Oecologia (2004) 140: 302–311
DOI 10.1007/s00442-004-1574-7


Anne Hemmi . Veijo Jormalainen

Genetic and environmental variation in performance of a marine
isopod: effects of eutrophication

Received: 5 March 2004 / Accepted: 25 March 2004 / Published online: 14 May 2004
# Springer-Verlag 2004

Abstract Environmental variation in food resources
modifies performance of herbivores, in addition to genetic
variation and maternal effects. In marine benthic habitats,
eutrophication may modify herbivores’ diets by changing
host species composition or nutritional quality of algae for
herbivores. We studied experimentally the effects of diet
breadth and nutrient availability for the host algae on
fitness components of the herbivorous isopod Idotea
baltica. We fed the adult isopods with the brown algae
Fucus vesiculosus and Pilayella littoralis and juveniles
with the green alga Cladophora glomerata. By using halfsib families, we were able to separate the genetic,
environmental and maternal effects on intermolt duration
and size of the juveniles. The mothers confined to the diet
consisting of both Fucus and Pilayella grew better and
produced larger egg mass than those having consumed
Fucus alone. Nutrient enhancement of algae did not
influence the performance of the adult herbivores. However, the juveniles achieved twice the weight as well as
shorter intermolt duration when consuming nutrienttreated C. glomerata. Mother’s nutrition, either nutrient
enrichment of her food algae or diet breadth, did not affect
juvenile survival or growth as such, but we found evidence
that the broader diet consumed by the mother mediated
offspring performance by further accelerating growth rate
of the offspring that fed on nutrient-treated alga. Intermolt
duration was a highly heritable trait, but size showed very
low heritability. Instead, maternal effects on size were
substantial, suggesting that differences among mothers...