This study evaluated the effects of light and nutrient conditions on RNA content and growth rates in larval and juvenile bluegill. Researchers manipulated light (high vs low) and nutrients (high vs low) in experimental tanks and measured RNA content and growth in fish at larval and juvenile stages. They found that larval bluegill had the highest RNA content under high light and high nutrient conditions, indicating dependence on food quantity over quality at early stages. No significant differences were found for juvenile fish.

1. Evaluating the impacts of food quality on bluegill growth rate during early ontogeny
Introduction
• Energy transfer through a food chain can be
influenced by food quality of primary producers
(carbon:nutrient ratios)1,2,3.
• Low quality at the producer stage limits the energy
transfer to top predators (Fig 1)1,2.
• Light availability and nutrient input influence the
amount of carbon that can be produced in primary
producers, thereby influencing C:nutrient ratios
(food quality)4.
• High light results in high C:nutrient ratios which
is poor food quality for top predators, whereas
high nutrient input decreases C:nutrient ratios
(Fig. 1)
• Bluegill have high P requirements so they are more
likely to be susceptible to decreased growth from P
limitation5,6
• Larval bluegill may be especially vulnerable to P-
limitation as they build bones
• RNA content is a useful tool because it is closely
linked to growth rate and is also a P-rich molecule
Objective: To evaluate the RNA content in larval and
juvenile bluegill raised under different light and nutrient
supply conditions.
Methods
• Experiment conducted in 24 5,000-L mesocosms at
Miami University’s Ecology Research Center
• Manipulated light and nutrients in a factorial design
• High (HL) vs Low (LL) Light – accomplished by
covering mesocosms with shade cloth
• High (HN) vs Low(LN) nutrients – added nutrients (N
and P) to HN treatments
• Half of the tanks were drained at the larval bluegill stage
(1 week into experiment) and the rest were drained at
the juvenile bluegill stage (6 weeks into experiment)
• 3 fish were randomly collected from each tank and
preserved with RNAlater® (Life Technologies)
• RNA was isolated from whole larval and juvenile fish
with Promega SV Total RNA Isolation kits
• RNA content was quantified using a Thermo Scientific
NanoDrop spectrophotometer
• Because RNA content is related to mass (Fig. 3), data
was mass-normalized before using 2-way ANOVA to
evaluate effects of light and nutrients
Conclusions
• Prediction 1 was partially supported
• Bluegill RNA content decreased with age only
in the HLHN treatment
• Prediction 2 was not supported
• No effects of food quality on RNA content
• High RNA content in the HLHN treatment suggests that
larval fish are more dependent on food quantity rather
than food quality
Future Research
• We plan to measure DNA of all fish to determine
RNA:DNA ratio
Acknowledgements: We would like to thank Rodney Kolb and the ERC staff for their help setting up the mesocosm experiment,
Andor Kiss and the Miami University Center for Bioinformatics and Functional Genomics for assistance with sample processing,
and the Williamson lab for loaning us equipment. This project was funded by NSF grant DEB-0949500 to M. González and M.
Vanni, a Miami University biology department Academic Challenge grant to A. Rock, and a Miami University DUOS award to E.
Barnes and A. Rock.
Predictions
1. RNA content should decrease with age (Fig. 2)
• Growth rate: larval > juvenile
• Growth rate typically decreases as organisms age
2. RNA content will be highest under low light/high
nutrients
• Food quality will be highest under low light/high
nutrient supply (Fig. 2)
Results
• RNA content was negatively correlated with fish mass
as expected (Fig. 3)
• Larval HLHN treatments had significantly higher RNA
content (μg/mg fish) than the other treatments (Fig. 4)
• Light (p=0.0004), Nutrients (p=0.003), and
Light*Nutrients (p=0.0001) effects were all
significant
• In the juvenile stage, RNA content was highest in the
LLLN treatment and lowest in the HLLN treatment (Fig.
4)
• Treatment differences were not significant
• Trends in RNA content were very similar to trends in
relative growth rate (Figs 4, 5)
Emma Barnes, Amber Rock, Luke Ginger, Michael Vanni, María González
Miami University, Oxford OH
Figure 4. Relationship between food quality, ontogeny (larval and juvenile
stages), and RNA content (mean ± SE) of bluegill. Dotted horizontal line
indicates average initial RNA content.
Figure 3. RNA content (μg/mg fish) vs. individual fish mass of larval and juvenile
fish. Dotted horizontal line indicates average initial RNA content, dotted vertical
line indicates average initial mass.
RNAContent
Juvenile
HL LL
HN Filled Circle Filled Square
LN Open Circle Open Square
Larval
Figure 2. Predicted relationships between food quality, ontogeny
(larval and juvenile stages), and RNA content of bluegill.
Figure 1. Light and nutrient supply influences primary
producer stoichiometry, and these effects can carry up
the food chain to affect herbivores and carnivores
Figure 5. Relationship between food quality, ontogeny (larval and juvenile
stages), and relative growth rate of bluegill.
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
RelativeGrowthRate(mg/day)
Larval Juvenile
Red = larval
Blue = juvenile
y = -0.0119x + 1.673
R² = 0.1212
P = 0.0004
0
1
2
3
4
5
6
7
8
0 50 100 150 200
RNAContent(μg/mgfish)
Fish Mass (mg)
Red = larval
Blue = juvenile
Red = larval
Blue = juvenile
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RNAcontent(µg/mgfish)
High
Light
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Light
High
Nutrient
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Nutrient
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Light
High
Nutrient
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Nutrient
High
Light
Low
Light
High
Nutrient
Low
Nutrient
High
Light
Low
Light
High
Nutrient
Low
Nutrient
Red = larval
Blue = juvenile
Red = larval
Blue = juvenile
Larval Juvenile
References:
1. Dickman, E., Newell, J., Gonzalez, M. & Vanni, M. J. Light, nutrients, and food-chain length constrain planktonic energy transfer efficiency across multiple trophic levels. Proc. Natl. Acad. Sci. U. S. A. 105, 18408–18412 (2008).
2. Boersma, M. et al. Nutritional Limitation Travels up the Food Chain. Int. Rev. Hydrobiol. 93, 479–488 (2008).
3. Sterner, R. W. & Elser, J. J. Ecological stoichiometry: the biology of elements from molecules to the biosphere. (Princeton University Press, 2002).
4. Sterner, R. W., Elser, J. J., Fee, E. J., Guildford, S. J. & Chrzanowski, T. H. The light: nutrient ratio in lakes: the balance of energy and materials affects ecosystem structure and process. Am. Nat. 150, 663–684 (1997)..
5. Sterner, R. & George, N. Carbon, nitrogen, and phosphorus stoichiometry of cyprinid fishes. Ecology 81, 127–140 (2000).
6. Vanni, M. J., Flecker, A. S., Hood, J. M. & Headworth, J. L. Stoichiometry of nutrient recycling by vertebrates in a tropical stream: linking species identity and ecosystem processes. Ecol. Lett. 5, 285–293 (2002).