Phenotypic links in complex life cycles: conclusions from studies with decapod crustaceans

I review studies on decapod crustaceans to draw conclusions about the importance of effects of past environmental conditions on development, phenotype, performance, and survival in animals. I consider 3 critical points of the life cycle: the allocation of reserves into eggs, the hatching of larvae, and metamorphosis from the larval to the juvenile phase. Biomass allocated to eggs varies among females as a response to changes in environmental conditions. These variations are propagated to the larval stages, influencing the biomass at hatching, subsequent larval developmental pathways, and survival during periods of limited starvation. Suboptimal conditions experienced by embryos increase the loss of mass during embryogenesis; size or biomass of the juvenile is either positively or negatively correlated with initial biomass. Positive correlations may be the normal pattern; negative correlations occur when individuals hatched with low initial biomass follow developmental pathways that lead to increased biomass at metamorphosis. In estuarine crabs, salinity experienced by embryos leads to salinity acclimation in early larval stages. Phenotypic links originate as transgenerational effects that propagate to the juvenile stages. There are least 3 types of effects: disruption of physiological processes; direct adaptive responses; and indirect consequences of adaptive mechanisms. All types appear within a species; they are produced as a response to a single environmental factor. Variability in phenotype remains latent and is expressed in terms of survival according to the environmental conditions experienced by a particular stage. The fate of individuals is thus affected by interactions between their immediate developmental processes and their environmental history.