Biology session

Sexual conflict occurs when the two sexes have conflicting optimal fitness strategies, which has several evolutionary or coevolutionary consequences, a series of adaptations and counter-adaptations. Prolonged mate guarding is one of the several male adaptations, since in many cases females copulate multiple times in their lives and the male copulating the last fertilises the majority or all of the eggs. A frequent means of prolonged mate guarding is the male-produced mating or copulatory plug, which occludes the female copulatory opening and prevents further inseminations. An extreme form of mate gaurding in some lepidopterans is the sphragis, which has a plug part that binds into the copulatory opening and a clearly visible shield part, which is a mechanical obstacle to the removal of the plug. It is quite common in the Parnassius genus and in the Clouded Apollo (Parnassius mnemosyne) butterfly. This is a hollow, bare, usually bright and, compared to body size, a large structure. However, males not always produce sphragis during mating, occasionally they produce smaller plugs or filaments, which are barely or not at all visible to the naked eye.

I assume that both production costs and the effectiveness in prolonged mate guarding is the highest for sphragides and the lowest for filaments. My question is whether the male Clouded Apollo butterfly could monopolise the female more effectively with a shield, than with other mating plugs. I investigated whether (i) mating plugs and filaments are more frequently lost than shields, (ii) shorter shields have a higher probability to be lost than longer ones, and (iii) what seasonal distributions and dynamics are typical in shields, plugs and filaments compared to each other?

We carried out field work from 2014 to 2018 in the Visegrádi-hegység. We attempted to capture all unmarked females, we marked them individually by colour combinations and by a numeric identifier (ID), and if they had shields, these were also marked for tracking purposes. Plugs and filaments were tracked based on their unique morphology with the help of recaptures and photomacrographs.

To monopolise females and secure paternity, the shield seemed to be the most effective genital appendix despite its presumable cost. It is more likely to remain on females for a longer time period and it is less likely to be lost than the smaller appendices. Lost shields are shorter than the population average. Shields are more common at the beginning of the flight period, while the other appendices show an increasing proportion towards the end. This may be the result of time-shifted sex ratios: males appear at the beginning of the flight period (and have more energy at this time), while females fly in the middle and towards the end. Therefore, I assume a more intensive competition at the beginning, when producing the presumably more expensive, but also more effective shield is more rewarding than later in the season.