation entre la durée d'incubation et la température est linéaire en coordonnées logarithmiques. Cette relation n'existe pas pour /. obscura et l'incubation dure 305 ± 57 (écart type) jours à toutes les températures. Les auteurs proposent des explications de ces différences.
m o n in all kinds o f freshwater environments, but in
Introduction
the southern parts o f N o r w a y the species is only c o m m o n in high altitude localities, except for l a r g e
T h r e e species o f Isoperla o c c u r in Fennoscandia : /. difformis,
I. grammatica
1949). / . grammatica
and /. obscura
l o w l a n d r i v e r s . This is the only Isoperla
species
(Brinck
w h i c h has been r e c o r d e d in the mid-alpine v e g e t a -
is the most c o m m o n in N o r w a y ,
tion belt, being r e c o r d e d u p to about 1 500 m a.s.l.
o c c u r i n g in all kinds o f s t r e a m s and rivers, but not
in southern N o r w a y .
in lakes. H o w e v e r , this species does not occur a b o v e the subalpine
v e g e t a t i o n belt, situated at
about
1 100 m a.s.l. in s o u t h e r n N o r w a y ( L i l l e h a m m e r 1974). / . difformis
has a s i m i l a r distribution, but is
far less c o m m o n a n d has not been r e c o r d e d a b o v e 700 m a.s.l. In n o r t h e r n N o r w a y / . obscura
is c o m -
In an a t t e m p t to obtain a b e t t e r understanding o f the distribution
and e n v i r o n m e n t a l strategies o f
N o r w e g i a n stoneflies, egg incubation and g r o w t h studies are b e i n g c a r r i e d out in the l a b o r a t o r y on different species. Through these studies we h o p e to be a b l e t o c a t e g o r i z e different types o f egg d e v e l o p ment and nymphal g r o w t h patterns in stoneflies. P r e v i o u s contributions to o u r synthesis (see Lilleh a m m e r et al., this v o l u m e ) include the studies by
1. Zoological Museum, University of Oslo, Sarsgt. 1, Oslo 5, Norway.
L i l l e h a m m e r 1975, 1976, B r i t t a i n 1978, 1983. Brit-
Article available at http://www.limnology-journal.org or http://dx.doi.org/10.1051/limn/1984027
92
tain et al. 1984 and Saltveit 1977, as well as these studies on
Isoperla.
T e m p e r a t u r e is a m a j o r f a c t o r influencing sto n e f l y d i s t r i b u t i o n ( L i l l e h a m m e r 1974). D i s t r i b u t i o n p a t t e r n s o f s p e c i e s m a y t h e r e f o r e be in part explai n e d b y their c a p a b i l i t y to adapt their life c y c l e stra t e g i e s to d i f f e r e n t kinds of t e m p e r a t u r e r e g i m e s . C o n t r o l l e d l a b o r a t o r y studies e n a b l e us to assess development time and temperature requirement of the d i f f e r e n t life c y c l e stages. T h i s paper presents d a t a on the t e m p e r a t u r e r e q u i r e m e n t s and limita t i o n s f o r the e g g stage o f /. difformis, I. grammatica a n d / . obscura.
1. —
Methods
Adult Isoperla, along with sufficient water for egg incu bation studies, were collected from the field sites, Saeterbekken (110 m a.s.l.) and Sorkedalselva (125 m a.s.l.) in the Oslo region (60° 00'N, 10° 30'E.) and Valdresflya (1 400 m a.s.l.) in the Jotunheimen mountains (61° 25'N, 8° 52'E), during the emergence period. The adults were transpor ted to the laboratory where they were kept in small plas tic boxes placed in constant temperature cabinets at 10°C. On most days the boxes were transferred to 20° C for a few hours to increase the chance of mating and oviposition. Each box contained a small Petri dish with water from the field site, together with small twigs and leaves, which provided shelter. The boxes were inspected daily and any egg batches removed and counted, before being placed at constant temperatures at 4 ° C intervals between 4 and 24° C. All egg batches were incubated in total darkness and were inspected daily for hatching. The duration of egg incu bation at the various temperatures was taken as the period in days from oviposition until 50 % of the eggs that even tually hatched in any one batch had hatched.
2. —
(2)
S.J. S A L T V E I T & A. L I L L E H A M M E R
Results
In / . difformis n o hatching o c c u r e d at 4 ° C (Table I ) . A t 8 ° C the e g g incubation p e r i o d w a s about 80 d a y s w i t h a h a t c h i n g success o f 90 % . T h e mean incubation p e r i o d decreased w i t h increasing tempe rature, b e i n g 15-20 d a y s at 20-24° C. T h e l o w hat c h i n g success in s o m e of the e g g batches w a s due to fungal infections. T h e e g g s o f / . grammatica d i d not hatch at 4 and 8 ° C, w h i l e the m e a n incubation p e r i o d at 12° C was 54 days and d e c r e a s e d w i t h increasing t e m p e r a t u r e ( T a b l e I I ) . H o w e v e r , the differences w e r e small bet w e e n 16 and 2 4 ° C. T h e hatching success w a s high
Table I. Egg incubation data for individual egg batches from Isoperla difformis from Saeterbekken, sho wing incubation temperature (T° C), number of eggs (n), days for first egg to hatch, mean (50 % ) incubation period in days, duration of hatching in days and percentage hatching success.
T° C
n
4 4 8 8 12 12 16 16 21 21 24
35 44 198 90 87 27 67 213 40 135 117
First egg Incubation Duration % to hatch period of hatching hatching (days) (days) (days)
.
76 80 40 42 27 28 19 14 17
81 83 43 46 28 28 19 IS 20
18 19 2 5 3 4 1 7 15
0.0 0.0 88.4 94.4 77.0 25.9 76.1 2.3 95.0 97.8 16.2
Table II. Egg incubation data for individual egg batches from Isoperla grammatica from Sorkedalen, sho wing incubation temperature (T° C), number of eggs (n), days for first egg to hatch, mean (50%) incubation period in days, duration of hatching in days and percentage hatching success.
T" C
n
4
55 24 130 94 108 160 63 78 189 199 113 117 78 79
8 8 12 12 12 16 16 16 16 20 20 24 24
First egg Incubation Duration % to hatch period of hatching hatching (days) (days) (days)
50 50 50 31 30 30 30 28 28 26 26
at all temperatures (90-100 % ) .
52 56 55 32 31 30 32 29 28 35 33
where
3 14 20 24 20 7 16 8 12 30 29
hatching
0.0 0.0 0.0 97.9 100.0 100.0 98.4 100.0 96.8 99.5 94.6 100.0 92.3 93.8
occurred
E g g s o f / . obscura hatched at 4, 8 and 12° C, but not at 16 and 20° C ( T a b l e I I I ) . H o w e v e r , the hat-
STUDIES ON EGG DEVELOPMENT
(3)
Table III. Egg incubation data for individual egg batches from Isoperla obscura from Valdresflya, sho wing incubation temperature (T° C), number of eggs (n), days for first egg to hatch, mean (50 % ) incubation period in days, duration of hatching in days and percent hatching success.
T° C
n
4 4 4 8 8 8 12 12 12 12 12 16 16 16 20 20
140 84 63 146 201 72 43 36 150 300 60 100 100 75 30 43
c h i n g success at 12° C w a s very l o w . At 4 a n d 8 ° C a very long and similar incubation period w a s found, v a r y i n g b e t w e e n 332 and 357 days at both t e m p e r a tures. T h e highest hatching success was at 4 ° C. F o r both / . difformis and / . grammatica the rela tionship b e t w e e n the e g g incubation period ( Y d a y s ) a n d t e m p e r a t u r e ( T ° C ) w a s highly significant, res pectively P < 0.001 and P < 0.01. T h e relationship w a s linear on l o g a r i t h m i c scales and w e l l e x p r e s s e d b y the e q u a t i o n : log Y - log a — b l o g T or Y - a T-b
First egg Incubation Duration % to hatch period of hatching hatching (days) (days) (days) 321 320 310 321 316 310 320 321 327
337 342 332 357 334 340 326 321 327
86 87 87 75 83 77 49 1 1
93
757 52.4 92.1 22.6 28.4 43.1 7.0 5.6 2.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
V a l u e s o f the constants a and b are given in F i g . 1. F o r / . obscura no significant relationship w a s found b e t w e e n the e g g incubation period ( Y - d a y s ) and t e m p e r a t u r e ( T ° C). T h u s e g g d e v e l o p m e n t seems independent o f t e m p e r a t u r e in the r a n g e tested.
DAYS
504
•
Isoperla difformis Y- 1782.9T
•
Isoperla grammatica
1.49
0
Y = 410.8T" -
8 6
20
10+
12
M 20 24
T C
Fig. 1. The relationship between egg incubation period (Y days) and water temperature (T° C) for Isoperla difformis and Isoperla grammatica. The equations for the regression lines are given for both species.
S.J. S A L T V E I T & A L I L L E H A M M E R
94
3. —
Discussion
E g g d e v e l o p m e n t in both /. difformis and / . gram matica w a s h i g h l y t e m p e r a t u r e dependent, w i t h a short incubation p e r i o d . A s i m i l a r basic relation ship b e t w e e n t e m p e r a t u r e and incubation p e r i o d has been found f o r o t h e r stonefly populations, such as Taeniopteryx nebulosa (Brittain 1977), Nemurella pictetii ( B r i t t a i n 1978) and Capnia atra (Brittain et al. 1984). T h e intercepts are higher in both /. diffor mis and / . grammatica, meaning that they r e q u i r e m o r e d e g r e e days f o r d e v e l o p m e n t than the o t h e r m e n t i o n e d species. These Isoperla species seems the r e f o r e r e s t r i c t e d to areas which are a b l e to p r o v i d e the r e q u i r e d n u m b e r of d e g r e e days for e g g deve l o p m e n t in a r e l a t i v e l y short p e r i o d . In /. obscura, h o w e v e r , d e v e l o p m e n t seems inde pendent of t e m p e r a t u r e in the range tested. T h e d e v e l o p m e n t p e r i o d in /. obscura is at least 10-11 m o n t h s , but s o m e e g g s have a l o n g e r d e v e l o p m e n t t i m e . T h e p r e s e n c e o f small n y m p h s in late August and S e p t e m b e r a l m o s t at the same t i m e as the adult e m e r g e ( L i l l e h a m m e r , unpubl. data), support the l a b o r a t o r y results. W e are uncertain about any dia pause. H o w e v e r , in s o m e p r e l i m i n a r y studies e g g s taken f r o m 12 and 16° C in January and transfer r e d to l o w e r t e m p e r a t u r e s did have a higher hat c h i n g success, a l t h o u g h the incubation p e r i o d d i d not differ from that found at 4 and 8 ° C. This is simi lar to the effect found when c o o l i n g d o w n e g g s of Amphinemura standfussi that did not hatch at 16 and 20° C (Saltveit 1977). H o w e v e r , a different effect w a s found in Diura nanseni w h e r e freezing b r o k e e g g diapause ( L i l l e h a m m e r 1976). In N o r w a y seven o t h e r species have a s i m i l a r alti tudinal distribution to /. obscura ( L i l l e h a m m e r 1974, 1984). F i v e o f these species have a long e g g develop ment time during the w i n t e r (winter eggs) (Lilleham m e r 1976, Saltveit 1977, unpubl. data), and this inclu des all the f o u r p r e d a t o r species ( S y s t e l l o g n a t h a ) o c c u r r i n g in the area. These species are n o r t h to north-eastern i m m i g r a n t s to Fennoscandia, and w e r e p r o b a b l y t h r o u g h i m m i g r a t i o n well adapted to these e n v i r o n m e n t s . H o w e v e r , e x c e p t f o r Diura bicaudata s i m i l a r life history patterns have so far b e e n found in l o w l a n d areas ( L i l l e h a m m e r 1976, S a l t v e i t 1977, unpubl. data). In D. bicaudata, occur ring in Great Britain, both s u m m e r and w i n t e r eggs h a v e been found ( K h o o 1968).
(4)
/. grammatica and /. difformis, h o w e v e r , are sou thern immigrants to Fennoscandia, but s h o w diffe rences in morphology in far northern areas. Studies o f the egg d e v e l o p m e n t in w i d e l y separated popu lations is necessary in o r d e r to p r o v i d e a n s w e r s to these questions concerning inter- and intraspecific variation in life history patterns. It w o u l d also be interesting to compare immigration history and egg development. Another interesting comparison would be one of the egg d e v e l o p m e n t types with phylogenetic location of the species and genera.
Acknowledgement
We are grateful to Dr. J E . Brittain for valuable discussion and for improving the English.
Literature cited Brinck (P.). 1949. — Studies on Swedish stoneflies. Opusc. ent. Sttppt. II, 250 pp. Briltain (J.E.(. 1977. — The effect of temperature on the egg incu bation period of Taeniopteryx nebulosa (Plecoptera). Oikos, 29 : 302-305. Brittain (J.E.). 1978. — Semivoltinism in mountain populations of Nemurella pictetii (Plecoptera). Oikos, 30 : 1-6. Brittain (J.E.). 1983. — The influence of temperature on nymphal growth rates in mountain stoneflies (Plecoptera,. Ecology, 64 ; 440-446. Brittain (J.E.), Lillehammer (A.) & Saltveit (S.J.). 1984. — The effect of temperature on intraspecific variation in egg biology and nvmphal size in the stoneflv Capnia atra (Plecoptera). /. Anim. Ecol., 53 : 161-169. Khoo (S.G.). 1968. — Experimental studies on diapause in stone flies. 11. Eggs of Diura bicaudata (L.). Proc. R. ent. Soc. Lond. A. 43 : 40-48. Lillehammer (A.). 1974. — Norwegian stoneflies. II. Distribution and relationship to environment. Norsk ent. Tidsskr., 21 : 195-250. Lillehammer (A.). 1975. — Norwegian stoneflies. IV. Laboratory studies on ecological factor influencing distribution. Norw. J. Ent.. 22 : 99-108. Lillehammer (A.). 1976. — Norwegian stoneflies. V. Variation in morphological characters compared to differences in ecologi cal factors. Norw. J. Enl.. 23 : 161-172. Lillehammer (A.). 1984. — Distribution, seasonal abundance and emergence of stoneflies (Plecoptera) in the Ovre Heimdalen area of the Norwegian Jotunheimen Mountains. Fauna Norvegia, Ser. B. Lillehammer (A.), Brittain (J.E.) & Saltveit (S.J.). 1984. — Egg deve lopment, nymphal growth and distribution of Fennoscandian stoneflies (Plecoptera). (Abstract). Annls Limnol., 20: 144. Saltveit (S.J.). 1977. — [Field and laboratory studies on stoneflies (Plecoptera), with special emphasis on the genus Amphinemura (Ris)]. (In Norwegian). Unpubl. thesis. Univ. of Oslo. 244 pp.
