to freeze or not to freeze: strategies and mechanisms of overwintering in terrestrial anurans david...
TRANSCRIPT
![Page 1: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/1.jpg)
To Freeze or Not to Freeze:To Freeze or Not to Freeze:Strategies and Mechanisms of Strategies and Mechanisms of
Overwintering in Terrestrial AnuransOverwintering in Terrestrial Anurans
David SwansonDept. of Biology, Univ. South Dakota
![Page 2: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/2.jpg)
![Page 3: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/3.jpg)
Anuran Overwintering Strategies
• Aquatic
• Terrestrial Burrowers
• Terrestrial - Shallow
• Freezing Tolerance vs. Freezing Avoidance
![Page 4: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/4.jpg)
Freezing Tolerance in Anurans
• Present in species using shallow terrestrial hibernacula
• Absent in burrowers or aquatic overwintering species
• Burrowing anurans little studied - Exposed to subfreezing temps?
![Page 5: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/5.jpg)
-8
-4
0
4
8
12100 cm
50 cm
20 cm
5 cm
O N D J F M
-18
-12
-6
0
6
12
So
i l T
emp
erat
ure
(°C
)
Average Minimum
Extreme Minimum
![Page 6: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/6.jpg)
STUDY SPECIES
• Terrestrial Burrowers– Great Plains Toad, Bufo cognatus– Woodhouse’s Toad, Bufo woodhousii– Plains Spadefoot, Spea bombifrons
• Terrestrial - Shallow– Chorus Frog, Pseudacris triseriata
![Page 7: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/7.jpg)
Pseudacris triseriata
Range: New Mexico to CanadaMass = 0.5 - 2.0 g ; SVL = 1.9 - 3.5 cm
![Page 8: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/8.jpg)
Spea bombifrons
Range: n. Mexico to s. Canada; Mass = 2-20 g
![Page 9: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/9.jpg)
Bufo cognatus
Range: n. Mexico to s. Canada; Mass = 3-35 g
![Page 10: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/10.jpg)
Bufo woodhousii
Range: Texas to North Dakota, Montana; Mass = 2-35 g
![Page 11: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/11.jpg)
Hypothesis # 1
• Toads and Spadefoot will not be freezing tolerant
• Chorus Frog will be freezing tolerant
![Page 12: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/12.jpg)
Acclimation Protocol
1 Captured in Sept-Oct2 Food & water, natural photoperiod, room
temperature (23oC) until early November3 Food removed, 10oC, total darkness for 2
weeks4 Temperature reduced to 2oC in mid-
November5 Freezing expts. in Jan-Feb
![Page 13: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/13.jpg)
Freezing Protocol
1 Placed in chamber at -1oC (dry or moist)2 Chamber temperature decreased 1oC/h3 Chamber temperature dropped until
freezing exotherm occurs (sometimes initiated by contact with external ice)
4 Chamber temperature maintained at -2.5oC to -4.5oC for 24 h
5 Thawing at 2oC and Recovery Tests
![Page 14: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/14.jpg)
Freezing Apparatus
![Page 15: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/15.jpg)
Supercooling Point
Rebound Temperature
Te
mp
era
ture
(oC
)1
0
-1
-2
-3
-4
Time
Tb Profile During Freezing Exposure
![Page 16: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/16.jpg)
Species Group n SCP (C) RT (C)
Frog Dry 10 -5.11.0 -1.10.1
Toads Dry 7 -4.21.0 -0.90.2
Spadefoot Dry 9 -4.30.7 -1.50.4
Frog Wet 4 -3.60.7 -0.30.1
Toads Wet 2 -1.5 -0.5
![Page 17: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/17.jpg)
Freezing Survival
Species n % Survival
Frog 17 47
Toads 6 0
Spadefoot 6 0
![Page 18: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/18.jpg)
Crystallization Temperature (o C)
0
20
40
60
80
100
-4 to -6 -3 to -4 -2 to -3 -1 to -2
% S
urv
ival
4
4
5
4Chorus Frog
Survival
![Page 19: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/19.jpg)
Freezing Tolerance in Anurans
• Documented in 5 species of frogs
• Can tolerate up to 65-70% of total body water as ice
• How is this accomplished?
![Page 20: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/20.jpg)
Aspects of Anuran Freezing Tolerance
• Low molecular weight carbohydrates (glucose and glycerol) serve anti-freeze and cryoprotectant functions
• Accumulation not anticipatory for those frogs using glucose
• Liver glycogen is the source
• Accumulation associated with changes in enzyme activities
![Page 21: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/21.jpg)
GLYCOGEN
GLUCOSE-1-P
GLUCOSE-6-P
GLUCOSE
Pi
glycogen phosphorylase (a)
phosphoglucomutase
Piglucose-6-phosphatase
Glucose F-6-P F-1, 6-P2
PFK-1
glycogen synthetase
glucose conc. in tissuesglucose conc. in tissues
freezing induces g-phos activity
inhibited by freezing
Wood frog Liver
inhibited by freezing
![Page 22: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/22.jpg)
Hypothesis # 2
• Chorus Frogs will mobilize glucose and show a pattern of enzyme activation during freezing similar to Wood Frogs
• Toads will fail to mobilize glucose and enhance enzyme activities during freezing
![Page 23: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/23.jpg)
Methods
• Acclimation and Freezing Exposure treatments similar (–2.5°C for 24 h), except inoculated freezing; Frozen compared to unfrozen controls
• Leg muscle and liver were removed on ice for both frozen and control groups
• Assays for tissue glucose and glycogen phosphorylase activity
• Also measured unfrozen summer animals
![Page 24: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/24.jpg)
0
10
20
30
40
50
250300
Unfrozen
Frozen
Summer
0
4
8
12
16
Glu
cose
(m
ol
gF
W-1)
Chorus Frog Toad
Muscle Liver Muscle Liver
Tissue Glucose
![Page 25: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/25.jpg)
0
10
20
30
40UnfrozenFrozenSummer
0
20
40
60
Ph
os
a (
mo
l min
-1 g
FW
-1)
To
tal P
ho
s (
mo
l min
-1 g
FW
-1)
Muscle Liver Muscle LiverFrog Toad
![Page 26: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/26.jpg)
Results and Conclusions - 1
• Chorus Frogs accumulate glucose, toads don’t
• Glucose accumulation associated with higher liver phos activity in frogs
• Development of freezing tolerance likely associated with winter increase in phos activity
![Page 27: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/27.jpg)
Results and Conclusions - 2
• Liver phosphorylase activity did not increase after freezing in chorus frogs
• Differs from other freeze-tolerant frogs
• One possible reason for this difference: transient increase in chorus frogs (increased activity for several hrs after freezing, but return to normal by 24 h in frozen state)
![Page 28: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/28.jpg)
Hypothesis # 3
• No transient elevation in phosphorylase activity will occur in chorus frogs
• Glycogen synthetase will not be inhibited by freezing
![Page 29: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/29.jpg)
Methods
• Same acclimation and freezing methods as previously
• Freezing Exposure Treatments:– 5 min– 2 hr– 24 hr
• Measured Tissue Glucose, Glycogen, Phosphorylase, Synthetase
![Page 30: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/30.jpg)
Control 5 min 2 hr 24 hr
mo
l g
FW
-1
0
50
100
150
200
250
300
350 Liver glucose
aa a
b
![Page 31: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/31.jpg)
Control 5 min 2 hr 24 hr
0
5
10
15
20
25
30
35Muscle glucose
a a
b
b
mo
l g
FW
-1
![Page 32: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/32.jpg)
0
20
40
60
80
100
0
20
40
60
80
100
active total percent active
Pe
rce
nt
acti
ve
form
Liver glycogen phosphorylase
Control5 min2 hr24 hr
mo
l m
in-1 g
FW
-1
![Page 33: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/33.jpg)
0
100
200
300
400
500
600
700
800
900
Independent Dependent
Liver glycogen synthetase
Control5 min2 hr24 hr
nm
ol m
in-1 g
FW
-1
![Page 34: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/34.jpg)
Control 5 min 2 hr 24 hr
0
200
400
600
800
1000
1200
1400
1600
1800 Liver glycogenm
ol g
FW
-1 g
luc
osy
l un
its
![Page 35: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/35.jpg)
0
20
40
60
80
100
120
140
Control 5 min 2 hr 24 hr
Muscle glycogenm
ol g
FW
-1 g
luc
osy
l un
its
![Page 36: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/36.jpg)
Results Summary
• Glucose accumulated rapidly• Neither phosphorylase nor synthetase
activities varied with time in liver• Liver glycogen did not vary with time,
but muscle glycogen increased – so muscle glycogen is not the source for increasing glucose in muscle
![Page 37: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/37.jpg)
GLYCOGEN
GLUCOSE-1-P
GLUCOSE-6-P
GLUCOSE
Pi
glycogen phosphorylase (a)
phosphoglucomutase
Piglucose-6-phosphatase
Glucose F-6-P F-1, 6-P2
PFK-1
glycogen synthetase
glucose conc. in tissuesglucose conc. in tissues
freezing induces g-phos activity
inhibited by freezing
Wood frog Liver
inhibited by freezing
![Page 38: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/38.jpg)
GLYCOGEN
GLUCOSE-1-P
GLUCOSE-6-P
GLUCOSE
Pi
glycogen phosphorylase (a)
phosphoglucomutase
Piglucose-6-phosphatase
Glucose F-6-P F-1, 6-P2
PFK-1
glycogen synthetase
glucose conc. in tissuesglucose conc. in tissues
no change with freezingno change with freezing
Chorus frog Liver
inhibited by freezing ??
![Page 39: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/39.jpg)
Freezing Survival differed among Winters in Chorus Frogs
0
20
40
60
80
100
1996 1998-1999 1999-2000
% s
urv
iva
l
n = 12n = 4 n = 8
Chorus Frog Freezing Survival
![Page 40: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/40.jpg)
Methods
• Poor survival in some years led us to question why survival differs among years
• 1998-99 and 1999-2000 frogs: 24-h frozen treatment– immediately euthanized– measured glucose and liver glycogen
• Compare values to 1996 winter data where frogs had good survival
![Page 41: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/41.jpg)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
1996 1998-1999 1999-2000
mea
n bo
dy m
ass
(g)
n = 4 n = 8 n = 12
0
20
40
60
80
100
1996 1998-1999 1999-2000
% s
urvi
val
n = 12n = 4 n = 8
![Page 42: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/42.jpg)
Body size and freezing survival
• Body size (mass) and rate of cooling • smaller frogs may cool faster
• cooling rate in 1998-1999 and 1999-2000 was lower than in 1996
• Liver glycogen reserves may be limited by body size
• Comparisons of 1998 and 1999 studies with 1996.
![Page 43: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/43.jpg)
0
5
10
15
20
25
control frozen Edwards (frozen)
mu
scle
glu
cose
(m
ol/g
FW
)
b
aB
A
![Page 44: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/44.jpg)
0
20
40
60
80
100
120
140
160
180
200
220
240
control frozen Edwards (frozen)
live
r g
luco
se (
mo
l/gF
W)
b
aB
A
![Page 45: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/45.jpg)
0
100
200
300
400
500
600
700
800
900
control frozen Edwards (unfrozen)
live
r g
lyco
ge
n (
mo
l/gF
W)
a
aB
A
![Page 46: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/46.jpg)
0
10
20
30
40
50
60
70
80
90
100
control frozen Edwards (frozen)
live
r %
act
ive
gly
cog
en
ph
osp
ho
ryla
se
a
aAA
![Page 47: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/47.jpg)
Body Mass (g)
0.4 0.6 0.8 1.0 1.2 1.4
Liv
er G
lyco
gen
(
mo
l/g
FW
)
0
200
400
600
800
1000
1200 R2 = 0.143, P = 0.033
![Page 48: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/48.jpg)
Spring Summer Fall0
10
20
30
40
50
100
200
300
400
500
600
700
800
Liver Glucose Liver Glycogen
Glu
co
se
(m
ol/g
FW
)
Gly
cog
en
(m
ol/g
FW
)
0.0
0.4
0.8
1.2
1.6
Mas
s (g
)Sp S F
Year: 2001
![Page 49: To Freeze or Not to Freeze: Strategies and Mechanisms of Overwintering in Terrestrial Anurans David Swanson Dept. of Biology, Univ. South Dakota](https://reader030.vdocuments.mx/reader030/viewer/2022032517/56649cb85503460f9497f167/html5/thumbnails/49.jpg)
Results and Conclusions
• High mortality in 1998-1999 and 1999-2000 likely related to low glucose levels
• Low glucose levels result from low liver glycogen, not low glycogen phosphorylase activity