Effect of Juvenile Hormone on Resistance against Entomopathogenic Fungus Metarhizium robertsii Differs between Sexes.

Markus J Rantala,Ivan M Dubovskiy,Jorge Contreras-Garduño,Mari Pölkki,Tatjana Krama,Indrikis A Krams

doi:10.3390/jof6040298

Abstract

Juvenile hormone has been suggested to be a potential mediator in the trade-off between mating and insects’ immunity. Studies on various insect taxons have found that juvenile hormone interferes with humoral and cellular immunity. Although this was shown experimentally, studies using highly virulent parasites or pathogens are lacking so far. In this study, we tested if juvenile hormone administration affected resistance against entomopathogenic fungi, Metarhizium robertsii, in the mealworm beetle, Tenebrio molitor. In previous studies with T. molitor, juvenile hormone has been found to reduce a major humoral immune effector-system (phenoloxidase) in both sexes and decrease the encapsulation response in males. Here, we found that juvenile hormone administration prolonged survival time after infection with M. robertsii in males but reduced survival time in females. This study indicates that the effects of juvenile hormone on insect immunity might be more complicated than previously considered. We also suggest that there might be a trade-off between specific and non-specific immunity since, in males, juvenile hormone enhances specific immunity but corrupts non-specific immunity. Our study highlights the importance of using real parasites and pathogens in immuno-ecological studies.

Highlights

The immunocompetence handicap hypothesis [1] suggests that the expression of secondary sexual traits honestly signals male quality because testosterone—needed to develop these traits—has immunosuppressive effects
In our previous studies on T. molitor, we found that juvenile hormone administration did not influence on beetles’ survival [8]
We found that juvenile hormone enhances resistance against the entomopathogenic fungi in the males of T. molitor, which contradicts the results by some previous studies [8,11,15], In this study, we found that juvenile hormone enhances resistance against the entomopathogenic which have found that juvenile hormone corrupts immunity

Summary

Introduction

The immunocompetence handicap hypothesis [1] suggests that the expression of secondary sexual traits honestly signals male quality because testosterone—needed to develop these traits—has immunosuppressive effects. Many studies in vertebrates have failed to reveal a clear relationship between the expression of secondary sexual ornamentation and immune defense. This might be because the physiological relationship between these traits is not as simple as originally. Many studies in insects and spiders have found that the expression of males’ secondary sexual characteristics correlates positively with their immune defense [3,4,5,6,7]. Since insects lack male-specific hormones such as testosterone, it has been suggested that in these animals, the immunocompetence handicap mechanism would be mediated by juvenile hormone (JH) [8]

Methods

Results

Conclusion