Selective Eating Research Articles

Field observations on the cyanogenesis polymorphism in Trifolium repens

We surveyed a population of Trifolium repens L. polymorphic for cyanogenesis to determine whether either of two biotic factors were concerned as selective forces affecting the balance between the cyanogenic and acyanogenic forms. We found no difference between the distributions of cyanogenesis scores for uninfected leaves and for leaves infected by the fungus Cymadothea trifolii Wolf. Acyanogenic plants, however, were more heavily eaten than cyanogenic ones, the principle herbivores being the slugs Arion ater L. and Agriolimax reticulatus Muller. Selective eating of isolated plants in a herbaceous border was due both to more acyanogenic leaves being touched and to more being eaten per a cyanogenic leaf. For plants embedded in the lawn selective eating was due mainly to the latter cause. Possible explanation for the differences in degree of selective eating between lawn plants and border plants and between this survey and choice experiments are discussed.

Effects of Saliva and Drying Temperature on Composition and Digestibility of Forage Samples Collected through Esophageal Fistulas

Five fresh legume and four fresh grass samples were fed to two esophageal-fistulated steers and collected through the fistulas. Care was taken that the whole sample was consumed, thus preventing selective eating. Replicate samples (control) were not subjected to saliva contamination and were compared with fistula samples in regard to percentage of ash, crude protein, acid-detergent fiber, acid-insoluble lignin and in vitro dry matter digestibility. The effects of drying temperature (45 and 65 C) on chemical constituents and in vitro dry matter digestibility of control and fistula samples were also studied. Fistula samples were significantly (P<.01) higher in ash (dry matter basis), acid-detergent fiber and acid-insoluble lignin (organic matter basis) than control samples. In vitro dry matter digestibility of only the legume fistula samples was significantly (P<.05) lower than that of the legume control samples when samples were dried at 45 C. At the higher drying temperature (65 C) control samples were significantly (P<.05) higher in acid-insoluble lignin and fistula samples were significantly (P<.05) lower in ash than their respective sample dried at 45 C. Samples obtained from the two esophageal-fistulated steers differed significantly (P<.05) only in percentage of ash and acid insoluble lignin.

Selective Eating of the Acyanogenic Form of the Plant Lotus corniculatus L. by Various Animals

WILD populations of the tetraploid plant Lotus corniculatus L. (birds' foot trefoil) are polymorphic for the presence or absence of a cyanogenic glucoside. This character is genetically controlled1, the gene responsible for producing the glucoside being dominant over its allelomorph. Hydrocyanic acid is evolved on hydrolysis of the glucoside when the stems or leaves are injured. Corkill2 has shown that with Trifolium repens L. the change in the colour of sodium picrate paper from yellow to brick red is proportional to the amount of hydrocyanic acid produced and hence to the glucoside content of the plant. The plants are scored from 0 (no glucoside) to 6 by matching the colour-change in the picrate paper against a series of standards.