Carotenoid-based sexual coloration and body condition in nesting male sticklebacks

The extent, corrected for body size, and intensity of nuptial coloration of breeding male three-spined sticklebacks Gasterosteus aculeatus L. from a Scottish freshwater population were highly variable but correlated, both in the field and after a period of nest-building in the laboratory. However, marked changes in coloration occurred between the field and the laboratory screenings and the coefficients of variation amongst males decreased. In general, intensity of coloration increased between the field and laboratory screenings, but changes in size-corrected extent were not consistently directional. For both indices, there was a negative relationship between the field value and amount by which colour changed between sampling sessions, with fish that were initially the dullest gaining most in colour. Size-corrected extent and (in particular) intensity of coloration in the field sample were associated positively with body condition measured post mortem and there was a negative, though non-significant, relationship between the extent of coloration and the proportion of white cells in the blood. No such associations were found for the laboratory colour screening. The concentration of astaxanthin in the lower jaw was related strongly and positively to both size-corrected extent and intensity of coloration at the laboratory screening and related negatively, though non-significantly, to proportional white cell counts. These data have implications both for the interpretation of previous laboratory studies and for the design of future experiments, and suggest that coloration is only a true indicator of male quality when measured in the field.     

Host‐plant genotype mediates supply and demand of animal food in an omnivorous insect

1. Omnivorous predators can protect plants from herbivores, but may also consume plant material themselves. Omnivores and their purely herbivorous prey have previously been thought to respond similarly to host‐plant quality. However, different responses of omnivores and herbivores to their shared host plants may influence the fitness, trophic identity, and population dynamics of the omnivores. 2. The aim of the present study was to show that an omnivorous heteropteran (Anthocoris nemorum L.) and two strictly herbivorous prey species respond differently to different genotypes of their shared host plant, Salix. Some plant genotypes were sub‐optimal for the omnivore, although suitable for the herbivores, and vice versa. 3. The contrasting patterns of plant suitability for the omnivore and the herbivores highlight an interaction between plant genotype and omnivores' access to animal food. Plant genotypes that were sub‐optimal for the omnivore when herbivores were experimentally excluded became the best host plants when herbivores were present, as in the latter situation additional prey became available. By contrast, the quality of plant genotypes that were intrinsically suitable for omnivores, did not improve when herbivores were present as these plant genotypes were intrinsically sub‐optimal for herbivores, thus providing omnivores with almost no additional animal food. 4. The differential responses of omnivores and their prey to the same host‐plant genotypes should allow omnivores to colonise sub‐optimal host plants in their capacity as predators, and to colonise more suitable host plants in their capacity as herbivores. It may thus be difficult for Salix to escape herbivory entirely, as it will rarely be unsuitable for both omnivores and pure herbivores at the same time.