Differences in phosphorus demand among detritivorous chironomid larvae reflect intraspecific adaptations to differences in food resource stoichiometry across lowland tropical streams
Limnol. Oceanogr., 56(1), 2011, 268-278 | DOI: 10.4319/lo.2011.56.1.0268
ABSTRACT: We tested whether assemblages of detritivorous chironomid larvae (Chironomidae: Diptera) varied in phosphorus (P) demand based on local nutrient conditions using a series of streams in lowland Costa Rica that exhibit a natural range in ambient dissolved P and detrital P due to inputs of solute-rich groundwater. Chironomids collected from three high-P streams had growth rates and P-excretion rates that were similar to, or lower than, those of chironomids collected from four low-P streams. Chironomids from a naturally low-P stream that was experimentally amended with P over 8 yr showed an increase in P-excretion rates but not growth rates, indicating an inability of these chironomids to use additional dietary P. Chironomids from a high-P stream showed greater evidence of P limitation (lower growth rates, P-excretion rates, and ribonucleic acid content) when fed low-P detritus compared to chironomids from a low-P stream. Our findings support the hypothesis that chironomid assemblages are adapted to local food quality in this heterogeneous landscape, thereby circumventing P limitation. Genetic analysis indicates that chironomid assemblages across the study streams are similar in species composition, suggesting that differences in P demand may be due to microevolution. The lower P demand among chironomids from low-P streams appears to limit their ability to respond to nutrient-enriched food, effectively stabilizing the food web in response to changes in nutrient availability.