A handful of frogs bounce back from brink of extinction

The vulnerability of microhylid frogs, Cophixalus spp., to climate change in the Australian Wet Tropics

The emergence of the global amphibian crisis has seen the extinction of 122 species worldwide, with 18.8% of Australia’s 213 amphibian species being threatened. Despite these declines, little is known about the biology and ecology of certain Australian threatened species. Hence, successful conservation and management of threatened amphibian species cannot be fully realised. Several environmental variables may influence amphibian adult or tadpole assemblages. These variables include, but are not limited to, water chemistry factors (i.e. pH, salinity, turbidity), predation, competition, hydroperiod and water flow. These variables will influence individual species differently, with each species displaying differences in tolerance to these specific variables. The coastal wallum vegetation along the eastern coast of Australia is the primary habitat for four specialist frog species (Litoria olongburensis, Litoria freycineti, Litoria cooloolensis and Crinia tinnula) that are listed as Vulnerable under the IUCN Red List. All species are referred to as ‘acid’ frogs due to their association with low pH waters. ‘Acid’ frog populations within protected areas are believed to be stable. However, populations of ‘acid’ frogs occurring outside of protected areas are at risk from ongoing habitat loss and fragmentation. It is therefore vital that conservation managers know which environmental factors influence ‘acid’ frogs to ensure these environmental variables remain constant and populations remain stable. Furthermore, it is imperative to determine if these environmental variables are the same within anthropogenic waterbodies and if ‘acid’ frogs utilise anthropogenic waterbodies. This knowledge would assist in the future prioritisation of waterbodies for conservation. However, the factors influencing ‘acid’ frog species tadpole and adult relative abundance and occupancy within protected and non-protected wallum heathland waterbodies have not been reported.

Reproduction in variable habitats is characterized by uncertainty and requires selection of suitable conditions. Environmental variability may be temporal, spatial, or both. The same site may differ in its suitability for reproduction at different times within a reproductive period, and several associated sites may differ at any one time (Stearns, 1992). The appropriate response to temporal variability depends on the predictability of the environment. In periodically changing habitats, reproduction at predictably successful times is the normal case, whereas in an unpredictable and changing habitat, assessing and reacting to rapidly changing conditions may be essential. Anurans spawning in rain-filled ponds of unpredictable duration may be expected to synchronize their spawning with rainfall, reproduce more than once per season in favorable years and skip reproduction in unfavorable years (see Barandun and Reyer, 1997a, 1997b; Barandun et al., 1997; and references therein). The response to spatial variability is more complex. In patchily distributed breeding sites, there are three possibilities: (1) individuals can return to their natal site throughout their life, provided the site persists over sufficient time; (2) they can disperse to new sites as juveniles and thereafter remain sedentary as adults; and (3) they can remain nomadic and search for new sites throughout their lives. Dispersal is a common phenomenon among all groups of organisms (Hanski and Gilpin, 1991) and can lead to genetic exchange among populations, colonization of new habitats, and recolonization after local extinction (Greenwood, 1982; Hansson, 1991). When a local population is saturated, dispersal can be favored even when there is only a small chance for individuals to become established in another population (Hansson, 1991). Dispersal does not exclude the possibility that some individuals may return to their natal sites. Whether sexually mature individuals exhibit site fidelity depends on the scale of environmental variability and life expectancy. When reproduction is likely to be successful at the same site throughout an individual's life, site fidelity may be the best choice. Several species of anurans breeding in stable and permanent ponds seem to choose this strategy (Heusser, 1960; Berven and Grudzien, 1990; Reading et al., 1991). Dispersal to new sites will be favored when the suitability of the habitat changes quickly or is unpredictable. Ovipositing in different ponds also spreads the risk of reproductive loss (Kaplan and Cooper, 1984). Empirical data, however, are scarce for anurans, mostly because of methodological constraints. Juvenile dispersal seems to be widespread, but adult dispersal and spawn distribution is poorly documented (Merrell, 1970; Daugherty and Sheldon, 1982; Reading et al., 1991). Bombina variegata uses various ponds for reproduction, most of them temporary (Bauer, 1987). We studied a population in a habitat with a variety of different temporary ponds, where pond conditions change unpredictably within and among years, mainly due to climatic conditions and human activities (Barandun and Reyer, 1997a). The question was whether individuals spawn in a single pond or spread the risk of reproductive failure, mainly due to desiccation (Barandun and Reyer, 1997b), by ovipositing in different ponds within a breeding season.

Philoria is a genus of frogs that are all confined to subtropical and temperate mountain areas in eastern Australia. These mountaintop species are likely to be affected by climate change. Several Philoria species are already threatened with extinction, so the impact of climate change on this group of frogs is of particular interest. Data collected on these species form a baseline for determining their detectability, response to environmental conditions and forecasting distribution under future climate scenarios.

Genetic data for 841 individual frogs in the genus<i> Litoria</i> sampled pre- and post-fire in the Kinglake region, Victoria, Australia <br>

Spread of the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd) poses the greatest emerging threat to global amphibian biodiversity. Bd's low host species specificity allows the disease it causes — chytridiomycosis — to affect many of the 7,000 species of amphibians and drive population declines and extinctions worldwide. Although discovered nearly 20 years ago, the origin of Bd and catalyst of the seemingly recent global disease event remain obscure. Today, this international epizootic continues to advance virtually uncontrolled. Modes of global Bd dispersal are not well understood, hampering the development and implementation of targeted biosecurity efforts to reduce spread. Bd is an aquatic pathogen most often associated with amphibian species that live in or near permanent bodies of water. It can neither survive desiccation nor extended exposure to elevated temperatures, but few environmental barriers appear to impede the spread of Bd. It has crossed oceans, infected terrestrial direct-developing amphibians that do not live in water, and been introduced to every continent (except Antarctica). Although low densities of Bd have been found in the environment outside of a host, amphibians consistently carry the highest pathogen loads and appear to be the primary host organisms that vector Bd. The international trade in live amphibians transports millions of animals annually. Most previous research has focused on this anthropogenic activity as the primary pathway of global Bd dispersal. This is a sensible assumption—the highly visible movement of Bd hosts together with the lack of disease control suggests that Bd-positive animals are commonly transported in these shipments. Unfortunately, all previous surveillance efforts that aimed to demonstrate this phenomenon were performed in animal markets in Bd-positive countries where contamination from domestic Bd could not be excluded as a potential source of infection. Upon close examination of global Bd distribution patterns, I found that regions of Bd presence do not exclusively overlap those of notable amphibian trade, raising questions as to the sources and pathways involved in pathogen dispersal. For instance, despite the absence of commercial amphibian importation to the islands of Dominica and Montserrat, chytridiomycosis drove the near-extinction of the Mountain Chicken frog (Leptodactylus fallax). Likewise, chytridiomycosis emerged in remote wilderness areas in Central America and Australia, again with no clear link to amphibian trade activity. Thus, despite the similar absence of commercial amphibian importation in Madagascar, it seems unlikely that this alone prevents the introduction of Bd. Meanwhile despite intensive field and market surveillance in Hong Kong — a global amphibian trade hub — Bd has neither been detected nor have amphibian declines been observed. Therefore, I hypothesized that additional pathways of Bd dispersal exist in the absence of commercial amphibian trade that can also transport this pathogen global distances. The…

Extinction that killed the dinosaurs may have led to frog explosion

Evidence clearly shows that climate change has affected ecosystems and individual species, challenging species survival and increasing extinction rates. Assessing species vulnerability to climate change is a key topic in ecology and conservation biology. Uncertainty remains as to which species will be most vulnerable and to what extent. An integrative framework has been developed to guide research towards evaluating species vulnerability. This approach proposes that a species’ vulnerability to climate change is dependent upon the synergistic combination of intrinsic (sensitivity) and extrinsic (exposure) factors. Following this framework, I examined how (i) sensitivity to environmental change (i.e. changes in calling phenology, thermal tolerances, and disease susceptibility) and (ii) exposure to environmental change (i.e. detectability, occupancy and species distribution, and thermal environment and microhabitat buffering) influenced the vulnerability of Philoria loveridgei, a direct-developing anuran, in subtropical rainforests of mid-eastern Australia. This allowed me to evaluate the vulnerability of this species to climate change. Sensitivity results indicated that calling phenology and breeding phenology of P. loveridgei were influenced primarily by the spring and early summer rainfall events associated with the start of the calling season. I hypothesise that these rainfall events increase soil moisture, and hence increase P. loveridgei nest moisture and subsequently forming a suitable environment for egg and larval survival. These early summer rainfall events would therefore cue the onset of the calling, associated with breeding. A diurnal calling pattern was identified for P. loveridgei, with a higher calling frequency during the early morning hours.

Burrowing is one of the many locomotor modes of frogs (order Anura) and is found within many clades. Burrowing is generally categorized into two groups: forward-burrowing and backward-burrowing. While forward-burrowing is more rare than backward-burrowing, we show that it has evolved independently at least eight times across anurans and is correlated with distinct features of the external and internal anatomy. The shape of the humerus is especially important for forward-burrowing, as many species use their forelimbs for digging. Using X-ray computed tomography data, we characterize shape variation in the humerus, including three-dimensional (3D) morphometrics, assess the morphology of muscles related to this variation in the humerus, and discuss the mechanical and evolutionary consequences of our results. We show that the humeri of most forward-burrowing frogs are morphologically distinct from those of non-forward-burrowers, including features such as a curved and thick diaphysis, the presence of a pronounced ventral crest, and relatively large epicondyles and humeral head. Our findings also suggest that pectoral muscle anatomy differs substantially among burrowing modes in frogs. This work provides a framework for predicting locomotor modes in taxa for which the natural history is poorly known as well as extinct taxa.

Batrachochytrium dendrobatidis is a fungus belonging to the Phylum Chytridiomycota, Class Chytridiomycetes, Order Chytridiales, and is the highly infectious aetiological agent responsible for a potentially fatal disease, chytridiomycosis, which is currently decimating many of the world's amphibian populations. The fungus infects 2 amphibian orders (Anura and Caudata), 14 families and at least 200 species and is responsible for at least 1 species extinction. Whilst the origin of the agent and routes of transmission are being debated, it has been recognised that successful management of the disease will require effective sampling regimes and detection assays. We have developed a range of unique sampling protocols together with diagnostic assays for the detection of B. dendrobatidis in both living and deceased tadpoles and adults. Here, we formally present our data and discuss them in respect to assay sensitivity, specificity, repeatability and reproducibility. We suggest that compliance with the recommended protocols will avoid the generation of spurious results, thereby providing the international scientific and regulatory community with a set of validated procedures which will assist in the successful management of chytridiomycosis in the future.