Change in Stress Response

1
To be or not to be...
Stressed?
Stress Responses Among Newly Emerged versus
Dispersing Male Red-sided Garter Snakes
Arianne Cease Advisors Dr. Robert Mason and
Deborah Lutterschmidt Department of
Zoology Oregon State University Corvallis, OR
2
Outline

• Background
• Stress
• Red-sided Garter Snake
• Experiment A
• Materials and Methods
• Results
• Experiment B
• Materials and Methods
• Results
• Conclusions

3
Stress
What is Stress?
Any event that disrupts an animal's internal /
external environment

• Examples
• snow, flood, heat
• predation
• lack of sleep
• food shortage
• chemical pollution

4
Stress

• Stress is mediated by hormones called
  glucocorticoids
• Cortisol (humans / fish)
• Corticosterone (reptiles / birds)

blood glucose levels
behaviors not crucial to immediate survival
adrenaline

• Reproduction
• Digestion
• Feeding
• Immune system

escape behavior
5
Outline

• Background
• Stress
• Red-sided Garter Snake
• Experiment A
• Materials and Methods
• Results
• Experiment B
• Materials and Methods
• Results
• Conclusions

6
Red-sided Garter Snake

• Field site

Thamnophis sirtalis parietalis
7
Spring Migration
Emergence
Annual Cycle
Fall Migration
8
(No Transcript)
9
Red-Sided Garter Snake

• Types of Stressors

• Predation

• Snow

• Flood

• Snake scientists

• Food shortage

10
Red-Sided Garter Snake
How do we induce stress?
11
Red-sided Garter Snake
How do we induce stress?
Stressor
12
DEN (actively courting)
13
ASPEN (intermediate)
DEN actively courting
14
To feeding ponds
ROAD (dispersing)
DEN actively courting
ASPEN
15
Stress in Red-sided Garter Snakes
Response to Stressors
Newly emerged and courting at den
Dispersing males at road

• Normal response to capture stress during summer

?

• Question How soon does this seasonal change
  occur after emergence?

p lt.05
Hypothesis Dispersing snakes will have
greater hormonal stress response than those
courting at the den.
Plasma corticosterone responses to capture stress
of 1 hr during two different seasonal periods in
male red-sided garter snakes
16
Outline

• Background
• Stress
• Red-sided Garter Snake
• Experiment A
• Materials and Methods
• Results
• Experiment B
• Materials and Methods
• Results
• Conclusions

17
Materials and Methods
Experiment A

• 3 groups Den (courting), Aspen, Road (dispersing)

ROAD (dispersing)
ASPEN
DEN actively courting
18
Materials and Methods
Experiment A

• 3 groups Den (courting), Aspen, Road (dispersing)

• We used a paired design where each snake is
  tested before and after capture stress

19
Materials and Methods
Experiment A

• 3 groups Den (courting), Aspen, Road (dispersing)

• We used a paired design where each snake is
  tested before and after capture stress

• Blood samples were then analyzed for
  corticosterone levels using radioimmunoassay

20
Results Corticosterone levels
21
Results Corticosterone levels
22
Results Corticosterone levels
23
Results Corticosterone levels
Courting snakes showed no difference
Dispersing snakes experienced increased
corticosterone levels
24
Outline

• Background
• Stress
• Red-Sided Garter Snake
• Experiment A
• Materials and Methods
• Results
• Experiment B
• Materials and Methods
• Results
• Conclusions

25
Materials and Methods
Experiment B

• We collected 70 males from the den midway through
  the mating season

26
Materials and Methods
Experiment B

• We collected 70 males from the den midway through
  the mating season

• We collected blood samples from a subset (n 14)
  of these males throughout the remainder of the
  mating season

27
Materials and Methods
Experiment B

• We collected 70 males from the den midway through
  the mating season

• We collected blood samples from a subset (n 14)
  of these males throughout the remainder of the
  mating season

• Blood samples were then analyzed for
  corticosterone levels to examine changes in
  hormone levels during the mating season using
  radioimmunoassay

28
Results Corticosterone levels
Corticosterone significantly declines during the
mating season
Dispersing males have significantly lower basal
corticosterone levels
29
Outline

• Background
• Stress
• Red-Sided Garter Snake
• Experiment A
• Materials and Methods
• Results
• Experiment B
• Materials and Methods
• Results
• Conclusions

30
Conclusions
Question
How soon do seasonal changes in stress responses
occur after emergence?

• Dispersing males exhibited a significant response
  to capture stress

• The seasonal change occurs during dispersal
  (approximately 2-3 weeks after emergence).

31
Conclusions

• Corticosterone levels significantly declined over
  the mating season

• Basal corticosterone levels were significantly
  lower in dispersing males at the road than in
  actively courting males at the den

Falling corticosterone levels may initiate
dispersal of snakes to the feeding ponds
32
Acknowledgements

• Dr. Robert Mason
• Deborah Lutterschmidt
• Dr. Kevin Ahern
• HHMI and URISC
• Members of the Mason Lab Dr. Suzanne Estes,
  Dr. Michael LeMaster,
  Heather Waye
• Dr. Rick Shine, Kristin Latham, Brock McLeod,
  Rachel McAlister, Lori McKee, friends and
  family
• Field Support Al Gerry Johnson, Ruth Nesbitt
• Red-sided garter snake volunteers