DigitalCommons@University of Nebraska - Lincoln · Eastern Pine and ... However, there was no effect on female body size (Clark & Kennedy,. 1967; Breed ...
University of Nebraska - Lincoln
DigitalCommons@University of Nebraska - Lincoln Eastern Pine and Meadow Vole Symposia
Wildlife Damage Management, Internet Center for
3-4-1981
GROWTH AND DEVELOPMENT RATES OF Microtus pinetorum UNDER DIFFERENT PHOTOPERIODS T. L. Derting Virginia Polytechnic Institute and State University, Blacksburg, VA
J. A. Cransford Virginia Polytechnic Institute and State University, Blacksburg, VA
Follow this and additional works at: http://digitalcommons.unl.edu/voles Part of the Environmental Health and Protection Commons Derting, T. L. and Cransford, J. A., "GROWTH AND DEVELOPMENT RATES OF Microtus pinetorum UNDER DIFFERENT PHOTOPERIODS" (1981). Eastern Pine and Meadow Vole Symposia. Paper 77. http://digitalcommons.unl.edu/voles/77
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GROWTH AND DEVELOPMENT RATES OF MICROTUS PINETOELM UNDER DIFFERENT PHOTOPERIODS T. L. D e r t i n g and J. A. Cranford Biology Department Virginia Polytechnic I n s t i t u t e & S t a t e University Blacksburg, VA 24061
Photoperiod and n u t r i t i o n a r e i m p o r t a n t v a r i a b l e s a f f e c t i n g r e p r o d u c t i v e a c t i v i t y and growth i n many r o d e n t s . F i e l d and l a b o r a t o r y s t u d i e s i n d i c a t e t h a t l o n g photoperiod (spring-summer) c a u s e i n c r e a s e d growth w h i l e s h o r t photoperiods ( f a l l - w i n t e r ) i n h i b i t t h e s e processes. I n t h e montane v o l e (Microtus montanus) r e c e n t l y weaned animals g a i n w e i g h t a t a much lower r a t e under s h o r t photop e r i o d s o r i n t o t a l d a r k n e s s t h a n under l o n g photoperiods (Vaughan e t a l . , 1973; P e t e r b o r g , 1978). Adult M. montanus had more o f f s p r i n g and l a r g e r mean l i t t e r s i z e s under LD 18:6 t h a n LD 6:18 ( P i n t e r & Negus, 1965). S i m i l a r l y , l o n g (LD 16:8) o r i n c r e a s i n g p h o t o p e r i o d s s t i m u l a t e d t h e o n s e t of p u b e r t y i n 5. a r v a l i s , w h i l e s h o r t (LD7:17) o r d e c r e a s i n g p h o t o p e r i o d s i n h i b i t e d t h e o n s e t o f p u b e r t y (Lecyk, 1962). S h o r t p h o t o p e r i o d s caused reduced spermatog e n e s i s and seminal v e s i c l e w e i g h t s i n male M. a r v a l i s , w h i l e long p h o t o p e r i o d s induced i n c r e a s e d o v u l a t i o n i n females. I n c o n t r a s t , p h o t o p e r i o d had no e f f e c t on t h e r e p r o d u c t i v e r a t e s of M. o r c h a d e n s i s (Marshall & Wilkinson, 1956). Dicrostonyx groenlandicus r e a r e d on LD 6:18 grew f a s t e r t h a n t h o s e on LD 20:4, b u t t h e l a t t e r group had l a r g e r t e s t e s ( H a s l e r , 1975). I n M. a g r e s t i s , l o n g p h o t o p e r i o d s s t i m u l a t e d male r e p r o d u c t i o n and caused g r e a t e r body w e i g h t g a i n t h a n d i d s h o r t photoperiod. Females produced fewer young, had lower o v a r i a n and u t e r i n e w e i g h t s , and fewer, s m a l l e r G r a a f i a n f o l i c l e s under s h o r t p h o t o p e r i o d s a s compared t o long. However, t h e r e was no e f f e c t on female body s i z e (Clark & Kennedy, 1967; Breed & C l a r k e , 1970; Baker and Ranson, 1932). Microtus p e n n s y l v a n i c u s j u v e n i l e s and a d u l t s had h i g h e r body weights under LD 18:6 t h a n LD 6:18 ( P i s t o l e , 1980). M. o r e g o n i r e p r o d u c t i v e a c t i v i t y i s s t i m u l a t e d by l o n g p h o t o p e r i o d , b u t due t o f o s s o r i a l h a b i t s t h i s s p e c i e s a p p e a r s t o b e l e s s s e n s i t i v e t o l i g h t t h a n more t e r r e s t r i a l forms (Cowan & A r s e n a u l t , 1958). There have been no r e p o r t s o f w i n t e r b r e e d i n g i n Clethrionomys g a p p e r i p o s s i b l y because o f t h e i r b e h a v i o r a l avoidance of l i g h t d u r i n g t h e w i n t e r (Evernden 6 F u l l e r , 1972)
.
F i e l d r e p o r t s of reproduction i n pine voles vary greatly. S e v e r a l s t u d i e s r e p o r t b r e e d i n g a l l y e a r (Rhoades, 1903; LinadaEe 1928; G l a s s , 1949: N o f f s i n g e r , 1967; P a u l , 1970; Goertz, 1971; Cengel e t a l . , 1978) w h i l e o t h e r s r e p o r t t h e occurrence of b r e e d i n g from February o r March through November (Hamilton, 1938; Benton, 1955; M i l l e r and Getz, 1969; Cengel e t a l . , 1978). N o f f s i n g e r (1976) found s i g n i f i c a n t l y reduced body weights i n males and females from January t o May and s i g n i f i c a n t d i f f e r e n c e s i n body l e n g t h due t o month. Molt t o a d u l t p e l a g e began a t 3 weeks o f a g e
and f i e l d d a t a h a s shown t h a t m o l t i n g i n d i v i d u a l s can be found d u r i n g any s e a s o n o f t h e y e a r (Benton, 1955). There a r e few l a b o r a t o r y s t u d i e s c h a r a c t e r i z i n g growth, developpinetorum. ment, and r e p r o d u c t i v e a c t i v i t y i n young and a d u l t Hamilton (1938) found an i n c r e a s e o f approximately 6g/wk i n j u v e n i l e body w e i g h t s whereas P a u l (1970) r e p o r t s a n i n c r e a s e of 2-3g/wk. Growth r a t e s o f i n d i v i d u a l s from l i t t e r s of 1 under LD 14:10 were o n l y s l i g h t l y l e s s t h a n t h o s e f o r i n d i v i d u a l s from l i t t e r s o f 2 o r 3 , w i t h weight g a i n showing a s h a r p i n c r e a s e j u s t p r i o r t o weaning (days 19-21) (Lockmiller, 1979).
M.
Compounds p r e s e n t i n p l a n t s which have a n t i g o n a d o t r o p h i c e f f e c t s may i n h i b i t r e p r o d u c t i o n i n many r o d e n t s . Two such compounds, Paracoumaric a c i d (PCA) and F e r u l i c a c i d (FA), a r e found a t low c o n c e n t r a t i o n s i n young p l a n t s b u t i n c r e a s e a s p l a n t s reach senescence. These compounds caused s i g n i f i c a n t r e d u c t i o n s i n montanus a t a dose o f 4 mg/g o f chow when u t e r i n e weight i n a d m i n i s t e r e d f o r 1 2 d&ys (Berger e t a l . , 1977) and i n M. p e n n s y l v a n i c u s s i g n i r i c a n t d i f f e r e n c e s i n u t e r i n e weights and mean number o f f o l l i c l e s p e r female o c c u r r e d w i t h 1 2 mg FA/g of chow o v e r a 2 1 day t e s t p e r i o d (Cranford e t a l . , 1980; P i s t o l e , 1980). There was no e f f e c t o f FA a t any r e a s o n a b l e dosage on u t e r i n e w e i g h t s o f j u v e n i l e M. p e n n s y l v a n i c u s .
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Animals o f t e n u s e environmental cues f o r t h e i n i t i a t i o n and t e r m i n a t i o n o f r e p r o d u c t i o n , such t h a t p r o d u c t i o n o f o f f s p r i n g o c c u r s d u r i n g o p t i m a l s e a s o n s (Reynolds and Turkowski, 1972; P e t t e r b o r ~ , 1 9 7 8 ) . Due t o t h e f o s s o r i a l n a t u r e of pinetorum t h i s s p e c i e s may b e less s e n s i t i v e t o p h o t o p e r i o d i c cues t h a n more t e r r e s t r i a l rodents. S i n c e most e v i d e n c e i n d i c a t e s y e a r round b r e e d i n g i t i s improbable t h a t p i n e v o l e s respond t o green o r dead v e g e t a t i o n a s a r e p r o d u c t i v e cue.
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T h i s s t u d y i n v e s t i g a t e d t h e e f f e c t s of 3 p h o t o p e r i o d i c regimes on growth and m a t u r a t i o n i n j u v e n i l e and a d u l t M. pinetorum, w h i l e t h e e f f e c t o f l i t t e r s i z e on growth of j u v e n i l e p i n e v o l e s was determined under two p h o t o p e r i o d i c regimes. The r o l e o f t h e i n h i b i t o r compound FA on animals under d i f f e r e n t p h o t o p e r i o d i c regimes was determined f o r j u v e n i l e M. pinetorum and a d u l t and j u v e n i l e 5. p e n n s y l v a n i c u s . MATERIALS AND METHODS To d e t e r m i n e t h e e f f e c t o f l i t t e r s i z e . a n d photoperiod on body w e i g h t s o f p i n e v o l e s from b i r t h t o 50 days of a g e , f i v e l i t t e r s each, o f s i z e 4 , 3 , 2 , and 1 youngweremaintained'under LD 16:8, f o u r l i t t e r s o f 2 young and f i v e l i t t e r s o f 3 were maintained under LD 8:16. I n d i v i d u a l s were weighed e v e r y 3 days u s i n g a Ohaus t r i p l e beam b a l a n c e 0 . 0 1 g) and a g e of molt noted.
(+
The e f f e c t s o f photoperiod on body weights o f youqg a d u l t s ( 7 wks. o f age) were determined u s i n g 43 animals (278, 39$)
m a i n t a i n e d under LD 16:8, and 28 animals (136, 15?) under LD 12:12. A t 11 weeks o f age one t h i r d o f t h e LD 16:8 group was switched t o One h a l f of t h e LD LD 12:12 and t h e o t h e r o n e - t h i r d t o LD 8:16. 12:12 group was switched t o LD 16:8. A l l animals were t h e n weighed weekly on an e l e c t r o n i c b a l a n c e (? O.lg) f o r a t o t a l of 1 4 weeks. To determine t h e e f f e c t o f photoperiod on r e p r o d u c t i v e development o f j u v e n i l e 5. pinetorum, groups o f 4 t o 7 i n d i v i d u a l s were r a i s e d under LD 8:16, LD 12:12, o r LD 16:8 u n t i l 5 weeks of age. A t t h i s time a l l i n d i v i d u a l s were s a c r i f i c e d and body, a d r e n a l , u t e r i n e , and o v a r i a n weight were determined f o r females, w h i l e body, a d r e n a l , seminal v e s i c l e , and t e s t e s w e i g h t s were recorded f o r males. A l l e x p e r i m e n t a l p i n e v o l e s were f i r s t o r second g e n e r a t i o n o f f s p r i n g o f wild-caught a d u l t s , and were housed a s p a i r s a f t e r weaning. Water and food (Wayne l a b blox) supplemented w i t h sunf l o w e r s e e d s , a p p l e s , and o a t s p r o u t s were a v a i l a b l e ad l i b i t u m . The i n h i b i t o r s u b s t a n c e FA, o b t a i n e d from A l d r i c h Chem. Corp., was used t o d e t e r m i n e t h e e f f e c t s of p l a n t i n h i b i t o r y compounds on r e p r o d u c t i o n i n j u v e n i l e M. pinetorum and a d u l t and j u v e n i l e M. pennsylvanicus. The b i o a s s a y s f o r e f f e c t s on s e x u a l m a t u r a t i o n were wet u t e r i n e weights and t e s t e s w e i g h t s . A d d i t i o n a l l y , body and a d r e n a l w e i g h t s were a s s a y e d a s a n i n d i c a t o r of t h e g e n e r a l c o n d i t i o n o f t h e t e s t i n d i v i d u a l s . P r e v i o u s t e s t s have shown t h a t t o t a l food consumption does n o t d i f f e r between c o n t r o l and e x p e r i m e n t a l animals. M. p e n n s y l v a n i c u s j u v e n i l e s were s e l e c t e d randomly from a colony of l a b animals a t 16-21g and approximately 20 days of a g e , w h i l e a d u l t s were s e l e c t e d a t 47-55g. A l l i n d i v i d u a l s were caged i n d i v i d u a l l y f o r t h e 2 1 day t e s t p e r i o d s , w i t h food and w a t e r a v a i l a b l e ad l i b i t u m . The t e s t chemical was d i s s o l v e d i n methanol, c o a t e d on t o ground l a b b l o x a t a dose of 1 2 o r 24 mg FA/g chow, and t h e chow a i r dryed f o r 24 h o u r s . Control chow was t r e a t e d i n t h e same manner b u t w i t h o u t t h e t e s t chemical. T e s t s were performed under LD 18:6, LD 16:8, and LD 12:12. M. pinetorum j u v e n i l e s were t e s t e d a s d e s c r i b e d above but were randomly s e l e c t e d a t 22 days of a g e (weaning). Due t o t h e i r slower m a t u r a t i o n r a t e , t e s t s were r u n f o r 30 days r a t h e r t h a n 21 days, under LD 16:8 and LD 12:12.
RESULTS Among l i t t e r s of 1 , 2 , 3 and 4 young i n LD 16:8 t h e r e was a c o n s i s t e n t t r e n d f o r s m a l l l i t t e r s t o weigh more t h a n l a r g e ones (1>2>3>4). L i t t e r s o f 2 were s i g n i f i c a n t l y h e a v i e r t h a n t h o s e of 4 (2 sample Z t e s t , p 2 0.05) a t 11 and 17-23 days of age w h i l e l i t t e r s of 3 and 4 were n o t s t a t i s t i c a l l y d i f f e r e n t . Under LD 12:12 l i t t e r s o f 2 were s i g n i f i c a n t l y h e a v i e r (p 2 0.05) t h a n t h o s e o f 4 at 1 4 and 1 7 days o f age. Though l i t t e r s o f 3 were c o n s i s t e n t l y l i g h t e r t h a n t h o s e o f 2 under LD 8:16 no s i g n i f i c a n t d i f f e r e n c e s o c c u r r e d . Growth r a t e s of i n d i v i d u a l s from l i t t e r s of
4 ( 0 . 4 5 g / i n d i v i d u a l / d a y ) were lower t h a n t h o s e f o r i n d i v i d u a l s from l i t t e r s of 1 , 2 , o r 3 (0.52g/individual/day). Under LD 16:8 t h i s d i f f e r e n c e o c c u r r e d from days 2-20 and under LD 12:12 from day 2-14. Comparisons between l i t t e r s of t h e same s i z e but r a i s e d under d i f f e r e n t p h o t o p e r i o d s show t h a t photoperiod a f f e c t s body weights and r e p r o d u c t i v e development o f young animals. The a v e r a g e weight of p i n e v o l e s j u s t p r i o r t o weaning (day 20) were 13.77 4 1 . 7 gms under LD 16:8, 14.72 4 1.89 under LD 12:12, and 14.70 2.04 under LD 8:16. A d d i t i o n a l l y i n LD 8:16 animals from l i t t e r s of 3 were s i g n i f i c a n t l y h e a v i e r (2 sample Z t e s t , p 5 0.05) t h a n t h o s e r a i s e d L i t t e r s of 2 under LD 8:16 e x h i b i t e d h i g h e r growth under LD 16:8. r a t e s t h a n t h o s e under LD 1 6 : 8 o r LD 12:12 from day 29 t o 44 postpartum. Other d a t a show t h a t under a l l 3 p h o t o p e r i o d i c regimes j u v e n i l e t o s u b a d u l t molt began about 28 days postpartum.
+
M.
The i n c r e a s e d growth o f pinetorum r a i s e d under LD 8:16 a s compared t o t h a t o f j u v e n i l e s r a i s e d under LD 12:12 and LD 16:8 i s c o r r e l a t e d w i t h i n c r e a s e d r e p r o d u c t i v e development i n females b u t n o t i n males. J u v e n i l e females a t 5 weeks o f age who were r a i s e d under LD 8:16 and LD 12:12 had s i g n i f i c a n t l y h e a v i e r u t e r i n e t r a c t s (Wilcoxon rank sum t e s t , p 2 0.015) t h a n t h o s e r a i s e d J u v e n i l e females maintained under LD 12:12 had under LD 16:8. g r e a t e r o v a r i a n and a d r e n a l w e i g h t s ( p 5 0.02) t h a n i r i d i v i d u a l s t e s t e d under LD 8:16. Among j u v e n i l e males t h e r e were no s i g n i f i c a n t d i f f e r e n c e s i n t e s t e s , seminal v e s i c l e o r a d r e n a l w e i g h t s f o r any p h o t o p e r i o d group. Photoperiod e f f e c t s were p r i n c i p a l l y l i m i t e d t o r e p r o d u c t i v e organs a s n e i t h e r males o r females d i f f e r e d i n body weight a t 5 weeks of age. Body w e i g h t s o f a d u l t animals switched between p h o t o p e r i o d i c regimes showed changes s i m i l a r t o j u v e n i l e s . Switching from LD 12:12 t o LD 16:8 ( s p r i n g summer) o r v i c e v e r s a (summer f a l l ) caused no change i n body w e i g h t s . However a s w i t c h from LD 16:8 t o LD 8:16 (summer t o w i n t e r ) r e s u l t e d i n a s h a r p i n c r e a s e i n body w e i g h t s , b u t t h e sample i s h i g h l y v a r i a b l e . A l l e x p e r i m e n t a l g. p e n n s y l v a n i c u s f e d FA showed a d e c r e a s e i n r e p r o d u c t i v e organ w e i g h t though t h i s e f f e c t was n o t s i g n i f i c a n t due t o h i g h v a r i a n c e s w i t h i n e x p e r i m e n t a l groups. No c o n s i s t e n t t r e n d s o c c u r r e d w i t h r e s p e c t t o change i n a d r e n a l w e i g h t s . Experimental and c o n t r o l a d u l t s maintained on LD 12:12 l o s t weight (6-8g) whereas t h o s e o n LD 16:8 gained weight (2g) ( s i g n i f i c a n t e f f e c t o f p h o t o p e r i o d , Wilcoxon rank sum t e s t , p 5 0.005); b u t t h e r e was no s y n e r g i s t i c e f f e c t between t h e i n h i b i t o r s u b s t a n c e and s h o r t p h o t o p e r i o d on r e p r o d u c t i v e organ weights. J u v e n i l e s showed n o e f f e c t o f p h o t o p e r i o d o n body weight.
M.
p i n e t o r u m showed a r e d u c t i o n i n testes weight Male j u v e n i l e when f e d FA under LD 1 6 : 8 and LD 12:12 w h i l e females showed a d e c r e a s e i n wet u t e r i n e w e i g h t s under LD 16:8 b u t n o t LD 12:12. Body w e i g h t s o f p i n e v o l e s under LD 12:12 d i d n o t d i f f e r from t h o s e t e s t e d under LD 1 6 : 8 a t t h e beginning o r end o f experimentation.
DISCUSSION Photoperiod h a s t h e o p p o s i t e e f f e c t on growth i n M. pinetorum a s compared t o M. pennsylvanicus where j u v e n i l e s have h i g h e r body weights under l o n g photoperiod ( P i s t o l e , 1980), and M. pinetorum j u v e n i l e s have lower body weights. Higher growth r a t e s under s h o r t photoperiods may b e of a d a p t i v e v a l u e f o r 3. pinetorum s i n c e t h e y r e s u l t i n e a r l i e r r e p r o d u c t i v e development of females and probably e a r l i e r r e p r o d u c t i o n . A d d i t i o n a l s t u d i e s a r e b e i n g conducted t o determine whether i n c r e a s e s i n body weight a r e c o r r e l a t e d w i t h i n c r e a s e d r e p r o d u c t i v e development i n s u b a d u l t and a d u l t M. pinetorum ( i . e . 1 0 , 15 and 20 weeks of a g e ) . Average weight g a i n s f o r M. pinetorum i n t h i s s t u d y were s l i g h t l y h i g h e r t h a n t h o s e r e p o r t e d by P a u l (1970) and Lockmiller (1979) b u t much lower t h a n t h o s e r e p o r t e d by Hamilton (1938). Though weight g a i n s were s i m i l a r f o r young from l i t t e r s of 1, 2 and 3, young from l i t t e r s of 4 had s i g n i f i c a n t l y lower weight g a i n r a t e s b e f o r e and a f t e r weaning which probably r e s u l t s from t h e i n c r e a s e d energy d r a i n on t h e a d u l t l a c t a t i n g female ( H a s l e r & Banks, 1975; Lockmiller, 1979). No s i g n i f i c a n t e f f e c t of FA occurred i n M. pinetorum a s expected because t h e y appear t o be continuous b r e e d e r s . The r e s u l t s f o r M. p e n n s y l v a n i c u s do n o t show t h e s i g n i f i c a n t e f f e c t s r e p o r t e d by P i s t o l e (1980) though t h e r e a r e c o n s i s t e n t t r e n d s which s u p p o r t h i s d a t a . I n 3. p e n n s y l v a n i c u s , photoperiod i s a n u l t i m a t e f a c t o r whereas p l a n t compounds a c t a s proximate f a c t o r s a f f e c t i n g growth and r e p r o d u c t i o n . The v a r i a n c e among t h e r e s p o n s e of i n d i v i d u a l s f e d FA s u g g e s t s t h a t a p o p u l a t i o n may be composed of r e s p o n s i v e and nonresponsive i n d i v i d u a l s , i n d i c a t i n g a g e n e t i c component. I n M. p i n e t o r u m photoperiod may be a proximate f a c t o r whereas p l a n t compounds a r e of no importance i n cueing r e p r o d u c t i o n . The d i f f e r e n t r e s p o n s e s of t h e s e 2 s p e c i e s may be due t o d i f f e r e n c e s i n t h e i r h a b i t a t s , a s M. p e n n s y l v a n i c u s a r e more exposed t o l i g h t ( s u r f a c e d w e l l e r ) and i t s changes, t h a n a r e M. pinetorum. Because photoperiod and p l a n t compounds appear t o p l a y a minor r o l e i n cueing p i n e v o l e s t o environmental c o n d i t i o n s , o t h e r f a c t o r s such a s n u t r i t i o n may be o f major importance f o r t h i s s p e c i e s .
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