New Zealand Frogs (Leiopelmatidae)

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New Zealand frogs

(Leiopelmatidae)

Class Amphibia

Order Anura

Family Leiopelmatidae

Thumbnail description
Medium-small and brown, reddish, or green frogs with broad heads, rounded pupils, and smooth soles of the feet

Size
7.9–2.0 in (20–50 mm)

Number of genera, species
1 genus; 4 species

Habitat
Humid forest, banks of rocks, and streams

Conservation status
Vulnerable: 2 species; Lower Risk/Near Threatened: 1 species

Distribution
New Zealand

Evolution and systematics

Leiopelmatidae is among the most primitive of living frogs. These frogs have skeleton characters otherwise known only in the tailed frogs, family Ascaphidae, and in the most primitive known fossil frogs, which date from the Jurassic. Because of their shared primitive morphologic features, the tailed frogs, genus Ascaphus, on some occasions have been grouped into the same family. All that the frogs in these families share are primitive features, however, and so there is no sound basis for considering them to be closely related. Leiopelmatidae is certainly an ancient group and dates from the time when New Zealand broke off from the rest of the continental landmasses sometime during the Mesozoic era. Within the genus, the species Leiopelma archeyi, L. hamiltoni, and L. pakeka are closely related, to the exclusion of L. hochstetteri. Of three additional subfossils, extinct species from the North Island of New Zealand, L. auroraensis and L. markhami, resemble L. hochstetteri, whereas L. waitomoensis seems to be related to the other extant species. No subfamilies are recognized.

Physical characteristics

These are small frogs, less than 2.0 in (50 mm) in length, with characteristically broad heads and smooth skin on the soles of the feet. They have rounded pupils, no visible eardrum, and little or no webbing between the toes. Parotoid glands (glandular swellings in the skin on the back of the head behind each eye) are present. Mostly, these frogs are various shades of brown, but some individuals have a reddish tint or are green. Skeletally, they have nine presacral vertebrae, of which the third, fourth, and fifth have free ribs; they also have inscriptional (abdominal) ribs between the blocks of muscle in the belly, terminating posteriorly with a broad, flat prepubic bone.

Distribution

The species are known from North Island, Maud Island, Stephens Island, and Great Barrier Island, New Zealand.

Habitat

The frogs inhabit humid native forest except on Stephens Island, where there is no forest remaining and the frogs are restricted to a fog-enshrouded and shrub-covered rock pile at the summit. Leiopelma hochstetteri is usually found alongside forest streams, particularly in rocky stretches of stream near cascades or even waterfalls. The other species are not restricted to standing or flowing bodies of water.

Behavior

Largely nocturnal and cryptic, these frogs forage on the forest floor or along the stream banks. During the day they generally hide underneath rocks or fallen wood or under other debris on the forest floor or by the streamside. When disturbed, all species sit motionless and rely upon their cryptic coloration to avoid detection. If physically molested, however, the frogs squeak, even though they otherwise make no sounds. If they become particularly agitated by a potential predator, the frogs stand high on their four legs, head down and turned in the direction of their persecutor. The frogs swim using alternating kicks of their legs rather than with a synchronous motion of the two legs, as in most other frogs.

Feeding ecology and diet

The diet consists of small invertebrates that are captured by lunges and bites, inasmuch as the frogs do not have protrusible tongues.

Reproductive biology

The New Zealand native frogs do not call and presumably find mates by olfaction. During mating, the male clasps the female around the waist with his arms in inguinal amplexus. The eggs are fertilized externally. All species of Leiopelma lay small clutches of up to two to three dozen unpigmented, yolky eggs. Those of Leiopelma hochstetteri hatch into whitish, free-living tadpoles that tend to remain hidden under stones or other cover in seepages and stream edges. The other species lay terrestrial eggs and have no free-living larvae, passing through complete development within the egg to emerge as tiny frogs. The male parent guards the eggs and, for a time, the newly emerged froglets.

Conservation status

Two of the species of Leiopelma are among the rarest frogs in the world. The IUCN considers Archey's frog to be Lower Risk/Near Threatened and Hamilton's frog (encompassing both L. hamiltoni and L. pakeka) as Vulnerable. All species are protected in New Zealand under the Wildlife Act and may not be disturbed except by permit.

Significance to humans

These frogs are of scientific interest because they are among the most primitive of living frogs, as well as for a peculiar system of chromosomal sex determination in Hochstetter's frog. The North Island populations of this species, uniquely, have a single, female-determining sex chromosome that exists without a homologue. Otherwise, these frogs are unseen by most people, since they are small, cryptic, and nocturnal. To see them, you have to go looking for them, and they may have been almost completely unknown even to the Maori people of New Zealand.

Species accounts

List of Species

Archey's frog
Hamilton's frog
Hochstetter's frog
Maud Island frog

Archey's frog

Leiopelma archeyi

taxonomy

Leiopelma archeyi Turbott, 1942, Tokatea, near Coromandel, New Zealand. Although it was encountered by naturalists as early as 1862 and its behavior was characterized in 1922, this species was not formally described until 1942.

other common names

None known.

physical characteristics

This is the smallest species of Leiopelma: it reaches less than 1.6 in (40 mm) in length in the Coromandel Peninsula, although larger specimens are common in the Waikato district. Females tend to be larger than males, but the sexes are otherwise indistinguishable. This is the most boldly patterned species of Leiopelma, with dark blotches and a dorsolateral glandular ridge elegantly underlined with dark spots. The skin glands are arranged in parallel longitudinal rows down the back. Parotoid glands are present behind each eye. Archey's frogs vary considerably in color. Some individuals are green, others may be largely red, and still others are an assortment of shades of tan or brown. There is a pale patch on the snout. The upper part of the iris is bright gold. The hind limbs are fairly short, and the feet are not webbed.

distribution

The range is restricted to North Island, New Zealand, where it occurs at elevations above 1,300 ft (400 m) in the Coromandel Peninsula and in the western Waikato district.

habitat

This species inhabits cool, moist, native forest or mist-enshrouded mountain ridges where there are adequate rocks, logs, or other fallen debris as daytime cover.

behavior

Largely terrestrial and nocturnal, the frogs hide during the day and forage at night, sometimes climbing to moderate heights in tree ferns and other moisture-holding plants. They squeak if disturbed, but they tend not to try to escape as readily as Hochstetter's frogs. Predators are not known.

feeding ecology and diet

The diet consists of small insects and other invertebrates.

reproductive biology

Up to a dozen large, yolk-filled eggs are laid under cover in cool, damp terrestrial sites. The larvae undergo development within the egg capsule and hatch when fully metamorphosed. The male attends the eggs and froglets, which clamber onto his back and legs.

conservation status

This species is designated Lower Risk/Near Threatened according to the IUCN and is protected under New Zealand's Wildlife Act.

significance to humans

None known.

Hamilton's frog

Leiopelma hamiltoni

taxonomy

Leiopelma hamiltoni McCullough, 1919, Stephens Island, New Zealand.

other common names

German: Hamilton-Frosch

physical characteristics

This species is virtually indistinguishable from the Maud Island frog, Leiopelma pakeka, but differs by usually being paler. Like the Maud Island frog, it reaches 2.0 in (50 mm) in length; females tend to be larger than males, but the sexes are otherwise identical. Dorsolateral glandular ridges are underlined with dark spots, and parotoid glands are present behind each eye. These frogs generally are pale brown or tan with a pale patch on the snout. The upper part of the iris is bright gold. The hind limbs are fairly short, and the feet are not webbed.

distribution

The species is restricted to a deforested, 6,460 ft² (600 m²) bank of rocks at an elevation of 900 ft (275 m) near the summit of Stephens Island, which is located in the Cook Straight off the northern tip of the South Island of New Zealand.

habitat

The frogs inhabit a bank of rocks, which, though previously bare, lately has been allowed to become overgrown with grass

and shrubs. The interior of the rock pile maintains conditions cool and moist enough to sustain the frogs.

behavior

This nocturnal frog squeaks repeatedly if molested. There is evidence that it may be preyed upon by tuatara (Sphenodon punctatus).

feeding ecology and diet

This frog most certainly eats small insects and other terrestrial arthropods.

reproductive biology

Hamilton's frog lays five to nine terrestrial eggs. The white embryos undergo virtually all their development within the egg and emerge as small frogs, about 0.4 in (11 mm) long. Males attend the eggs and hatchlings, which climb onto its back and legs.

conservation status

This is one the rarest and most localized species of frogs in the world. Its habitat and population status, as well as the whole of Stephens Island, are monitored and patrolled carefully. The frog is ranked Vulnerable by the IUCN (encompassing both Leiopelma hamiltoni and L. pakeka), and it is protected under New Zealand's Wildlife Act.

significance to humans

None known.

Hochstetter's frog

Leiopelma hochstetteri

taxonomy

Leiopelma hochstetteri Fitzinger, 1861, Coromandel, New Zealand.

other common names

None known.

physical characteristics

This is a rather stout, wide-faced frog up to 2.0 in (50 mm) long. Females are larger than males, but males have decidedly more robust forearms. The feet are webbed. The skin of the back is rugose, with many scattered glandular tubercules but with neither distinct parotoid glands behind the eyes nor dorsolateral glandular ridges. A small tubercle adorns the top of each eyelid. The belly skin is smooth and pink. Hochstetter's frogs may be dark olive brown to reddish tan, with some individuals being distinctly green. There are oblique dark bands on the legs and indistinct dark patches on the back. There is a pale patch on the snout from between the eyes to the nostrils.

distribution

This species is known only from scattered hilly localities on the northern half of the North Island of New Zealand, including the Coromandel, Waitakere, Dome, and Hunua ranges and East Cape, Mount Ranginui, western Waikato, and the vicinity of Waipu as well as the northern section of Great Barrier Island.

habitat

This frog normally is near streams, commonly beside cascading and rapidly flowing water, where there are rocks at the stream edge or a splash zone for refuge. It also inhabits rock-strewn trickles and seeps in damp forest.

behavior

These nocturnal frogs hide during the day under rocks but emerge to forage at night and wander some distance during rains. They are the most aquatic of the Leiopelma. If disturbed, a frog often jumps from under a rock into the stream and swims furiously underwater to hide under a submerged rock. In 20 minutes to half an hour, the frog reemerges and hides once more under a rock out of the stream, often the same one it was

under before. The frogs squeaks if disturbed and, under extreme duress, secretes a noxious white substance from its numerous skin glands. Its predators are not known but probably consist of native stream fishes, centipedes, and birds.

feeding ecology and diet

Food consists of small insects and other invertebrates.

reproductive biology

Females lay 10–15 large, yolky white eggs under rocks or fallen vegetation in seepages or the damp sides of streams. The eggs hatch into white, free-swimming tadpoles, which generally remain hidden under cover. They retain a large amount of yolk and may not feed during larval development. The forelimbs are not covered completely by an operculum. There is neither egg attendance nor protection of the tadpoles by the adults.

conservation status

This is the most widespread, most common, and least threatened of the native New Zealand frogs. Hochstetter's frog nevertheless is protected under New Zealand's Wildlife Act.

significance to humans

The frog is of scientific interest because of its uniqueness, primitive morphologic features, and high chromosomal variability. It appears to have been little known to the Maori.

Maud Island frog

Leiopelma pakeka

taxonomy

Leiopelma pakeka Bell Daugherty, and Hitchmough, 1998, Maud Island, New Zealand.

other common names

None known.

physical characteristics

This is a larger, duller version of Archey's frog, reaching 2.0 in (50 mm) in length. Females tend to be larger than males, but the sexes are otherwise indistinguishable. Dorsolateral glandular ridges are underlined with dark spots, and parotoid glands are present behind each eye. These frogs are generally brown with a pale patch on the snout. The upper part of the iris is bright gold. The hind limbs are fairly short, and the feet are not webbed.

distribution

Restricted to Maud Island in the Marlborough Sounds off the north coast of the South Island of New Zealand, this frog inhabits a remnant patch of forest about 0.06 mi² (0.15 km²) in extent.

habitat

The patch of forest on Maud Island is at an elevation of 295–980 ft (90–300 m) on an eastward-facing hillside. There are numerous

boulders, logs, and rocks toward the lower, damper, less steeply sloping part of the forest, where the frogs are most abundant. There are no permanent streams or seepages.

behavior

The frogs emerge from hiding places after dark and sit on rocks or logs or forage slowly on the forest floor.

feeding ecology and diet

The diet consists of terrestrial insects.

reproductive biology

Females lay up to 20 large, yolk-filled eggs in cool, damp depressions under cover on the ground. The whitish larvae undergo development within the egg capsule and hatch when fully metamorphosed. The male attends the eggs and froglets, which clamber onto his back and legs.

conservation status

This species is Vulnerable according to IUCN (encompassing both Leiopelma hamiltoni and L. pakeka) and is protected under New Zealand's Wildlife Act. This rare frog may be reasonably secure in its isolation: Maud Island is monitored carefully to keep out invasive mammals, and the frogs persist in fairly high density.

significance to humans

None known.

Resources

Books

Grigg, G., R. Shine, and H. Ehmann, eds. The Biology of Australasian Frogs and Reptiles. Chipping Norton, Australia: Surrey Beatty and Sons, 1985.

Robb, Joan. New Zealand Amphibians and Reptiles in Color. Auckland: Collins Publishers, 1980.

Periodicals

Abourachid, A., and D. M. Green. "Origins of the Frog-Kick? Alternate-Leg Swimming in Primitive Frogs, Familes Leiopelmatidae and Ascaphidae." Journal of Herpetology 33, no. 4 (1999): 657–663.

Bell, Ben D. "A Review of the Status of New Zealand Leiopelma Species (Anura: Leiopelmatidae), Including a Summary of Demographic Studies in Coromandel and on Maud Island." New Zealand Journal of Zoology 21, no. 4 (1994): 341–349.

——. "The Amphibian Fauna of New Zealand." New Zealand Wildlife Service Occasional Publications 2 (1982): 27–89.

Green, D. M., and D. C. Cannatella. "Phylogenetic Significance of the Amphicoelous Frogs, Ascaphidae and Leiopelmatidae." Ecology, Ethology, and Evolution 5, no. 2 (1993): 233–245.

Worthy, T. H. "Osteology of Leiopelma (Amphibia: Leiopelmatidae) and descriptions of three new subfossil Leiopelma species." Journal of the Royal Society of New Zealand 17, no. 3 (1987): 201–251.