The Functional Morphology of the Bursa Copulatrix of a Butterfly That Does Not Digest Spermatophores (Leptophobia aripa, Pieridae)

SIMPLE SUMMARY: Male butterflies transfer sperm to the female within a package of secretions named spermatophore. These secretions include nutritious substances (butterfly spermatophores are considered nuptial gifts) and compounds that influence different reproductive processes of females in a hormone-like way. During copulation, the spermatophore is deposited in a complex female bag-like organ known as the bursa copulatrix, where it is processed and digested. Thus, the bursa copulatrix mediates male–female interactions during and after copulation that are crucial to the reproductive success of males and females. We studied Leptophobia aripa, a common butterfly in Central Mexico that, contrary to what has been observed in most butterfly species previously studied, does not digest the spermatophore (i.e., spermatophores are not nutritious nuptial gifts in this species). We present a detailed description of the different elements of the bursa copulatrix and of its interaction with the spermatophore. We provide a functional interpretation of these interactions and propose a novel mechanism for the transfer of the sperm from the spermatophore to its final storage organ (another bag-like organ named the spermatheca). ABSTRACT: The bursa copulatrix of female Lepidoptera is a complex organ where crucial male–female reproductive interactions occur during and after copulation. The bursa copulatrix receives, stores, and digests the spermatophore and other substances transferred by the male during copulation, and is involved in changes in female receptivity, ovogenesis, and oviposition. Although females of the butterfly Leptophobia aripa do not digest the spermatophore, they possess a prominent signum. Since, in general, the function of the signum is considered to be the piercing or tearing of the spermatophore to initiate its digestion, its presence in L. aripa poses a conundrum. We undertook a microscopic study of the different components of the bursa copulatrix (ductus bursae and corpus bursae) and found structural differences that we interpreted in functional terms. We provide a detailed description of the signum and present experimental data regarding its effect on the spermatophore. Our observations led us to propose a novel hypothesis regarding the function of the signum.