The Photinus marginellus reproduce through means of reproduction called nuptial gifts. Nuptial gifts are nutritional contributions delivered from the male to the female during sexual intercourse (Lewis et al., 2004). The nuptial gifts are transferred through a spermatophore, which is a capsule of sperm produced by the male accessory glands, and function to carry the nuptial gift to the female during intercourse. The flash duration of the male determines their spermatophore mass. The longer the flashes last, the less spermatophore mass they have (Cratsley, 2004). As adults most Photinus do not feed, therefore, reproduction is primarily based on the resources received through the nuptial gift, and given to the larva (Lewis et al., 2004). Nuptial gifts are of precise economic importance within this insect group.
The male reproductive system for Photinus marginellus consists of four pairs of accessory glands, which are tightly coiled and spiral in shape. The most important of the four specific glands is the one containing the spermatophore components, which house the nuptial gifts (Lewis et al., 2004). The spermatophore, enclose the pre-spermatophore, which are also spiral in shape, with two rows of longitudinal pyramidal scales (Lewis et al., 2004). Aside from the most prominent gland, the male has three additional glands that are tubular and are each different in length. The long gland extends to approximately 18-24 mm in length, while the medium gland greatly declines in size into 5-7 mm long. The short, and last gland of the three is approximately only 1 mm in length (Lewis et al., 2004).

            During the early stages of intercourse, the four accessory glands of the male secrete different fluids, which then all combine in the male ejaculator duct with the sperm. The sperm have been pre-stored in the seminal vesicles of the male organism. When the sperm has come into contact with the fluid from the accessory glands, the sperm become packaged into ring-shaped bundles, and are attached at the end of the spermatophore (Lewis et al., 2004). This entire spermatophore now has a gelatinous structure due to the fluid and sperm combination. Within an hour of copulation, only part of the spiral-coiled, gelatinous spermatophore has been transferred from the Photinus marginellus male to the Photinus marginellus female’s spermatheca, the female’s reproductive storage for the encountered sperm. The remaining end of the spermatophore enters the Photinus female’s reproductive tract in a specialized structure called the spermatophore-digesting gland, where the digesting gland functions to disintegrate the remainder of the spermatophore within a few days (Lewis et al., 2004).
 Permission granted: Kathrin Stranger-Hall
Figure 1. The Spiral spermatophore of Photinus marginellus, inside the female reproductive tract. The spiral coils are visible, and the sperm rings have been released from the tip of the spermatophore into the female’s spermatheca. This depicts the early stage of copulation (within first hour) (Lewis et al., 2004).
        The female Photinus marginellus then uses the spermatophore protein (nuptial gifts) to develop their oocytes (a cell in an ovary, which undergoes mitosis to form an ovum).  The nuptial gifts, therefore, are important supplements for support and nutrients to the larva in the female.  Nuptial gifts have evolved to be more than just a benefit to the female, but a necessity as well. The nuptial gifts housed within the spermatophore of the Photinus marginellus male provide the Photinus marginellus females with energy reserves, most importantly for non-feeding Photinus adults (Lewis et al., 2004). In the non-feeding adults in particular, the energy reserves diminish gradually in the larva, and need the nutrients in the nuptial gifts from the Photinus male to supply the energy supplement. Also, parasites could further reduce the resources needed for female reproduction, which could be resupplied through the nuptial gifts as well (Lewis et al., 2004).
        Although production of a spermatophore is a beneficial necessity for the Photinus females for reproduction, and the Photinus males for sexual selection, it is costly for the males to produce them. The spermatophore mass decreases steadily, on average about 75%, between the first and fourth sexual encounter with a female (Lewis et al., 2004). Also, the cost of the spermatophore production may confine the male’s mating success. Even if the Photinus males have access to a female on a daily basis, the mating success declines, on average, during the last half of the Photinus male's adult existence (Lewis et al., 2004). Due to the limitations of the spermatophore production, this eventually leads to the nuptial gift ability to decrease as the mating season continues. The diminishing spermatophore mass, along with the decreasing nuptial gift ability, could potentially lead to weakening reproductive returns for the Photinus males (Lewis et al., 2004), meaning the males would be unable to provide the spermatophores, and can no longer copulate with a female.
        It is clear that nuptial gifts influence Photinus marginellus in very valuable ways. The nuptial gifts provide nutrients and energy to the larva and to the Photinus female. The cost of the nuptial gifts and production of spermatophore is very costly, and decreases with every female the male encounters in sexual intercourse. The less spermatophore the Photinus male can produce, the less nuptial gift availability (Lewis et al., 2004), which, therefore, affects sexual selection of the male (Cratsley, 2004). Early in the mating season, when the male is the most readily able to generate spermatophores, the sex ratios are male-biased, and can result in male-male competition due to the Photinus marginellus females primarily preferring the Photinus marginellus males that can provide the largest amount of nuptial gifts. This is again expressed to the female based on the intensity of the flashing signals the male provides. However, later in the mating season, females greatly outnumber the males as the spermatophore frequency declines. The lower the intensity of flashes from the male’s abdomen, states low spermatophore mass, which then causes the female to respond elsewhere for greater production of the beneficial spermatophores (Cratsley, 2004).  To look at more information and pictures of the difference between male and female Photinus marginellus look on the website for the  Muesum of Science, Boston; identifying genders. This page will show you the difference between the male and female light organelles and were they are placed. If you would like to gain more knowledge on nuptial gifts in relation with sexual selection, visit the journal article: Nuptial Gifts and Sexual Selection in Photinus Fireflies.

          The flashing light signals and how intense the Photinus marginellus male can radiate his bioluminescent glow are essential characteristics for the Photinus marginellus female to consider when choosing a male. These interactions play a giant role in sexual selection for reproduction between the Photinus marginellus male and Photinus marginellus female.


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