Elytral surface structure in Poecilus lepidus (Coleoptera: Carabidae): What about the nature of its inheritance?

Abstract

The cuticle of the ground beetle Poecilus lepidus (Leske) (Coleoptera: Carabidae) displays a complex variety of colour morphs that are genetically determined. Besides the colour of the elytra, there is a remarkable intersexual dimorphic difference in its surface structure between males and females, as there is in most Poecilus species. At least in Central European populations of P. lepidus, all males exhibit a bright elytral surface, whereas all females exhibit a matt surface; this difference is due to a nearly plain surface in males but a knobbly sculptured one in females. At first glance, this phenomenon may be easily interpreted as being a result of secondary sexual character inheritance. However, P. lepidus specimens are known from two other regions that differ markedly: females display the same bright elytral surfaces as males in the Italian Apennine Mountain and all over Bulgaria. In the present study, crossbreeding experiments with German and Bulgarian specimens resulted in a dominance of matt over bright in the classical Mendelian F2 3: 1 ratio, although only in females. All the males showed a bright elytral surface. These findings throw into question the interpretation as given above. Because classical modes of inheritance do not provide a sound interpretation of the data as here detailed, we discuss two forms of epigenetic mechanisms which might be responsible for the observed sexual dimorphism: (1) silencing of a gene by genomic imprinting, and (2) haplo-insufficient dominance of one allele to its counterpart. Ultimately, the observed pattern is interpreted by sex-limited inheritance that depends on the presence or absence of a particular allele.