What's in a name?

Figure 2: Dorsal view of P. signata with cruciform marking outlined (Image by: Nick Baker, EcologyAsia.com. Used with permission. With annotations by Lesley Chng.)

Pelophryne signata is known as the Saint Andrew's Cross Toadlet, thanks to the cruciform marking featured on its back (Figure 2). This X-shaped mark resembles its namesake, the Saint Andrew’s Cross. The Saint Andrew’s Cross is a diagonal cross, also referred to as saltire (Figure 3). A respected symbol, it is featured on the national flag of Scotland (Figure 4), being the emblem of the country’s patron saint, Saint Andrew the Apostle.¹

When he was crucified as a sacrifice to the gods, he felt unworthy to be bound to a Latin cross, as Jesus had been. He thus requested for a different, X-shaped cross, on which he was bound for three days with ropes at his hands and feet.²

Figure 3: Saint Andrew's Cross

Figure 4: National flag of Scotland, which features Saint Andrew's Cross

Saint Andrew's Cross is also featured in the common name of other organisms. Saint Andrew's Cross spiders (Argiope keyserlingi) weave orb webs that have a full or partial cross in the centre (Figure 5).³ Saint Andrew’s Cross is also the common name for Hypericum hypericoides, a plant from the mangosteen family that has flowers with four yellow petals emerging in a X formation (Figure 6).⁴

Figure 5: Saint Andrew's Cross spider (Argiope keyserlingi) (Image by: John Gollan, Australian Museum. Used in accordance with Fair Use.)

Figure 6: Saint Andrew's Cross (Hypericum hypericoides) (Image by: Mason Brock)

Pelophryne signata also goes by other common names such as Short-legged Dwarf Toad or Lowland Dwarf Toad. Both "Toadlet" or "Dwarf Toad" are terms referring to a small toad, which is apt for P. signata given its diminuitive size.

Biology

Behaviour

A nocturnal species,⁵  males produce calls at dusk,⁶  which have been described as buzzes that are ‘high-pitched’ and ‘insect-like’.⁷ Listen to the call here (obtained from NParks SG BioAtlas).⁸

Figure 7: Male P. signata calling in Bukit Barisan National Park, Indonesia (Image by: Paul Bertner. Used with permission.)

Diet

Pelophryne signata predate on invertebrates.⁹ The adults’ diet includes ants, beetles, and insect larvae. The tadpoles, however, do not need to actively feed while developing.¹⁰ As endotrophic larvae, they rely solely on parental sources of nutrition.¹¹ Their large eggs provide quantities of yolk that decline slowly, sustaining them throughout their metamorphosis.⁷

Reproduction

Pelophryne signata are oviparous,¹² laying large ivory-coloured eggs that are 10% of their total body length.¹³ They require phytothelms (water-filled cavities) in trees as microhabitats for the eggs and larvae (Figure 8).⁷ Once hatched, the tadpoles (Figure 9) are largely greyish and translucent. Their bodies are ovoid-shaped, narrowing at the posterior, with a total length of around 10 mm.¹⁴

Figure 8: Phytothelm used by P. signata tadpoles, sighted in 2008 in BTNR, Singapore (Image by T. M. Leong and S. C. Teo. Used in accordance with Fair Use. With annotations by Lesley Chng.)

Figure 9: Pelophryne signata tadpoles sighted in 2008 in BTNR, Singapore (Image by T. M. Leong and S. C. Teo. Used in accordance with Fair Use. With annotations by Lesley Chng.)

The tadpoles’ mouthparts (Figure 10) and gut offer clues about their feeding strategy. Their mouthparts are described as degenerate,¹⁴ consisting of a simplified oral disc, a single row of teeth on the upper anterior labium, and weakly keratinised jaw sheaths.⁷ The gut is feebly coiled in larvae at limb bud stages.¹⁴ Combined with observations that larvae do not actively forage, spending most of their time motionless, it is postulated that they rely solely on their yolk for nutrition.⁶

The tadpoles complete metamorphosis in approximately two weeks.⁷

Figure 10: Diagram showing anterior view of tadpole mouthparts (Image by: Rudolf Malkmus, Ulrich Manthey, Gernot Vogel, Peter Hoffmann & Joachim Kosuch. Used in accordance with Fair Use. With annotations by Lesley Chng.)

Habitat and ecology

Pelophryne signata inhabit flat or hilly primary forests, at no more than 1000 metres above sea level.¹³

Inger ¹⁵ considered P. signata to be ground-dwellers, highlighting observations of this species on the forest floor. Sightings on low vegetation up to 1.5m above ground had also been recorded, such as in saplings, tree trunks or bases. However, Grismer⁵ suggested that they are seldom on the forest floor, but prefer to perch up to 2m high on leaves and logs at night, or on low branches of shrubs during the day.

Distribution

Global

The geographic range of P. signata is not fully agreed upon by literature, possibly due to its prior synonymy with P. brevipes (See Synonyms) and limited data on this species as a whole. Research publications present different distributions spanning Malaysia and possibly Indonesia (Table 1). According to Leong and Teo,⁷  true P. signata occur in Peninsular Malaysia, Borneo, and the Natuna Islands of Indonesia. However, IUCN describes it as native to Brunei Darussalam and Malaysia, with presence in Indonesia uncertain.¹⁶ Inger & Stuebing also suggested the distribution to span all parts of Borneo, Peninsular Malaysia and Bunguran Islands in Indonesia.¹³ Thus, ranges of P. signata described across literature are not identical, but there is general agreement in its presence in parts of Malaysia.

Table 1: Geographic distribution of P. signata, according to selected literature. Blue-coloured cells indicate presence of the species in the country. Among the literature selected, it is clear that P. signata is most often reported in Malaysia.

Local

Although Singapore is seldom listed explicitly in the range of P. signata (possibly since it is located within the Malay Peninsula, just like Peninsular/West Malaysia), its presence locally has been documented in two studies. According to Leong & Teo,⁷ it has only been recorded in BTNR and its range is likely restricted to the Central Natural Reserves. This corroborates the postulation made by Lim,¹⁷ given that P. signata had not been seen or collected outside BTNR.

Conservation

IUCN lists P. signata as Near Threatened, but also highlights that further investigations are needed to determine suitable conservation action.¹⁶

In Singapore, P. signata are rarely sighted. Before the sighting of tadpoles in BTNR in 2008,⁷ the previous documented sighting of adults was in 1989.¹⁷ Prior to that, the last reported sighting was in 1900.¹⁷ The Singapore Red Data Book lists it as Critically Endangered, with its presence locally compromised by degradation of the BTNR forest.¹⁸ Given the species' reliance on tree cavities for reproduction (See Reproduction), its numbers will be severely impacted by loss of primary forests. Thus, a possible strategy to protect P. signata would be through the use of artificial arboreal breeding habitats. In Singapore, artificial habitats have been successfully constructed as part of a NUS student's Honours Project (Figure 11), so there is potential to implement this at a larger scale.

Figure 11: Screenshots from a newspaper article in The Straits Times on 24 July 2010, which pointed out a possible conservation strategy for P. signata in Singapore. 

Furthermore, any discrepancies regarding its status as a species (See Splitting of Species) could complicate efforts to protect it, making its conservation more challenging.

Taxonomic information

Importance

There are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we know we don't know. But there are also unknown unknowns. There are things we don't know we don't know. - Donald Rumsfeld

Species like P. signata exemplify the complexities of studying taxonomy. Taxonomy functions to enable an objective, universal system to retrieve information. As “documenters of diversity”, taxonomists are especially important in an age of rapid and widespread extinction.

However, if a species has been synonymised or used different names before, there could be lapses in understanding by virtue of “mislabelled information”. Some studies on P. signata, such as that by Leong & Teo⁷ actually cited research about P. brevipes. Because we cannot be absolutely certain if the species referred to is indeed what we now consider true P. signata, the validity of the study’s findings should be considered carefully. This reinforces the importance having original descriptions, type specimens and updated genetic databases to verify research.

That being said, the value of original descriptions and types specimens may be diminished for a species like P. signata. Being nocturnal, morphological features may actually play a negligible role in distinguishing the species. With this knowledge, the initial description by Boulenger back in 1894 seems insufficient to fully confirm its identity today.

So could P. signata be considered a distinct species? Yes, given strong evidence that its locality differs from closely-related species. But even then, further studies are needed to clarify our understanding of relationships in the Pelophryne genus. The case of P. signata could reflect challenges in studying taxonomy in the tropics, where high diversity is concentrated in remote, inaccessible habitats. There is ambiguity even with closely-related species - As evidenced from the lack of a definitive reason for the species’ synonymy and revalidation (See Splitting of species), to varied results produced by phylogenetic analyses (See Position in phylogenetic tree).

Diagnosis

Pelophryne signata are tiny - roughly the size of a Singapore 20 cents coin (Figure 12)! Male specimens average 20.7 mm while females are slightly larger, averaging 24.0 mm from snout to vent.¹⁵

Figure 12: Comparison of life size photo of P. signata with a 20 cents coin (Image by: A. Haas. Used in accordance with Fair Use. With addition of coin for comparison, and annotations by Lesley Chng.)

The head is slightly wider than the body, with an obliquely truncate snout.⁵ Thick fleshy webbing stretches across all fingers, but reaching the tip of only the first finger, while the others are half-webbed.¹⁰ The fingers end with wide, blunt discs.¹³ The visible tympanum is approximately half the diameter of the eye.⁵ The throat is cream-coloured and spotted.¹⁹ A yellow or cream-coloured band passes along the flanks¹⁰ from the eye to the groin. Small brick-red warts cover the black or brown back, which features the characteristic X-shaped marking.¹³

Unlike most members of family Bufonidae, P. signata lack paratoid glands,¹² which secrete bufotoxins in other bufonids.

Figure 13:

(A) Dorsal view of P. signata found in BTNR, Singapore (Image by: Nicky Bay, http://sgmacro.blogspot.com. Used with permission. With annotations by Lesley Chng.)

(B) Broad discs at finger tips of P. signata (Image by: Nick Baker, EcologyAsia.com. Used with permission. With annotations by Lesley Chng.)

Figure 14: Side view of P. signata found in BTNR, Singapore (Image by: Nicky Bay, http://sgmacro.blogspot.com. Used with permission. With annotations by Lesley Chng.)

Original description and type information

Boulenger's original description (Figure 15) in 1894 was based on two syntypes (Figure 16) from Borneo obtained by Mr A. Everitt, and deposited in the BMNH Natural History Museum, London. The species was initially described as Nectophryne signata, before being reassigned to Pelophryne by Barbour in 1938. See Synonyms. 

A notable observation about the original description is that it solely discusses morphological features to identify the species. The limitations of this should be considered, given our current understanding of P. signata as a nocturnal species. Knowing this, perhaps non-visual characteristics (such as calls) should have played a more pertinent role in identifying the species. 

Figure 15: Original description of Nectophryne signata by Boulenger (1894) as Nectophryne signata (Biodiversity Heritage Library)

Figure 16: Type specimen of Nectophryne signata (Biodiversity Heritage Library)

An adult collected from BTNR by Dennis H. Murphy on 27 November 1989 serves as the voucher specimen in Singapore (ZRC. 1. 12425-12429). Five larval specimens were also collected from BTNR by Leong & Teo in 2009,⁷  and deposited at the Zoological Reference Collection at the Raffles Museum of Biodiversity Research (ZRC. 1. 1760). 

Synonyms

Scientific name

Synonyms come about when different names are given to the same species. This may occur if a taxonomist names a species that was actually already described. In the case of P. signata, different names were assigned due to reconsiderations of its phylogenetic placement. The synonyms for P. signata are as follows:

• Nectophryne signata (Boulenger, 1894) - Based on original description.
• Nectophryne exigua (Boettger, 1900)
• Pelophryne brevipes (Peters, 1867) - This is a closely related species, but its history has been intertwined with P. signata, thus some researchers may consider it a synonym. See Splitting of species.

The transfer of the species from Nectophryne to Pelophryne was initiated by Barbour in 1938, who concluded that Nectophryne was an “unnatural assemblage”, due to anatomical differences in the "structure of fore and hind extremities." He also noted that the species in Nectophryne had different localities spanning Africa, India, Philippines and the Malayan region.²¹ Species were thus reassigned to separate genera, each with a smaller geographic range. The new genera proposed were Pedostibes and Pelophryne, with only two species remaining in Nectophryne.

Etymology of scientific name

Splitting of species

As a species, P. signata has experienced a complicated history. It was synonymised under Pelophryne brevipes in 1966 by Robert F. Inger, who also revalidated it as an individual species in 1985. 

The initial synonymy was due to morphological similarity (Figure 17). Both species have a cream-coloured band along the sides of the body, share similar size, shape, size of discs at finger tips and extent of webbing. Inger could “find no characters to separate the Mindanao series of brevipes from the heterogeneous sample of signata.”¹⁵ Despite acknowledging that distinctions between the two forms could potentially be found with further study, he concluded that P. signata and P. brevipes were certainly more closely related to each other compared to other species in Pelophryne. As of the time of publication of this page, no comparison between the larval stages of these species could be found. Given that tadpole mouthparts are a distinguishing feature of the Pelophryne genus, it remains uncertain if there is any difference between the larvae of P. signata and P. brevipes.

Figure 17: Morphologically similar species 

(A) Pelophryne signata (Image by: Foo Sai Khoon. Used in accordance with Fair Use.) 

(B) Pelophryne brevipes sighted in Municipality of Gingoog, Philippines (Image by: Kerry Cobb. Used in accordance with Fair Use.) 

The reasons for the subsequent revalidation, however, are less clear. Even though Inger's work in 1985²³ is frequently cited for this, a closer examination of the literature reveals the revalidation to be implied, rather than explicit. The two species were simply referred to separately, without further explanation. It is postulated that the revalidation was due to the different type localities of each species. The type specimen for P. signata was obtained from Borneo, Malaysia. Other specimens have also been obtained from Sumatra and Singapore. This thus serves as strong evidence that the distribution of P. signata spans Peninsular Malaysia, Borneo, and the Natuna Islands of Indonesia.⁷ On the other hand, the type locality of P. brevipes is Mindanao, an island in the Philippines. Likewise, its distribution was recognised to be restricted to the Philippine islands of Mindanao and Basilan. P. brevipes is thus regarded as a Philippine species. Furthermore, it has also been suggested that P. brevipes should be regarded as a Philippine endemic, so populations elsewhere would be considered a different species.²⁴

Nevertheless, species definition within the Pelophryne genus has proven to be challenging, persisting at typological level at best.¹⁵ This means that species are determined and identified based on local series of individual specimens that are highly similar morphologically (in size, webbing, characteristics of finger tips, tympanum diameter). Moderate variation in colouration is acceptable, as long as the gross pattern is consistent.¹⁵ The type specimens of P. signata were compared to specimens from Malaysia, Sumatra and Singapore. It was found that they were similar in terms of the dilated fingertips, tympanum width, and size range of male vocal sacs and female ova. Even with slight variation in dorsal colouration, from yellowish brown to light brown with dark spots, the cruciform dorsal pattern was noticeably uniform, thereby agreeing with the type specimen for P. signata. Understanding relations between these series at taxonomic level has been challenging, given that specimens obtained from a particular locality tend to be of a similar form.¹⁵

Gene sequences

When investigating gene sequences available in GenBank, it was found that barcoding data is lacking for P. signata. However, the mitochondrial genes for 12S rRNA, tRNA-Val and 16S rRNA are well documented and can be used for comparison between P. signata (Genbank ID: AB746456.1) and P. brevipes (Genbank ID: AB331720.1). Analysis using BLAST suggest 94% identical alignment. Given that the sequence investigated is only composed of 2345 bases, this suggests a significant portion of mismatches or gaps when comparing the sequences. It thus serves as strong evidence for species delimitation between P. signata and P. brevipes. However, there are limitations in the interpretation of this result, given that the genes involved have different evolutionary rates. The results of the comparison by BLAST can be further examined here.

At the time of publication of this page, there were no other gene sequences documented for P. signata on GenBank. Perhaps obtaining sequences for nuclear genes or for well-known markers of species delimitation in animals like the Cytochrome c oxidase subunit I (CO1) gene, could provide further evidence to support its status as an individual species.

Phylogenetic relationships

Importance

Quantifying the uncertainty of a phylogenetic estimate is at least as important a goal as obtaining the phylogenetic estimate itself - John P. Huelsenbeck and Bruce Rannala²⁵

Phylogenetic analyses are valuable supplements to traditional taxonomic methods. Using modern techniques, taxonomic classifications can be further examined based on species' relationships, and maybe even re-ascribed. Using DNA sequences alleviates some problems with historic classifications that rely on morphology, such as in instances of convergent evolution, or differentiating between cryptic species. A phylogeny can also give clues on when particular traits arose in a lineage.

For the several morphologically similar Pelophryne species, phylogenetic analyses can ascertain if there is enough evidence for each species to be considered different from all others, and suggest which species are more closely-related within a clade. But this is still subject to the results of not one, but multiple rounds of analyses. Conclusions should only be taken with certainty if they show consistently strong support across various phylogenies produced. But groups whose monophyly are not as well-supported should also be acknowledged, and given further examination when more genetic data is obtained.

Taxonomic ranking

Monophyly of genus

Species from the Pelophryne genus are can be easily distinguished from other Oriental bufonids.¹⁵ Being predominantly found in forests, most genera in family Bufonidae display partial webbing or no webbing at all (except aquatic species in the genus Pseudobufo, which have full webs). Pelophryne have fleshy webbing (Figure 12), which is unusual in this family. This could serve as evidence for the monophyly of Pelophryne. Within the genus, species can be further divided into one group with rounded toes, and another which P. signata falls into, with toes ending in blunt discs. This distinction is corroborated by molecular analysis by Matsui et al..²⁶

Figure 18: Webbing characteristic of Pelophryne genus

(A) Diagram illustrating fleshy webbing which extends more than halfway along the first finger (Image by: P. Y. Berry. Used in accordance with Fair Use. With annotations by Lesley Chng.)

(B) Manus (hand) and pes (foot) of another species in Pelophryne genus, P. murudensis (Image by: Indraneil Das. Used in accordance with Fair Use. With annotations by Lesley Chng.)

Other distinguishing characteristics of the Pelophryne genus include:

• Very small size, with specimens no more than 40 mm in total length
• No more than seven presacral vertebrae
• Dorsally expanded coccyx that is integrated with sacrum 

• Small clutches of eggs - Pelophryne signata averages at 16 eggs per clutch¹⁴

But certain aspects of this genus still need clarification. Inger¹⁹ noted high similarities among certain Pelophryne species - notably P. albotaeniata, P. brevipes, P. guentheri, P. macrotis and P. signata - with only “minor characters” that distinguish them (Figure 19). He also highlighted P. signata as being highly similar to P. brevipes. In 1954, he ultimately concluded that there were challenges in making a comprehensive comparison due to the insufficient P. signata specimens. But he pointed out the following morphological differences between the two:

• The tympanum in P. signata is distinct, but covered by skin in P. brevipes.
• Both feature a X-shaped mark on the back. However, in P. brevipes, “the mid-dorsal mark flares out at both ends.” But Inger did not include a visual reference to accompany this statement, so it is challenging to be fully certain about what this means.

• Pelophryne signata has a spotted cream-coloured throat and underside. However, the underside of P. brevipes is mostly covered by by a dark pigment.²⁷

That said, in 1966, Inger himself synonymised P. signata with P. brevipes on the basis of similar morphology (See Splitting of Species).

Figure 19: Other similar species from Pelophryne genus.

(A) Pelophryne albotaeniata sighted in Palawan, Philippines (Image by: Jonah van Beijnen. CC BY-NC 4.0)

(B) Pelophryne guentheri (Image by: Frogs of Borneo. CC BY-NC 3.0)

Position in phylogenetic tree

A 2009 study by Van Bocxlaer et al.²⁸ aimed to elucidate phylogenetic relationships of Bufonidae (Figure 20). Using a data matrix consisting of 4339 basepairs of mitochondrial and 1970 basepairs of nuclear DNA, Maximum Parsimony and Maximum Likelihood analyses were done to ascertain the phylogenetic placement of various bufonids. Finally, support values were obtained by non-parametric bootstrapping.

Figure 20: Phylogenetic tree proposed by Van Bocxlaer et al., produced using Maximum Parsimony and Maximum Likelihood. Numbers above and below the branches refer to Bayesian Posterior Probabilities and Maximum Likelihood Bootstrap values, respectively. Bootstrap values discussed are highlighted in yellow.

The cladogram produced suggests strong evidence for a sister relationship between Pelophryne and Ansonia, with a bootstrap value of 100. This study ultimately concluded molecular and biological similarities between the two taxa. They have similar adaptations for a terrestrial environment, such as laying few large eggs that hatch into endotrophic larvae in phytothelms.

The monophyly of Pelophryne as a distinct genus is also well-supported, with a bootstrap value of 100. Within Pelophryne, P. signata shares a most recent common ancestor with an unspecified Pelophryne species (This paper focused on the Ansonia, Pedostibes and Duttaphrynus genera, so the exact identity of this Pelophryne sp. was not specified). Pelophryne misera is considered as basal to P. signata and Pelophryne sp., but this relationship shows the least confidence, with a bootstrap value of 62. Finally, P. brevipes is the most basal in the clade. The bootstrap value for branching of P. signata and Pelophryne sp. is 94.

But these relationships were not replicated exactly in a more recent study by Pyron and Wiens.²⁹ In 2011, they conducted phylogenetic analyses on 2871 amphibian species using Maximum Likelihood (Figure 21). The data matrix examined 12 genes (nine nuclear and three mitochondrial). Similar to Van Bocxlaer et al., support values for this phylogeny were obtained by non-parametric bootstrapping.

Figure 21: Phylogenetic tree of amphibian species propsed by Pyron and Wiens, produced using Maximum Likelihood. Pelophryne signata and relevant bootstrap values are highlighted in yellow.

The resultant phylogeny gives a bootstrap value of 96 for the monophyly of family Bufonidae. It also suggests that Pelophryne is sister to Ansonia. On the surface, this corroborates the study by Van Bocxlaer et al.,²⁸ however, the bootstrap value of 60 should be noted. This is below the 70% threshold that Pyron and Wiens considered to be a well-supported clade, which could prompt further analyses to obtain more certain conclusions.

Within the Pelophryne genus, only three species were examined by Pyron and Wiens. The results suggest confidence in P. misera being more basal, while P. signata and P. brevipes arose later, given the bootstrap value of 100. The bootstrap value for branching of P. signata and P. brevipes is 92.

In general, both phylogenies suggest relatively high confidence in P. signata being distinct from its most closely-related species. But given that neither had a bootstrap value of 100 for this relationship, it cannot be concluded with full certainty that either pair consists of distinct species. Overall, the varied ancestry relationships presented by both phylogenies indicates the need for the Pelophryne genus to be further examined.

Glossary of terms

Bufotoxins: A family of toxins secreted by glands found on the skin of toads.

Endotrophic larvae: Non-feeding embryo or larvae that completely rely on parental sources for immediate developmental nutrition. Nutrition is mostly provided to each embryo by an attached yolk.

Paratoid glands: External skin glands on the back, neck or shoulder of toads. They secrete toxins as a defense mechanism to prevent predation.

Phytothelm: Cavity in a tree or terrestrial plant that accumulates water. It can serve as a microhabitat for insects and other small animals. 

Tympanum: Rounded external membrane located behind each eye on frogs and toads. It transmits sound waves to inner parts of the anuran's ear.

References

Image credits

Figure 1, 2: 

“St Andrew’s Cross Toadlet” by Nick Baker. Ecology Asia, 2018. URL: https://www.ecologyasia.com/images-stu/st-andrews-cross-toadlet_0491a.jpg (Accessed on 13 Nov 2018).

Figure 3: 

“Saint Andrew’s cross” by Offnfopt. Wikimedia Commons, 6 Apr 2015. URL: https://en.wikipedia.org/wiki/Saltire#/media/File:Saint_Andrew%27s_cross.svg (accessed on 15 Nov 2018). Image released into public domain.

Figure 4: 

“Flag of Scotland”. Wikimedia Commons. URL: https://en.wikipedia.org/wiki/Flag_of_Scotland#/media/File:Flag_of_Scotland.svg (accessed on 15 Nov 2018). Image released into public domain.

Figure 5:

“Saint Andrew’s Cross Spider” by John Gollan. Australian Museum, 25 Sep 2015. URL: https://australianmuseum.net.au/st-andrews-cross-spider (accessed on 15 Nov 2018).

Figure 6: 

“Hypericum hypericoides, sandy riverscour of the Locust Fork of the Black Warrior River, Blount County, Alabama” by Mason Brock. Wikimedia Commons, 25 Jul 2014. URL: https://en.wikipedia.org/wiki/Hypericum_hypericoides#/media/File:Hypericum_hypericoides.jpg (accessed on 15 Nov 2018). Image released into public domain.

Figure 7:

"Calling male toad (Pelophryne signata)" by Paul Bertner. Paul Bertner Rainforests Photography, 2013. URL: https://rainforests.smugmug.com/Members-only/Countries-Pro/Indonesia/i-FjDXc8z (accessed on 18 Nov 2018).

Figure 8: 

“Phytothelm of tree hole selected as a larval microhabitat for Pelophryne signata”. In Leong, T. M. & S. C. Teo, 2009. Endotrophic tadpoles of the saint andrew’s cross toadlet, Pelophryne signata (Amphibia: Anura; Bufonidae) in Singapore. Nature in Singapore, 2: 21-25.

Figure 9: 

“In-situ photograph of the early tadpoles (Gosner stage 32) of Pelophryne signata within the confines of the small tree hole”. In Leong, T. M. & S. C. Teo, 2009. Endotrophic tadpoles of the saint andrew’s cross toadlet, Pelophryne signata (Amphibia: Anura; Bufonidae) in Singapore. Nature in Singapore, 2: 21-25.

Figure 10:

“Spiracle not visible, only 1 row of teeth”. In Malkmus, R., U. Manthey, G. Vogel, P. Hoffmann & J. Kosuch., 2002. Amphibians & reptiles of Mount Kinabalu (North Borneo). A.R.G. Gantner Verlag Kommanditgesellschaft, Ruggell.

Figure 11:

"Helping frogs to breed better in the wild". Screenshots from "Helping frogs to breed better in the wild," by Victoria Vaughan. The Straits Times, 24 July 2010. URL: http://newshub.nus.edu.sg/news/1007/PDF/FROGS-st-24jul-pD12.pdf (accessed on 14 Nov 2018).

Figure 12:

“Lowland Dwarf Toad” by A. Haas. In Halliday, T., 2016. The book of frogs: A life-size guide to six hundred species from around the world. University of Chicago Press, Chicago.

Figure 13: 

“Saint Andrew’s Cross Toadlet (Pelophryne signata)” by Nicky Bay. Macro Photography in Singapre, 18 Sep 2012. URL: https://www.flickr.com/photos/nickadel/7999753875/ (Accessed on 9 Nov 2018).

Figure 14: 

“Saint Andrew’s Cross Toadlet (Pelophryne signata)” by Nicky Bay. Macro Photography in Singapre, 18 Sep 2012. URL: https://www.flickr.com/photos/nickadel/7999758958/ (Accessed on 9 Nov 2018).

Figure 15:

“Nectophryne signata”. In Boulenger, G. A., 1894. Nectophryne signata. Proceedings of the Zoological Society of London, 1894: 645.

Figure 16:

“Nectophryne signata”. In Boulenger, G. A., 1894. Nectophryne signata. Proceedings of the Zoological Society of London, 1894.

Figure 17:

(A)

“A distinct ‘X-shaped’ marking is displayed on its back” by Foo Sai Khoon. In Chua, E. K., 2015. Rainforest in a city. Simply Green, Singapore.

(B)

"Pelophryne brevipes male (KU 334658) from 1200 masl, Shrine Site, Municipality of Gingoog, Mt. Lumot, Misamis Oriental Province." by Kerry Cobb. In Sanguila, M. B., K. A. Cobb, C. D. Siler, A. C. Diesmos, A. C. Alcala, & R. M. Brown, 2016. The amphibians and reptiles of mindanao island, southern philippines, II: The herpetofauna of northeast mindanao and adjacent islands. Zookeys, 624(624): 1-132.

Figure 18:

(A)

“Key to Bufonidae”. In Berry, P. Y., 1975. The amphibian fauna of Peninsular Malaysia. Tropical Press, Kuala Lumpur.

(B)

"Left manus (2A) and pes (2B) of holotype of Pelophryne murudensis, new species (ZRC 1.11902)." by Indraneil Das. In Das, I., 2008. Two new species of Pelophryne (Anura: Bufonidae) from Gunung Murud, Sarawak (Northwestern Borneo). Raffles Bulletin of Zoology, 56(2): 435-443.

Figure 19:

(A)

“Palawan Toadlet” by Jonah van Beijnen. iNaturalist, 6 Jan 2014. URL: https://www.inaturalist.org/photos/4214112 (accessed on 14 Nov 2018).

(B)

“Pelophryne guentheri”. Frogs of Borneo, 2018. URL: http://frogsofborneo.org/bufonidae/146-bufonidae/peolphryne/guentheri/114-pelophryneguentheri (accessed on 14 Nov 2018).

Figure 20:

"Bayesian consensus phylogram for bufonid relationships." In Van Bocxlaer, I., S. D. Biju, S. P. Loader & F.  Bossuyt, 2009. Toad radiation reveals into-India dispersal as a source of endemism in the Western Ghats-Sri Lanka biodiversity hotspot. BMC evolutionary Biology, 9(1): 131.

Figure 21:

“Large-scale maximum likelihood estimate of amphibian phylogeny, containing 2871 species represented by up to 12,871 bp of sequence data from 12 genes (three mitochondrial, nine nuclear)”. In Pyron, R. A. & J. J. Wiens, (2011). A large-scale phylogeny of amphibia including over 2800 species, and a revised classification of extant frogs, salamanders, and caecilians. Molecular Phylogenetics and Evolution, 61(2): 543-583.  

This page was authored by Lesley Chng (lesley.chng@icloud.com)

Last curated on 13 December 2018