Leiopelma Hochstetteri Research Articles

Rapid recovery of a population of the cryptic and evolutionarily distinct Hochstetter's Frog, Leiopelma hochstetteri, in a pest‐free environment

SummaryNew Zealand's native frogs (genus Leiopelma) display a very high degree of endemism and belong to a distinctive and ancient evolutionary lineage. All four extant species are considered to be threatened or endangered, but the mechanisms behind their decline are poorly understood. Many of the potential factors causing population declines are confounded for the two species living on the mainland; in particular, habitat degradation and the presence of introduced mammalian pests have been difficult to disentangle in the past. Here we present data on a population of Hochstetter's Frog (Leiopelma hochstetteri) living in a pest‐free mainland sanctuary, the 3363‐ha Maungatautari Ecological Island. Survey data from this population shows a fourfold increase in numbers between 2009 and 2012 from a very low initial density. Our results suggest that for Hochstetter's Frog at least, and possibly the other mainland species of Leiopelma, introduced mammals are a major driving factor in population declines. Given that the frog population at Maungatautari was discovered by serendipity when planning for the pest‐free sanctuary was already well underway, this also highlights the conservation value of large pest‐free areas and ecosystem‐level management.

Recognising the value of all ‘restorative’ contributions

Recognising the value of all ‘restorative’ contributions

Habitat suitability and requirements for a threatened New Zealand amphibian

Habitat modification is one of the largest threats to global terrestrial biodiversity, yet management tools such as translocations often fail because of insufficient knowledge about species' habitat suitability and requirements in release areas. Resource selection is a useful technique that can address this issue. In 2014, we investigated resource selection of Hochstetter's frogs (Leiopelma hochstetteri) in mature (>30 year) exotic pine (Pinus radiata) plantations and regenerating native broadleaf forests in Torere Forest (Bay of Plenty, North Island), New Zealand, where harvesting of pines threatens this population. We then determined whether key habitats were present at the proposed target translocation site, Orokonui Ecosanctuary (Dunedin, South Island), New Zealand. In Torere Forest, we conducted daytime searches for frogs along streams and recorded microhabitats (e.g., cobbles) in used and random available plots. In Orokonui, we recorded microhabitats in randomly distributed plots because Hochstetters's frogs are presently absent. We used averaged mixed (binomial) models to identify important resources in pine plantations and native forests and to compare resource use between habitats. Finally, we predicted habitat use in Orokonui and Torere Forest to gain an indication of habitat suitability. Frogs predominantly selected cobble microhabitats in pine plantations and native forests but also partially decayed logs ≥15 cm in diameter within pine plantations. In contrast, high gravel cover and sand-silt were avoided by frogs. In response to limited cobble cover in pine plantations, frogs were more generalized in selecting resources (primarily logs) than in native forests. Habitat suitability was slightly lower in pine plantations compared to native forests, but mature pine plantations do provide suitable habitat for Hochstetter's frogs, at least in the short term prior to pine harvesting. Our study suggests that Orokonui provides suitable habitat for the proposed translocation of Hochstetter's frogs. © 2016 The Wildlife Society.

Selection on MHC class II supertypes in the New Zealand endemic Hochstetter's frog.

BackgroundThe New Zealand native frogs, family Leiopelmatidae, are among the most archaic in the world. Leiopelma hochstetteri (Hochstetter’s frog) is a small, semi-aquatic frog with numerous, fragmented populations scattered across New Zealand’s North Island. We characterized a major histocompatibility complex (MHC) class II B gene (DAB) in L. hochstetteri from a spleen transcriptome, and then compared its diversity to neutral microsatellite markers to assess the adaptive genetic diversity of five populations (“evolutionarily significant units”, ESUs).ResultsL. hochstetteri possessed very high MHC diversity, with 74 DAB alleles characterized. Extremely high differentiation was observed at the DAB locus, with only two alleles shared between populations, a pattern that was not reflected in the microsatellites. Clustering analysis on putative peptide binding residues of the DAB alleles indicated four functional supertypes, all of which were represented in 4 of 5 populations, albeit at different frequencies. Otawa was an exception to these observations, with only two DAB alleles present.ConclusionsThis study of MHC diversity highlights extreme population differentiation at this functional locus. Supertype differentiation was high among populations, suggesting spatial and/or temporal variation in selection pressures. Low DAB diversity in Otawa may limit this population’s adaptive potential to future pathogenic challenges.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0342-0) contains supplementary material, which is available to authorized users.

Analyses of the mitochondrial genome of Leiopelma hochstetteri argues against the full drowning of New Zealand

AbstractAimWe used endemic frogs to test the hypothesis that New Zealand was fully submerged during the Oligocene marine transgression (c. 25–35 Ma, the Oligocene drowning) and that all the land biota subsequently arrived by dispersal – including the poorly dispersing frogs.LocationNew Zealand.MethodsThe complete mitochondrial genome of the New Zealand native frog Leiopelma hochstetteri was sequenced, assembled and analysed, and compared with that of L. archeyi.ResultsUsing many phylogenetic analyses we examined the evolutionary relationships of the two species of Leiopelma, both for the deepest divergence within New Zealand and relative to other frogs. Our results give estimates of well over 65 Ma for the first divergence of leiopelmatid frogs within New Zealand, and over 150 Ma for the divergence of Leiopelma from its closest relative, the North American tailed frog Ascaphus truei.Main conclusionsThe identification of such a deep divergence among the extant Leiopelma species provides some of the strongest support yet for a mixed‐age model for the origin of New Zealand's terrestrial biota, where some elements are of vicariant origin and others have arisen by long‐distance dispersal. This contradicts a full drowning model and supports the view that there must have been some continuous land through the Oligocene.

Baseline cutaneous bacteria of free-living New Zealand native frogs (Leiopelma archeyi and Leiopelma hochstetteri) and implications for their role in defense against the amphibian chytrid (Batrachochytrium dendrobatidis).

Abstract Knowledge of baseline cutaneous bacterial microbiota may be useful in interpreting diagnostic cultures from captive sick frogs and as part of quarantine or pretranslocation disease screening. Bacteria may also be an important part of innate immunity against chytridiomycosis, a fungal skin disease caused by Batrachochytrium dendrobatidis (Bd). In February 2009, 92 distinct bacterial isolates from the ventral skin of 64 apparently healthy Leiopelma archeyi and Leiopelma hochstetteri native frogs from the Coromandel and Whareorino regions in New Zealand were identified using molecular techniques. The most-common isolates identified in L. archeyi were Pseudomonas spp. and the most common in L. hochstetteri were Flavobacterium spp. To investigate the possible role of bacteria in innate immunity, a New Zealand strain of Bd (Kaikorai Valley-Lewingii-2008-SDS1) was isolated and used in an in vitro challenge assay to test for inhibition by bacteria. One bacterial isolate, a Flavobacterium sp., inhibited growth of Bd. These results imply that diverse cutaneous bacteria are present and may play a role in the innate defense in Leiopelma against pathogens, including Bd, and are a starting point for further investigation.

FLUOROSIS AS A PROBABLE FACTOR IN METABOLIC BONE DISEASE IN CAPTIVE NEW ZEALAND NATIVE FROGS (LEIOPELMASPECIES)

This report describes the investigations into the cause and treatment of metabolic bone disease (MBD) in captive native New Zealand frogs (Leiopelma spp.) and the role of fluoride in the disease. MBD was diagnosed in Leiopelma archeyi and Leiopelma hochstetteri in 2008 at three institutions: Auckland Zoo, Hamilton Zoo, and the University of Otago. Most of these frogs had originally been held at the University of Canterbury for several years (2000-2004) but some were collected directly from the wild. Radiographs on archived and live frogs showed that MBD had been present at Canterbury, but at a lower rate (3%) than in the current institutions (38-67%). Microcomputed tomography showed that the femoral diaphyses of the captive frogs at Auckland Zoo had greater bone volume, bone surface, cross-sectional thickness, and mean total cross-sectional bone perimeter, which is consistent with osteofluorosis. On histology of the same femurs, there was hyperplasia, periosteal growth, and thickening of trabeculae, which are also consistent with skeletal fluorosis. An increase in fluoride levels in the water supply preceded the rise in the incidence of the above pathology, further supporting the diagnosis of osteofluorosis. Analysis of long-standing husbandry practices showed that ultraviolet B (UVB) exposure and the dietary calcium:phosphorus ratio were deficient when compared with wild conditions-likely causing chronic underlying MBD. To prevent multifactorial MBD in captive Leiopelma, the authors recommend increasing dietary calcium by incorporating into the captive diet inherently calcium-rich invertebrates; increasing exposure to natural or artificial (UVB) light; and using defluoridated water. Addressing these three factors at Auckland Zoo reduced morbidity, bone fractures, and mortality rates.

Designing a diet for captive native frogs from the analysis of stomach contents from free-ranging Leiopelma

Diets for captive amphibians are often inadequate and lead to poor health. To determine the natural diet of two New Zealand frog species, we analysed the stomach contents of 16 Archey's frogs (Leiopelma archeyi) from the Moehau Range of the Coromandel Peninsula and nine Hochstetter's frogs (Leiopelma hochstetteri) from the Moehau Range of the Coromandel Peninsula, the Hunua Ranges and Maungatautari. These specimens were obtained as by-catch from invertebrate pitfall traps from 2002 to 2008. Both species ate a wide range of invertebrates including springtails, mites, ants, parasitic wasps, amphipods and isopods. Leiopelma archeyi also ate snails. The mean ratio of maximum prey size ingested to snout–vent length in L. archeyi was 0.31 (range 0.16–0.5), and in L. hochstetteri was 0.42 (range 0.21–0.75). We suggest a reformulated captive diet based on the species and size of invertebrates ingested in the wild. This diet may assist in the prevention of metabolic bone disease.

Cranial muscles of the anuransleiopelma hochstetteriandascaphus trueiand the homologies of the mandibular adductors in lissamphibia and other gnathostomes

The frogs Ascaphus truei and Leiopelma hochstetteri are members of the most basal lineages of extant anurans. Their cranial muscles have not been previously described in full and are investigated here by dissection. Comparison of these taxa is used to review a controversy regarding the homologies of the jaw adductor muscles in Lissamphibia, to place these homologies in a wider gnathostome context, and to define features that may be useful for cladistic analysis of Anura. A new muscle is defined in Ascaphus and is designated m. levator anguli oris. The differences noted between Ascaphus and Leiopelma are in the penetration of the jaw adductor muscles by the mandibular nerve (V3). In the traditional view of this anatomy, the paths of the trigeminal nerve branches define homologous muscles. This scheme results in major differences among frogs, salamanders, and caecilians. The alternative view is that the topology of origins, insertions, and fiber directions are defining features, and the nerves penetrate the muscle mass in a variable way. The results given here support the latter view. A new model is proposed for Lissamphibia, whereby the adductor posterior (levator articularis) is a separate entity, and the rest of the adductor mass is configured around it as a folded sheet. This hypothesis is examined in other gnathostomes, including coelacanth and lungfish, and a possible sequence for the evolution of the jaw muscles is demonstrated. In this system, the main jaw adductor in teleost fish is not considered homologous with that of tetrapods. This hypothesis is consistent with available data on the domain of expression of the homeobox gene engrailed 2, which has previously not been considered indicative of homology. Terminology is discussed, and "adductor mandibulae" is preferred to "levator mandibulae" to align with usage in other gnathostomes.

A survey for the amphibian chytrid fungus Batrachochytrium dendrobatidis in New Zealand's endemic Hochstetter's frog (Leiopelma hochstetteri)

Chytridiomycosis is an emerging infectious disease of amphibians caused by the chytrid fungus Batrachochytrium dendrobatidis. It has been linked to many declines in amphibian populations worldwide, including New Zealand's native frog Leiopelma archeyi. Although chytridiomycosis has not yet been detected within any sampled population of the closely related Leiopelma hochstetteri, few populations have been surveyed. We tested for the presence of chytrid fungus in two populations of L. hochstetteri in the Auckland Region (Waitakere Ranges and Great Barrier Island). All of the individuals sampled tested negative for B. dendrobatidis, and no obviously sick frogs were found. Given our large sample size (n=124) we conclude that even if chytridiomycosis is present the prevalence is extremely low, suggesting these populations are not currently being negatively impacted by B. dendrobatidis. The apparent absence of chytridiomycosis in L. hochstetteri populations suggests this species may be resilient or immune to the fungus.

Hochstetter's frog (Leiopelma hochstetteri) egg, mobile larvae and froglet development

Egg strings and larvae of Hochstetter's frog (Leiopelma hochstetteri) were located at three widely separated North Island sites: in seeps at Brynderwyns in December 2004, in an open pool at Wharerino in March 2009, and in an underground pool near the Kaipawa Track, Coromandel, in late May 2009. Ten egg strings were also laid by captive frogs in water courses at Hamilton Zoo in April 2009. All egg strings held from 11 to 13 eggs. The egg strings laid in the Brynderwyns were regularly observed until metamorphosis was completed in March 2005. Twenty-four swimming larvae emerged from 25 capsules at c. 40 days after discovery, and at least 14 froglets were produced at c. 90 days. All of them developed in darkness, in a 120 ml pool <30 mm deep. The emerged froglets ranged from 9.8 to 10.8 mm snout-vent length. The detection of eggs, larvae and <11 mm froglets indicates that the egg laying period is at least from late September to May.

Using ecological niche modelling to infer past, present and future environmental suitability for Leiopelma hochstetteri, an endangered New Zealand native frog

Leiopelma hochstetteri is an endangered New Zealand frog now confined to isolated populations scattered across the North Island. A better understanding of its past, current and predicted future environmental suitability will contribute to its conservation which is in jeopardy due to human activities, feral predators, disease and climate change. Here we use ecological niche modelling with all known occurrence data ( N = 1708) and six determinant environmental variables to elucidate current, pre-human and future environmental suitability of this species. Comparison among independent runs, subfossil records and a clamping method allow validation of models. Many areas identified as currently suitable do not host any known populations. This apparent discrepancy could be explained by several non exclusive hypotheses: the areas have not been adequately surveyed and undiscovered populations still remain, the model is over simplistic; the species’ sensitivity to fragmentation and small population size; biotic interactions; historical events. An additional outcome is that apparently suitable, but frog-less areas could be targeted for future translocations. Surprisingly, pre-human conditions do not differ markedly highlighting the possibility that the range of the species was broadly fragmented before human arrival. Nevertheless, some populations, particularly on the west of the North Island may have disappeared as a result of human mediated habitat modification. Future conditions are marked with higher temperatures, which are predicted to be favourable to the species. However, such virtual gain in suitable range will probably not benefit the species given the highly fragmented nature of existing habitat and the low dispersal ability of this species.

Characterisation of microsatellite markers for the primitive New Zealand frog, Leiopelma hochstetteri

Hochstetters frog (Leiopelma hochstetteri) is one of only four endemic frog species within New Zealand. Here we describe the first 11 polymorphic microsatellite loci for this species developed using high-throughput genomic sequencing technology. Genetic diversity was assessed in 34 individuals sampled from a single location. We also tested these in the critically threatened L. hamiltoni, which may number fewer than 150 frogs, with six markers showing amplification.

Habitat-use model for the New Zealand endemic frog Leiopelma hochstetteri

Leiopelma hochstetteri is the most widespread and abundant endemic frog species in New Zealand, although it now survives only in spatially fragmented populations throughout the North Island of New Zealand and the Great Barrier Island of northeastern New Zealand. The species is known to occur in wet areas adjacent to shaded streams in forested catchments; however, no quan- titative ecological data exist to enable characterisation of its habitat. In the present study, novel data on the current distribution and habitat requirements of this species are reported for 1 population in the Waitakere Ranges, northwestern New Zealand, which is considered as a conservation manage- ment unit for the species. Frogs were found within most streams surveyed (68.2%). Statistical model- ling demonstrates that frogs most likely occur in small, erosive streams with coarse substrates and cold waters, surrounded by mature or undisturbed riparian vegetation. Anthropogenic activities such as clearing or logging are identified as threats to this frog species.

Phylogeography of Leiopelma hochstetteri reveals strong genetic structure and suggests new conservation priorities

Leiopelma hochstetteri belongs to a singular anuran lineage endemic to New Zealand that diverged from other frogs about 200 million years ago. The species now is reduced to a series of isolated populations in the northern half of the North Island and Great Barrier Island. We have used mitochondrial and nuclear sequence data to examine the genetic affinities of extant populations of L. hochstetteri. Phylogenetic reconstructions reveal that populations are highly structured. Each of the geographically isolated populations harbours independent mtDNA lineages as well as different degrees of nuDNA differentiation. Moreover, molecular dating reveals that this structure originated in the early Pleistocene. This pattern of genetic structure likely results from unfavourable climatic conditions during the Pleistocene combined with the low dispersal ability of the species. Isolated populations in forested refugia existed even in the southern part of the distribution of the species during glacial cycles. Previously published variation in chromosome numbers and isozyme data are consistent with the new evidence. We identified 13 evolutionary significant units (ESUs) that should serve as the focus for future management and conservation of this species.

Characterisation (δ13C and δ15N isotopes) of the food webs in a New Zealand stream in the Waitakere Ranges, with emphasis on the trophic level of the endemic frog Leiopelma hochstetteri

Leiopelma hochstetteri, the most widespread of New Zealand's native frogs, is recognised as threatened, and is fully protected by legislation. As a first step to characterise the diet and trophic level of L. hochstetteri within streams in the Waitakere Ranges, Auckland, stable carbon and nitrogen isotope analyses were undertaken on a variety of sympatric terrestrial and aquatic plant and animal species, including adult frogs. These results show that: (1) aquatic and terrestrial food webs are linked by terrestrial inputs into the stream; (2) invertebrate and vertebrate predators separate well into distinct trophic groups, and (3) L. hochstetteri occupies an intermediate trophic position among predators, with a diet, at least as an adult, comprising terrestrial invertebrates. Shortfin eels and banded kokopu are identified as potential predators of L. hochstetteri, but data for rats are inconclusive. These results have important implications for the conservation of New Zealand native frog species and riparian stream habitat.

Effect of pest–management operations on the abundance and size–frequency distribution of the New Zealand endemic frog Leiopelma hochstetteri

In New Zealand, introduced mammals, especially rats, have been considered a primary factor in the extinction of amphibians. (Leiopelma hochstetteri) is a riparian frog, and is the most widespread of the surviving species of native frogs in New Zealand. At present, all populations of this frog species coexist with introduced mammals, which in some cases have been subject to pest–management operations without monitoring the potential benefits or damage to the frogs. We investigated the influence of a 7–year rat management operation on frog abundance in the Waitakere Ranges, New Zealand. We identified which habitat characteristics had significant influence on frog abundance; confirmed that the study areas represented similar habitats both inside and outside the pest–managed area, and finally evaluated the effects of the pest–management activities. Frog abundance was positively correlated with percentage area covered by boulders and percentage area covered by water. Since the study sites were similar in terms of those variables, we could make a reliable comparison of frog abundance in relation to pest management. Presence/absence of pest–management operations did not have any significant effect on frog abundance. Size–frequency distribution data suggest that there has been recruitment of young frogs both inside and outside pest–management areas in the past 7 years.

Discovery and spatial assessment of a Hochstetter's frog (Leiopelma hochstetteri) population found in Maungatautari Scenic Reserve, New Zealand

We describe the discovery, genetic status, and survey of a Hochstetter's frog population (Leiopelma hochstetteri) found in Maungatautari Scenic Reserve, New Zealand. The strongest genetic affinities of the Maungatautari population are with a population of frogs at Mt Ranginui, approximately 55 km away, according to the single genetic sample taken. Frogs were found over an area of at least 120 ha on Maungatautari, and the encounter rate (0.66 frogs/ person hour) and relative abundance (2.7/100 m) was low compared to most other populations. The survey results suggest that the population is relatively small, and that introduced mammals, particularly ship rats (Rattus rattus) and feral pigs (Sus scrofa) may pose a significant threat. Weather conditions and observer experience/bias were also likely to have influenced our results. Eradication of introduced mammals from Maungatautari is scheduled for late 2006. Continued monitoring of frogs will document their response to mammalian pest eradication, and the functional importance of Hochstetter's frog in a large mainland island free of introduced mammals.

Anatomical features of Leiopelma embryos and larvae: Implications for anuran evolution

A controversial issue in anuran systematics is the relationship of Leiopelma to other anurans because recent phylogenetic constructions imply different relationships among the basal frogs. Of particular evolutionary interest is whether early development of Leiopelma resembles an ancestral salamander-like larva, an anuran tadpole, or neither. In the 1950s, Neville G. Stephenson hypothesized that direct development is the primary mode of development in amphibians, based on the fact that Leiopelma spp. lack a free-living (=feeding) larval stage. Although this hypothesis has not been generally accepted, it has not been formally refuted. We review Stephenson's work on Leiopelma and examine the anatomy of embryos/"larvae" of the four extant Leiopelma species for evidence of vestigial larval features that might refute the "direct-developing ancestor" hypothesis. We describe internal oral features in early developmental stages of Leiopelma and compare Leiopelma with a closely related basal anuran, Ascaphus, to assess whether their early developmental stages share any derived features. In Leiopelma hochstetteri, embryos/larvae have open gill slits and some faint rugosities around one gill slit that may be vestiges of gill rakers or filters. They also have more intestinal loops, indicative of an elongated alimentary tract, at earlier rather than late embryonic/larval stages. Collectively, these features support the view that the ancestor of Leiopelma had a free-swimming, free-feeding, aquatic larva. The palatoquadrate of Leiopelma archeyi reorients approximately 40 degrees from a more horizontal to a more vertical position through embryonic/"larval" development. This amount of cranial remodeling is intermediate between that seen in salamanders (17-27 degrees) and that reported for Ascaphus (64 degrees ) and other basal frogs (71-78 degrees) at metamorphosis. We found no internal oral features that Leiopelma shares specifically with Ascaphus. However, Leiopelma embryos have a ventrally positioned mouth and a downturned rostrum, characteristic of Ascaphus and other stream-adapted tadpoles.

Chromosome Polymorphism in Archey's Frog (Leiopelma archeyi) from New Zealand

Abstract The most primitive frogs in which a sex chromosome system has been determined are members of the endemic New Zealand genus Leiopelma. Two species, Leiopelma pakeka and Leiopelma hochstetteri, have female heterogamety of the ZW/ZZ and 0W/00 types, respectively. Despite its great karyotypic similarity to L. pakeka, a third species, Leiopelma archeyi, has not been know previously to possess heteromorphic sex chromosomes. Herein a highly differentiated putative W chromosome characterized by the addition of a completely heterochromatic short arm is reported from a female L.archeyi from the Whareorino forest of the North Island of New Zealand.