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