Snakes – Why No Legs?

One of our members, Jonathan Tan, recently wrote an essay on why snakes have evolved to be legless. We’ve invited him to share it here to help our readers better understand their fascinating evolutionary history. 

Disclaimer: our understanding of the evolution of snakes is itself continuously evolving, so this essay may contain points of contention. 

What causes a new trait to evolve in an organism? When a character becomes fixed, it is usually because it provides a selective advantage that increases that organism’s fitness over competitors’. Many characters also affect fitness only within particular niches, not universally; evolving wings for instance, would probably be less useful in the water than on land.  But tracing the original selective advantage of characters is not simple, as they can subsequently be adapted and repurposed for completely different uses such as how the wings of penguins are used as flippers. This is especially so for taxa with a wide variety of habitats and lifestyles, such as snakes. Today, snakes can be found in aquatic (both freshwater and marine), terrestrial, fossorial, and even arboreal environments. The defining character of snakes to most people is often their lack of legs. But having diversified extensively into so many different niches, the adaptive advantages, selection pressures, and environment that first resulted in their evolution of limblessness can be difficult to figure out. To do so, we must first identify the original conditions in which the very first snakes lived.

What sort of habitat did the first snakes live in?

There are two main hypotheses for the form of the last common ancestor of snakes: a terrestrial burrower, or a marine swimmer[1]. Phylogenetic reconstruction using snake fossils as well as extant species can tell us which is likelier. A reconstruction[2] found it certain that the ancestors of both crown group and total group snakes were terrestrial, but not necessarily fossorial. Analysis [1] of the inner ear vestibular shapes of modern snakes correlating them with habitat type led to the deduction that both Dinilysia patagonica, a Cretaceous era snake sister to all modern snakes, as well as a hypothetical ancestor of all modern snakes had burrowing lifestyles (Figure 1). Furthermore, most basal snake clades are burrowers[3], as can also be seen from Figure 1. Evidence for the fossorial origins of snakes can also be found in the morphology of other limbless squamates. There are two main ecomorphs: the short-tailed (tail at most half body length) and long-tailed (tail about 1.5 times body length). Short-tailed limbless squamates such as amphisbaenians and legless skinks are all burrowers; long-tailed ones such as legless anguids all live on the ground surface[4]. Snakes fall morphologically into the former group, making it highly likely that the ancestral snake was also a burrower, and that its non-fossorial descendants retained this body plan when they recolonised surface niches. Other parts of snake anatomy also suggest their fossorial origins. Snakes have unique eye structures[5] and optic nerves[6] that are the result of the restructuring of original squamate eyes[7]. This secondary re-evolution of visual acuity would be expected if snakes descended from a fossorial ancestor, as most limbless tetrapods have poor vision with reduced eyes due to their subterranean lifestyles[7]. The loss of external ear openings and inability to hear sounds above 1500 Hz in snakes also correlates with the poor hearing of other fossorial limbless squamates compared to surface dwelling forms[8]. Both phylogenetic evidence and morphological comparisons with other limbless squamates thus suggest snakes first evolved in a fossorial habitat.

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Figure 1 Phylogeny of snakes (nested within squamates) showing habitat type and corresponding vestibule shapes[1]. E indicates the hypothetical common ancestor of crown group snakes (70.1% probability burrowing type), F indicates D. patagonica (93.4% probability burrowing type). The more basal snake clades, represented by R. caecus and T. jamaicensis, and A. scytale, are burrowers.

Why did snakes evolve to live in fossorial habitats?

What might have made fossorial habitats such promising environments that snakes evolved to occupy it? Firstly, they provide excellent concealment and protection from predators that lack similar burrowing abilities[9]. A surface predator would be unable to spot snakes concealed in the soil or leaf litter, and if it were to dig for them, a snake could still escape by quickly burrowing away or going deeper. Even today, save for non-fossorial snakes, almost all limbless tetrapods such as amphisbaenids or caecilians burrow in soil or take shelter in crevices for safety[7]. Fossorial habitats also contain a wide variety of small prey items (e.g. rodents and invertebrates) which seek refuge in leaf litter and subterranean environments[9], making it attractive for small carnivores such as snakes. Although many snakes of today take on prey larger than their own heads due to their highly kinetic skulls[9], ancestral state reconstruction[2] suggests the first snakes targeted smaller prey.  Fossorial snakes of today continue to specialise in eating small animals such as rodents, other snakes, or in the extreme case of scolecophidians, ant/termite larvae[10]. Finally, the opportunity to exploit a new niche in the face of competition from other squamates may also have driven snakes underground. Competition with closely related taxa often drives evolution of novel characters to occupy new niches[11], and sometimes in distinct, determinative patterns. For instance, the very same combination of different ecomorphs evolved in anoles independently on four separate Caribbean islands[12]. Similarly, where there is an empty fossorial niche, a limbless squamate is likely to evolve, an event that has happened at least 20 times[4]; even small isolated patches of new fossorial habitat can give rise to novel limblessness evolution, such as the Calyptommatus lizards endemic to the Sao Francisco sand dunes[13]. The presence of so attractive an unfilled niche meant that snakes adapted to fill it; and in the process they became limbless.

How does limblessness help in fossorial habitats?

So how did limblessness benefit snakes when they were adapting to fossorial habitats? Primarily, this had to do with ease of movement. Serpentine body plans, characterised by elongated bodies and limblessness, are very effective for movement through dense herbaceous foliage and loose soil[9]. Fossil evidence shows that snakes became elongated before losing their legs[14]. Elongation – reduction of body diameter to length ratio –  allowed them to access a larger proportion of crevices while expending less energy trying to squeeze through[7]. When they then lost their limbs, snakes further reduced their effective body diameter, improving their ability to hunt for prey in narrow tunnels and small cracks, as well as flee from predators into the soil/leaf litter or find shelter amongst rocks. Elongation also preadapted them to evolving reduced limbs, as it provided the additional vertebrae necessary for lateral undulation to replace walking and the need for functional limbs. Lateral undulation may be more energy efficient than quadrupedal movement because there is no need to lift the body against gravity[15]; retaining extraneous legs that affected the body’s streamlining would also have reduced the efficiency of this new form of movement. Lateral undulation being common in limbless tetrapod lineages (Table 1) which are almost all fossorial, it likely had strong functional advantage in fossorial habitats where there is little space for limbs to work. With legs having lost their main function to be replaced by lateral undulation, even becoming a hindrance in tight spaces and when slithering through substrate, limblessness would have helped snakes better occupy their fossorial niche.

 

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Table 1 Locomotion methods of limbless vertebrates. Note that all the tetrapods share lateral undulation as a form of movement[7]

Conclusion

Limblessness evolved as an outcome of the adoption of a previously unfilled fossorial niche by early snakes, giving them an even greater adaptive advantage in foraging and avoiding predators in an environment where already food was abundant and predators few. But while this accounts for the initial evolution of limblessness, it does not answer why many modern snakes continue to be limbless even as they diversified into new habitats, as they clearly retain the ability to re-evolve legs (e.g. Tethyan snakes from the Cretaceous[16] ). Instead, snakes seem to have evolved a variety of means to overcome the limitations of being limbless in non-fossorial habitats, such as rectilinear motion to climb trees, or sidewinding in deserts[9]. Perhaps there are secondary benefits to limblessness in these new niches, such as camouflage or stealth; or legs on such an elongated body may just be ineffective as a mode of locomotion. While we can understand under what conditions they lost their legs, why losing them was beneficial at the time, and even the process of losing them relative to other traits, we still do not fully understand why they continue to lack them. For now at least, snakes will continue to remain just a little bit of a mystery.

References

[1] – Yi, H. & Norell, M. A. (2015) The burrowing origin of modern snakes. Science Advances. 1 (10), 19 March 2017. Available from: http://advances.sciencemag.org/content/1/10/e1500743 [Accessed 19 March 2017].

[2] – Hsiang, A. Y., Field, D. J., Webster, T. H., Behlke, A. D. B., Davis, M. B., Racicot, R. A. & Gauthier, J. A. (2015) The origin of snakes: revealing the ecology, behaviour, and evolutionary history of early snakes using genomics, phenomics, and the fossil record. BMC Evolutionary Biology. 15 (87), 19 March 2017. Available from: http://bmcevolbiol.biomedcentral.com/articles/10.1186/s12862-015-0358-5 [Accessed 19 March 2017].

[3] – Zug, G. R., Vitt, L. J. & Caldwell, J. P. (2001) Herpetology: an introductory biology of amphibians and reptiles. 2nd edition. San Diego, CA, Academic Press.

[4] – Wiens, J. J. & Brandley, M. C. (2009) The evolution of limblessness. In: Hutchins, M. (ed.).Grzimek’s Animal Life Encyclopedia. Internet edition. Farmington Hills, Michigan, Gale Cengage.

[5] – Walls, G. L. (1942) The vertebrate eye and its adaptive radiation. Bloomfield Hills, Michigan, The Cranbrook Institute of Science.

[6] – Northcutt, R. G. & Butler, A. B. (1974) Retinal projections in the northern water snake Natrix sipedon sipedon (L.). Journal of Morphology. 142 (2), 117-135.

[7] – Gans, C. (1975) Tetrapod limblessness: evolution and functional corollaries. American Zoologist. 15 (2), 455-467.

[8] – Wever, E. G. (1967) Tonal differentiation in the lizard ear. The Laryngoscope. 77 (11), 1962-1973.

[9] – Parker, H. W. & Grandison, A. G. C. (1977) Snakes – a natural history. 2nd edition. Ithaca, New York, Cornell University Press.

[10] – Parpinelli, L. & Marques, O. A. V. (2015) Reproductive biology and food habits of the blindsnake Liotyphlops beui (Scolecophodia, Anomalepididae). South American Journal of Herpetology. 10 (3), 205-210.

[11] – Schulter, D. (2000) The Ecology of Adaptive Radiation. Oxford, United Kingdom, Oxford University Press.

[12] – Losos, J. B., Jackman, T. R., Larson, A., de Queiroz, K. & Rodriguez-Schettino, L. (1998) Contingency and determinism in replicated adaptive radiations of island lizards. Science. 279 (5359), 2115-2118.

[13] – Wiens, J. J., Brandley, M. C. & Reeder, T. W. (2006) Why does a trait evolve multiple times within a clade? Repeated evolution of snakelike body form in squamate reptiles. Evolution. 60 (1), 123-141.

[14] – Martill, D. M., Tischlinger, H. & Longrich, N. R. (2015) A four-legged snake from the Early Cretaceous of Gondwana. Science. 349 (6246), 416-419.

[15] – Chodrow, R. E. & Taylor, C. R. (1973) Energetic cost of limbless locomotion in snakes. Federation of American Societies for Experimental Biology. 32, 422.

[16] – Leal, F. & Cohn, M. J. (2016) Loss and re-emergence of legs in snakes by modular evolution of Sonic hedgehog and HOXD enhancers. Current Biology. 26 (21), 2966-2973.

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13th May 2017 (Sat): FREE Guided Herp Walk @ Macritchie Reservoir

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A long-tailed macaque mother and baby pair (photo taken by HSS member, Sankar).

In an effort to promote an awareness of Singapore’s natural and historical heritage, and to promote conversations amongst Singaporeans, the HSS has begun the Herp Walk! We want to raise awareness, in particular, about Herps! These misunderstood creatures are often thought of as scary or unnecessary, but we want to show Singaporeans that Herps are important and integral to the Singaporean ecosystem!

Our coming walk commemorates Mother’s Day and will take place on Saturday, 13 May 2017, 8.00AM-11.00AM.

Mother’s Day is just around the corner; do bring your mums outdoors and join us for a pleasant morning walk through the Petai Trail of Macritchie Reservoir! (Although it is not mandatory, we highly encourage participants to sign up alongside their mothers.) Our experienced nature guides will point out and share interesting facts about our local wildlife as we go. With enough luck, we may chance upon species like the Oriental Whip Snake and the Flying Dragon!

Register at this link! See you there!

 

Herpy Anniversary to us at Sungei Buloh Wetland Reserve!

On 2nd April, we organized our very first Herp Walk at Sungei Buloh Wetland Reserve. Bleary-eyed, (from having woken up at 5.30AM), the HSS guides and participants shuffled into the Wetland Centre at 8AM. Despite the early start, we were excited to explore the Reserve!

Right off the bat, as we walked out onto the main bridge connecting the Wetland Centre and the trail, a flurry of activity greeted us. Serin’s sharp eyes spotted the distinctive movement of two Smooth-coated Otters further up the river.

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Photo by Mahesh Krishnan, one of our Participants

Closer to where we were standing, we were able to get a great view of two Saltwater Crocodiles (Crocodylus porosus), including the famous “Tailless”. Saltwater Crocs are the largest reptile alive today. They are apex predators, and it takes a well-functioning ecosystem to support predators of their size! So their presence is somewhat indicative of the health of Sungei Buloh Wetland Reserve.

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Photo by Mahesh Krishnan

Evolutionarily speaking, crocodiles are more closely related to birds than they are to other “reptiles”. Birds and crocodilians are both grouped under the clade Archosauria, along with the extinct dinosaurs. So the crocodiles we see today are of somewhat “royal” lineage, and it’s really cool to be able to observe them up close!

Further up the road, we saw a frog, albeit one we didn’t want to see! A Gunther’s Frog (Sylvirana guentheri) sat perched on a leaf at the side of an embankment. This species is not native to Singapore and is possibly an invasive species. It has been recorded locally since 1977 [1]. It was worrying to encounter this species so far within the Nature Reserve.

 

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Photo by Mahesh Krishnan

We walked along a little further and were ecstatic to find a normally skittish Draco sumatranus lizard resting on a leaf. We shortly realized that the truth was much more morbid. The Draco, a female, had a single thread of spider silk wrapped around her neck. It is not entirely clear what transpired, but one possibility is that the lizard had gotten accidentally tangled in the web and strangled by it. This was also a testament to how strong spider silk can be!

draco
Photo by Toh Weiyang, a HSS volunteer

These lizards are able to escape predators by gliding from tree to tree, by expanding their ribcages to spread patagia that they have. You can read more about this at this link.

We were soon treated to our very first snake of the walk! A lovely Paradise Tree Snake (Chrysopelea paradisi) that quickly slithered up a tree. Much like the Draco, it is able to glide from tree to tree! It accomplishes this by flattening its body like a ribbon and jumping off a tree! You can read more about this at this link.

paradise
Photo by Mahesh Krishnan

Not too far ahead, we were treated to two more snakes, both Oriental Whip Snakes (Ahaetulla prasina). These are some of the most common snakes in Singapore, and can even be found in urban areas bordering green spaces. Of course, they are harmless and mean humans no harm!

whip
Photo by Mahesh Krishnan

We also caught a glimpse of a juvenile Malayan Water Monitor (Varanus salvator) catching and attempting to eat a crab. These ubiquitous creatures are the second-largest lizards in the world, after the Komodo Dragon (Varanus komodoensis). Despite their intimidating appearance, they are harmless and will not attack humans unprovoked.

monitor
Photo by Mahesh Krishnan

Finally, near the end of the trail, Serin spotted a Mangrove Pitviper (Trimeresurus purpureomaculatus) coiled up in the foliage at the side of the embankment. These are one of the seven highly venomous snakes that can be found in Singapore and are not commonly seen due to their sit-and-wait behaviour. They are restricted to mangrove habitats like Sungei Buloh.

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Photo by Toh Weiyang

We ended off the walk with a group photo at the Main Bridge. It was a fantastic herp session, with many different herps showing up. A big thank you to ALL the participants and volunteer guides!walk

We’ve enjoyed every day of the last two years because of amazing walks like this. It’s been another wild year of showing Singaporeans how cool reptiles and amphibians are. We would not be able to do this without the constant, enthusiastic support of all of our volunteers and guides! And of course, none of this would be possible without the support of the Singaporean public (That’s YOU!) and the Nature community! A big thank you to anyone who has supported us in any small way over the last two years. Singapore has lots of biodiversity to be seen. We hope we can continue bringing them to you for many more years to come!

References

[1] – Leong T. M. & K. K. P. Lim, 2011. Occurrence of Günther’s frog, Hylarana guentheri (Amphibia: Anura: Ranidae) in Singapore. Nature in Singapore. 4: 135-141.

 

Genomics and Venomics of the sexually dimorphic Temple Pitviper

We invited Dr Ryan McCleary, Postdoctoral Researcher at Utah State University, to contribute a guest writeup about the effort to sequence the genome of the Temple Pitviper.

The Temple (or Wagler’s) Pitviper, Tropidolaemus wagleri, is a venomous snake found in tropical Asia, from southern Thailand; through peninsular Malaysia and Singapore; and into Indonesia (Sumatra and nearby islands). It belongs to the family Viperidae and subfamily Crotalinae (the pit vipers), which have the common characteristics of enlarged, front-rotating fangs and heat-sensing facial pits. The Temple Pitviper itself is extremely unique.

©Herpetological Society of Singapore
A male Wagler’s Pitviper from one of the HSS Herp Walks

Although most snakes have very minor differences between the sexes (what we call “sexual dimorphism”), the Temple Pitviper’s differences are extreme. The females get fairly large-bodied and have colorful spots over their surface, with white, yellow, green, and blue speckling over a black background with yellow bands. The males, on the other hand, are much smaller and narrower in girth, with a fairly uniform light green color and white and/or maroon spots or bars down the body. They are so different that it is really easy to mistake them as being different species. What is even more incredible is that both males and females start off looking the same…like little males! How the change occurs over time is really not known, nor is when exactly it happens.

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Female Wagler’s Pitviper, Photo by Serin Subaraj

Besides the sexual dimorphism, Temple Pitvipers also have a unique venom. Like many vipers, the venom is quite complex, with many different types of toxic proteins present. However, the Temple Pitviper is the only species known to contain a specific family of proteins, the waglerins, in its venom. These waglerins are relatively small (compared to many other toxin protein families) and function as extremely selective inhibitors of neuromuscular activity. It is because of this activity that their venom is currently being studied for potential use in human medicine.

Many Singaporeans may also be familiar with this snake because it is an abundant resident of the Temple of the Azure Cloud (Snake Temple) in Penang, Malaysia. In the Temple, the snakes go about their business unhindered by humans and vice versa. These snakes also rarely bite humans in nature.

We are interested in many aspects of this snake, starting with its natural history and going all the way through the evolution of its venom. We are interested in the genetic basis of the size and coloration differences between the sexes and how this relates to the habits of the species in nature. Do they consume different prey?

Noel 2
Photo by Noel Thomas

Do they inhabit slightly different microhabitats? Is there a sex-based difference in venom composition? The genome will help us to understand the mechanisms by which these snakes produce their venom and exactly what compounds may be found in the venom, including some that may be used as leads for the development of human pharmaceuticals or research tools. Besides this, there are currently two other snake genomes that have been undertaken—the Burmese Python and the King Cobra. The addition of the Temple Pitviper will expand our understanding of snakes in general and venomous snakes in particular, both in terms of their evolution and their relationships with each other.

There is a lot to do before we can answer these questions, but we currently have a great opportunity. Although we have begun the sequencing of the genome, we have not yet utilized an extremely powerful tool known as PacBio sequencing, due to constraints on funding. This type of sequencing is very important to include for various reasons, but one way to think of it is that the normal sequencing is a bunch of puzzle pieces – with no direction and lots of time, you can still make the picture look right. However, PacBio sequencing is like having the photo on the puzzle box to help guide you and make things a lot easier. Pacific Biosciences (the creators of PacBio technology) have selected our project as one of five (out of 200+ applicants) to compete for complimentary PacBio sequencing, but we need your help!

If you would like to see our project—the only project from Singapore and the only one utilizing a herp species—succeed, you can help by voting for us. The winner of the competition will be selected by popular vote. Anybody can get on the website and vote once every day through the end of the competition (5 April 2017) using up to three different e-mail addresses per name.

Noel
Photo by Noel Thomas

 

The website for our project, which includes a video, can be found at:
http://www.pacb.com/smrt-science/smrt-grant/pag2017/temple-pitviper/
We have a Facebook page at:
https://www.facebook.com/TemplePitviperGenome/
And a Twitter feed at:
@TemplePitviper or #TemplePitviperGenome

The competition is stiff, and we need every vote we can get. Thanks for helping!

Ryan McCleary
Postdoctoral Researcher
Utah State University (previously with National University of Singapore)

2nd April 2017 (Sun): FREE Guided Herp Walk @ Sungei Buloh Wetland Reserve

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Did you know that these beautiful herptiles can be found in our local wetlands?

In an effort to promote an awareness of Singapore’s natural and historical heritage and to promote conversations amongst Singaporeans, the HSS has begun the Herp Walk! We want to raise awareness, in particular, about Herps (reptiles and amphibians)! These misunderstood creatures are often thought of as scary or unnecessary. But we want to show Singaporeans that Herps are important and integral to the Singaporean ecosystem!

This walk, which marks our 2nd Year Anniversary will take place on Sunday, 2 April 2017, 8.00AM-11.00AM

Here’s your chance to explore the trails of Sungei Buloh Wetland Reserve with experienced nature guides and learn shareable facts about our local wildlife as we go. With enough luck, we may even chance upon the critically endangered Saltwater Crocodile. Register at this link! See you there!

FREE Guided Herp Walk @ Bukit Timah

©Herpetological Society of Singapore
Beautiful Wagler’s Pit Vipers are often encountered in BTNR!

In an effort to promote an awareness of Singapore’s natural and historical heritage, and to promote conversations amongst Singaporeans, the HSS has begun the Herp Walk! We want to raise awareness, in particular, about Herps! These misunderstood creatures are often thought of as scary or unnecessary. But we want to show Singaporeans that Herps are important and integral to the Singaporean ecosystem!

This walk will take place on Sunday, 12 February 2017, 8.00AM-11.00AM

Come down for a brisk walk up Bukit Timah Nature Reserve, which has recently re-opened! Learn about the Primary Rainforest and see the animals that live within! Hopefully, we’ll be able to see some reptiles and amphibians on the way up and down. Register at this link!

Herping Ubin

Today was the HSS’ first Herp Walk held on Pulau Ubin! Previously, night walks had been held in collaboration with the Vertebrate Study Group (VSG) branch of the Nature Society as part of Pesta Ubin 2016, and HSS members also helped survey for herptiles during BioBlitz Ubin in December last year. Given the rich herpetofauna that we observed during those events, it was a no-brainer to have our first Herp Walk of 2017 at everyone’s favourite kampong getaway. However, we were also heartbroken to learn that the recent oil spill had now affected the mangroves of Ubin; more about this towards the end of the post.

As we started off on the walk, we were greeted by two of Ubin’s iconic Oriental Pied Hornbills (Anthracoceros albirostris) just next to the jetty! These charismatic birds were once extinct from Singapore, before making a return through natural dispersal from Johor; Ubin was their first foothold. It was good to see them still doing well.

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Oriental Pied Hornbill (Anthracoceros albirostris)

Our first herp of the day proved to be a male Sumatran Flying Dragon (Draco sumatranus)! This amazing gliding lizard was high up a coconut tree, flashing its yellow dewlap to ward off rival males. As we scanned the trunks of the neighbouring trees, we spotted a Green Crested Lizard (Bronchocela cristatella) and two more Flying Dragons, basking in the bright sunshine. The Green Crested Lizard, like its introduced competitor the Changeable Lizard, is able to change colour; depending on its mood or need for camouflage, it can switch between black and green.

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Green Crested Lizard (Bronchocela cristatella
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Sumatran Flying Dragon (Draco sumatranus)

It wasn’t long before one of our participants spotted the first snake of the day: an adult Oriental Whip Snake (Ahaetulla prasina), probably the most commonly sighted snake in Singapore. A minute later, a juvenile Oriental Whip was discovered in a bush just next to the adult! Instead of being neon green, young Oriental Whips are a dull brown, perhaps so that their very slender bodies can better resemble small twigs.

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Adult Oriental Whip Snake (Ahaetulla prasina)
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Juvenile Oriental Whip Snake (Ahaetulla prasina)

As we moved on to the mangroves, the fiddler crabs (Uca sp.) were out in force, with dozens of males flashing their bright orange claws to defend their territories and attract females. Mangroves are important habitat for lots of animals including reptiles, such as monitor lizards, snakes, and crocodiles. The Restore Ubin Mangroves project, which aims to promote natural regrowth of the mangrove forests by making the hydrography more favourable for new seedlings to grow, will thus hopefully also create more habitat for these herps to flourish!

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Male Fiddler Crabs (Uca sp.)

Many birds made an appearance throughout the walk, including these two bright balls of energy: an Orange-bellied Flowerpecker (Dicaeum trigonostigma), and a Crimson Sunbird (Aethopyga siparaja)! The former was feeding on the berries of the Singapore Rhododendron (Melastoma malabathricum), also known as Sendudok, while the latter flitted about looking for flowers to suck nectar from. These birds are important to forest ecosystems as they disperse the seeds of plants and help pollinate their flowers.

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Crimson Sunbird (Aethopyga siparaja)
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Orange-bellied Flowerpecker (Dicaeum trigonostigma)

We ended off the walk with a sighting of the introduced Changeable Lizard (Calotes versicolor), and another Green Crested Lizard (Bronchocela cristatella). Both these species have similar niches, though the more aggressive Changeable Lizard seems to have pushed the Green Crested out of parkland and urban areas. Ubin however seems to be one of the few places where both can be easily spotted, possibly due to the unique mix of secondary forest and kampong habitat found throughout the island.

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Bitter rivals: Changeable Lizard (Calotes versicolor) and Green Crested Lizard (Bronchocela cristatella)
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Guides and participants from today’s walk

After the walk ended, most of the guides headed over to Chek Jawa to take a look at the impact of the oil spill. Many of the mangrove roots were covered in sticky black oil, though most of the mudflat seemed clean. There were many workers deployed to clean up the oil that had evaded the absorbent booms just offshore, as well as some volunteers, all wearing protective body suits, boots and gloves. We also received word from our friends at NUS Toddycats that were helping with the cleanup, that a nationally Critically Endangered Keel-bellied Whip Snake (Dryophiops rubescens) had been found coated with oil. Gently retrieving the snake, we rushed it back to the NParks office on Ubin where it was slowly cleaned by staff and left to recover before release. Note: snakes should not be handled except by trained experts, and only where it is necessary and does not harm the snake’s welfare. Do not try this at home!

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Keel-bellied Whip Snake (Dryophiops rubescens). The grimy appearance of its scales is due to oil from the spill
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The snake being cleaned by NParks staff and HSS volunteer Noel Thomas
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Oil cleaned from the snake

 

 

 

 

 

 

 

 

 

 

As the example of the Keel-Bellied Whip Snake demonstrates, oil spills can affect a very wide variety of wildlife; even an arboreal snake like this one may accidentally stumble into oil that has been washed up onto mangrove trees. If we are to protect our biodiversity and herptiles from such threats, we need to be well-prepared to ensure that the oil never reaches the shore, or even better, doesn’t spill into the sea in the first place.  Given the large role that oil has in our economy, this will almost certainly not be the last such disaster. Hopefully going forward, this tragic incident will teach us the lessons needed to better handle future incidents and minimise the impact on our precious wildlife.