Western Kentucky University

Poster Title

A Comparative Analysis of Voltinism Patterns of Stoneflies (Plecoptera) from an Intermittent-perennial Stream Continuum

Institution

Western Kentucky University

Abstract

Aquatic insects that inhabit intermittent streams must possess life history mechanisms to survive during periods when surface flow is lacking. Nymphal growth (= voltinism) can be characterized as determinate or indeterminate. The principal difference between the two forms of voltinism lies in whether the length of nymphal growth is determined by local climatological or hydrologic conditions. Although there has been considerable research on life history patterns of stoneflies from mid-order streams and small rivers, zero-order (intermittent) and first-order streams (springs) are rarely studied. We initiated a comparative life history study of four species of stoneflies (Plecoptera) that inhabit an intermittent-perennial stream system. The intermittent section emanates on sandstone and flows before dropping vertically down a 20 m break. Surface flow ceases during June and does not resume until late autumn. Natural flow patterns of the lower (perennial) section are enhanced by the upper (intermittent) section only during winter and spring, yet is maintained during summer by two small springs. We hypothesized that each of the four species would exhibit identical life history attributes (i.e., adult flight activity, egg development time and timing of hatching, seasonal nymphal growth patterns) in each stream section (intermittent vs. perennial). Regular sampling has occurred since May 2002, as well as monitoring water temperature, precipitation, and stage height. Each species has displayed similar fight periods in each section. Examination of nymphal growth histograms through June 2003 has demonstrated that the hydrologic discrepancy has not altered nymphal growth patterns, suggesting that each species displayed a determinate voltinism pattern.

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A Comparative Analysis of Voltinism Patterns of Stoneflies (Plecoptera) from an Intermittent-perennial Stream Continuum

Aquatic insects that inhabit intermittent streams must possess life history mechanisms to survive during periods when surface flow is lacking. Nymphal growth (= voltinism) can be characterized as determinate or indeterminate. The principal difference between the two forms of voltinism lies in whether the length of nymphal growth is determined by local climatological or hydrologic conditions. Although there has been considerable research on life history patterns of stoneflies from mid-order streams and small rivers, zero-order (intermittent) and first-order streams (springs) are rarely studied. We initiated a comparative life history study of four species of stoneflies (Plecoptera) that inhabit an intermittent-perennial stream system. The intermittent section emanates on sandstone and flows before dropping vertically down a 20 m break. Surface flow ceases during June and does not resume until late autumn. Natural flow patterns of the lower (perennial) section are enhanced by the upper (intermittent) section only during winter and spring, yet is maintained during summer by two small springs. We hypothesized that each of the four species would exhibit identical life history attributes (i.e., adult flight activity, egg development time and timing of hatching, seasonal nymphal growth patterns) in each stream section (intermittent vs. perennial). Regular sampling has occurred since May 2002, as well as monitoring water temperature, precipitation, and stage height. Each species has displayed similar fight periods in each section. Examination of nymphal growth histograms through June 2003 has demonstrated that the hydrologic discrepancy has not altered nymphal growth patterns, suggesting that each species displayed a determinate voltinism pattern.