Trade-offs in insect disease resistance

Abstract

The ability to mount an efficient immune response should be an important life-history trait as parasitism can impact upon an individual's fecundity and survival prospects, and hence its fitness. However, immune function is likely to be costly as resources must be divided between many important traits. Whilst many studies have examined host resistance to particular parasite types, fewer have considered general immune responses. Studies that have considered general immune responses tend to do so in vertebrate models. However, the complexity of the vertebrate immune system makes the examination of evolutionary aspects of immune function difficult.

Using larvae of the genus Spodoptera (Lepidoptera: Noctuidae) as a model system, this study examines' genetic and phenotypic aspects of innate immunity. The aims were to assess the levels of additive genetic variation maintained in immune traits, to consider possible costs that could maintain this variation, and to assess the role of phenotypic plasticity in ameliorating those costs.

A key finding of this study was that high levels of additive genetic variation were maintained in all of the measured Immune traits. Analysis of the genetic correlations between traits revealed potential trade-offs within the immune system and between immune components and body condition. In addition, it was shown that larvae living at high densities invest more in immune function than those living in solitary conditions, suggesting that larvae can minimise the costs of immune function by employing them only when the risk of pathogenesis is high.