User:Sachi.sb/Photinus pyralis

Lead
Photinus pyralis, better known as the common Eastern firefly, is a species of flying beetle, notably known for its light-producing abilities by means of an organ on its abdomen (A). It is the most common species of firefly in North America, and is typically found east of the Rocky Mountains. Photinus fireflies are often confused with fireflies of the similar-sounding genus Photuris, which are also found in America.

These fireflies are most noticeable around twilight in the spring and summer months, and fly close to the ground, usually around long blades of grass (F). Due to the characteristic flight of the males, this species is also often called the big dipper firefly; the trajectory appears to follow a J-shape, lighting on the upswing (B,G). During flight, this J-pattern is used alongside light flashing to attract females, who rest on vegetation instead of flying and signal back to males if interested(H, 2). The firefly flashes are stimulated by light-activated proteins, not rhythmic impulses as originally thought.

Although their conservation status is classified as “Least Concern”, these fireflies do face some dangers. Aside from natural predators, the biggest threats to their populations include light pollution, pesticide use, climate change, and human building and development in their habitats (L).

Photinus pyralis contain steroid compounds called “lucibufagins” which serve as one of their many defense strategies as they can repel spiders and other insects. However, the Photuris fireflies with whom the common Eastern fireflies are regularly confused actually use the presence of these lucibufagins to prey on the P. pyralis. Male common Eastern fireflies can be lured by female Photuris fireflies through light signal mimicry, and are eaten when they get close enough. Through this, Photuris can acquire the lucibufagins for themselves, demonstrating that this spider-repellant, while a defense mechanism for the most part, can also serve as an attractant to some predators (D).

Description
Common Eastern fireflies are small soft-bodied beetles that range between 5 and 25 mm in size. They have flat black or brown bodies with wings that extend the length of their entire thorax and abdomen. Plates with red and black spots cover their head, and yellow markings can be seen extending the rest of their bodies, usually around their wings (6).

Both males and females of this species have light-emitting organs on the ventral side of their abdomens, but while this organ extends the length of the last three segments of the males’ abdomens, only the second to last segment of the females’ abdomens bioluminesce (9).

Although some species of fireflies can be diurnal, Photinus pyralis, as well as most of the other flying fireflies are nocturnal (6).

Geographic Range/Habitat
Common Eastern fireflies are found in a variety of habitats, ranging from temperate to tropical environments (3). Although they can be found across most of North America, they are most densely populated in the northeastern region of the United States and Canada.

Some natural habitats of these fireflies include meadows, fields, wetlands, desert canyons, and dense forests, and while they can successfully thrive in all of these areas, they require moisture to survive at all life stages. P. pyralis also tend to form microhabitats using a variety of organic material such as leaf litter and rotting vegetation so they can better signal to other fireflies, establish hunting territories, and secure shelter to lay their eggs and survive through winter months. They are especially drawn to areas with damp soil and long grasses to better conceal females and offspring (13).

Historical Range & Migration
Population studies have been done to investigate whether P. pyralis has always been endemic to the northeast regions of North America, especially because the species continues to occupy a wide variety of habitats across the continent. It has been discovered that ancestrally, the North American population originated in Texas during the Miocene epoch before migrating to the central states of the USA and more recently, the Northeast coast. Through the tracking of single nucleotide polymorphisms (SNPs) along with other genetic markers, researchers have concluded that the common Eastern firefly possibly migrated during interglacial periods, which researchers suggest could account for the divergence to other Photinus species (3).

Mating
Like all beetles, the entire life cycle of a common Eastern firefly consists of four unique life stages starting with the eggs, moving to the larval stage, followed by a pupa, before finally completing the cycle as a fully formed adult. The time it takes for these fireflies to complete all four stages can vary drastically, especially because they inhabit such a wide range of environments that the resources available to them vary significantly. However, all fireflies will spend most of their time in their feeding stage as larvae with most taking approximately two years before they begin to pupate. During this time, they will experience multiple instars, or molting periods. Because all fireflies are very vulnerable on the ground during the larval stage, they have evolved to produce light as an aposematic signaling mechanism to drive away predators, regardless of whether or not they continue to be chemiluminescent in adulthood like the common Eastern firefly (5, 13).

At the end of the larval stage, P. pyralis  will descend into the microhabitats this species tend to build, whether that be slightly above damp soil, on rotting vegetation, or in the small burrows before shedding their exoskeleton and becoming pupae. A few weeks following the pupa stage, the P. pyralis will grow into a fully formed adult that is capable of flight. Upon emergence as an adult, the common Eastern firefly will live for approximately another three weeks to two months, during which time it will continue its light-signaling so as to attract a mate (13).

Among fireflies of the genus Photinus, males will first attract a female’s  attention with their light flashing patterns, but once they reach the females they will be selected based on the size and quality of the “nuptial gifts” they can offer. These nuptial gifts, also known as spermatophores, are a combination of sperm and high levels of protein, hormones, defensive compounds, and other nutrients which the females will subsequently use to feed the eggs should she choose to mate with the male (10). During the adult stage of their lives, Photinus fireflies do not eat, so all activity is fueled by energy that is consumed and subsequently stored during the larval stage; this becomes especially important regarding reproductive activity. Consequently, these nuptial gifts are a big factor in determining which male fireflies females choose to mate with; although it ends up being a high cost to males, those with larger spermatophores tend to see increased reproductive success because they are able to provide females with more nutrients to sustain future offspring (1).

The female common Eastern firefly is polyandrous, that is, they will mate with multiple males over multiple nights albeit they will only mate with a single male in one night. This has been shown to increase female fecundity as well as overall lifespan (1).

Extensive research has been done regarding female P. pyralis preference of larger spermatophores, especially because females will prioritize spermatophore size to pick a mate out of a large group of males whose light patterns she finds attractive. It was found that females were more likely to mate with virgin males who had never mated because their nuptial gift sizes were larger in comparison to males who had mated the previous night. Because common Eastern fireflies do not eat in adulthood, spermatophore size decreases with each mating because males have less and less resources to put in each one after each successive mating. This is still an area of research because females do not have an actual way to determine which spermatophores are larger than others because they are created and transferred during copulation (12).

Biotechnology Research
Since discovering that P. pyralis glows through bioluminescence, much research has been done to both figure out the mechanism by which the fireflies can emit light as well as how that tool can be used advantageously in biotechnological contexts. In 2018, when the Photinus pyralis genome was sequenced, the gene that produced luciferase, the light-producing enzyme, was discovered and scientists were able to clone it (J). Since then, luciferase has become a tool for many different research strategies.

The first use of luciferase was as a reporting marker in many high throughput assays; because it is known that luciferase is activated by oxygen, luciferin, and ATP, the assays were specifically pertaining to reduction-oxidation reactions that occurred in various organisms (K). It is a highly sensitive marker and is very easy and efficient to use, so it is very widely used among scientists. Recent studies have shown that the luciferase protein has been found specifically in peroxisomes of many eukaryotes, the organism responsible for carrying out oxidative reactions and producing hydrogen peroxide as a byproduct that is quickly removed. More research is being done about how this information can be used for further advancement in the field of molecular and cell biology (7).