A comparison of Gammarus pseudolimnaeus feeding preferences utilizing green and senescent leaves of four species of riparian vegetation.

Abstract

Relatively few studies have been done on herbivory in bryophytes and aquatic macrophytes. One example of chemical deterrence of herbivory in an aquatic macrophyte is in Nasturtium officinale (watercress). Previous studies have indicated that the amphipod Gammarus pseudolimnaeus avoids green N. officinale tissue. To determine whether G. pseudolimnaeus is primarily a detritivore or is deterred specifically by secondary compounds in N. officinale, feeding preferences of G. pseudolimnaeus for green versus senescent leaf tissue were studied in fifteen replicates of four species of associated riparian vegetation, Alnus rugosa (speckled alder), Caltha palustris (marsh marigold,), Lemna minor (duckweed), and Fontinalis hypnoides ( a moss). Relative consumption of angiosperm and bryophyte tissue was also of interest. Samples were collected from Carp Creek, Michigan. Green and senescent leaf tissue from one species of plant was placed in each petri dish with G. pseudolimnaeus. All data was analyzed using chi-squared tests. In all species, senescent tissue was consumed significantly more than green tissue (p<0.05). Almost no green angiosperm tissue was consumed, and the frequency of green bryophyte tissue consumption was significantly higher than for green angiosperm tissue (p<0.05).These results suggest that G. pseudolimnaeus prefers decomposing plant tissue, apparently feeding primarily as a detritivore. Possible reasons for avoidance of green angiosperm tissue include chemical deterrence and/or failure of invertebrates to recognize green leaves as food. The function of bryophyte secondary compounds in deterring herbivory may differ markedly from angiosperm secondary compounds.