Feeding preferences of Gammarus pseudolimnaeus when presented with fresh and senescent leaves of associated riparian vegetation.

Abstract

The purpose of this study was to investigate if the amphipod, Gammarus pseudolimnaeus, feeds preferentially upon fresh vs. senescent leaves of four species of plant occurring in its habitat. The four species of plant used in this experiment were: Alnus rugosa, Caltha palustris, Lemna minor, and a bryophyte, Fontinalis hypnoides. The specimens used in this experiment were obtained from Carp Creek, in Cheboygan Co., Michigan. Sixty petri dishes were used, fifteen for each species of plant, each dish containing one samaple of senescent leaf tissue, and one sample of fresh leaf tissue. To each dish three G. pseudolimnaeus were added, totaling 25 mm of amphipod per dish. The amphipods were allowed to feed at room temperature for 36 hours, after the initial experiment performed in a refrigerator failed after 24 hours. With all four species, G. pseudolimnaeus demonstrated a statistically significant preference for senescent leaves over fresh leaves. For the three vascular plants, there is little doubt that the G. pseudolimnaeus consistently prefers the senescent leaves, and that this is the result of the presence of secondary metabolites. For the bryophyte, it is clear that the senescent leaves were preferred to some degree, but the cause of this preference is less evident. It is not yet well-documented if bryophytes produce their own secondary metabolites, or if they obtain them from microbial associations or mineral uptake. There is also evidence to indicate that there may be sufficient benefits for herbivores living in cold water to consume fresh bryophyte leaves in spite of risk associated with consuming toxins.