Transcript PowerPoint: Old Grad Poster 1

Self-maintenance versus reproduction: effect of experimentally
increased food availability on female incubation behavior, chronic
stress levels, and offspring condition in house wrens
Cassie J. Lothery*, Charles F. Thompson, and Scott K. Sakaluk
Abstract
Corticosterone (CORT), the “avian stress hormone,” increases in the
plasma during times of chronic or acute stress (e.g., low food
availability or presence of a predator, respectively), and can mediate a
shift toward self-maintenance behaviors that ensure survival (e.g.,
foraging or nest abandonment). Birds incubating eggs face the
potentially stressful problem of how to allocate their time and energy
between maintaining egg temperature and obtaining enough food to
meet their own metabolic demands.
We tested the hypothesis that female house wrens (Troglodytes
aedon), which incubate their eggs without male help, face a trade-off
during incubation between self-maintenance (e.g., leaving the nest to
forage for food) and warming their eggs, and that this trade-off results
in increased levels of chronic stress. We predicted that foodsupplemented females would (i) spend more time incubating their
eggs, (ii) have lower CORT levels, and (iii) produce offspring in better
condition than control females. As predicted, food-supplemented
females spent more time incubating their eggs than control females.
Although CORT significantly increased over the incubation period,
food-supplemented females did not have significantly lower CORT
levels than controls nor were their offspring in better condition than
those of control females.
Nestbox with sliding trap door
mechanism
Male house wren
Photo by Paulo E. Llambias
Behavior, Ecology, Evolution, and Systematics Section
School of Biological Sciences, Illinois State University, Normal, IL
*[email protected]
Methods
Study Site
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Mackinaw Study Area in McLean Co. Illinois.
Upland and bottomland forest habitat.
Experimental Design
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Experimental females received 15 g of live
mealworms (Tenebrio molitor) and 5-10 freshly
freeze-killed crickets (Acheta domesticus or
Gryllodes sigillatus) daily during incubation.
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Control females were given no supplement, but
their nests were visited with the same frequency
as experimental nests.
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Using a repeated measures design, a blood
sample was obtained from each female at clutch
completion and at hatching.
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Female blood samples were obtained within 3 min
of closing the nestbox to measure baseline CORT.
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Nestling cutaneous immune response was
measured by injecting 50 µL of PHA dissolved in
PBS into the wing web of 11-day-old nestlings.
The cutaneous immune response was calculated
as the difference between the post- and preinjection wing-web thickness.
•
Nestling innate immune response was tested
using nestling plasma in a bactericidal assay
(measured as percent killing ability).
Principle of Allocation
• Every organism has a limited amount of resources that can be
allocated to growth, reproduction, and maintenance.
Control Nest
Experimental Nest
Food-supplemented females had significantly greater
incubation constancy (0.71 ± 0.02, Control; 0.78 ± 0.02,
Experimental) than control females (NCON = 18, NEXP = 23;
t(0.05), 39 = - 2.70, P = 0.01).
•Nestling Condition and Health-state
Nestling PHA response was not significantly affected by female
treatment
Linear mixed model F(1, 25.9) = 0.37, P = 0.55
Nestling bacteria-killing ability was not significantly affected by
female treatment
Linear mixed model F(1, 34.5) = 0.10, P = 0.75
Nestling hematocrit was not significantly affected by female
treatment
Linear mixed model F(1, 31.3) = 1.98, P = 0.17
Nestling mass was not significantly affected by female
treatment
Linear mixed model F(1, 35.7) = 0.11, P = 0.75
Female CORT concentration at clutch completion was
significantly related to nestling final mass.
•Female CORT Concentration
Conclusion
•Our results suggest that incubation is costly to female house
wrens because CORT concentration increased over the course
of incubation, indicative of increased stress.
•Our results further indicate that the stress of incubation cannot
be ameliorated by supplemental feeding.
Corticosterone (CORT)
• CORT is a glucocorticoid hormone that is responsible for
metabolic functions in birds and is known as “the avian stress
hormone.”
• When faced with acute or chronic stress, CORT shifts behavior
away from reproduction and toward immediate survival.
•Incubation Behavior
CORT concentration significantly increased from clutch
completion to hatching (Repeated measures ANOVA; F(1,42) =
7.49, P = 0.009), but there was no significant treatment*time
interaction (NCON = 20, NEXP = 24; F(1,42) = 0.16, P = 0.69).
Introduction
• To survive and reproduce, organisms must engage in trade-offs
that allocate resources optimally.
Results
Results
•Supplemental feeding of females had no effect on the condition
or health-state of their offspring, but female CORT concentration
at clutch completion was negatively correlated with the final mass
of their nestlings.
Two house wren nestlings at hatching
Why study house wrens?
• During incubation, females are solely responsible for regulating
egg temperatures and are faced with the dilemma of obtaining
enough food to meet their metabolic demands while applying
heat to their eggs.
• House wrens readily accept as nest sites human-made
nestboxes and are tolerant of human activity at the nest.
House wren nestling 11 days later
Acknowledgements
National Science Foundation
Beta Lambda Chapter, Phi Sigma
School of Biological Sciences, Illinois State University
Wren Crew 2010 and 2011
ParkLands Foundation
Dr. Joe Casto
Dr. Craig Gatto
Marilyn Nguyen
Sandrine Clairardin
Megan Lawler