Winter-emerging chironomidae (Insecta: Diptera) in Minnesota trout streams
2012-12
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Winter-emerging chironomidae (Insecta: Diptera) in Minnesota trout streams
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2012-12
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Abstract
The Chironomidae (Diptera) is among the few aquatic insect families with species
that are reliably able to grow, develop, and emerge as fully functional adults throughout
the cold winter months that characterize the midwestern United States. However, few
studies document their role in trout streams during this time of year. The intent of this
dissertation is to enhance the field of Chironomidae research by focusing on the winter
dynamics of these insects, including their response to severe flood events, their
incorporation in the winter diet of trout, and the morphological and molecular description
of three new cold-adapted Chironomidae species. The resistance and resilience of the
winter chironomid community was assessed following a severe flood that impacted many
streams in southeast Minnesota during the late summer of 2007. Methodology included
collections of chironomid surface-floating pupal exuviae from 18 southeast Minnesota
streams; streams were selected to include representation of localities that incurred
moderate to extreme levels of flooding disturbance. These data were compared to data
from the same localities during prior winters. Significantly more taxa emerged during the
winter after late-summer flooding as compared to historic collections, and the number of
species emerging in winter was positively correlated with rainfall severity, indicating the
winter-active Chironomidae are resistant to late summer spates. This indicates that
chironomids are an available winter food resource to stream trout recovering from
devastating floods. In attempt to examine the importance of Chironomidae and other
winter-active aquatic insects to the winter diet of brown trout (Salmo trutta L.), stomach contents were collected from trout inhabiting three southeast Minnesota streams; these data were compared to organisms collected in the stream drift and benthos. Results
indicated that trout diets differ by stream and by fish size, with larger trout feeding
heavily on Trichoptera and Physella, and smaller fish relying more on Gammarus and
Chironomidae larvae. Stomach contents were more similar to the benthos than the drift,
indicating a greater reliance on benthic feeding during winter. Trout in all streams
selected Trichoptera and Chironomidae over other prey, and appeared to maintain sizeselective
predation throughout winter. Winter-emerging Chironomidae appear to enhance
the trout diet in all streams, and chironomid larvae were particularly dominant in the diet
of one trout population. Three new chironomid species within the genus Micropsectra, a
genus commonly found in the winter trout diet, were discovered from a study of five
Minnesota streams. These species, Micropsectra neoappendica, n. sp., Micropsectra
penicillata, n. sp., and Micropsectra subletteorum, n. sp., were described using
morphological and molecular methods, along with one additional species, Micropsectra
xantha Roback, which was redescribed. Two of the new species initially appeared identical to species known from the Palearctic, however molecular data indicated they
are genetically distinct. Subsequently, reexamination of morphological characters
revealed slight, but consistent diagnostic differences. These results emphasize the
importance of using molecular tools in conjunction with traditional morphological
techniques when studying Chironomidae diversity, especially when relying on diagnoses
from other regions. The culmination of these studies sheds light on the dynamics of
winter-emerging Chironomidae in southeastern Minnesota trout streams, their
distribution and abundance, and the larger role they play in stream communities.
Description
University of Minnesota Ph.D. dissertation. December 2012. Major: Entomology. Advisor: Leonard C. Ferrington, Jr. 1 computer file (PDF); xviii, 261 pages, appendices A-H.
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Anderson, Alyssa Mae. (2012). Winter-emerging chironomidae (Insecta: Diptera) in Minnesota trout streams. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/142960.
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