Density–dependent prophylaxis in the mealworm beetleTenebrio molitorL. (Coleoptera: Tenebrionidae): cuticular melanization is an indicator of investment in immunity

Abstract

If there are costs involved with the maintenance of pathogen resistance, then higher investment in this trait is expected when the risk of pathogenesis is high. One situation in which the risk of pathogenesis is elevated is at increased conspeci¢c density. This paper reports the results of a study of density-dependent polyphenism in pathogen resistance and immune function in the mealworm beetle Tenebrio molitor. Beetles reared at high larval densities showed lower mortality when exposed to a generalist entomopathogenic fungus and a higher degree of cuticular melanization than those reared solitarily. The degree of cuticular melanization was a strong indicator of resistance, with darker beetles being more resistant than lighter ones regardless of rearing density. No di¡erences were found between rearing densities in the levels of phenoloxidase, an enzyme key to the insect immune response. The results show that pathogen resistance is phenotypically plastic in T. molitor, suggesting that the maintenance of this trait is costly.

Activation of host constitutive immune defence by an intestinal trypanosome parasite of bumble bees

“…Indeed, the induction of anti-bacterial peptides has been shown to be specific, with different types of pathogen inducing the production of different peptides (Lemaitre, Reichhart & Hoffmann, 1997;Engstrom, 1999). Furthermore, 5 recent work suggests that invertebrates can alter the constitutive defence response of their offspring with respect to current levels of perceived parasite threat (Moret & Schmid-Hempel, 2001), and, similarly, that host populations can vary the constitutive defence according to population density, which acts as a correlate for the threat of infections (Wilson & Reeson, 1998;Barnes & Siva-Jothy, 2000;Wilson, Cotter, Reeson, et al, 2001). Apart from the perceived risk of infection, host condition and environmental stress, e.g., resource limitation, temperature, and humidity, are well-known factors that explain variation in the level of the constitutive immune response (e.g., Ferguson & Read (2002)).…”

Juvenile immune system activation induces a costly upregulation of adult immunity in field cricketsGryllus campestris

“…The accumulation of proPO instead of PO might reduce the risk of oxidative damage to host tissues by quinones and other reactive oxygen metabolites that are produced by the active enzyme (Sö derhäll & Cerenius 1998;Kumar et al 2003). Despite the obvious relevance of a distinction between inactive proPO and active PO, previous studies in the field of ecological immunology assessed only the activity of the active enzyme, PO (Barnes & Siva-Jothy 2000;Wilson et al 2001;Moret & Siva-Jothy 2003).…”

Development and evolution of insect pigmentation: Genetic mechanisms and the potential consequences of pleiotropy

“…This includes innate immunity, wound healing, and parasite defense. The presence of a brown-black pigment accompanying cellular innate immunity is a unique characteristic of arthropods [62] and can be used as an indicator of immune investment [63]. During wound healing in Drosophila, melanization serves as a "scab" to protect the epidermal opening during cellular repair [64].…”