Variable male investment in devices impeding female remating in the Clouded Apollo butterfly (Parnassius mnemosyne (LINNAEUS, 1758))

Abstract

Sexual conflict over mating may induce prolonged male mate-guarding in time in the absence of males to prevent female remating via devices such as mating plugs, widespread in insects. In most Lepidoptera, internal plugs are common, while in two butterfly families large external devices, called sphragides, evolved independently. The lack of, or incomplete sphragides in a few individuals were reported in sphragis-bearing species. Previous studies focused on typifying species-specific devices in many species based on a few specimens. In contrast, we investigated alternative mate-guarding devices in detail of a sphragis-bearing butterfly and aimed to introduce their Hungarian terminology. We conducted a six-year observational field study in a Clouded Apollo Parnassius mnemosyne population. Inspecting 492 females, we identified three different devices, filament, stopple and shield (a part of the sphragis), increasing in size and structure complexity, implying differential male investment and effectiveness in securing paternity. Shield dimensions, colour and all devices’ shapes varied considerably. Shields were far more frequent than other devices. Some devices were lost, and a few were video-recorded when removed by males, showing some roles of different parts of the male external genitalia. We discuss potential causes of device variation and the role of removal attempts, and assess potential costs and benefits for both sexes.