Gammarus pseudolimnaeus prefers to feed on senescent riparian vegetation as opposed to green riparian vegetation.

Abstract

The coevolution of herbivores and plants has been emphasized as a critical coevolutionary interaction. Since plants cannot ""move"" they need to find other ways to adapt, so their entire population is not consumed. Some plants develop toxins to deter herbivores from eating them. At the same time herbivores develop better ways to perhaps digest these toxins. This is called coevolution. Four species of plants located along the banks of Carp Creek, Michigan were selected to be fed to the amphipods Gammarus pseudolimnaeus. Three of the plants were angiosperms Alnus rugosa (speckled alder), Caltha palustris (marsh marigold), and Lemna minor (duckweed). The fourth plant was a bryophyte, Fontinalis hypnoides (water moss). After starvation, green and senescent leaves of each type of plant were presented to G. pseudolimnaeus for 60 hours of feeding. The G. pseudolimnaeus were found, using Chi square tests, to statistically prefer the senescent vs. the green leaves in all cases. This pattern is most likely due to the presence of toxins found in many fresh green leaves of angiosperms and bryophytes. The results may also be due to tissue qualities, or perhaps the presence or absence of bacterial or fungal colonies on the leaves. The results of this experiment can be used to make inferences about other riparian vegetation and the role invertebrates play in the food webs of stream systems.