Invertebrate Diversity on Sleepy Grass (Achnatherum Robustum) Infected with the Alkaloid-Producing Neothyphodium Fungal Endophyte
Sleepy grass (Achnatherum robustum) is a cool-season native grass of the southwestern United States that is inhabited by a fungal endophyte of the genus Neotyphodium. The relationship between Neotyphodium and host grasses is thought to be mutualistic. The endophyte produces several types of alkaloids that are known to cause toxicosis in vertebrate herbivores such as cattle. In fact, plants infected with the endophyte are avoided by some vertebrate herbivores. In this investigation, it was hypothesized that the alkaloid levels produced by a plant's endophytic fungi result in a change in community composition on the plant. To test this hypothesis, a vortex sampler was used to collect invertebrates from individual sleepy grass plants at three sites in southern New Mexico. The invertebrates were sorted into morphospecies, which were used to calculate a diversity index for each individual plant. Alkaloid concentrations in plant tissues were determined using high-pressure liquid chromatography. Invertebrate abundance, species richness and diversity were correlated with plant size and the alkaloid levels produced by each plant. Plant volume significantly affected abundance, species richness, and diversity of invertebrates. Alkaloid concentration in plant tissues was positively related to species richness. These results question the hypothesis that alkaloids associated with endophytes reduced abundance and diversity of invertebrate communities on host grasses.