Nothomyrmecia
Nothomyrmecia | |
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N. macrops workers | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Class: | Insecta |
Order: | Hymenoptera |
Family: | Formicidae |
Subfamily: | Myrmeciinae |
Genus: | Nothomyrmecia Clark, 1934 |
Species: | N. macrops
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Binomial name | |
Nothomyrmecia macrops Clark, 1934
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Nothomyrmecia, also known as the dinosaur ant or dawn ant, is an extremely rare genus of ants consisting of a single species, Nothomyrmecia macrops. These ants live in South Australia, nesting in old-growth mallee woodland and Eucalyptus woodland. The full distribution of Nothomyrmecia has never been assessed, and it is unknown how widespread the species truly is; its potential range may be wider if it does favour old-growth mallee woodland. Possible threats to its survival include habitat destruction and climate change. Nothomyrmecia is most active when it is cold because workers encounter fewer competitors and predators such as Camponotus and Iridomyrmex, and it also increases hunting success. Thus, the increase of temperature may prevent them from foraging and very few areas would be suitable for the ant to live in. As a result, the IUCN lists the ant as Critically Endangered.
As a medium-sized ant, Nothomyrmecia measures 9.7–11 mm (0.38–0.43 in). Workers are monomorphic, showing little morphological differentiation among one another. Mature colonies are very small, with only 50 to 100 individuals in each nest. Workers are strictly nocturnal and are solitary foragers, collecting arthropod prey and sweet substances such as honeydew from scale insects and other Hemiptera. They rely on their vision to navigate and there is no evidence to suggest that the species use chemicals to communicate when foraging, but they do use chemical alarm signals. A queen ant will mate with one or more males and, during colony foundation, she will hunt for food until the brood have fully developed. Queens are univoltine (they produce just one generation of ants each year). Two queens may establish a colony together, but only one will remain once the first generation of workers has been reared.
Nothomyrmecia was first
Description
Nothomyrmecia is a medium-sized ant measuring 9.7–11 mm (0.38–0.43 in) in length. Workers are
A long and retractable stinger is present at the rear of the abdomen. It has been described as "prominent and effective" and is capable of inflicting a painful sting to humans.[2][4] A 'sting bulb gland' is also present in Nothomyrmecia; this is a small exocrine gland of unknown function, first discovered and named in 1990. It is situated in the basal part of the insect's sting, and is located between the two ducts of the venom gland and the Dufour's gland.[8] Despite its many plesiomorphic features, the sting apparatus of Nothomyrmecia is considered less primitive than those found in other ants such as Stigmatomma pallipes.[9] It is the only known species of ant that contains both a sting and a 'waist' (i.e. it has no postpetiole between the first and second gastral segments).[10]
Queens look similar to workers, but several morphological features distinguish the two castes from each other. The queen's body is usually larger.
In all castes, these ants have six maxillary
The eggs of Nothomyrmecia are similar to those of Myrmecia, being subspherical and non-adhesive. The larvae bear a primitive body structure with no specialised
In general, the body structure of all Nothomyrmecia castes demonstrates the primitive nature of the species.
The feature of non-functional, vestigial wings may have evolved in this species relatively recently, as wings might otherwise have long-since disappeared completely had they no function for dispersal. Wing-reduction could somehow relate to population structure or some other specialised ecological pressure. Equally, wing-reduction might be a feature that only forms in drought-stressed colonies, as has been observed in several Monomorium ant species found throughout semi-arid regions of Australia. As yet, scientists do not fully understand how the feature of non-functional, vestigial wings arose in Nothomyrmecia macrops.[2]
Taxonomy
Discovery
The first collection of Nothomyrmecia was made in December 1931 by amateur entomologist, Amy Crocker,[a] whose colleagues had collected a range of insect samples for her during a field excursion, including specimens of two worker ants, reportedly near the Russell Range, inland from Israelite Bay in Western Australia.[2][4] Crocker then passed the ants to Australian entomologist John S. Clark. Recognised shortly afterwards as a new species, these specimens became the syntypes.[4] Entomologist Robert W. Taylor subsequently expressed doubt about the accuracy of recording of the original discovery site, stating the specimens were probably collected from the western end of the Great Australian Bight, south from Balladonia.[2] The discovery of Nothomyrmecia and the appearance of its unique body structure led scientists in 1951 to initiate a series of searches to find the ant in Western Australia.[6] Over three decades, teams of Australian and American collectors failed to re-find it; entomologists such as E. O. Wilson and William Brown, Jr., made attempts to search for it, but neither was successful.[14] Then, on 22 October 1977, Taylor and his party of entomologists from Canberra serendipitously discovered a solitary worker ant at Poochera, South Australia, southeast of Ceduna, some 1,300 km (810 mi) from the reported site of the 1931 discovery.[2][15] In 2012, a report discussing the possible presence of Nothomyrmecia in Western Australia did not confirm any sighting of the ant between Balladonia and the Western Australian coastal regions.[16] After 46 years of searching for it, entomologists have dubbed the ant the 'Holy Grail' of myrmecology.[17][18]
Naming
In 1934 entomologist John S. Clark published a formal description of Nothomyrmecia macrops as a new species and within a completely new genus and tribe (Nothomyrmecii) of the Ponerinae.[4] He did so because the two specimens (which then became the syntypes) bore no resemblance to any ant species he knew of, but they did share similar morphological characteristics with the extinct genus Prionomyrmex. Clark notes that the head and mandibles of Nothomyrmecia and Prionomyrmex are somewhat similar, but the two can be distinguished by the appearance of the node (a segment between the mesosoma and gaster).[4] In 1951, Clark proposed the new ant subfamily Nothomyrmeciinae for his Nothomyrmecia, based on morphological differences with other ponerine ants.[19] This proposal was rejected by American entomologist William Brown Jr., who placed it in the subfamily Myrmeciinae with Myrmecia and Prionomyrmex, under the tribe Nothomyrmeciini.[20] Its distant relationship with extant ants was confirmed after its rediscovery, and its placement within the Formicidae was accepted by most scientists until the late 1980s.[2][21] The single waist node led scientists to believe that Nothomyrmecia should be separate from Myrmecia and retained Clark's original proposal. This proposal would place the ant into its own subfamily, despite many familiar morphological characteristics between the two genera. This separation from Myrmecia was retained until 2000.[21][22][23][24]
In 2000, entomologist Cesare Baroni Urbani described a new Baltic fossil Prionomyrmex species (P. janzeni). After examining specimens of Nothomyrmecia, Baroni Urbani stated that his new species and N. macrops were so morphologically similar that they belonged to the same genus. He proposed that the name Prionomyrmex should replace the name Nothomyrmecia (which would then be just a synonym), and also that the subfamily Nothomyrmeciinae should be called Prionomyrmeciinae.[24]
In 2003, Russian palaeoentomologists G. M. Dlussky and E. B. Perfilieva separated Nothomyrmecia from Prionomyrmex on the basis of the fusion of an abdominal segment.[25] In the same year, American entomologists P. S. Ward and S. G. Brady reached the same conclusion as Dlussky and Perfilieva and provided strong support for the monophyly of Prionomyrmex. Ward and Brady also transferred both taxa as distinct genera in the older subfamily Myrmeciinae under the tribe Prionomyrmecini.[25][26] In 2005 and 2008, Baroni Urbani suggested further evidence in favour of his former interpretation as opposed to Ward and Brady's.[27][28] This view is not supported in subsequent relevant papers, which continue to use the classification of Ward and Brady, rejecting that of Baroni Urbani.[29][30][31][32]
The ant is commonly known as the dinosaur ant, dawn ant, or living fossil ant because of its plesiomorphic body structure.[10][30][33] The generic name Nothomyrmecia means "false bulldog ant".[10] Its specific epithet, macrops ("big eyes"), is derived from the Greek words makros, meaning "long", or "large", and ops, meaning "eyes".[10][34][35]
Genetics and phylogeny
Studies show that all hymenopteran insects that have a diploid (2n) chromosome count above 52 are themselves all ants; Nothomyrmecia and another Ponerinae ant, Platythyrea tricuspidata, share the highest number of chromosomes within all the Hymenoptera, having a diploid chromosome number of 92–94.[2][36]
Genetic evidence suggests that the age of the
Myrmeciinae |
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Distribution and habitat
Nothomyrmecia is present in the cool regions of South Australia within mallee woodland and especially old-growth areas populated with various Eucalyptus species, including Eucalyptus brachycalyx, E. gracilis and E. oleosa.[40] It is possible that it also occurs in Western Australia, from where it was first collected.[40][41] The full distribution of Nothomyrmecia has never been assessed, and it is unknown how widespread it really is. If it does favour old-growth mallee woodland, it could have the potential for a wider range than is currently known from surveys and museum specimens. In 1998, Nothomyrmecia colonies were located in 18 areas along the Eyre Peninsula by a team of entomologists, a stretch of 400 km (250 mi).[40][42]
Nests are found in degraded limestone soil with Callitris trees present.[41][43] Colony construction only occurs when the soil is moist.[2] Nest entrance holes are difficult to detect as they are only 4–6 mm (0.16–0.24 in) in width, and are located under shallow leaf litter with no mounds or soil deposits present; guards are regularly seen. A single gallery, 4–5 mm (0.16–0.20 in) in diameter, forms inside a Nothomyrmecia colony. This gallery descends steeply into the ground towards a somewhat elliptical and horizontal chamber that is 3–5 cm (1.2–2.0 in) in diameter and 5–10 mm (0.20–0.39 in) in height. This chamber is typically 18 to 43 cm (7.1 to 16.9 in) below the soil's surface.[2]
Behaviour and ecology
Foraging, diet and predators
Workers are nectarivores and can be found foraging on top of Eucalyptus trees, where they search for food and prey for the larvae.[44][45] Workers are known to consume hemolymph from the insects they capture, and a queen in a captive colony was observed consuming a fly.[2][5] Captured prey items are given to larvae, which are carnivorous.[2] The workers search for prey in piles of leaves, killing small arthropods including Drosophila flies, microlepidopterans and spiderlings. Prey items are usually less than 4 mm (0.2 in) in size, and workers grab them using their mandibles and forelegs, then kill them with their sting.[22][46] Workers also feed on sweet substances such as honeydew secreted by scale insects and other Hemiptera; one worker alone may feed on these sources for 30 minutes.[2][47][48] Pupae may be given to the larvae if a colony has a shortage of food. Workers are able to lay unfertilised eggs specifically to feed the larvae; these are known as trophic eggs. Sometimes the adults, including the queen and other sexually active ants, consume these eggs. Workers transfer food via Trophallaxis to other nestmates, including winged adults and larvae; the anal droplets are exuded by the larvae, which are taken up by the workers.[2]
Age caste polyethism does not occur in Nothomyrmecia, where the younger workers act as nurses and tend to the brood and the older workers go out and forage. The only ant known other than Nothomyrmecia which does not exhibit age caste polyethism is Stigmatomma pallipes.[5] Workers are strictly nocturnal, and only emerge from their nests on cold nights.[5][42] They are most active at temperatures of 5–10 °C (41–50 °F), and are much more difficult to locate on warmer nights. Workers are possibly most active when it is cold because at these times they encounter fewer and less aggressive competitors, including other more dominant diurnal ant species that are sometimes found foraging during warm nights. Cold temperatures may also hamper the escape of prey items, so increasing the ants' hunting success.[46] Unless a forager has captured prey, workers stay on trees for the remainder of the night until dawn, possibly relying on sunlight to navigate back to their nest.[46] There is no evidence that they use chemical trails when foraging; instead, workers rely on visual cues to navigate around. Chemical markers may play an important role in recognising nest entrances. The ants are solitary foragers.[46] Waste material, such as dead nestmates, cocoon shells, and food remnants, are disposed of far away from the nest.[2]
Workers from different Nothomyrmecia colonies are not antagonistic towards one another, so they can forage together on a single tree, and they attack if an outsider tries to enter an underground colony.[46] Ants such as Camponotus and Iridomyrmex may pose a threat to foragers or to a colony if they try to enter; foraging workers that encounter Iridomyrmex ants are vigorously attacked and killed. Nothomyrmecia workers counter this by secreting alarm pheromones from the mandibular gland and Dufour's gland.[33][46] Foraging workers also engage in alternative methods to protect themselves from predators. Adopting a posture by opening the jaws in a threatening stance or deliberately falling onto the ground and remaining motionless until the threat subsides are two known methods. With that said, Nothomyrmecia is a timid and shy species that retreats if exposed.[2]
Life cycle and reproduction
Eggs are not seen in nests from April to September. They are laid by late December and develop into adults by mid-February; pupation does not occur until March. Nothomyrmecia is univoltine, meaning that the queen produces a single generation of eggs per season, and it sometimes may take as many as 12 months for an egg to develop into an adult. Adults are defined as either juveniles or post-juveniles: juveniles are too young (perhaps several months old) to have experienced overwintering whereas post-juveniles have. The pupae generally overwinter and begin to hatch by the time a new generation of eggs is laid.[5] Workers are capable of laying reproductive eggs; it is not known if these develop into males, females or both.[54] This uncertainty results from the suggestion that, because some colonies have been shown to have high levels of genetic diversity, worker ants could be inseminated by males and act as supplementary reproductives.[46] Eggs are scattered among the nest, whereas the larvae and pupae are set apart from each other in groups. The larvae are capable of crawling around the nest. When the larvae are ready to spin their cocoons, they swell up and are later buried by workers in the ground to allow cocoon formation. Small non-aggressive workers that act as nurses provide assistance for newborns to hatch from their cocoons. At maturity, a nest may only contain 50 to 100 adults.[2][44][55] In some nests, colony founding can occur within a colony itself: when a queen dies, the colony may be taken over by one of her daughters, or it may adopt a newly mated queen, restricting reproduction among workers; this method of founding extends the lifespan of the colony almost indefinitely.[56][57]
Relationship with humans
Conservation
Before its rediscovery in 1977, entomologists feared that Nothomyrmecia had already become extinct.[14] The ant was listed as a protected species under the Western Australian Wildlife Conservation Act 1950.[40] In 1996, the International Union for Conservation of Nature listed Nothomyrmecia as Critically Endangered, stating that only a few small colonies were known.[1] The Threatened Species Scientific Committee states that the species is ineligible for listing under the Environment Protection and Biodiversity Conservation Act 1999. This is because there is insufficient evidence to demonstrate that populations are declining. Colonies are also naturally depauperate (lacking in numbers of ants), and their distribution is potentially quite extensive across southern Australia, due to the ants' preference for old-growth mallee woodland.[40] With 18 sites known for this species, and the potential for many more being discovered, there seems little immediate possibility of extinction.[40][58] With this said, it is unknown how widespread the species actually is, and scientists are not yet clear what, if any, threats affect it.[40]
Suspected
Conservationists suggest that conducting surveys, maintaining known populations through habitat protection and fighting climate change may ensure the survival of Nothomyrmecia.
Significance
Nothomyrmecia macrops is widely regarded as the most plesiomorphic living ant and, as such, has aroused considerable interest among the entomological community.[3][17] Following its rediscovery it was the subject of a prolonged and rigorous series of studies involving Australian, American and European ant specialists and it soon became one of the most studied ant species on the planet.[15] Nothomyrmecia can be cultured with ease, and could potentially prove a useful subject for research into learning in insects as well as the physiology of nocturnal vision.[3][17] Since its chance discovery at Poochera, the town has become of international interest to myrmecologists, and it is possibly the only town in the world with ant-based tourism. Promoting it as a tourist attraction, Nothomyrmecia has been adopted as the emblem of the Poochera community.[59][60] Pictures of the ant have been stencilled onto the pavements, and a large sculpture of Nothomyrmecia has been erected in the town.[60][61][62]
Notes
- ^ Referred to as Miss. A. E. Baesjou in Clark's article.
References
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- ^ a b Dlussky, G.M.; Perfilieva, K.S. (2003). "Paleogene ants of the genus Archimyrmex Cockerell, 1923 (Hymenoptera, Formicidae, Myrmeciinae)" (PDF). Paleontological Journal. 37 (1): 39–47.
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Cited literature
- Hölldobler, B.; Wilson, E.O. (1990). ISBN 978-0-674-04075-5.
External links
- Media related to Nothomyrmecia macrops at Wikimedia Commons
- Data related to Nothomyrmecia macrops at Wikispecies
- Nothomyrmecia at Arkive.org