1) A study tested whether more active eastern fence lizards consumed more food by measuring the food consumption of lizards in their home enclosures after measuring their activity levels in an open field trial. 2) The results showed no significant relationship between activity levels and food consumption. Larger lizards and males consumed more food on average. 3) The correlation between activity levels and body size seen in previous studies is likely due to innate differences like growth rate rather than more active lizards eating more.

1. Kimberly Reylander Renee Rosier, Ph. D.; Advisor Tracy Langkilde, Ph.D
Department of Biology
Eberly College of Science
Results
Future Directions
Methods
Discussion
High innate activity rates ≠ higher consumption rate
•For a range of taxa, more active individuals also tend to grow
more quickly and to a larger body size, which can impact
fitness. This relationship exists in eastern fence lizards,
Sceloporus unduatus, and can vary even among siblings.
•Current hypotheses suggest that the activity/body size
correlation exists because more active individuals (1) eat more
or (2) encounter food items more frequently. Alternatively, this
relationship could be the result of differences in innate energy
requirements (e.g., growth rate).
•We tested whether more active individuals eat more using sibling
eastern fence lizards in the laboratory.
•We measured food consumption of these
same lizards in their home enclosures.
•We measured prey consumption over a four
day period following a day of fasting. Lizards
were provided with known quantities of
soldier fly larvae (mass and number) and the
mass and number of prey items remaining
was used to determine the proportion of prey
consumed by each lizard.
Feeding Procedure:
Activity Procedure:
•In 2011, juvenile lizards were maintained
individually in the laboratory from hatching
until 2 weeks of age.
•Each lizard was placed in a new
environment (open field) with a gridded
paper floor for 20 minutes and were video
recorded for later analysis (Figures 1 and 2)
•Lizards were tested 3 times each at 8, 9,
and 10 days of age.
•Activity was measured as the number of
lines crossed during trials; the average from
the 3 trials was used for analysis. Figure 1 (above): Open field
trial setup.
Figure 2 (below): Open field
trial showing a lizard and
gridlines used to measure
activity.
Acknowledgments:
We thank Tracy Langkilde for using her lab resources to conduct this
experiment. Thanks to Renee Rosier for poster editing and poster template.
This project was funded in part by a National Science Foundation grant to
T.L. (DEB-0949483)
* all methods are approved by the Penn State Institutional Animal
Care and Use Committee, approval #27696
Figure 6. Maze arenas with
concealed mealworms to test
how many are eaten or
discovered.
Prey Encounter Rates
•Activity rates will be correlated with prey encounter rates.
This will test to see if more active lizards will find more food
in a new environment (Figure 6). Their consumption rates
will be controlled before and after the maze test.
•These lizards will also be
tested in an open field trial to
determine their activity rates.
•How efficiently the lizards
eat in their home enclosures
will also be recorded..
Boldness
•Boldness, or risk-taking
behavior, may also correspond
with feeding behavior. We can
use open field trials from these
trials to assess boldness.
Lizard activity rates does not significantly affect their eating habits
(activity: F = 1.26 , df = 1,58 , P= 0.284; Figure 3) . This relationship was
unaffected by body size, sex, or family group (all interactions P > 0.277)
Figure 3. There was no
significant relationship
between open field activity
and prey consumption (r2 =
0.025).
•The results of this study reveal that more active lizards
did not consume more prey in their home environments
than did less active lizards, regardless of their body size
or sex.
•Prey consumption was affected by body size and sex,
however, suggesting that feeding rates may be more
dependent on innate energy requirements.
•The results presented here indicate that the correlation
between body size and activity rates in previous studies
is most likely the result of innate differences, such as
growth rate.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 50 100 150 200
ProportionEaten
Number of Lines Crossed
Figure 5. Average proportion
of prey consumed by for
males and females.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
2.5 2.6 2.7 2.8 2.9 3 3.1
ProportionEaten
Average Snout-Vent length (cm)
Figure 4. Snout-vent length
(SVL) and proportion of prey
consumed during the feeding
experiment (r2 =0.29).
Larger lizards (by body length) consumed a significantly greater
proportion of their available prey. (SVL: F =12.02, df = 1,9, P = 0.011,
Figure 4)
Bigger lizard = higher consumption rate
Statistical Procedure:
• We tested for a relationship between open field activity and
proportion of prey consumed using a mixed model ANCOVA with prey
consumption as the dependent, sex and family group as factors, and
snout vent length (SVL) and lines crossed as a covariates. All analyses
were conducted using JMP software.
Males Ate More than Females
Males consumed marginally significantly more of their available prey
than did females (sex: F = 3.84, df = 1,57, P = 0.058; Figure 5)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
Female Male
ProportionEaten