Sexual size dimorphism and the integration of phenotypically plastic traits

1. Sexual size dimorphism (SSD) reflects adaptive differences in male and female reproductive roles. Understanding the mechanisms generating SSD is of broad ecological and evolutionary interest, because body size is closely linked to fitness. 2. Sex-specific phenotypic plasticity in growth as a response to environmental conditions represents one of the major sources mediating variation in SSD. We investigated phenotypic plasticity associated with predation and seasonal time constraints in development as a source of SSD in the Azure damselfly, 3. Coenagrion puella. We complemented this with an analysis of trait correlations (integration) of body size with behavioural, physiological and life-history traits to investigate how dimorphism manifests. 4. Our results reveal that: (i) plasticity in SSD is mediated by environmental variation; and (ii) environment-dependent, sex-specific changes in the association of body size with growth rate and fat storage mediated changes in the offset of SSD. 5. Our results highlight sex-specific trait responses to the environment channel manifestation of SSD. These findings may be crucial to understanding large parts of the widely documented intraspecific variation of SSD.