Zealand Frog Research Articles

Suitability of radio telemetry for monitoring two New Zealand frogs (Leiopelma archeyi and L. hamiltoni)

Suitability of radio telemetry for monitoring two New Zealand frogs (Leiopelma archeyi and L. hamiltoni)

Colour variation and behaviour of the cryptic New Zealand frog Leiopelma archeyi

Colour variation and behaviour of the cryptic New Zealand frog Leiopelma archeyi

Balancing act: modelling sustainable release numbers for translocations

AbstractTranslocated populations often share demographic, environmental and genetic risks associated with relict populations. Models that predict translocation impacts on source and founder populations are therefore necessary to ensure that harvesting for release does not jeopardize either population. However, current models generally focus on maximizing the long‐term demographic viability and retention of allelic diversity in the founder population only. We therefore risk estimating a release number that is considered ‘appropriate' for maintaining viability and allelic diversity in the founder population but is in fact detrimental to the source. Our objectives were to determine a sustainable number of individuals for release that maximized the viability and allelic diversity of source and founder populations. We developed a spatially explicit individual‐based model that simulated hypothetical translocation scenarios for the threatened New Zealand frog, Leiopelma pakeka, which was restricted to Te Hoiere/Maud Island and has been heavily targeted for translocations. Source and translocated populations were simulated over 200 generations, representing 200 years across various initial population sizes from 20 to 300 frogs. To account for the potential loss of allelic diversity from the source population via harvesting, along with genetic drift and founder events typically associated with translocations, an additional set of simulations determined the probability of retaining a single diploid locus within populations with rare and common alleles. Our results showed that at least 120 frogs were required for populations to remain viable and maximize allelic retention in the long‐term, regardless of allelic diversity. However, harvesting more than 150 frogs led to ongoing or the onset of declines in the viability and allelic retention of source populations. We recommend that future translocations of L. pakeka harvest no more than 140 frogs from each of the sub‐populations on Te Hoiere/Maud Island. We also recommend the described approach to simulate hypothetical translocation scenarios for other managed species.

‘Get together, work together, write together’: a novel framework for conservation of New Zealand frogs

‘Get together, work together, write together’: a novel framework for conservation of New Zealand frogs

Using molecular diet analysis to inform invasive species management: A case study of introduced rats consuming endemic New Zealand frogs.

The decline of amphibians has been of international concern for more than two decades, and the global spread of introduced fauna is a major factor in this decline. Conservation management decisions to implement control of introduced fauna are often based on diet studies. One of the most common metrics to report in diet studies is Frequency of Occurrence (FO), but this can be difficult to interpret, as it does not include a temporal perspective. Here, we examine the potential for FO data derived from molecular diet analysis to inform invasive species management, using invasive ship rats (Rattus rattus) and endemic frogs (Leiopelma spp.) in New Zealand as a case study. Only two endemic frog species persist on the mainland. One of these, Leiopelma archeyi, is Critically Endangered (IUCN 2017) and ranked as the world's most evolutionarily distinct and globally endangered amphibian (EDGE, 2018). Ship rat stomach contents were collected by kill‐trapping and subjected to three methods of diet analysis (one morphological and two DNA‐based). A new primer pair was developed targeting all anuran species that exhibits good coverage, high taxonomic resolution, and reasonable specificity. Incorporating a temporal parameter allowed us to calculate the minimum number of ingestion events per rat per night, providing a more intuitive metric than the more commonly reported FO. We are not aware of other DNA‐based diet studies that have incorporated a temporal parameter into FO data. The usefulness of such a metric will depend on the study system, in particular the feeding ecology of the predator. Ship rats are consuming both species of native frogs present on mainland New Zealand, and this study provides the first detections of remains of these species in mammalian stomach contents.

Historical trends in frog populations in New Zealand based on public perceptions

Surveys were distributed to New Zealand land users in 1998 and 2008 to acquire information about New Zealand frogs with the aim of compiling and mapping their distribution and inferred population trends without costly and time-consuming field surveys. The overall frog population trend was reported as declining, with possible causes reported as an increase in agriculture, an increase in the distribution of predatory fish and disease. The resultant maps could be used for four main purposes: 1) to identify regions where Litoria populations are known to occur, which can be eliminated when considering suitable regions for translocation of Leiopelma; 2) to identify growing or stable populations of Litoria species, which may assist future disease surveys, population monitoring and to identify sources of genetic material that may serve as an Ark for declining Australian populations; 3) to highlight populations that are in decline to enable effective targeting of detailed disease studies; and 4) to approximate the stability of amphibian populations in the absence of more accurate, but costly, scientific monitoring.

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.

Differential polymorphism in cutaneous glands of archaic Leiopelma species

Endemic New Zealand frogs of the genus Leiopelma are from a basal lineage of extant anurans that release defensive secretions onto their skin when disturbed. Here, we characterize the gross anatomy and microscopic structure of the skin of L. archeyi, L. hochstetteri, and L. pakeka using stereoscopic, light and transmission electron microscopy. The terrestrial L. archeyi and L. pakeka possess dimorphic granular glands, categorized as type I and II, based on their frequency and morphological traits, whereas the semi-aquatic L. hochstetteri lacks type I glands. This is the first report of differential dimorphism in anurans of the same genus. This dimorphism could be interpreted as an adaptation to different physiological or ecological needs of these species. However, species within this ancient genus share similar general gland morphology with other anurans, namely, a secretory unit containing storage granules ensheathed by myoepithelial cells. Type I glands are ellipsoid, large and contain a homogeneous mass of electron-dense granules (1.8 ± 0.08 μm in diameter). Type II glands are round and contain larger heterogeneous granules (4.06 ± 0.16 μm) of varying densities. Exposure to noradrenaline causes the contraction of myoepithelial cells, resulting in bulk discharge of type I glands through the epidermal duct onto the skin surface. Differential release of secretions from dimorphic glands may be indicative of their functional specialisation in antipredatory or regulative roles. Mass spectrometric techniques were used to de novo sequence peptides present in the skin secretions of Leiopelma species. A total of 30 previously undescribed peptides from Leiopelma species were fully or partially sequenced. These peptides exhibited no similarity to any known compounds.

Skin peptide defences of New Zealand frogs against chytridiomycosis

AbstractOver the past few decades, amphibian populations have undergone drastic declines on a global scale. Declines in many anuran populations have been linked to the emergent skin‐invasive amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd). Antimicrobial peptides in the skin are thought to act as important components of the innate immune system that may protect some species from infectious diseases. The four archaic species of Leiopelma in New Zealand are of great conservation concern and a severe population crash of Leiopelma archeyi between 1996 and 2001 has been tentatively linked with the outbreak of Bd. Here, we investigated the in vitro activity of skin secretions of six frog species in New Zealand against Bd zoospore growth. The activity of skin secretions produced by frogs in the wild varied significantly between species, with those of Le. archeyi being the most active. The skin secretions of native Leiopelmatid species showed greater Bd zoospore inhibition (31.0–71.9%) than the naturalized Litoria species (17.4–18.2%). Leiopelma archeyi has the most active peptides, even though it is the only native species with known susceptibility to Bd infections.

Amphibian declines: promising directions in understanding the role of disease

The decline of amphibian populations worldwide is a recognized phenomenon. A variety of important causes have been linked to the declines but perhaps the most renowned cause, in terms of popular press exposure, funding dispersal and papers published, is disease. In particular, chytridiomycosis, a disease caused by the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd), is a lethal emerging infectious disease that has had profound effects in some amphibian species, but occurs without catastrophic effects in others (Fisher, Garner & Walker, 2009b). Bd affects species differentially. In many cases it is the major threat to animals already stressed by other critical challenges, such as habitat destruction, pollution, invasive species and climate change. In addition to its impact on amphibian populations, the spread and presence of Bd is likely to impact human activities via effects on the pet, bait and food trade (Schloegel et al., 2009, 2010).

Conservation status of New Zealand frogs, 2009

A reappraisal of the conservation status of the New Zealand frog fauna is presented using the 2008 version of the New Zealand Threat Classification System. Of New Zealand's four extant endemic species, three are judged to be ‘Threatened’ (Leiopelma hamiltoni being ‘Nationally Critical’, and L. pakeka and L. archeyi being ‘Nationally Vulnerable’) and one ‘At Risk’ (L. hochstetteri ‘Declining’). Three Leiopelma species are listed as extinct—they are known from bone deposits in caves throughout the country until some time in the last 1000 years. Three introduced and naturalised Litoria species are abundant in New Zealand although two (L. aurea and L. raniformis) are threatened in their country of origin (Australia). An additional unidentified frog taxon from northern Great Barrier Island is listed as ‘Data Deficient’.

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.

Classic problems of southern. hemisphere biogeography re-examined Panbiogeographic analysis of the New Zealand frog Leiopelma, the ratite birds and Nothofagus

1. The widely disjunct distribution patterns of the ratite birds and the southern beeches Noithofagus, as well as the apparently anomalous presence of the primitive frog Leiopelma in the New Zealand archipelago, are usually interpreted as due to the fragmentation of pan Austral biota distributed over the ancient southern supercontinent Gondwana. The distribution patterns of these taxa and their relatives are re-examined using Croizat's panbiogeographic method. 2. The biogeography of the New Zealand frog genus Leiopelma and its relatives is discussed in detail. These frogs are shown to exhibit a trans-Pacific biogeographic pattern rather than a trans-Antarctic, Gondwanan or Pangaean biogeographic pattern as claimed by vicariance theorists. 3. Analysis of the geographic distributions of Nothofagus-Fagus and the ratite birds through the construction and orientation of biogeographic tracks for these taxa is discussed in detail. The geographic distribution of Nothofagus-Fagus is shown to be biogeographically homologous with that of Leiopelma and its relatives because both groups of taxa display trans-Pacific tracks. In contrast the ratite birds have trans-Atlantic Ocean and trans-Indian Ocean tracks. 4. The geographic sympatry of the ratite birds, Nothofagus and leiopelmatid frogs in eastern Australasia and southern South America is due to the composite geological nature of these areas. The relationship between the polyphyletic nature of New Zealand as a geological taxon and biogeography is discussed. Zusammenfassung Uberprufung klassischer Probleme der Biogeographic der Sudhemisphare. Panbiogeographische Analyse des neuseelandischen Frosches Leiopelma, der ratiten Vogel und von Nothofagus 1. Die weite disjunkte Verbreitung ratiter Vogel und der sudlichen Rotbuchen der Gattung Nothofagus sowie das scheinbar anormale Vorkommen des primitiven Frosches Leiopelma im neuseelandischen Archipel werden im allgemeinen als Folge eines Zerfalls einer panaustralischen Lebensgemeinschaft aufgefast, die im alten Superkontinent Gondwana vorkam. Die Verbreitungsmuster dieser Taxa und ihre Verwandtschaftskreise werden mit Hilfe der panbiogeographischen Methode von Croizat untersucht. 2. Die Biogeographic des neuseelandischen Frosches Leiopelma und seiner Verwandten wird eingehend erortert. Es wird festgestellt, das diese Frosche viel mehr ein transpazifisches Verbreitungsmuster zeigen als ein transatlantisches. Eine Gondwana- oder transgaeische Verbreitung wird von den Vikarianztheoretikern behauptet. 3. Die Analyse der geographischen Verbreitung von Nothofagus-Fagus und der ratiten Vogel wird mit Hilfe der Rekonstruktion und Orientierung der geographischen Ausbreitung dieser Taxa eingehend durchgefuhrt. Es zeigt sich, das die geographische Ausbreitung von Nothofagus jener von Leiopelma and seinen Verwandten entspricht; beide Gruppen haben eine transpazifische Verbreitung. Im Unterschied dazu haben die ratiten Vogel eine transatlantische and transindische Verbreitung. 4. Die Sympatrie der ratiten Vogel, von Nothofagus and den leiopelmatiden Froschen im ostlichen Australasien and sudlichen Sudamerika ist auf die uneinheitliche geologische Entwicklung dieser Gebiete zuruckzufuhren. Die Beziehungen zwischen der polyphyletishen Natur Neuseelands als geologisches Gebiet and der Biogeographic werden erortert.

Flight of the Huia: Ecology and Conservation of New Zealand's Frogs, Reptiles, Birds and Mammals

The Huia Heteralocha acutirostris (Passerifonnes: Callaeidae) was a remarkable bird, endemic to New Zealand and famous for its sexual dimorphism in beak shape, which allowed differentiation of invertebrate resource collection by foraging pairs. Huia were once widespread throughout New Zealand, but declined rapidly following human settlement due to predation by introduced mammals, habitat loss, hunting and collecting, until their extinction in the early 20th Century. The plight of the Huia is, tragically, parallel to the stories of many of New Zealand?s endemic vertebrates, and is a fitting frontispiece for Kerry-Jane Wilson?s new book which delves into the ecological history of the New Zealand fauna.

B-chromosome origin in the endemic New Zealand frogLeiopelmahochstetterithrough sex chromosome devolution

The endemic New Zealand frog Leiopelma hochstetteri has variable numbers of mitotically stable B chromosomes. To assess whether the B chromosomes were derived from the autosome complement, they were isolated by micromanipulation and their DNA amplified by degenerate oligonucleotide primed PCR. Southern hybridizations of B chromosome DNA probes to genomic DNA from males and females characterized by differing numbers of B chromosomes demonstrated that the B chromosomes were derived from the univalent W sex chromosome characteristic of North Island populations. The presence of homologous B chromosome specific sequences from geographically distinct populations indicates a single origin of the B chromosomes. Furthermore, a primitive homology shared by B chromosomes and the W sex chromosome from an ancestral WZ/ZZ karyotype, which is still present in frogs from Great Barrier Island, shows that the B chromosomes originated soon after the univalent W sex chromosome had originated. Sequence analysis revealed that B chromosome DNA is composed of repeat sequences and has the potential to form stable hairpin structures. The molecular dynamics of these structures may reflect an inherent propensity to undergo rapid change in nucleotide sequence and chromosome structure.

B-chromosome origin in the endemic New Zealand frog Leiopelma hochstetteri through sex chromosome devolution.

The endemic New Zealand frog Leiopelma hochstetteri has variable numbers of mitotically stable B chromosomes. To assess whether the B chromosomes were derived from the autosome complement, they were isolated by micromanipulation and their DNA amplified by degenerate oligonucleotide primed PCR. Southern hybridizations of B chromosome DNA probes to genomic DNA from males and females characterized by differing numbers of B chromosomes demonstrated that the B chromosomes were derived from the univalent W sex chromosome characteristic of North Island populations. The presence of homologous B chromosome specific sequences from geographically distinct populations indicates a single origin of the B chromosomes. Furthermore, a primitive homology shared by B chromosomes and the W sex chromosome from an ancestral WZ/ZZ karyotype, which is still present in frogs from Great Barrier Island, shows that the B chromosomes originated soon after the univalent W sex chromosome had originated. Sequence analysis revealed that B chromosome DNA is composed of repeat sequences and has the potential to form stable hairpin structures. The molecular dynamics of these structures may reflect an inherent propensity to undergo rapid change in nucleotide sequence and chromosome structure.

The evolution of hypervariable sex and supernumerary (B) chromosomes in the relict New Zealand frog, Leiopelma hochstetteri

AbstractChromosomes exhibiting elevated levels of differentiation are termed hypervariable but no proposed mechanisms are sufficient to account for such enhanced evolutionary divergence. Both hypervariable sex and supernumerary (B) chromosomes were investigated in the endemic New Zealand frog, Leiopelma hochstetteri, which is chromosomally polymorphic both within and between populations and has sufficiently elevated variation that different populations can be identified solely by their C‐banded karyotypes. This frog is further distinguished by the univalent, female‐specific W‐chromosome (0W/00 sex determination) uniquely possessed by North Island populations. This sex chromosome exhibited variation in morphology, size, and heterochromatin distribution, sufficient to resolve 11 different types, including isochromosomes. Five of the 12 populations examined also had supernumerary chromosomes that varied in number (up to 15 per individual) and morphology. Specific variations seen among the hypervariable chromosomes could have resulted from heterochromatinisation, chromosome fusions, loss‐of‐function mutations, deletions, and/or duplications. Frogs of the same species from Great Barrier Island, however, had neither supernumeraries nor the female‐specific chromosome. The 0W/00 sex chromosome system must have been derived after the isolation of Great Barrier Island from North Island populations by raised sea levels between 14 000 and 8000 years ago. Furthermore, biochemical divergence between populations is minor and therefore the chromosomal variation seen is comparatively recent in origin. The one characteristic common to all known hypervariable chromosomes is curtailment or lack of recombination. Their accelerated evolution therefore is possible via the mechanism of Muller's ratchet, either alone or in concert with other factors.

Heteromorphism for a Highly Repeated Sequence in the New Zealand Frog Leiopelma hochstetteri

Heteromorphism for a Highly Repeated Sequence in the New Zealand Frog Leiopelma hochstetteri

Cytogenetics of the endemic New Zealand frog, Leiopelma hochstetteri: extraordinary supernumerary chromosome variation and a unique sex-chromosome system

Cytogenetic data from 6 populations demonstrated unusual supernumerary chromosome variation in the primitive frog, Leiopelma hochstetteri. Frogs from the Coromandel Peninsula of the North Island of New Zealand averaged very high numbers of supernumerary chromosomes while individuals from other populations outside of the Coromandel region rarely had more than 1 distinctive supernumerary chromosome found only in females. The maximum number observed was 16 supernumeraries, present in 1 individual from Mt. Moehau. Supernumeraries showed meiotic instability as they failed to pair during prophase I in spermatocytes. In lampbrush preparations from oocytes, supernumeraries appeared as univalents or as highly unusual stellate aggregations consisting of up to 7 chromosomes joined at their telomeres. Lateral loops on lampbrush supernumeraries indicated transcriptional activity. Contrary to a previous hypothesis, high supernumerary chromosome numbers in L. hochstetteri were not correlated with meiotic abnormalities. Neither were supernumerary chromosomes correlated with variations in heterochromatin distribution in the regular chromosomes. Rather, heterochromatin distribution was shown to vary geographically between populations. Sex determination in L. hochstetteri was found to be through a supernumerary, univalent W chromosome. Females in all populations invariably had 1 distinctive supernumerary chromosome not present in males. This chromosome could be distinguished from other supernumerary chromosomes by distinctive C-banding patterns and larger size. The W chromosome has undergone more rapid evolutionary change than the autosomes. Both telocentric and metacentric iso-chromosome forms were found in most populations. Heterochromatin distribution on the W chromosome varied between populations, from very little heterochromatin restricted to the centromere in Coromandel populations to an almost completely heterochromatic W chromosome among frogs from the East Cape region. In lampbrush preparations, the W chromosome was morphologically distinct from other supernumeraries. Loss of a Z chromosome leading to a univalent sex-determining W chromosome is difficult to explain through prevailing theories of sex-chromosome differentiation. The 0W♀/00♂ sex-determination system of L. hochstetteri appears to be unique among animals.