The physiological ecology of the filamentous alga Spirogyra

Holly L Adrian, Purdue University

Abstract

Spirogyra is an aquatic weed problem in the Midwest. Despite its ubiquity, little is known about the ecology of Spirogyra populations. In this study, the seasonal distribution of this alga, the environmental controls responsible for this periodicity, and the genetic variation of a population were determined. A two year field study in Surrey Lake, Indiana, determined that Spirogyra was a spring blooming alga. These populations consisted of four morphologically distinct filament forms, each exhibiting its own seasonal distribution. A 45 $\mu$m wide filament form grew from February to May. A 70 $\mu$m form grew from April to mid-June. A 100 $\mu$m form grew from February to mid-June. Finally, a 130 $\mu$m form grew in February, 1992. The 70 and 100 $\mu$m forms contributed to the peak amount of biomass observed in late May/early June. Multiple regression analysis indicated that abundance of the 45, 70, and 100 $\mu$m forms correlated with maximum temperature. The 130 $\mu$m form correlated with maximum irradiance. The 45 and 70 $\mu$m forms also correlated with nitrogen and phosphorus, respectively. Laboratory experiments were used to verify if temperature, irradiance, or nutrients were the true environmental parameters controlling growth of each filament form in the field. Results suggested that the 45 $\mu$m form could not survive at 35$\sp\circ$C. The 70 $\mu$m form declined when nutrients were reduced. The 100 and 130 $\mu$m forms lost mat cohesiveness when exposed to high irradiance. Therefore, each filament form appeared to be sensitive to specific environmental controls. The ploidal variation and genetic relatedness of this Spirogyra population was determined by chromosome counts, estimation of total DNA by fluorescent DAPI staining, and by RAPD analysis. Results of chromosome counts and DAPI staining indicated that the most likely ploidal complex consisted of the 45 $\mu$m and 100 $\mu$m forms. However, RAPD analysis indicated that all forms were genetically different strains. Therefore, the Surrey Lake population of Spirogyra was complex. Filament forms were genetically different; this variation may have allowed each filament form to take advantage of a specific niche, resulting in a unique and predictable seasonal distribution pattern.

Degree

Ph.D.

Advisors

Lembi, Purdue University.

Subject Area

Botany|Freshwater ecology|Ecology

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