Four species of net-spinning caddisflies, Hydropsyche simulans Ross, Cheumatopsyche lasia Ross, Cheumatopsyche campyla Ross and Chimarra obscura (Walker) are common in the regulated portions of the Brazos River. Hydropsyche simulans spun capture nets with the largest meshdimensions; the two Cheumatopsyche species' nets had the next largest meshes, and Chimarra obscura spun nets with the smallest dimensions. Cheumatopsyche lasia and C. campyla constructed nets with similar sized meshes. The number of individuals m~2 and standing crop biomass were not significantly different among low, medium, and high velocities. Early hydropsychid instars fed on detritus while later instar H. simulans and C. campyla had larger proportions of animal material. Guts of later instar C. lasia individuals had a greater percentage of algae and diatoms.

The initial studies reported in this dissertation were attempts to induce mutations in those genes which control dissociation in cells of Nei sseria gonorrhoeae. These studies led to an investigation of survival curves of cells grown in liquid media. Instead of survival curves reflecting the diploid nature of gonococci, multiple cell kinetics were observed. It was found that large clumps contained a predominance of cells of the T2 type and that when these clumps were dispersed by DNAase, it appeared that dissociation of T2 was inhibited. The notion of a mechanism of T2 to T4 dissociation being due to genetic transformation was disspelled by these data.

Diagnostic medical mycology has been slow to advance due to a lack of species specific antigens in organisms which cause serious diseases in man. Toward this end, an HPLC analysis was done of the following fungal antigens: histoplasmins HKC-43 and H-42, blastomycin KCB-26, an alkali-soluble, water soluble antigen from Blastomyces dermatitidis (b-ASWS), a coccidioidin prepared from a toluene lysate of the mycelial-arthroconidia phase of Coccidioides immitis, and an alkali-soluble, water-soluble antigen from Coccidioides immitis (c-ASWS). The HPLC survey included size-exclusion chromatography (SEC), ion exchange chromatography (HPIEC), and reversephase chromatography (RP). Resolution was poor with both SEC and HPIEC but was excellent with RP chromatography. The use of RP will allow sufficient separation for further antigenic and structural analysis.

The responses of freshwater (Daphnia magna. Pimephales promelas) and saltwater (Mysidopsis bahia. Cyprinodon variegatus) toxicity test species to elevated calcium concentrations and changing salinity conditions were investigated. The use of salinity as a criterion for selection between saltwater and freshwater test species was investigated by conducting both calcium and salinity toxicity tests. Salinity was determined to be an inappropriate criterion under conditions encountered in this study.

Drumming behavior is described for the first time in 16 North American species of Plecoptera, and signals of a 17th species, Isogenoides zionensis, are further detailed. The effective distance over which drumming signals may be transmitted was tested for four communication modes. Results indicate that substratum vibrations are far superior to sound in the transmission of drumming signals, and that dense substrates such as rocks are poor channels for signal transfer. Long communication periods between stonefly pairs of Taeniopteryx burksi resulted in some alterations from initial signaling characteristics.

Two compartment (sediment and water) flow-through model ecosystems were constructed to investigate the compartmentalization of different organic chemicals. Lindane, naphthalene, and mirex were pumped into the systems and resultant compartmental chemical concentrations determined. Steady state concentrations were compared to those predicted by two environmental fate models - EXAMS (Exposure Analysis Modeling System) and SLSA (Simplified Lake and Stream Analysis) which were developed by EPA-Athens, Georgia and HydroQual, Inc., respectively.