Age and size at maturity: a quantitative review of diet-induced reaction norms in insects.

Optimality models predict that diet-induced bivariate reaction norms for age and size at maturity can have diverse shapes, with the slope varying from negative to positive. To evaluate these predictions, we perform a quantitative review of relevant data, using a literature-derived database of body sizes and development times for over 200 insect species. We show that bivariate reaction norms with a negative slope prevail in nearly all taxonomic and ecological categories of insects as well as in some other ectotherm taxa with comparable life histories (arachnids and amphibians). In insects, positive slopes are largely limited to species, which feed on discrete resource items, parasitoids in particular. By contrast, with virtually no meaningful exceptions, herbivorous and predatory insects display reaction norms with a negative slope. This is consistent with the idea that predictable resource depletion, a scenario selecting for positively sloped reaction norms, is not frequent for these insects. Another source of such selection-a positive correlation between resource levels and juvenile mortality rates-should similarly be rare among insects. Positive slopes can also be predicted by models which integrate life-history evolution and population dynamics. As bottom-up regulation is not common in most insect groups, such models may not be most appropriate for insects.

Carotenoid-based plumage coloration reflects hemoparasite infection and local survival in breeding great tits.

Carotenoid-based sexual coloration has been hypothesised to be prevalent across many vertebrate taxa because it reliably reflects individual phenotypic quality in terms of foraging efficiency or health status due to the trade-off between signal colour and use of carotenoids for immune function and detoxification. We investigated the ventral, yellow coloration of breeding adult great tits (Parus major L.) in relation to sex, age, breeding habitat, local survival and infection status with respect to Haemoproteus blood parasites. The extent of plumage coloration (estimated as hue and lutein absorbance) was generally higher in rural than in urban birds. Males had higher values of hue than females. In both male and female yearlings, the plumage of unparasitised individuals had a greater hue of yellow than parasitised ones, while older males revealed the opposite pattern. The survival of infected yearlings was worse than that of uninfected yearlings, while the opposite was true for old breeders. Survivors had generally higher values of hue than non-survivors. These results are consistent with predictions of functional hypotheses, suggesting that carotenoid-based plumage coloration serves as a signal reflecting individual quality in terms of health status and local survival.