Motyxia | |
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Motyxia sequoiae (Loomis & Davenport, 1951) photographed in its own light. | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Subphylum: | Myriapoda |
Class: | Diplopoda |
Order: | Polydesmida |
Family: | Xystodesmidae |
Tribe: | Xystocheirini |
Genus: | Motyxia Chamberlin, 1941 |
Type species | |
Motyxia kerna Chamberlin, 1941 | |
Species | |
M. alia Contents | |
Synonyms | |
AmplocheirChamberlin, 1949 |
Motyxia is a genus of cyanide-producing millipedes (collectively known as Sierra luminous millipedes or motyxias [1] ) that are endemic to the southern Sierra Nevada, Tehachapi, and Santa Monica mountain ranges of California. Motyxias are blind and produce the poison cyanide, like all members of the Polydesmida. All species have the ability to glow brightly: some of the few known instances of bioluminescence in millipedes.
Adult Motyxia reach 3 to 4 cm in length, 4.5 to 8 mm wide, with 20 body segments, excluding the head. Females are slightly larger than males. Like other polydesmidans ("flat-backed" millipedes) they lack eyes and have prominent paranota (lateral keels). They are typically tan to orange-pink in color (except M. pior), with a dark mid-dorsal line. M. pior is the most variable in color, and ranges from dark gray to greenish-yellow to bright orange. They lack bumps on the metatergites (the dorsal plates possessing paranota), giving a somewhat smooth appearance. [2] The anterior 2–3 diplosegments are oriented cephalically (towards the head), a trait most distinct in M. sequoiae, nearly indistinct in Motyxia porrecta. They are fluorescent under black light (millipedes in the tribe Xystocheirini display some of the brightest fluorescence of the U.S. Xystodesmidae species). Most uniquely they are bioluminescent: emitting light of their own production. [1]
There are 11 species of Motyxia. [3] They are some of the few known bioluminescent species of millipedes, a class of about 12,000 known species. [4] Motyxia sequoiae glows the brightest and Motyxia pior the dimmest. [5] Light is emitted from the exoskeleton of the millipede continuously, with peak wavelength of 495 nm (the light intensifies when the millipede is handled). [6] Emission of light is uniform across the exoskeleton, and all the appendages (legs, antennae) and body rings emit light. The internal organs and viscera do not emit light. Luminescence is generated by a biochemical process in the millipede's exoskeleton. [6] The light originates by way of a photoprotein, which differs from the photogenic molecule luciferase in firefly beetles. [7]
Motyxia's photoprotein contains a porphyrin and is about 104 kDa in size. [7] [8] However, the structure of the luminescent photoprotein remains uncertain, and its homology to molecules of closely related arthropods is unknown.
Besides Motyxia, the only known bioluminecscent millipedes are Paraspirobolus lucifugus (Spirobolellidae), from Japan and Taiwan, and Salpidobolus (Rhinocricidae), both in the order Spirobolida. [9] Another luminescent species of dubious existence from North America has been claimed, but it has not been found since the 1890s and the luminescence attributed to it is believed to have been larval phengodid beetles, also known as glowworms. [1]
Scientists familiar with Motyxia were at odds over the function of bioluminescence in Motyxia and various studies and theories had been proposed.
One study found Motyxia that glowed brighter also tended to have larger cyanide glands and were thus more toxic to predators. While this implicates Motyxia's bioluminescence as an evolution for protection from predators, this study also notes that higher elevation millipedes glowed brighter. This finding led to the discovery that the more faint glow of the low-elevation millipedes was an older trait than the brighter glow of the high-elevation millipedes. Ultimately, the scientists of this study concluded that bioluminescence “may have initially evolved to cope with metabolic stress triggered by a hot, dry environment and was repurposed as a warning signal by species colonizing high-elevation habitats with greater predation risk.” [10]
Another study provides further evidence for Motyxia's bioluminescence as a predator-deterrent. Researchers from the University of Arizona and other institutions collected 164 M. sequoiae from the Giant Sequoia National Monument and painted half to conceal their bioluminescence. Additionally, 300 clay millipedes were created, half with luminescent pigment. These specimens were placed randomly in a line overnight, with live ones tethered to the ground. In the morning, about one-third of the millipedes were attacked, primarily by southern grasshopper mice. Interestingly, luminescent millipedes experienced less than half the predation rate of their non-luminescent counterparts, hinting at a potential correlation between luminescence and reduced predation. [11]
The discovery of the Motyxia bistipita after nearly 50 years revealed new characteristics about the species and genus. In 1967, two small millipedes were discovered in San Luis Obispo, and were coined as a new species, Xystocheir bistipita. For almost 50 years, these two millipedes were the only sightings of the species, until they were rediscovered in 2013 in San Luis Obispo once again. The rediscovered specimens were brought to a lab and examined, where it was discovered that the species was bioluminescent. With this new piece of information, the Xystocheir bistipita was found to have a closer phylogenetic relationship with the Motyxia species and was renamed Motyxia bistipita. [12]
M. bistipita lives in low elevations of the Sierra Nevada mountains in California, in a hotter, drier climate than other Motyxia. The glow is believed to be a response to heat; the bioluminescent proteins help neutralize the body's byproducts caused by heat. The bioluminescence later evolved as a warning signal to predators that the body contained cyanide. [13] [12]
Motyxias occur in live oak and giant sequoia forests, and notably also in meadows. The presence of xystodesmid millipedes in meadows is atypical for the family. Most species are observed under canopies of broad-leaf deciduous forests. All Motyxia species are exclusively nocturnal. During the day, individuals are burrowed beneath the soil. At night, they emerge (by an unknown mechanism not related to light since they're blind) and feed on decaying vegetation. Individuals of the species M. sequoiae have been observed climbing on tree trunks, possibly consuming algae and lichens adhering to the bark.
Natural predators of motyxias include rodents, [5] geophilid centipedes, and larval phengodid beetles. [1]
The life cycle of M. sequoiae was studied in detail in the early 1950s. [2] Eggs are round, about 0.7mm in diameter, and are laid in masses of 70–160 eggs. After about two weeks the larvae hatch with seven body segments and three pairs of legs, and measure about 1.7mm long. Juveniles exhibit bioluminescence as early as hatching. Additional legs and body segments develop with each molt, during which the animals construct a protective spherical cocoon or molt chamber out of soil. Larvae go through seven developmental stages (instars) before reaching adulthood. In males, the single pair of reproductive structures (gonopods) begin to develop in the 4th instar, before which male and females have equal numbers of walking legs, and after which males have one fewer pair. [2]
Motyxia species occur in an approximate 280 km (175 mi) vertical range across three counties in California: Los Angeles, Kern and Tulare counties. [1] Species predominately occur in the Santa Monica, Tehachapi, and southern Sierra Nevada Mountains. The northernmost species is M. pior, which occurs as far north as Crystal Cave in Sequoia National Park. The southernmost species is M. monica, which has a disjunct distribution: a population in southern Kern County, and an isolated one in the Santa Monica Mountains near the city of Los Angeles. The range of the eight species largely do not overlap, although M. tularea overlaps with M. kerna and M. sequoiae. [14]
List of Species [15]
Species | Taxon author | Geographic range [14] | Notes |
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M. alia | Causey & Tiemann, 1969 | "Central Tulare Co., valleys of South Fork of Kaweah River, North Fork of Tule River, and Yokohl River." [1] | Originally described as Motyxia sequoia alia. |
M. bistipita | (Shelley, 1996) | Low elevations of the Sierra Nevada mountains in California | Originally described as Xystocheir bistipita |
M. kerna | Chamberlin, 1941 | Southern Tulare Co. to northern Kern Co., | |
M. monica | Chamberlin, 1944 | Kern Co., south of the Kern River, and a disjunct population in the Santa Monica Mountains. | |
M. ollae | Causey & Tiemann, 1969 | "Southern Tulare County, valleys of Deer Creek, Pothole Creek, and Tule River." [1] | Originally described as Motyxia sequoia ollae. |
M. pior | Chamberlin 1941 | Tulare Co., Sequoia National Park | |
M. porrecta | Causey & Tiemann, 1969 | Kern River Valley | |
M. sequoia [a] | (Chamberlin, 1941) | East Fork of the Kaweah River, Tulare Co. | Originally described as Xystocheir sequoia. |
M. sequoiae [a] | (Loomis & Davenport, 1951) | Headwaters of the Tule River (Middle fork), Tulare Co. | Originally described as Luminodesmus sequoiae. |
M. tiemanni | Causey, 1960 | Northern Kern Co. | |
M. tularea | (Chamberlin, 1949) | Central Tulare Co. to extreme northern Kern Co. | Originally described as Xystocheir tularea. Two subspecies: M. t. tularea. and M. t. ollae. |
The speciation of Motyxia is believed to have been driven by geological events and a drying climate following the most recent Pleistocene glaciation, while reproductive isolating mechanisms include rivers which are at their fullest levels in times when adults are most active, and marked differences in rainfall and suitable habitat across mountainous terrain. [1]
Motyxia is a member of the family Xystodesmidae, a group of large and colorful millipedes, and M. monica is the southernmost species of Xystodesmidae in western North America. [1] Within Xystodesmidae, Motyxia is placed in the tribe Xystocheirini along with the genera Anombrocheir , Parcipromus , Wamokia , and Xystocheir , all of which are native to California. [16]
According to Paul E. Marek, one of the most heavily involved researchers of these millipedes, "much about Motyxia remains mysterious." There is still a lot to learn about Motyxia's mating habits, their emergences into the night, and the exact evolutionary reasons for their bioluminescence. [17]
The Lampyridae are a family of elateroid beetles with more than 2,000 described species, many of which are light-emitting. They are soft-bodied beetles commonly called fireflies, lightning bugs, or glowworms for their conspicuous production of light, mainly during twilight, to attract mates. Light production in the Lampyridae is thought to have originated as a warning signal that the larvae were distasteful. This ability to create light was then co-opted as a mating signal and, in a further development, adult female fireflies of the genus Photuris mimic the flash pattern of the Photinus beetle in order to trap their males as prey.
Bioluminescence is the production and emission of light by living organisms. It is a form of chemiluminescence. Bioluminescence occurs widely in marine vertebrates and invertebrates, as well as in some fungi, microorganisms including some bioluminescent bacteria, and terrestrial arthropods such as fireflies. In some animals, the light is bacteriogenic, produced by symbiotic bacteria such as those from the genus Vibrio; in others, it is autogenic, produced by the animals themselves.
Luciferin is a generic term for the light-emitting compound found in organisms that generate bioluminescence. Luciferins typically undergo an enzyme-catalyzed reaction with molecular oxygen. The resulting transformation, which usually involves breaking off a molecular fragment, produces an excited state intermediate that emits light upon decaying to its ground state. The term may refer to molecules that are substrates for both luciferases and photoproteins.
Glowworm or glow-worm is the common name for various groups of insect larvae and adult larviform females that glow through bioluminescence. They include the European common glow-worm and other members of the Lampyridae, but bioluminescence also occurs in the families Elateridae, Phengodidae and Rhagophthalmidae among beetles; as well as members of the genera Arachnocampa, Keroplatus and Orfelia among keroplatid fungus gnats.
Foxfire, also called fairy fire and chimpanzee fire, is the bioluminescence created by some species of fungi present in decaying wood. The bluish-green glow is attributed to a luciferase, an oxidative enzyme, which emits light as it reacts with a luciferin. The phenomenon has been known since ancient times, with its source determined in 1823.
Aequorin is a calcium-activated photoprotein isolated from the hydrozoan Aequorea victoria. Its bioluminescence was studied decades before the protein was isolated from the animal by Osamu Shimomura in 1962. In the animal, the protein occurs together with the green fluorescent protein to produce green light by resonant energy transfer, while aequorin by itself generates blue light.
Luminescent bacteria emit light as the result of a chemical reaction during which chemical energy is converted to light energy. Luminescent bacteria exist as symbiotic organisms carried within a larger organism, such as many deep sea organisms, including the Lantern Fish, the Angler fish, certain jellyfish, certain clams and the Gulper eel. The light is generated by an enzyme-catalyzed chemoluminescence reaction, wherein the pigment luciferin is oxidised by the enzyme luciferase. The expression of genes related to bioluminescence is controlled by an operon called the lux operon.
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A photocyte is a cell that specializes in catalyzing enzymes to produce light (bioluminescence). Photocytes typically occur in select layers of epithelial tissue, functioning singly or in a group, or as part of a larger apparatus. They contain special structures called photocyte granules. These specialized cells are found in a range of multicellular animals including ctenophora, coelenterates (cnidaria), annelids, arthropoda and fishes. Although some fungi are bioluminescent, they do not have such specialized cells.
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Lucihormetica luckae is a species of giant cockroach (Blaberidae) from Ecuador.
Brachoria is a genus of polydesmidan millipedes in the family Xystodesmidae inhabiting the Eastern United States. Also known as the Appalachian mimic millipedes, at least 30 species are known, with highest diversity in the Appalachian Mountains, especially the Cumberland Plateau and Ridge and Valley Province.
Bioluminescent bacteria are light-producing bacteria that are predominantly present in sea water, marine sediments, the surface of decomposing fish and in the gut of marine animals. While not as common, bacterial bioluminescence is also found in terrestrial and freshwater bacteria. These bacteria may be free living or in symbiosis with animals such as the Hawaiian Bobtail squid or terrestrial nematodes. The host organisms provide these bacteria a safe home and sufficient nutrition. In exchange, the hosts use the light produced by the bacteria for camouflage, prey and/or mate attraction. Bioluminescent bacteria have evolved symbiotic relationships with other organisms in which both participants benefit each other equally. Bacteria also use luminescence reaction for quorum sensing, an ability to regulate gene expression in response to bacterial cell density.
Xystocheir is a genus of millipedes in the family Xystodesmidae. The genus is endemic to California in the United States, where it is distributed in the Coast Ranges and the Sierra Nevada.
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