Lipid reserves correlate negatively with immune defense ... · Dara Satterfield, Amy E. Wright, and...
Transcript of Lipid reserves correlate negatively with immune defense ... · Dara Satterfield, Amy E. Wright, and...
We caught 76 wild fall-migrating monarchs in Athens, GA
in September-November 2010 and recorded:
•Sex, mass, forewing length and wing condition
•Wing area and color using digital image analysis
•OE infection status via tape sample
•Total OE parasite count by vortexing body to remove
OE spores and counting at 100X
• Lipid mass by grinding dried body and isolating lipids
using petroleum ether with rounds of heating and
centrifuging (after Alonso-Mejia et al. 1997)
(1) Parasites can reduce migration success
•The protozoan parasite Ophryocystis elektroscirrha (OE)
reduces adult monarch longevity and flight performance.
•OE prevalence declines during fall migration, indicating
infected adults migrate less well than healthy adults.
In fall-migrating monarchs:
• Does parasite infection reduce lipid reserves?
• Is there a trade-off between immune defense and
lipid reserves?
We thank Michael Maudsley and Meagan Weathers for help with field work and PO assays, Andy
Davis for image analysis, and Tom Maddox and his lab team for help with lipid extractions.
Lipid reserves correlate negatively with immune defense
but not parasite load in migrating monarchs Dara Satterfield, Amy E. Wright, and Sonia Altizer Odum School of Ecology, University of Georgia
Monarchs in eastern North America
migrate up to 2500 km each fall to
overwinter in central Mexico.
To survive migration and overwintering,
monarchs use lipid reserves acquired as
larvae and during fall migration.
(2) Migration and immunity compete for host energy
•Past research in birds suggests that the energetic cost of
migration can decrease investment in immune function.
Hypothesis: OE infection lowers migration success
in part by reducing monarch lipid reserves.
Hypothesis: Because immune function is costly,
monarchs with greater immune defenses will have
less energy to fuel migration (lower lipid reserves).
Host
energy
Fig. 1. Exposed lipids
in monarch abdomen
Fig. 2. Adult monarch (L, Photo by F. Clarke) and OE spores (R, at 400x)
from abdomen of infected monarch
Fig. 3. Theoretical trade-off between immune function (e.g.,
hemocytes) and energy available for migration (lipids)
• Immune measures
From hemolymph, we examined two measures of
innate immunity:
o Hemocyte count using hemocytometer slides
o Phenoloxidase (PO) activity, a measure of
melanization, by treating hemolymph with PO
assay buffer and recording absorbance over
time with microplate reader
Fig. 4. Adult
monarchs
migrating
towards
Mexico
Fig. 5. Measuring forewing length
Fig. 6.
Preparing
dried monarch
body for lipid
extraction
Fig. 8.
Hemocytes
at 400X
Fig. 9. PO
assay showing
melanin
production
Lipid mass was similar for infected
and uninfected fall migrants
Fig. 10. Lipid
mass did not
differ
significantly
between
infected and
uninfected fall
migrants
(t(72)=0.44,
p=0.66).
Lipid mass decreased with greater
immunity (PO activity)
Fig. 11. Relative lipid mass declined
significantly with greater phenoloxidase
activity (r(38)=-0.39, p=0.01).
Fig. 12. Size and
lipid mass: Early
fall migrants had
significantly greater
forewing length
than late fall
migrants
(F(2,73)=4.09,
p<0.01) but
significantly lower
lipid mass than
middle fall migrants
(F(2,71)=2.53,
p=0.03).
N=25 N=49
Fig. 13. Immune
measures: Early
fall migrants had
significantly
greater PO
activity than
middle fall
migrants (F(2,
38)=2.66, p=0.03)
and higher
hemocyte counts
(NS).
Early, middle & late fall migrants† differed
**
Fall migrants
*
*
Relative lipid mass and phenoloxidase activity were negatively correlated, suggesting a trade-
off between energy allocated for immune defense versus for migration.
Infected and uninfected migrants had similar lipid mass. One explanation for this is that the
most severely infected monarchs died before reaching Athens, GA.
Migrants early in the migration had greater forewing length, consistent with previous studies
showing that larger monarchs have a migratory advantage. Early migrants also had greater
immune function, suggesting these early migrants may also be more immunologically robust.
†Early: 9/28-10/11
Middle: 10/12-10/25
Late: 10/26-11/10
Fig. 7.
Lipids
suspended
in
petroleum
ether