Hypermnestra, , Bryk, 1935

Matsumoto, Kazuma & Orr, Albert G., 2021, The occurrence of a sphragis and genital modification in Hypermnestra, Archon and Sericinus (Lepidoptera: Papilionoidea: Papilionidae), Journal of Natural History 55 (15 - 16), pp. 1033-1057 : 1050

Hypermnestra

The sphragis of Hypermnestra is a mass of unformed male secretion, but it may appear somewhat structured due to its overlaying the unusual external female genitalia, with a fleshy projection just behind the ostium, on which the thick coat of secretion forms a still more projecting sphragis. We consider the sphragis in Hypermnestra to be a protosphragis, because of its irregular and crude formation; moreover, there is no sclerotisation of the female external genitalia (sterigma) and the ostium bursae is not exposed as in typical sphragis-bearing species. The lack of sharp or stout recurved structures on the male genitalia that might be used for sphragis removal also supports the view that Hypermnestra is at early stage of evolving a sphragis.

The sterigma of female Hypermnestra is not obviously specialised to reject plugging by the male but is highly modified from the ancestral condition found in most non-sphragisbearing butterflies and the ostium is still rather exposed. Moreover, the fleshy projection seems to support the sphragis. The projection itself is relatively soft (at least when macerated), but after a male smears it with a large amount of secretory material, it provides a core, supporting a sphragis at the right angle to the abdomen to create an obstacle to remating with another male. If so, the female genitalia of Hypermnestra may be secondarily adapted to retain a sphragis. Possibly the females actively grip a small sphragis that will inhibit remating; in this way they might receive a larger spermatophore. Probable sphragis-retaining female genitalia among sphragis-bearing Papilionidae are otherwise only known in Parides proneus (Hübner) ( Orr 1988, 1995). The female genitalia in this species are exposed but equipped with a sclerotised bar in front of the ostium, which anchors a small sphragis. It is possible that this is a female adaptation to retain the sphragis meaning that a small sphragis is still effective, thus enabling males to commit more secretory material to a large spermatophore. In general, it is possible that in certain circumstances females evolve the capacity to hold a sphragis when additional matings are no longer advantageous. This may be because the male has already provided a significant nuptial gift, together with the small sphragis, or, in cases where male ejaculates are small and spermatophores have little nutritional value, bearing a sphragis may free a female from the risks and costs of unwanted copulation (i.e. waste of time and energy, risk of predation or physical damage). Orr and Rutowski (1991) demonstrated that females of Cressida cressida , which receive no nutrients from the male ( Orr 1988), display the sphragis to avoid unwanted second matings, which in this species may prove fatal ( Orr 1999). Wedell et al. (2002) demonstrated that there is a genetic variation in female mating frequency in Pieris napi (Linnaeus) in Sweden and suggested that the variation can be related to a trade-off between the nutritional benefit and time available for oviposition in the unpredictable Swedish weather. Mated female H. helios may benefit from bearing a sphragis while ovipositing, because the species lives in a dry open habitat and females lay eggs singly on a small hostplant ( Igarashi 1979), hence ovipositing females probably conspicuously visit many hostplants and they may frequently encounter and be harassed by searching males, a situation where the female may benefit by retaining an effective sphragis.