Split Identity: The Flower Crab is Now Four and Other Stories

Life has changed slightly now that I am a full-time graduate student. This allows me a little time during 'office hours' for some research blogging to resurrect this space.

Hot off the press today with lots of interesting new findings is the latest issue of the Raffles Bulletin of Zoology published by the Raffles Museum of Biodiversity Research. I'll highlight two that papers that are closest to my heart.

Male crabs formerly known as Portunus pelagicus. Photo J. Lai.

The first, A Revision of the Portunus pelagicus (Linnaeus, 1758) species complex (Crustacea: Brachyura: Portunidae), with the recognition of four species by Lai et al. found that the crab formerly known as the swimming (or more commonly known in markets as 'flower') crab, P. pelagicus actually has a split identity - it is made up of four similar-looking species.

A species complex is a group of closely related species where scientists are unable to clearly differentiate. Traditionally, taxonomist use a selection of form or appearance to identify and classify organisms. This however, becomes increasingly tricky with very similar looking specimens. Using newer techniques such as molecular phylogenetics to complement morphology, scientist are now able to analyse characters and differences at genetic level and thus shed more light on species within a complex.

Based on morphology and DNA characters, the authors split the original flower crab into 4 species: P. pelagicus from Southeast and East Asia to Northern Australia; P. armatus circum Australia; and P. reticulatus and P. segnis slightly separated in the Eastern and Western Indian Ocean respectively.

It is interesting is that the original P. pelagicus was first described by Carl Linnaeus, the father of modern day scientific classification, and what Linnaeus did not have at that time is the sophisticated DNA analysis technology and know-how that is available today. We have come a long way since then. Now, what would this finding hold in the commercial realm...

Banded leaf monkey carrying infant. Photo A. Ang.

The next paper by Ang et al. records the Reproduction and Infant Pelage Colouration of the Banded Leaf Monkey (Mammalia: Primates: Cercopithecidae) in Singapore.

Prior to the study, little was known about the ecology of the banded leaf monkey (Presbytis femoralis) in Singapore. There were also reports of orange-coloured infants by scientists and veteran naturalists which is not characteristic of the species.

The authors spent 843 hours in the field and confirmed from at least 6 births that infant monkeys are born white, with black markings on the back (dorsum). This is consistent with the same species in Johor, Malaysia.

I had the pleasure of following the first author during their field trips and found that these monkeys were indeed difficult to study and follow due to their shyness and the forebodingly thick, spiky vegetation and boggy terrain. Despite this, Andie has been doggedly following them for the past one and a half years to collect these important natural history information about our local monkeys.

In addition, she collected data on their diet, genetic information from their feces and population size. All of which would contribute to the conservation of the species which now looks more optimistic for one which was formerly said to be doomed to extinction here.

References:

1. Lai, J. C. Y., P. K. L. Ng, P. J. F. Davie. 2010. A Revision of the Portunus pelagicus (Linnaeus, 1758) species complex (Crustacea: Brachyura: Portunidae), with the recognition of four species. Raffles Bulletin of Zoology 58(2): 199-237.
2. Ang, A., M. R. B. Ismail, R. Meier. 2010. Reproduction and Infant Pelage Colouration of the Banded Leaf Monkey (Mammalia: Primates: Cercopithecidae) in Singapore. Raffles Bulletin of Zoology 58(2): 411-415.

Onch Slugfest

Onch slugs (family Onchidiidae) are a group of shell-less gastropod molluscs in the same class as the more familiar snails and slugs. However, they are mostly found in coastal habitats or in the inter-tidal area.

Like snails, onch slugs have a pair of simple eyes on stalks that are only good for detecting light. Most of them look like shell-less snails or a bumpy brownish lump - the word "onch" literally means lump. They are not the prettiest of organisms, but their humble appearance grants them excellent camouflage. It definitely follows the wise adage that if you do not want to be eaten, do not look like food!

One unique characteristic of onchs is that they breath air using a simple lung, unlike marine slugs such as nudibranchs that get oxygen via feathery gills. Hence, onchs are considered pulmonates (from the Latin word pulmonarius, meaning of the lung). In this aspect, onchs are more similar to land snails and slugs.

Since onchs need to breath air, they are usually found above the water level on rocks, tree trunks or even man-made surfaces and in the inter-tidal area during low tide where they feed on algae and organic detritus. They scrape bits of algae off the surface with a rough rasp-like mouthpart called a radula.

Coupling in onchs is a strange affair. These slugs are hermaphrodites bearing both male and female organs. When they get together, they jab each other with hard and sharp love darts in a courtship ritual prior to mating where sperm is exchanged.

A soft-bodied animal living out of water will often face 2 major problems that is dangerous to its health - drying out and predators. Onch slugs are extremely well suited to their habitats and combat desiccation and predators with both structural and behavioural adaptations.

A thick mucus is secreted, covering the skin of the animal to prevent desiccation. In addition, the mucus is also thought to be foul tasting, and any predator attempting to swallow an onch will get a mouthful of a yucky gooey lump. In some species, the mucus leaves a trail for the onch to follow back to their own home.

Some onch can also burrow into the substrate to avoid heat, strong currents and predators. This one below burrowed into the mud within seconds upon sensing danger. Couple excellent camouflage, multi-purpose mucus and a nifty burrowing behaviour, onchs have a lot going for them where survival is concerned.

Unfortunately, on the whole, these charming creatures remain a poorly studied group and little is known about the biology of onch slugs in Singapore. Hopefully, more work can be done in this area to demystify these amazing little slugs.

Further reading:

1. McFaruume, I. D. 1980. Trail-following and trail-searching behavior in homing of the intertidal gastropod mollusc, Onchidium verruculatum. Marine and Freshwater Behaviour and Physiology 7(1): 95-108.
2. Ng, P. K. L. and Sivasothi. N. 1991. Mangrove slugs (Onchidiidae). A Guide to the Mangroves of Singapore Volume 2. Singapore Science Centre.

Estuarine Crocodile: An Ambush Predator

Last month, Peiting of The Simplicities in Life wrote about an estuarine crocodile (Crocodylus porosus) stalking a common sandpiper (Actitis hypoleucos). Since the crocodile did not end up with the bird in its jaws, it led to some speculation that it could have been just on its way up to its favourite busking spot.


Today at the mangrove reserve, two estuarine crocodiles were present and a similar stalking event occurred. One of the subadult crocodiles glided stealthily from the west bank of Sungei Buloh Bersah and approached a common sandpiper on the opposite bank.

Here, it can be seen how having its eyes and nostrils positioned on top of the head allows the crocodile to see above the water and breathe while keeping the rest of its body hidden. Since the species is able to hold its breath comfortably for up to 5 minutes and if forced, stay submerged for more than an hour, it is likely that this exercise which happened within 5 minutes could have been solely to watch the sandpiper.

The reptile then swam past where the sandpiper stood and positioned itself where the bird was heading - in other words, was leading the bird. In an ambush set up, what the crocodile is doing is essentially predicting where its prey will be and positioning itself in the predicted path of its prey.

It seemed that the crocodile's prediction was right and the sandpiper passed right in front of the crocodile. A few moments passed. Both animals appeared to hesitate and that gave the sandpiper an opening to take off, landing on the fallen tree behind.

Despite the fact that no bird ended up in the jaws of this crocodile, this event strengthens the view that the previous record was probably not born out of coincidence and sheds some light on the hunting technique employed by one of our top mangrove predators. As for the crocodile, after the sandpiper's timely flight, it turned itself around to face the opposite end of the river bank.

Though a small bird like the sandpiper may seem like an insignificant meal for a reptile about 1.6 m long, for a "cold-blooded" animal which does not require to burn energy to maintain a constant body temperature, a small bird meal can probably go a long way.

Also, bird-eating is in agreement with studies done on the diet of the species where smaller crocodiles fed mainly on insects, crabs and shrimp then graduate to larger vertebrate prey such as fish, birds and mammals.

After all, it would be a waste for an animal to have evolved one of the strongest bites over the millions of years of its existence if it was hunting only shrimps, beetles and halfbeaks.

Further reading:

1. Taylor, J. A. 1979. The foods and feeding habits of subadult Crocodylus porosus Schneider in Northern Australia. Australian Wildlife Research 6(3): 347-359.

Mangrove Plants 1: Getting to the root of things

Often, I get besieged by botanists (including closet botanists and ornithologists) due to my botanical inaptitude. So here I am atoning for my zoological bias and aversion to all things from kingdom Plantae.

To start off, the swampy mangrove is a good place to introduce and highlight how highly adapted plants can be since there are less than 30 true mangrove plant species in Singapore and many have developed unique adaptations for the habitat.

Here, conditions on the ground is mostly muddy and unstable with low oxygen and high salt content from the sea. This poses various challenges to plants - imagine living in salty quick sand!

Hence, from ground up, plants that have evolved roots for support and coping with low oxygen and salt immediately gain a competitive advantage over those that do not.

One such group is Rhizophora. If asked how does one increase stability? Rhizophora's answer would be to grow more legs.

Members in this group develop prop or stilt roots that branch and loop from the trunk and branches. The result is a network of charmingly grotesque gothic pillars at the bottom of the tree.

When exposed during low tide, these long roots also help with oxygen intake.

These roots also have an additional trick that blocks salt from seawater entering the roots in a process called ultrafiltration.

In Bruguiera and Ceriops, the trees send their roots out far and wide, and increases anchorage by having bent, kneed roots at intervals that resemble the legs of people doing sit-ups on the ground.

This curious structures not only adds stability by increasing surface area of attachment and binding more sediment, but the parts that stick out also helps obtain oxygen.

In Bruguiera, the roots are also said to be able to perform ultrafiltration to remove salt.

Avicennia and Sonneratia also spread their roots far and wide for stability, but have spike-like breathing roots in place of kneed roots.

In spy or adventure movies, characters sometimes hide underwater and breathe using straws or tubes poking out of the surface. Breathing roots, or pneumatophores, work in a similar way.

The roots of Sonneratia are capable of ultrafiltration, but not in Avicennia. The latter, has other tactics which will be discussed in a future post.

But what is most interesting is how unrelated (or only distantly related) groups have somehow acquired similar adaptations at root level for mangrove living. Rhizophora, Bruguiera and Sonneratia can exclude salt when taking in seawater (ultrafiltration), while Avicennia and Sonneratia solve oxygen shortage with spike-like breathing roots.

This phenomenon is what scientists term as convergent evolution. Another example would be how dolphins (order Cetacea) and manatees (order Sirenia) have separately evolved fluked tails for swimming. Oops, mentioned mammals in a plant post.

Further reading:

1. Ng, P. K. L. and Sivasothi. N. 1991. How plants cope in the mangroves. A Guide to the Mangroves of Singapore Volume 1. Singapore Science Centre.

Life Saving 123: Marine Animal Defenses at Pulau Semakau

The rich habitat along the sea shore provides lots of feeding opportunities for animals. However, this comes at a price. Compared to animals on land or in the sea, inhabitants here are vulnerable to predators coming both from the sea and land. Consequently, many have evolved anti-predator defences so as not to end up at someone else's dinner table. Examples of these could be found during our exploratory walk at Pulau Semakau today.

The most basic anti-predator defence has got to be fleeing. If you can't catch me, you can't eat me. Those that do that exceedingly well all eluded my capture on camera. The focus today will thus be on those that could not get away fast enough.

If you cannot get away fast enough, then better hope that your enemies cannot see you.

The hairy crab (Pilumnus sp.) is covered with long hair that breaks up the crab's outline and binds sediments to help it blend with its surroundings. If that does not work, it will dash into the closest crevice for cover.

Taking camouflage one step further, cuttlefish and squids such as this big-finned reef squid (Sepioteuthis sp.) can change their colour to match their surroundings. Another trick they may use is to release a cloud of ink to confuse predators while they make their escape.

If you are as slow as a snail, more extreme tactics will have to be used. A turban snail (Turbo sp.) has a hard shell which it can retract fully into to protect its soft body.

On its foot is a trap-door-like operculum that seals up the

opening. The thick and tough operculum has a rounded surface and protects the snail from the prying pincers of crabs and other predators.

The shape and colour of the operculum resemble cat's eyes and is sometimes made into jewelry.

Sometimes, best defence is offense.

The flower crab (Portunus pelagicus) packs a nasty pinch from its sharp pincers. When threatened, the aggressive crab faces its aggressor head on, pincers ready. On top of that, it is heavily armoured with a shell packed with numerous spikes to discourage predators from swallowing it.

The hell's fire sea anemone (Actinodendron sp.) defends itself from any animal that dares to touch it with a painful sting. This comes from stinging cells tipped with venom and they look like little harpoons under the microscope.

If you are a small shrimp with minimal defensive powers, then it is best to find a powerful ally.

Apparently the stinging cells of sea anemones are so effective that the anemone shrimp (Periclimenes brevicarpalis) have found a way to take advantage of them by living among them for protection. But as if free protection is not enough, this species has been observed feeding on the tentacles of its host anemone!

Today's exploratory walk at Pulau Semakau also saw new records of 3 sea cucumber species for the island's shore. Even though they look helpless, sea cucumbers are able to protect themselves too. Some contain toxins or taste downright foul to predators, others try to confuse enemies by vomiting their guts and other organs out while some produce sticky threads to bind attackers in a gooey mess. Very neat.

From left: Ball sea cucumber (Phyllophorus sp.), Holothuria notabilis, and brown sandfish sea cucumber (Bohadschia vitiensis).

At the end of this trip, I still wonder how people squat over ankle-high water without getting their backsides wet. Must acquire this veritable skill.

Further reading:

1. Bruce, A. J. and Svoboda, A. 1983. Observations upon some pontoniine shrimps from Aqaba, Jordan. Zoologische Verhandelingen 205: 3-44.

Pulau Hantu Recce Trip

The maiden post on the first field trip on the first day of the year is also the first time for me on Pulau Hantu.

After we arrived, a heavy downpour sent the intrepid explorers scuttling for shelter.

We eventually headed out along the northern coast though the small mangrove patch within the lagoon where it was mostly soft and sandy.

Sponges as well as algae dotted the area and we found quite a few golf ball sponges (Cinachyrella australiensis) along a stretch. These multi-celled animals have small dimples all over giving them a golf ball-like appearance.

The golf ball sponge produce spike-like spicules that act like the skeleton of the sponge.

Sponges are filter feeders that obtaining food by trapping bits of particles in the water. A larger body that is supported by spicules will therefore enable the sponge to trap more food.

The yellow internal skeleton can be seen radiating out from the centre of the sponge. Some of these needle-sharp spicules stick out of the surface and can cause great discomfort if they pierce and break in human skin when handled.

Passing the rock walls, many nerite snails (family Neritidae) were seen on and along the rocky surface facing the sea. These gastropods feed on algae which they scrape off using their rasp-like radula, an action which is similar to licking ice-cream!

Further out, a seasonal Sargassum bloom blanketed most of the reef and we had to thread gingerly to avoid stepping on unseen organisms. These algal blooms supposedly tend to occur between December to February which coincides with heavy rain and temperature changes. Over at the northern shore, algal blooms involving a different group of algae (dinoflagellates) have been blamed for the mass death of fish and other marine organisms a few days before this.

A tiger-tailed sea horse (Hippocampus comes) was found hiding among the coral reef. The sea horse is in fact a rather odd-looking fish. It is a rather weak swimmer but it makes up for it by having a prehensile tail that can grasp seaweed or rocks to prevent itself from being swept away by strong currents.

This grumpy looking red egg crab (Atergatis integerrimus) was sitting in a tide pool but moved away as we approached.

Red egg crabs are reef dwellers and can grow to a width of 10 cm.

Although they look very attractive, the bright colours actually serve to warn predators that it is poisonous.

The toxins they contain are not broken down even after cooking and they should not be eaten.

Lying in a tidal pool among the Sargassum was a Bohol nudibranch (Discodoris boholiensis). This sponge-eating mollusc has the ability to break off non-vital parts of itself when attacked while the main body makes its escape. The lost parts will then regenerate later.

One of the last animals of the day literally warmed the cockles of my heart. A heart cockle (Corculum cardissa) spotted by Peiya.

This mollusc has a shell made up of two parts - one convex side and a slightly flatter side. They have been reported to host photosynthetic algae in its body in a relationship known as symbiosis. The cockle benefits from food produced by its tenant, while the algae is sheltered and protected from predators.

Soon, it was time to go and we had to leave our heart-shaped cockle behind. Cool weather, great company and lots to discover. I could really enjoy this!

Thanks to Ron for the organism ID.

Further reading:

1. Farmer, M. A., Fitt, W. K. and R. K. Trench. 2001. Morphology of the Symbiosis Between Corculum cardissa (Mollusca: Bivalvia) and Symbiodinium corculorum (Dinophyceae). The Biological Bulletin 200: 336-343.