Allocation of pederin during lifetime ofPaederus rove beetles (Coleoptera: Staphylinidae): Evidence for polymorphism of hemolymph toxin

Abstract

Pederin, a hemolymph toxin found in the rove beetle genusPaederus, is quantified in individual specimens ofP. fuscipes andP. riparius. Whereas males always contain only small quantities of the toxin (0.1–1.5 µg), females are not so restricted (0.2–20.5 µg) and in most cases possess roughly 10-fold that in males. There are, however, females containing as little pederin as the males, and so two clearly separate groups of females can be discerned. These two groups hint at two types of females defined by the eggs they lay. About 85% of the females, i.e., those containing much of the substance, transfer pederin into every egg and thus are denoted (+)-females. The remaining 15%, the (−)-females, contain at best small amounts of the toxin, which is transferred in minute quantities into the first eggs while the subsequent ones lack pederin. With respect to the pederin content of their eggs, there is no overlap between these two types of females. If fed with pederin, (−)-females can transfer it into the eggs like (+)-females. After hatching the larvae store pederin when present. Larvae are not able to biosynthesize the toxin on their own, but storage of that received in the egg is very efficient, and the difference between larvae with and without pederin is preserved until imaginal eclosion. In (+)-females, pederin increases, probably reflecting a biosynthetic capacity, but in males and presumptive (−)-females the amount of pederin never exceeds the quantity transferred by parental (+)-females. Consequently, males and (−)-females probably are unable to biosynthesize pederin. This polymorphism of females may have a genetic basis. Individuals of all stages nevertheless sequester pederin if it is supplied with the diet.