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Thesis (Ph. D.)--University of Missouri-Columbia, 1996. / Typescript. Vita. Includes bibliographical references (leaves 97-105). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1996. / Typescript. Vita. Includes bibliographical references (leaves 97-105). Also available on the Internet.

No description available.

The Nearctic species of the genus Isonychia Eaton are revised. Eighteen species are recognized, of which three are described as new; eleven species names are placed in synonymy. Isonychia campestris McDunough is recognized as a fully valid geographically restricted species. Two subgenera, Isonychia sensu stricto and Prionoides Kondratieff and Voshell are recognized on the basis of adult and nymphal characteristics. Isonychia s.s. includes four species groups: bicolor group with four species, arida group with one species, sicca group containing five species, and diversa group with one species. The subgenus Prionoides includes seven species. A Neotype is designated for l. arida (Say). Previously undescribed characters of the nymphal gills are described and illustrated. The male genitalia and eggs are illustrated for every species. The distribution of each species is mapped. Diagnostic keys to male adults and nymphs are presented. A discussion of the nomenclatural history of the genus and each species is included. Diagnostic characters, rearing and collecting techniques are also discussed. The life histories and life cycles of two populations of Isonychia (Isonychia) bicolor (Walker) and one population of Isonychia (Prionoides) obscura Traver are presented in detail. Many features used in the past as specific criteria, especially in the bicolor and sicca Groups are found to be related to developmental periods of given populations involving geography, elevation, water temperature and stream size. The life cycle of I. bicolor is probably bivoltine at both sites. At the trout stream site there is a large-sized spring emerging generation and a much smaller summer emerging generation with considerable overlap. Isonychia obscura Traver is univoltine with adult emergence in mid-June and with egg diapause during the summer months. Additional life history information is also presented for I. (l.) tusculanensis Berner and I. (P.) serrata Traver. The evolution of the genus Isonychia and the two subgenera l. (Isonychia) and I. (Prionoides) is hypothesized. The North American biogeography of Isonychia may have included an invasion of North America via the "asiamerican" land mass of the Cretaceous. The early Isonychia mayflies may have been adapted to low order cool streams of high elevations. This lineage was probably similar to the subgenus Prionoides. Isonychia s.s. has been successful in colonizing the upper and lower austral zones and appears to be a warm water adapted group. / Doctor of Philosophy

published_or_final_version / Ecology and Biodiversity / Doctoral / Doctor of Philosophy

Aravaipa Creek is one of the few, small, permanent desert streams in Arizona. It has diverse fish and invertebrate faunas but the invertebrates are not well-known. I collected benthic and 24 hr. drift samples there during 1980-1981 and found 31 taxa. The most abundant species were Baetis insignificans and Choroterpes inornata (Ephemeroptera), which exhibited the nocturnal drift periodicity characteristic of drifting invertebrates studied elsewhere. In the laboratory, observations of the drifting behaviors of five species of mayflies were made in 5 and 10 cm/s current speeds. These provided evidence that drifting insects are not necessarily swept away by the current (accidental drift), but are probably exhibiting a specific behavior triggered by local conditions such as lack of cover or food (active drift). I also tested the relationship between drift rates and the presence and absence of food (periphyton) using B. insignificans and C. inornata. With both species, the number of insects drifting increased significantly when periphyton was not present; therefore lack of food may be an important cause of drift. The sizes of the nymphs used in these experiments were determined; I found that drifters were either similar in size to non-drifters (C. inornata), or that drifters were larger than nymphs that did not drift (B. insignificans). These results suggest that direct competition by size does not play a role in determining which individuals drift. Drifting appears to be a dispersal mechanism for benthic invertebrates; it maintains the numbers and distribution of the benthos according to the rapidly changing distribution of their food resources which occurs in streams. This process fits some recent models of population regulation by dispersal.

The primary objective of this study is to describe the life history of Camelobaetidius mexicanus living in Honey Creek in south central Oklahoma. Specific objectives were to determine emergence phenology and behavior, describe nupital flight and female oviposition, measure subimaginal and imaginal life spans, examine egg morphology and time to hatching, describe larval microdistribution, analyze gut contents and to determine voltinism from nymphal head capsule widths and adult emergence.