Genetic adaptations to grazing and mowing in the unpalatable grass Cenchrus incertus

Summary

To identify morphological and life history adaptations to grazing, mowing, and cultivation, seeds of the grass Cenchrus incertus were collected from two populations in each of three types of sites: cemeteries (mown occasionally), pastures (grazed continuously), and orchards (plowed twice a year). Seeds from each population were germinated and grown in a common greenhouse.

Plants originating from the two cemetery populations had, on average, the most leaves and the most tillers per plant at each census, and they were on average the shortest in stature. Cemetery plants had on average the greatest number of panicles and of burs per plant, but the fewest burs per panicle. The occasionally-mown but ungrazed cemetery populations in this study were therefore more similar to grazed populations described in other studies; the pasture and orchard populations in this study were more similar to ungrazed populations described in other studies. We suggest that this may be due to the low acceptability of Cenchrus incertus, which makes its defoliation relatively infrequent in unmown sites.

Some of the traits that distinguished the cemetery populations from the orchard and pasture populations, such as shorter stature, are probably direct adaptations to defoliation. Others may be secondary effects of these, or the result of allocation trade-offs.