Microbial biofilms on leaf litter can assimilate nutrients, thus altering the elemental composition (i.e. stoichiometric composition) of detritus. Aquatic macroinvertebrates consuming stoichiometrically-altered detritus may increase, decrease, or not change growth rates depending upon their body stoichiometry. Invertebrates with high body phosphorus (P) can allocate more P to rRNA, increasing protein production and growth. Thus, if diet nutrient limitation is alleviated, high P invertebrates are expected to increase growth rates. Conversely, low P invertebrates might not respond or decrease growth rates, due to the metabolic costs of eliminating excess nutrients. Diptera from two families were used in growth studies and fed either maple or oak leaves with different levels of carbon:phosphorus (C:P) to determine if diet P influenced growth rates and body stoichiometry of these high P organisms.
Tipula abdominalis from the family Tipulidae, were hypothesized to increase growth and consumption rates, and decrease body C:P as diet C:P decreased. It was also hypothesized that the proportion of consumed material composed of a particular element used in growth would increase (GGE), and that the diet ratio at which neither C or P is limiting, and at which maximum growth would occur, would decrease as diet C:P decreased (TERC:P). It was observed that T. abdominalis growth and consumption varied based on leaf type and elemental composition. Tipula abdominalis fed oak had high growth (5.4% day-1) and consumption (1.98mg mg tipulid-1 day-1) compared to maple diets, while individuals fed maple increased growth (2.6 to 5.0% day-1) and consumption (1.1 to 2.1mg mg tipulid-1 day-1) across treatments as maple C:P decreased. Tipula abdominalis were overall homeostatic in body stoichiometry. Contrary to expectations, GGEs decreased as diet C:P decreased, maintaining stoichiometric homeostasis. Also, current TER calculations were not representative of observed growth rates. Thus, results indicate that leaf stoichiometry and leaf type interact to influence growth rates.
Three genera of Chironomidae (Chironomus, Polypedilum, Micropsectra ) were fed a gradient of diet C:P to determine if there are differences in taxon-specific growth responses to changes in diet stoichiometry. It was hypothesized that genera with higher body P would increase growth more than genera with lower body P, and that body P in high P genera would increase as they consumed more dietary P. The three genera had different growth responses to decreased diet C:P that did not appear to be influenced by organism body stoichiometry or diet stoichiometry. Chironomus fed maple and oak and Micropsectra fed maple had similar growth rates (17.5% day-1), while having significantly different body C:P, 141 and 249 for Chironomus fed oak and maple, respectively, and 359 for Micropsectra fed maple. Despite similarities in diet C:P ranges (1000 to 8000), Chironomus and Polypedilum had different growth responses: Chironomus had high growth, while Polypedilum fed maple did not grow and lost mass (- 4.8% day-1), and Polypedilum fed oak exhibited relatively low growth rates (5.9% day-1). Leaf type and genus identity appear to be important factors in determining growth response. However, most Dipterans in this study either increased growth or had no response to dietary P enrichment. Understanding how organism genus identity interacts with leaf type and leaf stoichiometry to influence growth rates will allow more accurate predictions of community changes in nutrient enriched systems.
|Advisor:||Entrekin, Sally A.|
|Commitee:||Choinski, John, Evans-White, Michelle, Larson, Katherine|
|School:||University of Central Arkansas|
|School Location:||United States -- Arkansas|
|Source:||MAI 52/04M(E), Masters Abstracts International|
|Subjects:||Biology, Microbiology, Evolution and Development|
|Keywords:||Chironomidae, Diptera, Nutrient enrichment, Stoichiometry, Stream, Tipula abdominalis|
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