Tuatara: Volume 8, Issue 3, April 1961
New Zealand Native Frogs
New Zealand Native Frogs
Although presumably the ancestors of the native frogs reached New Zealand during the Cretaceous period, a record of their presence was not made until the early gold-mining days of the mid-nineteenth century. While A. S. Thomson, surgeon to the 58th Regiment, was watching the gold-panning activities of a group of prospectors in a mountain stream near Coromandel, a frog was found under one of the boulders. It was eventually given to Thomson who described it (1853) but did not name it. His description indicates that it was a specimen of what is now known as Leiopelma hochstetteri.
A few years later, the Austrian naturalist, Hochstetter, collected frogs of the same type from the Coromandel peninsula during the voyage of the frigate Novara. In 1861 these specimens were described and named after Hochstetter by Fitzinger. Subsequently a fuller description and a change in family classification were made by Steindachner (1869), whose account was translated by Hutton in 1879.
In 1919, a second species, found on Stephens Island in Cook Strait, was named Liopelma hamiltoni by McCulloch in honour of its discoverer.
Although a number of early records of the finding of small brown and green frogs high on the mountain ridges of the Coromandel peninsula are available (McLaren, 1898; Smith, 1921; Archey, 1922; Graham, 1924), these frogs were not recognised as belonging to a new species until 1942. In that year E. G. Turbott described the species and gave it the name of Leiopelma archeyi in honour of Dr. Gilbert Archey, who wrote the first account of its interesting intracapsular development (Archey, 1922).
In spite of a time lapse of over 100 years since their first discovery, many problems concerning the New Zealand frogs still remain to be solved. The following account attempts to indicate some of these.
Early classifications of the frogs into families showed considerable variation. In 1924, however, G. K. Noble, who had recognised the affinities of Leiopelma Fitzinger with Ascaphus Stejneger of North America, placed the two genera in a new family, the Liopelmidae. In 1931 he placed this family in a separate sub-order, the AMPHICOELA, in recognition of the fact that the two genera are more primitive, as far as certain important anatomical features are concerned, than any other known anurans. The name of the sub-order refers to the amphicoelous condition of the vertebrae, the term usually indicating that the centra are biconcave and the intervertebral cartilage undivided. That this term is inadequate to convey fully the vertebral condition of Ascaphus and Leiopelma has recently been pointed out by Ritland (1955), but as a basis of classification serving to separate the two genera from other living frogs and toads it still fulfils its purpose.
Another primitive characteristic distinguishing Leiopelma and Ascaphus from other adult anurans is the presence of two tail-wagging muscles, though neither genus possesses a tail in the adult stage. In addition, these two genera have nine presacral vertebrae, one more than the maximum number recorded for any other living frog or toad.page 100
The characters mentioned above are not the only ones illustrating the essentially primitive nature of Leiopelma and Ascaphus but most of the others are shared by some members of other anuran families. As might be expected, each genus has also developed certain specialised, adaptive characters but sometimes controversy exists about whether a particular character is to be regarded as primitive or specialised. For example, many zoologists would class the absence of certain middle ear structures in Leiopelma and Ascaphus as representing a secondary loss of a specialised nature. This is by no means necessarily so, as N. G. Stephenson (1951 b, pp. 243-7) has already pointed out. On the other hand, the unique intromittent organ of Ascaphus, developed as an extension of the cloaca, is clearly of a specialised nature (Noble, 1931). The tadpoles of Ascaphus have an equally unique arrangement of tooth ridges or plates. These features appear to be of particular value in the swift-flowing mountain streams frequented by the genus, the arrangement of larval teeth assisting in attachment and the erectile cloaca of the adult male ensuring adequate fertilisation.
Of the three species of Leiopelma, L. hochstetteri has the greatest external resemblance to Ascaphus, but the methods of development of the two genera are quite different. Ascaphus has a free-swimming tadpole stage, while the entire development of Leiopelma, at least in the two species of which eggs have been found, is intracapsular, the embryo developing entirely within a gelatinous capsule formed from the original egg. It hatches as a tailed froglet with legs, the tail being resorbed within a comparatively short time.
In 1942, Turbott pointed out that Fitzinger's original spelling of the generic name Leiopelma had been altered by Gunther in 1868 to Liopelma and that the alteration had been copied by later authors. Turbott emphasised that the original spelling used by Fitzinger should be retained and that it should also be extended to the family name (i.e. Leiopelmidae instead of Noble's Liopelmidae). The family name itself is a matter of some contention. In 1923, Fejervary proposed the name Ascaphidae for the family containing the genus Ascaphus. This predated Noble's family Liopelmidae (1924), which was designed to include both Liopelma Gunther 1868 laps. cal. = Leiopelma Fitzinger 1861 and Ascaphus Stejneger 1897. Noble chose the oldest generic name as the basis for his family name. N. G. Stephenson pointed out (1951 b) that if this name is to be used it should more correctly be Leiopelmatidae.
The oldest generic name is not, however, a necessary requirement of taxonomic procedure for the formation of a family name, so that the name Ascaphidae does have priority over Liopelmidae or Leiopelmatidae. It also has the advantage of avoiding the errors of formation and of spelling of Noble's family name. As the name Ascaphidae is already in fairly wide use, it seems better to conform to this terminology as long as Ascaphus and Leiopelma remain together in one family.
At the present time, the genus Leiopelma Fitzinger is considered to include three species; Leiopelma hochstetteri Fitzinger, L, hamiltoni McCulloch and L. archeyi Turbott. In compiling the following key to their identification, reference has, of course, been made to descriptions and keys provided by earlier workers including Fitzinger (1861), Steindachner (1869), McCulloch (1919) and Turbott (1942).
Tympanic membrane, eustachian tubes and vocal sacs absent. Teeth present in upper jaw. Teeth on prevomers in two straight or slightly oblique patches situated between the choanae and towards or slightly behind the posterior margins of the latters. Fingers free. A whitish metacarpal tubercule present on each side of palms of hands. A smaller, whitish, inner metatarsal tubercle present on sole of foot. Outer metatarsal tubercle absent. More or less distinct oblique black bands on dorsal surface of limbs. Under-surface of body mottled greyish-brown.
Key to the Species
|1||Habit robust. Parotoid glands absent. Toes half-webbed. Femur relatively longer and heels not overlapping when femurs are placed at right angles to body. Colour of dorsal surface often very dark brown and fairly uniform but may vary to a much lighter, olive-brown. In the latter case the black banding on the legs is more apparent. Distribution: Warkworth, Waitakere Ranges, Coromandel Peninsula and coastal areas south of peninsula.||L. hochstetteri|
|2||Habit slender. Parotoid glands present. Webs greatly reduced (not more than quarter-webbed) or absent. Femur relatively shorter and heels overlapping when femurs are placed at right angles to body. Black markings usually conspicuous on dorsal surface of body and on limbs.|
|A. Maximum body length 41 mm. Colour pattern variable, ranging from green through combinations of green and brown to light or dark brown. Distribution: Coromandel Peninsula.||L. archeyi|
|B. Maximum body length greater than 41 mm. Dorsal colour so far recorded either light or dark brown. Distribution: Stephens Is., Maud Is.||L. hamiltoni|
Several points in connexion with this key require further elaboration. The absence of a tympanic membrane (a round patch, corresponding to an eardrum, found behind and below the eye in many frogs) in Leiopelma should make this genus easy to distinguish in the field from any of the species of Hyla now found in New Zealand.
The parotoid glands of L. archeyi and L. hamiltoni form conspicuous, ridge-like swellings behind the eye. Each consists of a double row of round to oval, yellowish glands lying beneath the surface of the skin and opening through it. They produce a white secretion. Nothing is known of its effect on possible predators of Leiopelma, but in some toads the secretion of the parotoids is known to be highly toxic. Glandular ridges and isolated patches of glands also occur elsewhere on the body and limbs. The extent of these appears to be variable within each species.
Although the maximum body length of L. archeyi has been given as 41 mm., this measurement has been recorded only once for the species. Measurements up to 39 mm. are not unusual from areas on the Tokatea Ridge. The maximum length so far recorded for L. hamiltoni is 47 mm. L. hochstetteri appears to conform to the body length range of L. hamiltoni.
Where the colour pattern is described above as being ‘variable’, this means variable throughout the species, not in a particular individual. Frogs kept in captivity for two years maintained constant, individual colour patterns and could readily be recognised by these.
In a recent publication (Stephenson and Stephenson, 1957, p. 869), McCulloch's original specimen of L. hamiltoni was described as being ‘patterned in green and brown‘. It is difficult to say just how this misconception arose. But further checking of McCulloch's description has shown clearly that the frog in question was light brown. Of the specimens of L. hamiltoni from Maud Island described by Mr. Bell all were either light or dark brown.
Leiopelma hochstetteri has been recorded from a number of localities in the North Island. These include Warkworth (forty miles north of Auckland), several places in the Waitakere Ranges, the Coromandel Peninsula and areas along the north-east coast south of the Coromandel Peninsula.
L. archeyi is known only from the Coromandel Peninsula, where it may either occur alone, or may closely overlap the range of L. hochstetteri. In the latter case it is a common occurrence to find members of both species under the same log or stone. The best known areas for L. archeyi are probably Mt. Moehau and the Tokatea Ridge.
Until very recently, Leiopelma hamiltoni was known only from Stephens Is. in Cook Strait and there from a very restricted area. This consisted of a barren boulder bank at the top of the island at a height of about a thousand feet. So localised was the spot and so rigorous the conditions that it was thought for some years that the frogs had became extinct. A party led in 1950 by Mr. W. H. Dawbin, formerly of the Victoria University of Wellington, then located a frog. A few more have since been found. In view of the precarious existence led by this species, page 103 it was of great interest to find that in 1958 Mr. Bell, a senior Field Officer of the Wild Life Branch of the Department of Internal Affairs, had drawn the attention of the Department to the existence of a colony of frogs on Maud Island in Pelorus Sound. Three of these frogs were ultimately sent to the writer for detailed study, in an attempt to discover whether they should be retained as members of the species L. hamiltoni McCulloch, or should be regarded as members of a new species. These frogs have been carefully examined and measured externally and have been studied internally by means of alizarin transparencies and by sectioning of certain regions. In addition, Mr. Bell made a series of detailed measurements of nineteen frogs on Maud Island. Against these were checked measurements of two specimens of L. hamiltoni, one from the Canterbury Museum and one from the Dominion Museum. As a result of these anatomical and statistical investigations it seems better not to try to assign any difference in specific status at present to the Stephens Is. and Maud Is. frogs.
The position of the nostrils relative to the tip of the snout and to thieve was previously thought to be of use in distinguishing L. archeyi from L. hamiltoni. McCulloch (1919) described the nostril of L. hamiltoni as being midway between the tip of the snout and the eye. In L. archeyi, as described by Turbott (1942), the nostril is nearer to the eye than to the tip of the snout. This condition was confirmed by a lengthy series of measurements carried out by the writer on Mt. Moehau and Tokatea in January, 1959. The first specimen of the Maud Is. frog measured showed the same relative condition of the nostrils as in L. archeyi. Most of the others measured by Mr. Bell showed the same condition but in two the nostril was equidistant between the tip of the snout and the eye. Measurements of two specimens of the Stephens Is. frog, kindly carried out by Mr. McCann of the Dominion Museum and Mr. Turbott of the Canterbury Museum, indicated that in one animal the nostrils were: equidistant and in the other they were nearer to the eye. These facts, together with the difficulty of carrying out the particular measurement satisfactorily in the field and the small difference involved (usually only about 1 mm.) suggests that it would be highly undesirable to base a specific diagnosis on this character alone. In any case, L. hamiltoni, whether from Maud Is. or Stephens Is., appears to show some variation in this feature.
A comparative anatomical survey of the three species recently completed by the writer (E. M. Stephenson, 1960) indicates that L. archeyi has the essential skeletal characteristics of an immature or juvenile L. hamiltoni, but that it becomes sexually mature while still in this condition. This phenomenon of heterochrony, implying a change along the time axis of development of an organism, is well known in Amphibia, extreme examples being furnished by cases of neoteny among certain newts. In these cases the newts concerned remain as permanent larvae which become sexually reproductive. Heterochrony can obviously be a factor of importance in speciation and general evolution.
Because of the facts stated above, differentiating between young specimens of L. hamiltoni and mature brown specimens of L. archeyi on page 104 external features alone, could be difficult, unless the localities are known. Taken as a whole, however, populations of the two species are clearly defined.
Certain features in connection with the life history of Leiopelma have not been recorded. In no species has the actual process of mating been recorded. Almost certainly it occurs at night, for during the day the frogs shelter under stones, logs or in clumps of vegetation. They normally become active only in the dark. This is also the typical, although not invariable pattern of the frogs when kept in captivity.
Leiopelma archeyi lays clusters of two to eight or more eggs, each surrounded by a gelatinous capsule. The eggs are heavily yolked, unpigmented and measure 4 mm. to 5 mm. in diameter. They are found in or under rotting logs, or in the soft decaying wood of damp tree stumps. The exact time of egg laying or of fertilisation is uncertain but well developed embryos can be found in the capsules in November and December. For an account of the development of Leiopelma archeyi, refer to Archey (1922), and to N. G. Stephenson (1951a). When the tailed froglets are ready to hatch, they pierce the capsule with rotating muscular movements of their tails, helped by a glandular secretion. An interesting and important fact, discovered by Archey and confirmed more fuy by N. G. Stephenson, is that if the embryos are released from their capsules into water they will continue to develop, indicating that the intracapsular mode of development is perhaps less specialised than is generally thought.
Several times, male frogs have been found sitting over clusters of eggs. Their exact function is not known. Possibly, although this seems unlikely, they are exhibiting brooding tendencies known in some amphibia. Possibly they are ensuring external fertilisation. Supporting the latter view is the fact that they have been found over clusters of eggs at a relatively early stage in development and that it is quite common to find infertile eggs in a cluster. Yet another possibility is that the urinary excretion of the frogs provides additional moisture for the eggs.
Until 1949, nothing was known of the egg-laying or breeding habits of Leiopelma hochstetteri. Then, following a discovery made by Mr. Gittos of Warkworth, Mr. Turbott was able to collect eggs buried in wet mud of a seepage above a stream. L. hochstetteri also has an intracapsular development in which the embryos do not have a free-living tadpole stage, but hatch from the egg as tailed froglets.
Nothing is at present known about the mating or development of Leiopelma hamiltoni. Presumably it follows the general L. archeyi pattern but the finding of the first cluster of eggs will be an interesting discovery.
Although Leiopelma hochstetteri has primarly been regarded as a stream-dwelling frog, it has often been found under logs or stones well away from surface water. This is particularly evident in patches of bush along the Tokatea Ridge in the Coromandel Peninsula. In this region, as has already been mentioned, L. hochstetteri and L. archeyi overlap in range and both species may be found together under logs or stones. It was at page 105 first thought that a mating barrier must exist between them but recent observations hint at the possibility of some interbreeding. In January, 1959, while measuring frogs on the Tokatea Ridge, the writer found a frog which at first glance appeared to be a bright green specimen of L. archeyi. Further examination showed that it had a well-defined half-web and in most other characteristics could be regarded as a member of the species L. hochstetteri. A glandular ridge was present behind the eye but it did not have the same degree of development as the normal parotoid of L. archeyi. No other instance of green coloration in L. hochstetteri has been recorded. One of several possible suggestions is that some degree of interbreeding may be occurring between L. archeyi and L. hochstetteri on the Tokatea Ridge, but much more information is needed on this point.
Although the results of a statistical study in progress are not yet available, some indication is seen that an overall size difference, possibly indicating subspeciation, exists between populations of L. archeyi on Mt. Moehau and on the Tokatea Ridge. For a fuller account of field observations carried out in these and other areas, refer to Stephenson and Stephenson, 1957.
Obviously, much still remains to be learnt about these interesting, rare and primitive frogs. An accurate account of the process of mating and egg-laying would be of particular interest. It is to be hoped that any observer of amplexus (pairing) will record it by means of photographs if possible or by an accurate sketch. No one has yet recorded whether the embrace is in the pectoral or the pelvic region. The latter type is found in Ascaphus and other primitive genera and could be expected in Leiopelma.
Whatever the gaps in our knowledge, it is essential that any observations of the native frogs must not be carried out at the expense of the animals themselves. The genus is protected by law and no specimens may be collected without the permission of the Hon. Minister for Internal Affairs. The frogs are highly susceptible to drying and must be protected from this danger if they are being handled. Logs and stones must be replaced in their exact positions and vegetation must not be unnecessarily disturbed. It should be emphasised, however, that some of the important discoveries connected with Leiopelma were not made initially by trained zoologists and that this could, through chance, be the case again.
ARCHEY, G., 1922 - The Habitat and Life History of Liopelma hochstetteri. Rec. Canterbury (N.Z.) Mus., 2, pp. 59-71.
FEJERVARY, G. J. DE, 1923 - Ascaphidae, a new family of tailless Batrachians. Ann. hist.-nat. Mus. hung., 20, p. 178.
FITZINGER, L. J., 1861 - Eine neue Batrachier-Gattung aus New-Seeland. Verh. zool.bot. Ges. Wien, II, p. 217.
GRAHAM, G., 1924 - Note in ‘The Patu Paiarehe’ by John White. J. Polynesian Soc., 33, pp. 210-11.
GUNTHER, A., 1868 - First account of spp. of Tailless Batrachiens added to the collection of the British Museum. Proc. Zool. Soc. Lond., pp. 478-90.
HUTTON, F. W., 1879 - On the New Zealand Frog. Translated from the Zoology of the Voyage of the Novara (Fitzinger). Trans. N.Z. Inst., 12, pp. 250-251.
McCLAREN, J. M., 1898 - On the Geology of Te Moehau. Trans. N.Z. Inst., 31, pp. 494-498.
McCULLOCH, A. R., 1919 - A new Discoglossid Frog from New Zealand. Trans. N.Z. Inst., 51, pp. 447-449.
NOBLE, G. K., 1924 - A New Spadefoot Toad from the Oligocence of Mongolia. Amer. Mus. Novit., 132, p. 9.
—— 1931— The Biology of the Amphibia. New York. McGraw Hill.
RITLAND, R. M., 1955 - Studies on the post cranial morphology of Ascaphus truei. I. Skeleton and spinal nerves. J. Morph., 97, pp. 119-178.
SMITH, S. P., 1921 - Letter in N.Z. J. Sci. Tech., 3, p. 308. (With note by J. Allan Thomson.)
STEINDACHNER, F., 1869 - Reise der Fregatte Novara. Zoologischer Theil, Vol. I, Amphib., p. 33.
STEPHENSON, ELSIE M. and N.G., 1957 - Field Observations on the New Zealand Frog, Leiopelma Fitzinger. Trans. Roy. Soc. N.Z., 84, pp. 867-882.
STEPHENSON, ELSIE M., 1951 - The Anatomy of the Head of the New Zealand Frog, Leiopelma. Trans. Zool. Soc. Lond., 27, pp. 255-305.
—— 1952— The Vertebral Column and Appendicular Skeleton of Leiopelma hochstetteri Fitzinger. Trans. Roy. Soc. N.Z., 79, pp. 601-613.
—— 1960— The Skeletal Characters of Leiopelma hamiltoni McCulloch, with particular reference to the effects of heterochrony on the Genus. Trans. Roy. Soc. N.Z., 88, in press.
STEPHENSON, N. G., and THOMAS, E. M., 1945— A Note concerning the Occurrence and Life History of Leiopelma Fitzinger. Trans. Roy. Soc. N.Z., 75, pp. 319-320.
STEPHENSON, N. G., 1951a— On the Development of the Chondrocranium and Visceral Arches of Leiopelma archeyi. Trans. Zool. Soc. Lond., 27, pp. 203-253.
—— 1951b— Observations on the Development of the Amphicoelous Frogs, Leiopelma and Ascaphus. J. Linn. Soc. (zool.), 42, pp. 18-28.
—— 1955— On the Development of the Frog, Leiopelma hochstetteri Fitzinger. Proc. Zool. Soc. Lond., 124, pp. 785-795.
THOMSON, A. S., 1853 - On the Discovery of a Frog in New Zealand. Edin. New Philos. Journ., 55, pp. 66-69. Reprinted 1920 in N.Z.J. Sci. Tech., 3, pp. 220-222.
TURBOTT, E. G., 1942 - The Distribution of the Genus Leiopelma in New Zealand, with a description of a New Species. Trans. Roy. Soc. N.Z., 71, pp. 247-253.
—— 1949 - Discovery of the Breeding Habits of Leiopelma hochstetteri Fitzinger. Rec. Auck. Inst. Mus., 3, pp. 373-376.