Egg-size manipulations in the seed beetle Stator limbatus: consequences for progeny growth

Studies that have demonstrated consequences of variation in egg size for progeny growth and development are often confounded by genetic correlations among life-history characters; relationships between egg size and progeny life-history characters do not always reflect cause and effect. Thus, experimental approaches to manipulating egg size in order to quantify the consequences of egg-size variation for progeny growth and development have been developed. I used egg-size plasticity in response to oviposition environment to manipulate egg size in a seed beetle, Stator limbatus, to test the hypothesis that progeny developing from larger eggs survive better, develop faster, and attain a larger adult body size than progeny developing from smaller eggs. Females exposed to Cercidium floridum during egg maturation laid eggs that were substantially larger than those laid by females exposed to Acacia greggii during egg maturation. The larger eggs laid by females exposed to C. floridum took significantly longer to hatch but had shorter total egg-to-adult development times than eggs laid by females exposed to A. greggii (when reared to adulthood on A. greggii). There was no evidence from the between-treatment comparisons that egg size affected egg-to-adult survivorship or the size at which progeny emerged as adults. Within-treatment correlations between egg size and progeny life-history characters were generally consistent with the between-treatment analyses, except that female progeny developing from larger eggs tended to emerge as larger adults than female progeny developing from smaller eggs. This result is interpreted as a consequence of heritable variation in body size rather than a cause-and-effect relationship between egg size and progeny body size.