Differential grazing by the mollusc arion hortensis fér. On cyanogenic and acyanogenic seedlings of the white clover. trifolium repens l

Abstract

The average amount of releasable cyanide in cyanogenic seedlings of white clover was found to increase by a third from age 5 days to age 35 days. Over this period levels of cyanide decrease in cotyledons, but increase in stems and young leaves. The slug, Arion hortensis was introduced to mixed populations of mostly cyanogenic and mostly acyanogenic seedlings of white clover of known age for 12 hour periods, and grazing levels of known phenotype seedlings was scored according to whether damage to the seedlings was lethal or not. Slugs did not discriminate between seedling phenotypes with respect to grazing. No difference in the level of damage between phenotypes was detected at 5 days age. At 16, 23 and 35 days age, very few grazed cyanogenic seedlings suffered lethal damage, although most grazed acyanogenic seedlings were lethally damaged. At these ages, most seedlings suffering non-lethal damage were cyanogenic. It is concluded that older seedlings of cyanogenic white clover are protected from lethal grazing damage by the slug Arion hortensis. This may influence the frequency of cyanogenic morphs in populations more than discriminatory grazing on adult plants. © 1986 The Genetical Society of Great Britain.