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Today’s Guardian has a fun quiz – can you name the 10 real animals, and spot the five fictional red herrings?

A recent review paper by Zafir et al on the status of the Sumatran rhinoceros, Dicerorhinus sumatrensis, makes for rather depressing reading. The Sumatran rhino is currently listed as Critically Endangered by the IUCN (click here for an explanation of what this means), and Zafir’s review of current research suggests that there may be just 216 adult rhino left in the wild.

 

The Sumatran rhino is the smallest rhino species and is rather more hairy than its African cousins. It has two horns and lives in tropical rainforest, eating leaves. Although previously found throughout South-East Asia, its population is now restricted to reserves in Peninsular Malaysia, Sumatra and Borneo and it is the most endangered rhino species on our planet. Zafir’s review shows there have been large drops in the rhino populations in many reserves over the last 20 years. In Sumatra’s Kerinci-Seblat National Park, for example, there were an estimated 28 rhinos in 1995, but by 2007 the Sumatran rhino was deemed extinct in this reserve, while in 1995 Taman Negara National Park in Malaysia was a stronghold with 44 rhino, but extensive photo-trapping in 2004 didn’t produce any rhino photographs and track encounter rates were low, suggesting this population has also dramatically decreased.

 Fig 1 from Zafir et al, showing Sumatran rhino distribution.
1 Bukit Barisan Selatan National Park

2 Way Kambas National Park
3 Danum Valley Conservation Area
4 Tabin Wildlife Reserve
5 Royal Belum State Park
6 Taman Negara National Park
7 Endau Rompin National Park
8 Gunung Leuser National Park
9 Kerinci Seblat National Park.

 Poaching remains one of the main threats to the survival of the Sumatran rhino, with 1kg of horn selling for $45,000. A similarly large threat, however, is the effect of small population size – unfortunately, once a population is reduced it can enter a phenomenon known as the ‘Allee effect’, essentially a vicious cycle where the fact that the population is small increases its chances of getting smaller and going extinct through chance events.

 

For example, entirely due to chance there may be a larger number of male rhinos born one year, say a 2:1 skew instead of the normal 1:1 ratio. In a large population this skew would have little effect – if the offspring are 20,000:10,000 then there are still plenty of females around. In a small population though this could be catastrophic – if only three offspring are born that year we now have two males and only one female, and this can affect the long-term prospects of the population. In the case of the Sumatran rhino, these ‘stochastic’ (random) events would also be exacerbated by their long gestation and dependency period of calves – rhino usually only have one calf every three years. Another example is that as a population decreases, it gets more difficult to find a mate and to reproduce. In addition, inbreeding and lack of genetic diversity can also have an enlarged detrimental effect in small populations. These combined factors can result in birth rates too low to replace the population, and so the population will gradually diminish to extinction.

 

The good news is that Zafir et al think the Sumatran rhino can be saved, and they outline the strategies that need to be concentrated on to do so. These include moving (‘translocating’) individuals in isolated populations (that are unlikely to be large enough to be self-sustaining) into a semi captive sanctuary in Sumatra. Here the rhinos can be monitored closely and males and females can be introduced at the best time for reproduction, hopefully maximising reproduction rates. A similar sanctuary has been established on Borneo. The second main strategy is to increase anti-poaching measures for those reserves that do have good rhino populations, as well as greater judicial enforcement when poachers are caught. We need to keep those rhino of breeding age alive to reproduce and build up the populations. These methods will entail considerable funding, although as the authors point out, no more money than was recently paid for an auctioned comic book;  the alternative is yet another species vanishing forever as we watch from the sidelines.

 

Reference

AWA Zafir et al 2011. Now or never: what will it take to save the Sumatran rhinoceros Dicerorhinus sumatrensis from extinction? Oryx 45(2): 225-233

 Further Info
International Rhino Foundation
The Rhino Resource Centre
Animal Info
Ultimate Ungulate 

Allee Effect:
The Encyclopedia of Earth
Endless Forms

Some animals are capable of producing their own light, termed bioluminescence. Reasons for creating this light vary from attracting mates (e.g. fireflies) or prey (e.g. angler fish), for camouflage (e.g. the cookiecutter shark), and to warn off predators (e.g. firefly larvae), and it can be pretty spectacular – check out this fascinating BBC’s Blue Planet footage:

One interesting example is a marine snail, Hinea brasiliana that lives in the intertidal zone (the area that is underwater at high tide, but exposed at low tide). The snail produces blue-green light from cells within two patches on its body – which, unusually, are hidden within the opaque shell that protects the snail’s soft body from predators. This would usually totally negate the point of bioluminescent – if nobody else can see it, what’s the point in emitting light flashes? Research by Deheyn and Wilson, however, has shown that the snail gets around this problem by having a specially adapted shell. It specifically allows light in the blue-green spectrum to pass through it and also diffuses the light, so that the shell is lit up. The researchers think that the snail’s light flashes may act as a deterrent to predators – while its clever shell may prove to be useful  in directing the design of future human-made light diffusing materials.

References

DD Deheyn and NG Wilson. 2011. Bioluminescent signals spatially amplified by wavelength-specific diffusion through the shell of a marine snail. Proceedings of the Royal Society B 278: 2112-2121

This fortnight’s photo(s) of choice are a set of night shots by photographer Martin Dohrn that I spotted on the BBC Wildlife Magazine website. He’s taken some really interesting thermal images and beautiful after-dark shots of African wildlife that give an unique view of life in the bush. Check them out here.

Interesting news articles on the BBC’s website today discuss animals with extraordinarily long life-spans, including a lobster that can live to age 85 and a jellyfish that is essentially immortal, and how time-lapse photography has revealed how emperor penguin huddles function to keep all the group members warm at -45 degrees C. Well worth a read.

On May 4th, a red-crested tree rat, Santamartamys rufodorsalis, showed up at an eco-lodge in Columbia. What was more surprising than usual about this animal sighting was that this species was last seen in 1898 and was thought to be extinct! The rather charming rodent stuck around for an impromptu first-ever photo-call, before disappearing back into his cloud forest home.

Red-crested tree rat (photo thanks to Lizzie Noble)

The team with a landed Great White Shark

The team with a landed Great White Shark

I’m currently absorbed by the new series of ‘Shark Men’, which follows a group of marine biologists and fishermen who haul in (live) great white sharks to take samples and radio-tag them before releasing the sharks back into the wild to relay back their secrets via satellite.

Great white sharks are very under-researched and simple questions about their lives, such as where females give birth to their young, are still mysteries. The Shark Men aim to answer some of these questions and, as well as tagging, they take blood samples for testing hormone levels, DNA samples, and photos for ID referencing the sharks in future. It certainly makes for compelling watching – and I’d love to be a member of their crew; talk about a job where you’d be jumping out of bed with excitement every morning!

Shark Men California is on National Geographic Wild in the UK, daily at 5pm (repeat at 8pm) – and here‘s a clip of the old series to whet your appetite.

Nephilengys malabarensis (thanks to Pen Araneae)Human males in the pubs and clubs this Bank Holiday weekend participating in the UK’s human mating ritual have it easy compared to the male spiders of the species Nephilengys malabarensis, found in South-East Asia. Researchers have demonstrated that these males risk amputation and death in their attempts to woo their women.

Kralj-Fiser et al ran experimental encounters between male and female N. malabarensis. As with many spider species, the female, at 20mm, is much larger than the male, who is a mere 4mm long by comparison. Males approached the female warily, waving their legs and shaking the web to test the female’s  mood. If she was receptive, she orientated towards the male and he then approached and mated, inserting his palps into the female’s genital tract, transferring his sperm to the female.

Palps

Mating always resulted in amputation of the palp, either immediately (87.5% of palp insertions) or via self-amputation of disfigured palps by the male after mating, leaving the males as sterile eunuchs. Despite this sacrifice by the male, 75% of successful matings ended with the male being attacked and eaten by the female!

While it would seem logical that becoming a eunuch is not the best evolutionary strategy to take, counter-intuitively, becoming a eunuch is a successful mating strategy for these males. For a mating strategy to be successful, the male’s actions need to result in the best chances of offspring. Male N. Malabarensis spiders can only fill their palps with sperm once because spermiogenesis (the final stage of sperm manufacture) stops when males reach adulthood, so it is likely that one chance at mating with each palp is all they get, making amputation less of a loss than for species that can mate multiple times with multiple females. Additionally, the broken palp usually breaks off while still in the female, acting as a plug and blocking mating access for subsequent males, thus ensuring that any offspring are the eunuch male’s progeny. Furthermore, surviving male eunuch spiders were subsequently most aggressive in guarding their females against incursion by rival males, and usually won male-male contests, perhaps due to enhanced agility after the loss of the large palps. All these actions help to increase the male’s odds of paternity of the female’s future eggs, passing on his genes to the next generation. So, for this species at least, becoming a eunuch is a surprising but successful male mating strategy.

Reference

S Kralj-Fiser, M Gregoric, S Zhang, D Li and M Kuntner. 2011. Eunuchs are better fighters. Animal Behaviour 81: 933-939

All sea turtle species are classed as threatened or endangered by the IUCN and the hawksbill sea turtle, Eretmochelys imbricata, is considered critically endangered. Mammalian predators, such as mongooses, can destroy more than 80% of turtle nests on beaches so, if nest predation could be predicted, this is a life-stage on which conservationists could have a large impact. With this in mind, Leighton et al used seven years’ of data on hawksbills on Bath beach in Barbados to analyse the impact of nest predation by the small Asian mongoose, Herpestes javanicus, a species introduced into the Caribbean by humans in the late 1800s to control rodent numbers in the sugar cane plantations.

Hawksbill turtle (thanks to Prilfish)

Bath is one of the hawksbills’ primary nesting beaches and the turtles visit year-round, with a peak in June-August. Sea turtles are aquatic, spending nearly all their lives at sea, but the females have to come onto land to lay their eggs. At Bath female hawksbill turtles come out of the ocean and onto the beach at night to dig nests where they lay their eggs before heading back to the sea. The eggs stay hidden beneath the sand for around 60 days, after which hatchling turtles emerge and race to the tideline to begin their aquatic lives. Aside from crabs and insects, which can remove portions of a clutch of turtle eggs, the Asian mongoose is the only predator of hawksbill eggs at this site.

Data were collected during daily beach inspections where the researchers carefully checked nests to determine the incubating eggs’ fate. The results showed that mongooses preyed on 27% of nests over the seven years (individual yearly rates varied from 17.8 to 38.9%). Interestingly, the risk of predation was highest for newly-laid nests and this risk declined rapidly with nest age before gradually rising again near hatching time. There was also higher predation in nests dug in areas with vegetation, rather than open beach; those in vegetation had less than 50% chance of survival to hatching. For nests on the open beach (but not for those in vegetation) there was a strong impact from the density of nests –a large number of other nests within 5metres lead to greatly increased predation rates. Finally, the later in the season a nest was laid, the lower its survival. These results suggest that anti-predator conservation efforts for the hawksbill turtle should be concentrated on protecting new nests, and nests close to, or in, vegetation.

Reference

PA Leighton, JA Horrocks and DL Kramer. 2011. Predicting nest survival in sea turtles: when and where are eggs most vulnerable to predation? Animal Conservation 14: 186-195

Further Info

– Animal Diversity Web – Hawksbill turtle
– Arkive – Hawksbill turtle
–  See turtles – Hawksbill turtle
Sea Turtle Conservancy  

This is a great shot, not only due to the beautiful colours, and the fact that underwater photography is tricky, but also because this is a macro photo and yet perfectly in focus – apparently the cuttlefish is only 1cm long in real size. Neil Liddle’s got some lovely other shots from around the world on his Flickr page too, which are well worth a look.

Flamboyant Cuttlefish Macro