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Archive for February, 2011

Following the Madagascar theme of the currently running BBC documentary (Wed BBC2 8pm), today’s photo is a video clip of one of Madagascar’s unique animals, the streaked tenrec Hemicentetes semispinosus.

Tenrecs are Madagascar’s equivalent of a hedgehog or a shrew. Among the streaked tenrec’s strange quirks are the fact that it keeps its family together by communicating using specialised quills (see the clip below) – and it needs to, because tenrecs have the highest number of offspring in one litter of any mammal… up to 32 babies all at once!

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Cane toad (by Sam Fraser-Smith)The cane toad Bufo marinus is originally from South and Central America. In 1935, 101 adult cane toads (followed by a further 62,000 juveniles by 1937) were released in Australia to act as a natural control (through predation) of destructive sugarcane beetles. As often seems to occur however, this biological control itself got out of control – the cane toad rapidly expanded its range and population, and has seriously affected native Australian species.

Cane toads can produce up to 35,000 eggs per female several times each year. The tadpoles quickly develop in just 15-70 days and within a year the toads are adults and ready to breed. Toad appetites are wide-ranging so, unfortunately, the cane toads don’t stick to their proposed diet of sugarcane beetles, but also eat other invertebrates and small vertebrates, such as native Australian frogs, putting pressure on these populations. The cane toad is poisonous in all of its life stages (i.e. as egg, tadpole and toad) and while in the Americas predators such as caiman, snakes and birds have evolved to be able to safely eat the cane toad, this poison has meant that few Australian predators can do so and live to tell the tale; this low death rate results in the toad population continually increasing. The cane toad’s predator poisoning has been shown to detrimentally affect Australian predator populations, for example three lizard species’ populations declined by 80-90% once the cane toad moved in. Additionally, the decline of these lizards resulted in increased populations of their insect prey, as the latter came under less pressure from the predators.Cane toad (by Sam Fraser-Smith)

The cane toad, therefore, is listed by the IUCN’s Invasive Species Group as one of the world’s 100 worst invaders . Despite much research into species-specific diseases or biological control methods that could be used to reduce their numbers, no successful method has yet been found, so the search continues for a means to limit or eradicate the cane toad without affecting native Australian frog species.

References

Shanmuganathan T et al. 2010. Biological control of the cane toad in Australia: a review. Animal Conservation 13 Suppl 1: 16-23

Further Information

Australian Museum
Save the frogs
Cane toads in Oz
IUCN global invasive species database

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Bumblebee (thanks to Sids1)It is likely to come as a surprise to most non-entomologists that there are around 250 species of bumblebee, and that the UK has 24 native bumblebee species including the rare Shrill Carder Bombus sylvarum  and Great Yellow Bombus distinguendus, both of which are under threat of national extinction (two other species have gone extinct in the UK in the last 70 years).

Aside from providing us with honey and wax, bees and many other insect perform an essential ecosystem function estimated to be worth $14.2 billion in 2005 within the EU25 countries – the pollination of our crops and other plants. In addition, some wild plant species can only be pollinated by bumblebees. Changing land use, however (such as the cessation of crop-rotation, destruction of hedgerows, and increased use of pesticides), has put many pollinators under threat, and bumblebees are no exception.

Although each nest contains 50-400 bumblebees, the effective population (which only counts those members that can breed and so contribute directly to the next generation) is only around 1.5 per nest, because the queen bumblebee is the only members of the nest who can produce offspring (and she is fertilised by a single male who has just one set of chromosomes, termed haploid). Bumblebees eat pollen and nectar and where their preferred plants are at low density their nests can be sparsely distributed, resulting in low effective population densities in many preserved area, thatBumblebee (thanks to cygnus921) are not self-sustainable in the long-term.

Conservationists, therefore, have realised we cannot rely solely upon nature reserves to keep bumblebee species extant (surviving). For once, each one of us who owns a garden or allotment can make a direct and significant contribution to conservation by planting bee-friendly plant species, such as heather, foxglove and lavender – and as bees are umbrella species, simultaneously you will be conserving less pretty, but no less deserving, other bugs.

Find out more about what you can do personally to keep our bumblebee species alive at The Bumblebee Conservation Trust – you can even contribute to science by reporting which bumblebee species visit your garden.

References

Goulson D et al. 2011. Translating research into action; bumblebee conservation as a case study. Journal of Applied Ecology 48: 3-8

Further Information

The Bumblebee Conservation Trust 
BugLife
Hymettus Ltd
Bees, Wasps and Ants Recording Society
Xerces Society
Bumblebee.org
Bees and Chicks
– Bumblebee videoclips – BBC

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I’ve been catching up today on the BBC’s latest documentary series ‘Madagascar’ on iplayer. As the name suggests, David Attenborough is exploring the island of Madagascar in a three-part series.

As usual with the BBC the episode is full of beautiful photography with sweeping vistas and rare species. 80% of Madagascar’s plant and animal species are endemic – meaning they are not found anywhere else in the world – including the 80 species of lemur inhabiting Madagascar’s various ecosystems, and some really weird and wonderful looking bugs and reptiles such as the pygmy chameleon who is the world’s smallest reptile and is about the size of a passing ant.

I also always enjoy the BBC’s ‘behind the scenes’ sections that explain how the wildlife photographers got their footage – it’s incredible the lengths these men and women go to, and what they will put themselves through, to get a 30 seconds recording of a rare animal performing some behaviour never previously seen.

Highly recommended series – watch it if you can.

BBC2 – Madagascar

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Ants (by MrMatthewJ)Ants are eusocial insects – they form permanent colonies where only the queen reproduces and all the individual ants are closely related to each other. The ants in a nest all have tasks to perform, such as raising the larvae or defending the nest from intruders. Male ants (drones) are solely present for reproduction; they usually have wings and form mating swarms with virgin queens, after which the males die and the queens lose their wings and essentially become egg-producing machines looked after by the workers. These worker ants are all offspring of the colony’s queen and are all sterile females – they are in fact more closely related to each other than they would be to any offspring and so they work to raise further ‘sisters’ produced by the queen.

There are over 9,000 species of ant worldwide, with many different life strategies. Some species (e.g. army ants) are voracious omnivores (i.e. they eat anything), stripping the forest of living species as they march through. Others (e.g. leafcutter ants) harvest leaves, which they bring back to their nest and use to grow the fungus that they eat. Honeypot ants feed up young worker ants who then become inactive living storage pots ready to feed the nest in times of food scarcity. Other ants enslave ants of a different species, who subsequently carry out all the nest activities required for the slave-Leaf cutter ant (by dullhunk)makers.

Research into one slave-making ant species, Protomognathus americanus, investigated the choice scout ants make when deciding whether to attack a potential slave ant nest or not. Protomognathus americanus cannot survive without slaves (Temnothorax species), relying on them to raise their larvae, forage for food, feed the slave-making species, and defend the nest. Gathering new slaves is, therefore, key to the colony’s survival and during summer scout ants investigate the surrounding area in search of potential slave ants. Once they find a suitable nest, the scout has to decide whether to attack the nest by itself (and try to make off with slave pupae; ants go through four development stages, from egg to larva to pupa to adult ant) or to return to its nest and get reinforcements before attacking. Protomognathus americanus do not have large colonies (usually just a queen, 4-5 slave-maker workers and around 30 slaves), so it is critical that the scout makes the correct decision as their death could detrimentally affect their colony’s survival.

The researchers offered experimental scout ants the choice of two different slave-species’ nests as potential raiding targets, and expected the scouts to chose to attack poorly defended slave nests, as this would be a lower risk strategy. They found to their surprise, however, that the scouts would more often chose to attack larger colonies of slave ants, despite the increased risk of death from the increased number of defending slave ants. The researchers suggest that the scouts may be using the number of slave ants as an indicator of the number of slave ant pupae potentially available for kidnap, as a higher number of slave ants generally indicates a higher number of pupae in the nest. In addition, although the risk of attacking a large slave ant nest is higher for the scout, the potential benefit (in terms of kidnap victims) is also greater and this could reduce the number of raids the slave-making colony needs to make that season – actually reducing the cumulative raiding risk over the length of the summer.

Army ants (by smccann)The slave-making ants don’t have it all their way though. A paper back in 2009 showed that Protomognathus americanus’s workers revolt against their captors by killing and neglecting the slave-making pupae. In the experimental colonies an average 67% of slave-making worker pupae and 83% of queen pupae died. By contrast, less than 10% of slave ant pupae died in Temnothorax colonies, so Temnothorax slaves are selectively killing the slave-maker pupae they are supposed to be raising. By decreasing the number of slave-making ants, this rebellion is likely to decrease the number of attacks, and the power of these attacks, on surrounding slave species’ ant nests, to whom the slaves are likely to be related.

[A particular point I liked about this research was that, according to the methods section of the 2011 article, the scientists put the Protomognathus americanus nests into bags for transporting from the US woodlands where the nests were found to the German laboratory for the experiments – and fed the ants on cookies and tuna in the interim. Somehow feeding your experimental subjects cookies was not quite what I expected to read in a scientific journal on ants!]

References

Achenbach A & Foitzik S. 2009. First evidence for slave rebellion: enslaved ant workers systematically kill the brood of their social parasite Protomognathus americanus. Evolution 63(4): 1068-1075

Burnie D (ed). 2004. Animal. Dorling Kindersley, London. p576

Pohl S & Foitzik S. 2011. Slave-making ants prefer larger, better defended host colonies. Animal Behaviour 81: 61-68

Further Information

Wikipedia
Myrmecos 
Wild about ants 
– London’s Natural History Museum’s leafcutter ant ‘AntCam

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The New York Times website has a slideshow of species recently lost to extinction, or currently hanging on by a thread. I’d recommend having a look, although it makes for very depressing reading.

There are continual arguments about why we should bother to save animals that are on the verge of extinction – or why we should care if a species does go extinct. My personal view, for what it’s worth, is that I find animals inherently beautiful (e.g. the golden toad) and/or interesting (who knew there was a snail that used to give birth to live baby snails [which is what ‘viviparous’ means]?!) and it is absolutely tragic that no one will see a golden toad alive ever again. From a more selfish, human-centric point of view, many animal and plant species could provide us with medical help (e.g. this amazing frog – now extinct). Finally, although extinctions have always happened naturally, the current rate at which species are disappearing is far higher than the usual background rate of extinction (I’ll look for some refs to back this up, but it is published data) – and, far too often, it is human-related effects, such as overhunting, deforestation, the building of dams, or the introduction of invasive species to an ecosystem, that is to blame for a species’ demise. Frankly, what right does any of us have to wipe out a complete species; what gives another species any less right to live on this planet than a human?

Further Information

Strange Behaviours: lost and gone forever
Action BioScience: the sixth extinction

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Parasites are organisms (living things) that require a host organism to survive and reproduce, usually at the host’s expense. Examples are many and include those that live on the outside of their host (ectoparasites e.g. fleas, ticks), and those that live inside their hosts (endoparasites e.g. tapeworms, liver flukes), ranging in size from microscopic viruses that hide inside our cells to large multicellular animals such as parasitic wasps and botflies (if you like gory horror stories, read about the latter here – science is often weirder than fiction!).  

Researchers at Liverpool and Glasgow Universities (1) investigated the nematode Heterorhabditis bacteriophora’s infection of greater waxmoth larvae (nematodes form the Nematoda phylum and are essentially tube-shaped worms, hence their alternative name “roundworms”). Heterorhabditis is an obligate parasite – meaning it cannot survive without a host. As a larval worm, it lives in the soil until it finds an insect larva host to enter. Once inside the insect, Heterorhabditis releases a bacteria species, Photorhabdus luminescens, that kills the insect host and digests it to form a nutrient-rich soup that Heterorhabditis eats. Living off the pre-digested insect, Heterorhabditis matures and reproduces hermaphroditically (i.e. the nematode is both male and female) and the new nematode larvae mature within the dead insect host. Eventually the insect host is devoured and it splits, releasing thousands of new Heterorhabditis larvae into the environment ready to infect another insect host and restart the life-cycle.

While this macabre scene is taking place inside the dead waxmoth larvae, the waxmoth remains potentially attractive to predators, such as birds, because, unlike after a normal death, the larva doesn’t dry out and shrivel. While birds are not affected by Heterorhabditis,  being eaten by a bird would be a big problem for the nematode as it will be killed by the bird’s digestive system.

Robin (thanks to Smudge9000)Heterorhabditis has an ingenious way to avoid this early demise. A few days after Heterorhabditis infects the waxmoth larva, the larva changes colour – it becomes bioluminescent (glows) for a short while, but it also permanently changes to bright pink in colour. Birds have good colour vision, and the research team demonstrated that European robins, Erithacus rubecula, were significantly more likely to choose to eat uninfected waxmoth larvae over infected ones. The team also noticed that if birds did peck at or eat a pink, infected larvae they would later be more likely to choose uninfected larvae, leading the team to suspect that the nematode also makes the waxmoth taste unpleasant. By changing its hosts colour, and reinforcing this colour warning with a foul taste, Heterorhabditis persuades potential avian predators not to eat infected larvae, allowing the parasite to continue its lifecycle in the waxmoth without interference.

References

1. Fenton A et al. 2011. Parasite-induced warning coloration: a novel form of host manipulation. Animal Behaviour 81: 417-422

Further Information

Parasites 
Daily Parasite
Wikipedia
The Life Tree
Aberystwyth University
Nematodes
University of Nebraska-Lincoln
Earthlife
Berkeley University
Wikipedia
Bioluminescence
San Diego Natural History Museum
– National Geographic: why deep-sea creatures glow

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