''Motyxia'' is a genus of
cyanide-producing millipede
Millipedes (originating from the Latin , "thousand", and , "foot") are a group of arthropods that are characterised by having two pairs of jointed legs on most body segments; they are known scientifically as the class Diplopoda, the name derive ...
s (collectively known as Sierra luminous millipedes or motyxias
[) that are endemic to the southern ]Sierra Nevada
The Sierra Nevada ( ) is a mountain range in the Western United States, between the Central Valley of California and the Great Basin. The vast majority of the range lies in the state of California, although the Carson Range spur lies primari ...
, Tehachapi, and Santa Monica
Santa Monica (; Spanish language, Spanish: ''Santa Mónica'') is a city in Los Angeles County, California, Los Angeles County, situated along Santa Monica Bay on California's South Coast (California), South Coast. Santa Monica's 2020 United Sta ...
mountain ranges of California. Motyxias are blind and produce the poison
A poison is any chemical substance that is harmful or lethal to living organisms. The term is used in a wide range of scientific fields and industries, where it is often specifically defined. It may also be applied colloquially or figurati ...
cyanide
In chemistry, cyanide () is an inorganic chemical compound that contains a functional group. This group, known as the cyano group, consists of a carbon atom triple-bonded to a nitrogen atom.
Ionic cyanides contain the cyanide anion . This a ...
, like all members of the Polydesmida
Polydesmida (from the Greek ''poly'' "many" and ''desmos'' "bond") is the largest order of millipedes, with more than 5,000 species, including all the millipedes reported to produce hydrogen cyanide (HCN). This order is also the most diverse of ...
. All species have the ability to glow brightly: some of the few known instances of bioluminescence
Bioluminescence is the emission of light during a chemiluminescence reaction by living organisms. Bioluminescence occurs in multifarious organisms ranging from marine vertebrates and invertebrates, as well as in some Fungus, fungi, microorgani ...
in millipedes.
Description
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 polydesmida
Polydesmida (from the Greek ''poly'' "many" and ''desmos'' "bond") is the largest order of millipedes, with more than 5,000 species, including all the millipedes reported to produce hydrogen cyanide (HCN). This order is also the most diverse of ...
ns ("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.[ 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
Fluorescence is one of two kinds of photoluminescence, the emission of light by a substance that has absorbed light or other electromagnetic radiation. When exposed to ultraviolet radiation, many substances will glow (fluoresce) with color ...
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
Bioluminescence is the emission of light during a chemiluminescence reaction by living organisms. Bioluminescence occurs in multifarious organisms ranging from marine vertebrates and invertebrates, as well as in some fungi, microorganisms inc ...
: emitting light of their own production.[
]
Bioluminescence
There are 11 species of ''Motyxia''.[ They are some of the few known bioluminescent species of millipedes, a class of about 12,000 known species.][ ''Motyxia sequoiae'' glows the brightest and ''Motyxia pior'' the dimmest.][ Light is emitted from the exoskeleton of the millipede continuously, with peak wavelength of 495 nm (the light intensifies when the millipede is handled).][ 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.][ The light originates by way of a photoprotein, which differs from the photogenic molecule ]luciferase
Luciferase is a generic term for the class of oxidative enzymes that produce bioluminescence, and is usually distinguished from a photoprotein. The name was first used by Raphaël Dubois who invented the words ''luciferin'' and ''luciferase'' ...
in firefly beetles.[
''Motyxias photoprotein contains a ]porphyrin
Porphyrins ( ) are heterocyclic, macrocyclic, organic compounds, composed of four modified pyrrole subunits interconnected at their α carbon atoms via methine bridges (). In vertebrates, an essential member of the porphyrin group is heme, w ...
and is about 104 kDa
The dalton or unified atomic mass unit (symbols: Da or u, respectively) is a unit of mass defined as of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at rest. It is a non-SI unit accepted f ...
in size.[ 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
Rhinocricidae is a family of millipedes, that occurs disjunctly in Malesia and neighbouring parts of Australasia and in the Neotropics
The Neotropical realm is one of the eight biogeographic realms constituting Earth's land surface. Physic ...
), both in the order Spirobolida
Spirobolida is an Order (biology), order of "round-backed" millipedes containing approximately 500 species in 12 family (biology), families. Its members are distinguished by the presence of a "pronounced Suture (anatomy), suture that runs "verti ...
. 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.
Theories for Bioluminescence Functionality
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.”
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.
Motyxia bistipita
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''.
''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.
Ecology and behavior
Motyxias occur in live oak
Live oak or evergreen oak is any of a number of oaks in several different sections of the genus ''Quercus'' that share the characteristic of evergreen foliage. These oaks are generally not more closely related to each other than they are to o ...
and giant sequoia
''Sequoiadendron giganteum'' (also known as the giant sequoia, giant redwood, Sierra redwood or Wellingtonia) is a species of coniferous tree, classified in the family Cupressaceae in the subfamily Sequoioideae. Giant sequoia specimens are the la ...
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, geophilid centipedes, and larval phengodid beetles.[
]
Life cycle
The life cycle
Life cycle, life-cycle, or lifecycle may refer to:
Science and academia
*Biological life cycle, the sequence of life stages that an organism undergoes from conception to reproduction
*Life-cycle hypothesis, in economics
*Erikson's stages of psy ...
of ''M. sequoiae'' was studied in detail in the early 1950s.[ 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
In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is a process by which an animal casts off parts of its body to serve some beneficial purpose, either at ...
, during which the animals construct a protective spherical cocoon or molt chamber out of soil. Larvae go through seven developmental stages (instar
An instar (, from the Latin '' īnstar'' 'form, likeness') is a developmental stage of arthropods, such as insects, which occurs between each moult (''ecdysis'') until sexual maturity is reached. Arthropods must shed the exoskeleton in order to ...
s) before reaching adulthood. In males, the single pair of reproductive structures (gonopods
Gonopods are specialized appendages of various arthropods used in reproduction or egg-laying. In males, they facilitate the transfer of sperm from male to female during mating, and thus are a type of intromittent organ. In crustaceans and millipe ...
) 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.[
]
Distribution
''Motyxia'' species occur in an approximate 280 km (175 mi) vertical range across three counties in California: Los Angeles
Los Angeles, often referred to by its initials L.A., is the List of municipalities in California, most populous city in the U.S. state of California, and the commercial, Financial District, Los Angeles, financial, and Culture of Los Angeles, ...
, Kern
Kern or KERN may refer to:
People
* Kern (surname), includes a list of people with the name
* Kern (soldier), a light infantry unit in Medieval Irish armies
Places
* Kern, Alaska, a ghost town in Alaska
* Kern, Austria, see Sankt Marienkir ...
and Tulare counties.[ 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
Sequoia National Park is a List of national parks of the United States, national park of the United States in the southern Sierra Nevada (U.S.), Sierra Nevada east of Visalia, California. The park was established on September 25, 1890, and toda ...
. 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''.[
]
Species
List of Species
Classification and evolution
The speciation
Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within ...
of ''Motyxia'' is believed to have been driven by geological events and a drying climate following the most recent Pleistocene glaciation
The Quaternary glaciation, also known as the Pleistocene glaciation, is an alternating series of glacial and interglacial periods during the Quaternary period that began 2.58 Ma (million years ago) and is ongoing. Although geologists describe ...
, 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.[
''Motyxia'' is a member of the family ]Xystodesmidae
Xystodesmidae is a family of millipedes in the suborder Leptodesmidea within the order Polydesmida (the "flat-backed" or "keeled" millipedes). The family Xystodesmidae was created by the American biologist Orator F. Cook in 1895 and named after ...
, a group of large and colorful millipedes, and ''M. monica'' is the southernmost species of Xystodesmidae in western North America.[ Within Xystodesmidae, ''Motyxia'' is placed in the ]tribe
The term tribe is used in many different contexts to refer to a category of human social group. The predominant worldwide use of the term in English is in the discipline of anthropology. The definition is contested, in part due to conflict ...
Xystocheirini along with the genera '' Anombrocheir'', '' Parcipromus'', '' Wamokia'', and '' Xystocheir'', all of which are native to California.
Future Studies
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.
Notes
References
Further reading
*
External links
Glowing Millipedes: National Public Radio, Science Friday
* ttp://www.apheloria.org/Paul_Marek/Motyxia.html Evolution of bioluminescence in millipedes: apheloria.org
{{Taxonbar, from=Q3325373
Polydesmida
Millipedes of North America
Bioluminescent millipedes
Endemic fauna of California
Fauna of the Sierra Nevada (United States)
Millipede genera