Archey’s frog is almost indistinguishable from the fossilised remains of frogs that lived 150 million years ago, leading to its description as a “living fossil”. One of the world’s most primitive frogs, it has bizarre features such as tail-wagging muscles (despite having no tail to wag) and no eardrums. It therefore does not communicate by sound, but is instead thought to employ scent. The male guards the eggs in moist nests and the tailed froglets that hatch out crawl onto the father’s back where they remain for several weeks whilst they develop. It is primarily threatened by a virulent fungal disease (chytridiomycosis), as well as introduced predators such as rats and mice.
Evolutionary Distinctiveness
Order: Anura
Family: Leiopelmatidae
The prehistoric New Zealand frogs (of the family Leiopelmatidae) are the most ancient and primitive frogs in the world, diverging from all other frog and toad lineages over 200 million years ago in the former southern supercontinent of Gondwana. The ancestor of these species actually colonised New Zealand over 80 million years ago, when it was still part of the Gondwana, and the Leiopelmatidae shares a similar biogeographic distribution to several other ancient plant and animal groups, such as southern beeches, tuatara, and the giant extinct moa. This means New Zealand frogs started to evolve independently as a lineage before the formation of the Atlantic Ocean, over 50 million years before the first bird appeared in the fossil record. They are part of a small suborder of frogs called the “archaeobatrachia” or ancient frogs. The archeobatrachia comprise less than 7% of all of the frogs and toads, including some of the most evolutionarily distinct amphibian species. Each one therefore represents a disproportionately high amount of distinct evolutionay history in today’s biodiversity.The four surviving species of New Zealand frog are found only in New Zealand, and these species are regarded as “living fossils” since they are very similar to frog fossils found in Queensland, Australia from the late Jurassic period around 150 million years ago. Fossil records actually show that New Zealand had seven leiopelmatid frog species just 1000–2000 years ago. The scientific names of the three extinct species are Leiopelma auroraensis, Leiopelma markhami and Leiopelma waitomoensis, which was previously the largest species of New Zealand frog at a total length of 100 mm – over twice the size of the largest New Zealand frog species alive today. These species were considerably larger, squat and toad-like leiopelmatids, which probably walked rather than hopped, and were found both on New Zealand’s North Island (L. markhami and L. waitomesis) and South Island (L. markhami and L. aurorensis). It is likely that all were wiped out by the (presumably accidental) introduction of the Pacific rat (Rattus exulans) by Polynesian settlers less than 1,000 years ago. The surviving species are restricted to the vicinity of North Island – Archey’s New Zealand frog and Hochstetter’s New Zealand frog occur only on the North Island, while the Maud Island frog and Hamilton’s frog are restricted to Maud Island in the Marlborough Sounds and Stephen’s Island in Cook Strait. A primitive feature retained by Leiopelma frogs is their tail-wagging muscles (known scientifically as the caudalipuboischiotibialis muscles), although they no longer have a tail to wag. Other unique or unusual features of these frogs include the presence of elongate pieces of cartilage in the muscles of the abdomen (also called “inscriptional ribs”), round pupils, and an abnormally high number of vertebrae, or back bones – they have 9 presacral vertebrae with atypical concave ends, instead of the eight found in all other living frogs except their closest relatives, the tailed frogs from north-western U.S.A and Canada. Also, they cannot croak like most other species of frog (instead letting out a thin high-pitched squeak) because eardrums and vocal sacs have never developed in this group of frogs. Where aquatic in nature, they also swim differently to all other frogs (apart from the tailed frogs), in that they use alternate leg kicks which cause their heads to move from side to side during swimming in a rather energy inefficient way. It is thought that New Zealand frogs began their terrestrial (or ground dwelling) lifestyle before advanced swimming evolved in frogs. In keeping with their place as four of the world’s most primitive frogs, the way in which the skull remodels during metamorphosis within the egg, where the tadpole changes into a froglet, is said to be intermediate between a salamander and the tailed frogs (which are the next most primitive frogs on earth). Archey’s frog possesses a further unusual trait which it does not share with all the other members of its family. In several populations of this species, females have been found to have 22 pairs of chromosomes (the structures found in the nucleus of a cell that are each composed of a very long, continuous strand of DNA, along which all the genes of the organism are found) plus a unique W-chromosome, which is type of sex determining chromosome similar to that found in birds. Males lack a sex chromosome entirely and only possess the standard 22 pairs of chromosomes. These populations typically have many extra, superfluous chromosomes as well. This additional genetic information does not seem to play any role in the individuals but is apparently genetic “junk”.
Order: Anura
Family: Leiopelmatidae
The prehistoric New Zealand frogs (of the family Leiopelmatidae) are the most ancient and primitive frogs in the world, diverging from all other frog and toad lineages over 200 million years ago in the former southern supercontinent of Gondwana. The ancestor of these species actually colonised New Zealand over 80 million years ago, when it was still part of the Gondwana, and the Leiopelmatidae shares a similar biogeographic distribution to several other ancient plant and animal groups, such as southern beeches, tuatara, and the giant extinct moa. This means New Zealand frogs started to evolve independently as a lineage before the formation of the Atlantic Ocean, over 50 million years before the first bird appeared in the fossil record. They are part of a small suborder of frogs called the “archaeobatrachia” or ancient frogs. The archeobatrachia comprise less than 7% of all of the frogs and toads, including some of the most evolutionarily distinct amphibian species. Each one therefore represents a disproportionately high amount of distinct evolutionay history in today’s biodiversity.The four surviving species of New Zealand frog are found only in New Zealand, and these species are regarded as “living fossils” since they are very similar to frog fossils found in Queensland, Australia from the late Jurassic period around 150 million years ago. Fossil records actually show that New Zealand had seven leiopelmatid frog species just 1000–2000 years ago. The scientific names of the three extinct species are Leiopelma auroraensis, Leiopelma markhami and Leiopelma waitomoensis, which was previously the largest species of New Zealand frog at a total length of 100 mm – over twice the size of the largest New Zealand frog species alive today. These species were considerably larger, squat and toad-like leiopelmatids, which probably walked rather than hopped, and were found both on New Zealand’s North Island (L. markhami and L. waitomesis) and South Island (L. markhami and L. aurorensis). It is likely that all were wiped out by the (presumably accidental) introduction of the Pacific rat (Rattus exulans) by Polynesian settlers less than 1,000 years ago. The surviving species are restricted to the vicinity of North Island – Archey’s New Zealand frog and Hochstetter’s New Zealand frog occur only on the North Island, while the Maud Island frog and Hamilton’s frog are restricted to Maud Island in the Marlborough Sounds and Stephen’s Island in Cook Strait. A primitive feature retained by Leiopelma frogs is their tail-wagging muscles (known scientifically as the caudalipuboischiotibialis muscles), although they no longer have a tail to wag. Other unique or unusual features of these frogs include the presence of elongate pieces of cartilage in the muscles of the abdomen (also called “inscriptional ribs”), round pupils, and an abnormally high number of vertebrae, or back bones – they have 9 presacral vertebrae with atypical concave ends, instead of the eight found in all other living frogs except their closest relatives, the tailed frogs from north-western U.S.A and Canada. Also, they cannot croak like most other species of frog (instead letting out a thin high-pitched squeak) because eardrums and vocal sacs have never developed in this group of frogs. Where aquatic in nature, they also swim differently to all other frogs (apart from the tailed frogs), in that they use alternate leg kicks which cause their heads to move from side to side during swimming in a rather energy inefficient way. It is thought that New Zealand frogs began their terrestrial (or ground dwelling) lifestyle before advanced swimming evolved in frogs. In keeping with their place as four of the world’s most primitive frogs, the way in which the skull remodels during metamorphosis within the egg, where the tadpole changes into a froglet, is said to be intermediate between a salamander and the tailed frogs (which are the next most primitive frogs on earth). Archey’s frog possesses a further unusual trait which it does not share with all the other members of its family. In several populations of this species, females have been found to have 22 pairs of chromosomes (the structures found in the nucleus of a cell that are each composed of a very long, continuous strand of DNA, along which all the genes of the organism are found) plus a unique W-chromosome, which is type of sex determining chromosome similar to that found in birds. Males lack a sex chromosome entirely and only possess the standard 22 pairs of chromosomes. These populations typically have many extra, superfluous chromosomes as well. This additional genetic information does not seem to play any role in the individuals but is apparently genetic “junk”.
Description
Archey’s frog is the smallest species of New Zealand frog, with females measuring about 37 mm snout to rear in total length and males being slightly smaller at 31 mm. The species varies in colour from mainly green (rarely) through combinations of green and brown to mainly brown. Some individuals from the Whareorino part of the species’ range may be quite brightly coloured with pinks and brick reds complementing the background colour. The skin has defensive granular glands, which are concentrated into discrete patches arranged down the back and sides in about six longitudinal rows. These glands are also found on the upper surface of the legs, feet and arms. There is no webbing in the hind toes and no eardrum.
Ecology
This species is terrestrial (or ground dwelling) but may climb several metres into bushes and trees during the night, before returning to their ground-level retreats at dawn. They are chiefly nocturnal (or night-active), spending most of the day hidden under stones or logs away from streams and creeks. The Whareorino Forest population in the King Country (discovered in 1991) may be more arboreal (tree-dwelling) than the Coromandel populations. It occurs in the same areas (also known as occurring “sympatrically”) with another New Zealand frog species called Hotchstetter’s frog (EDGE rank 38).Mating takes place in shallow depressions hidden beneath logs or stones, where it is cool and moist. The male clasps the female around the waist (a behaviour termed “inguinal amplexus”) and fertilises her eggs are they are laid. Egg clusters are later laid in strings and each egg is unpigmented and measures from 8–11 mm in diameter. Reproduction in Archey’s frog is therefore independent of a water body. This species is able to withstand substantial desiccation, and studies have found that frogs dehydrated to 92% of their body weight rehydrated to 99% over four hours when placed on wet foliage. Sometimes Archey’s frogs, particularly the males, occupy the oviposition or egg-laying site for several weeks prior to the laying of eggs, and also guard the eggs until they hatch. Froglets do not reach maturity until at least 3 to 4 years and New Zealand frogs do not go through an external free-living tadpole stage, but instead develop totally within a gelatinous capsule in the egg, with the young hatching as tailed froglets that climb onto the father’s back for protection. Male Archey's frogs carry the infants on their back and care for them for several weeks until metamorphosis is nearly complete, i.e. all adult characteristics (including tail loss and the ability to feed independently) have developed. Such care may keep the young moist, reduce predation and possibly reduce fungal or microbial infections. Archey’s frogs generally become active at night and feed on small insects, worms and other invertebrates. They do not produce a loud breeding call but they do squeak or chirp when annoyed, distressed or engaging in sexual activity. They have no true vocal sacs or eardrums so the dominant frequencies and overtones of call notes depend on resonance frequencies in the head and body of these frogs rather than any vibration frequency of the vocal chords. Their defensive mechanisms include remaining motionless for long periods of time and assuming a stiff-legged stance, rearing up and extending the legs. New Zealand frogs are also known to have poison glands around their heads which may deter attack, at least by local predators. Introduced rats have been found to not consume the head of Archey’s frogs, therefore avoiding ingestion of the areas of the frog containing poison glands. Lastly, Archey's frogs are highly camouflaged and this, combined with their nocturnal habits and lack of vocalisations, makes them extremely hard to locate.
Habitat
This is a terrestrial (ground dwelling) species, occurring mostly at higher altitudes in forested ranges and more open sub-alpine scrub. Archey’s frog occupies a broad range of forest environments and is not closely associated with watery habitats such as lakes, ponds or streams.
Distribution
There are two main concentrations of this North Island New Zealand frog species – one in Coromandel Peninsula and the other in the Whareorino Forest, west of Te Kuiti. Archey’s frogs prefer to live at a relatively high altitude from about 400-1000 metres above sea level.
Population Estimate
Total wild population is currently unknown. Formerly, this species was recorded in the tens of thousands, but declines since 1996 have reduced the numbers throughout their range. Night-time search studies of Whareorino Forest published in 2003 have revealed the density of Archey’s frog to be 0.28 frogs per m2.
Population Trend
Archey’s frog is thought to be in decline by the IUCN Red List of Threatened Species. The decline was first noted in 1996 when one study of a population on the Tapu Ridge indicated a population decline of 88% (433 frogs down to 53 frogs) over the period 1996-2002.
Status
Archey’s frog is listed as Critically Endangered in the IUCN Red List of Threatened Species because of a drastic population decline, estimated to be more than 80% over the last ten years, inferred from the apparent disappearance of most of the population, probably due to the disease chytridiomycosis caused by the chytrid fungus (Batrachochytrium dendrobatidis).
Total wild population is currently unknown. Formerly, this species was recorded in the tens of thousands, but declines since 1996 have reduced the numbers throughout their range. Night-time search studies of Whareorino Forest published in 2003 have revealed the density of Archey’s frog to be 0.28 frogs per m2.
Population Trend
Archey’s frog is thought to be in decline by the IUCN Red List of Threatened Species. The decline was first noted in 1996 when one study of a population on the Tapu Ridge indicated a population decline of 88% (433 frogs down to 53 frogs) over the period 1996-2002.
Status
Archey’s frog is listed as Critically Endangered in the IUCN Red List of Threatened Species because of a drastic population decline, estimated to be more than 80% over the last ten years, inferred from the apparent disappearance of most of the population, probably due to the disease chytridiomycosis caused by the chytrid fungus (Batrachochytrium dendrobatidis).
Threats
Systematic field surveys carried out since the 1970s indicate that a marked decline of Archey's frog occurred in the central Coromandel Range over 1996-98. On Tapu Ridge this species was formerly abundant but had become scarce by December 1996. At Tokatea Saddle, 30 km north, no equivalent decline was detected in February 1997, but Archey’s frog was very scarce by November 1998. It is currently unknown exactly why Archey’s frog has declined so precipitously across much of its range. The most likely explanation appears to be disease of some kind, in particular chytridiomycosis caused by the chytrid fungus (Batrachochytrium dendrobatidis) that has been reported as a frog pathogen in many areas of the world. Chytrid fungus infection was first identified in this species in September 2001 from a specimen collected June 2001 at Te Moehu in the Coromandel Peninsula. Several factors, including the severity and rapidity of the population crash, the geographic spread of the decline (from south to north), and the discovery of frogs with chytridiomycosis, all point to disease being the major cause of the decline of Archey’s frog. Other probable threats to this species include climate change (especially drought - 29 dead individuals were collected in Tokatea Saddle in January 1995 during a drought); disturbance of habitat by researchers; illegal collection of frogs; impact of chemical such as biocides; and other factors that have not yet been identified. The impact of introduced predators such as rats and mice may have also seriously affected wild populations of Archey’s frog. Five dead individuals found in the Whareorino Forest showed signs of rat predation. However, the rats left the head of their victims intact, which strongly suggests that the defensive glands around the head of the frog successfully deterred the predator from finishing their meal. Other anecdotal evidence suggests that indigenous (local non-introduced) predators as varied as the giant kokupu, tuatara and weka may avoid New Zealand frogs, possibly as a result of their poison glands.
Conservation Underway
New Zealand has been protecting its indigenous amphibian species since 1921, when legislation was passed making it an offence to harm or remove frogs from their environment. The New Zealand Department of Conservation (DOC), acting through its Native Frog Recovery Group and Native Frog Recovery Plan, administers the conservation management of Archey’s frog and issues permits for appropriate species research. The DOC employs a frog ecologist who is responsible for the conservation and management plans concerning Archey’s frog populations. They monitor the frog populations, survey for outbreaks of disease, and conduct emergency translocations when necessary. The DOC also has a collaborative programme with Auckland Zoo which has recently established a new facility for captive breeding and maintaining Archey’s frog, established in October 2004 in order to generate back-up populations in the event of some ecological catastrophe wiping out the wild population. This programme has been successful in producing more than 6 clusters of eggs laid in captivity, and a resident veterinary scientist is conducting research here on native frog diseases. Auckland Zoo is also working in collaboration with a scientists from Land Care Research and Otago University on hormone profiling in Archey’s frogs to allow identification of gender, which would be a great asset in captive breeding. The recent declines of Archey’s frog and the positive identification of chytrid fungus has stimulated urgent research and management of the species, including pathology, population monitoring, captive management and molecular research. This involves the DOC and Massey, Otago and Victoria Universities. The Carter Holt Harvey Native Frog Research Centre at Aukland Zoo works with the Department of Conservation to seek a cure for the chytrid fungus currently threatening frogs around the world. Additionally, a research group at the University of Otago is investigating methods of treating chytrid fungus infection, studying how this fungal pathogen spreads from one frog to another in a terrestrial environment, and screening for agents that can be used to kill Batrachochytrium dendrobatidis in the environment.Population monitoring in the wild of New Zealand frogs has been coordinated by Professor Ben Bell at Victoria University, Wellington. This is the longest data set in the world for monitoring a population of frogs, as Professor Bell has been studying the population demographics of Archey’s frogs for the last 40 years. This research is ongoing. Conservation actions in the wild also consist of protecting habitat and removing mammalian predators (such as rats and mice) from frog habitat, or ensuring that they do not gain or increase access to existing frog populations. Further introduced frog species (there are already 3 species of non-native Australian treefrogs established in New Zealand) may out-compete native New Zealand frogs and/or introduce more virulent diseases, so it is also a priority of the DOC to ensure against the accidental introduction of other amphibian species. In 1999, Australian banjo frog Limnodynastes dumerilii tadpoles were reported from the Waitakeres. Several thousand tadpoles for this species were subsequently found and destroyed.
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