Document Type

Thesis - University Access Only

Award Date

1998

Degree Name

Master of Science (MS)

Department / School

Biology and Microbiology

Abstract

Ornamental traits are sexually selected traits that an organism uses to attract a mate or defend against a rival. Studies have shown that ornamental traits are more sensitive to environmental change relative to naturally selected traits. Hyalella azteca is a freshwater macroinvertebrate that has been used in numerous studies to establish water quality criteria in freshwater ecosystems. The objectives of the current study were to l) experimentally assess population level responses of H. azteca to nitrogen enrichment, 2) experimentally assess the ornamental trait response signature of H. azteca to nitrogen enrichment and 3) characterize the ornamental trait response signature of natural populations of H. azteca in lakes of differing trophic status. Amphipods were reared in 9 aquaria over a 7 week experimental period and were randomly dosed with ammonium nitrate (NH4NO3). Three control tanks received blank doses (0 mg/L NH4 NO 3), three aquaria received low level doses (10 mg/L NH4 NO 3) and three tanks received high level doses (50 mg/L NH4N03). Additionally, amphipods were collected from 9 randomly selected lakes in the Northern Glaciated Plains ecoregion. Morphological traits from experimental and lake amphipods were measured. Survival of amphipods was significantly different in all three treatments with highest survival in control amphipods. Male morphological traits (total body, mean second antenna and mean gnathopod length) and second antenna symmetry seemed to respond to a subsidy-stress condition in that largest response signatures were observed in low treatment tanks and smallest response signatures were observed in high treatment tanks. Male second antennae length was significantly shorter in high treatment tanks relative to controls and low treatment groups. Female morphological traits (total body and mean second antenna length) were progressively smaller in the treatment tanks relative to the control tanks. The smallest ornamental traits (mean second antenna and mean gnathopod length) in male amphipods sampled from lakes were observed in hypereutrophic lakes and largest ornamental traits were observed in mesotrophic lakes. However, total body length was largest in hypereutrophic lakes. Second antennae length was again the only character displaying significant differences in the analyses. Total body length, second antennae length and brood size in female amphipods sampled from lakes were progressively smaller in more enriched lakes. Results from this study indicate that second antennae of H. azteca may be the most sensitive to ammonia stress and nutrient enrichment. Future research with a variety of stressors and benthic macroinvertebrates is recommended. Ornamental traits in benthic macroinvertebrates that are more sensitive to disturbance may respond more predictably in future studies.

Library of Congress Subject Headings

Hyalella

Freshwater invertebrates -- Monitoring

Freshwater ecology

Biological monitoring

Format

application/pdf

Number of Pages

121

Publisher

South Dakota State University

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