Research News: Bioluminescent snail has special shell

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

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Immortal animals and how emperor penguins keep warm

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.

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Research News: Mating is a risky business for male spiders

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.

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

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Photo of the Fortnight: cuttlefish

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.

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Research news: squid vary their defence tactic depending on the predator

In order to survive, prey species need to use different tactics to put-off or escape from predators with different hunting techniques, and recent research has demonstrated that longfin inshore squid, Loligo pealeii, do exactly that.

Staudinger et al analysed experimental predator-prey trials filmed in an indoor research tank between squid and bluefish (Pomatomus saltatrix; 35 trials; 86 interactions) and squid and flounder (Paralichthys dentatus; 29 trials; 92 interactions). Squid are prey for many species of fish, mammals and seabirds and are soft-bodied without the defence of shells, spines, or stinging cells. They, therefore, have evolved a wide range of defence behaviours including the ability to change colour in order to camouflage with their background, and the squirting of ink while fleeing to confuse predators, but the researchers wanted to know whether these behaviours consistently differed depending on the type of threat.

In the trials where squid were confronted with bluefish, which actively swim around in a school (group) hunting for their prey, the squid were more likely initially to use a ‘stay’ response (69%, 59/86 interactions) such as dropping to the bottom of the pool while changing their colour to camouflage against the floor’s gravel and sand substrate. The squid would then remain motionless on the pool bottom unless a bluefish demonstrated it had spotted them by orientating into an attacking posture, upon which the squid would switch to a ‘flee’ behaviour such as flight or inking and fleeing.

When attacked by the ambush predator flounder, which hid in the tank substrate, however, squid less rarely used ‘stay’ tactics (20%, 17/92 and never dropped to the floor to camouflage themselves. Instead the squid switched to ‘flee’ as their most frequent initial response to a flounder attack (44%, 40/92 attacks), using various ‘flee’ strategies including the group of squid scattering in multiple directions,  and a blanch-ink-jet behaviour (where the squid turned transparent, ejected an ink cloud and then jetted away from the threat).

The two different initial responses to bluefish and flounder were statistically significant behavioural differences, demonstrating that the squid recognised the danger posed by each predatory species and took different avoidance action depending on the type of threat.

Although further research needs to be done to ascertain whether these squid anti-predator responses are species-specific (i.e. to bluefish and flounder) or more general (i.e. the response is similarly divided for all ambush and all cruising predators), this paper is an interesting start to deciphering the complexities of the longfin squid’s predator responses.

Reference

MD Staudinger, RT Hanlon, F Juanes. 2011. Primary and secondary defences of squid to cruising and ambush fish predators: variable tactics and their survival value. Animal Behaviour 81: 585-594.

Further Info

– Wikipedia – Longfin inshore squid
– Animal diversity web
– Marine biological laboratory  

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Is your garden bumblebee-friendly?

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, that 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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Slave-making ants

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-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.

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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Photo of the fortnight: extinct species

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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Research News: Nematode parasite causes insect host to change colour

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.

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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Research News: Spiders fooled into becoming lunch by assassin bugs

Most predators rely on their camouflage and behaviour to get close enough to their prey to strike before the prey notices them and can take avoidance actions. A few predators, however, use an alternative plan – they don’t hide their presence but instead use deceptive means to stop the prey recognising that they are in fact a predator. These “aggressive mimics” use lures that represent a different species to trick their prey into coming closer; for example the anglerfish uses a dangling lure that imitates a worm or bug to encourage smaller fish to approach this ‘food’ before the small fish instead becomes the meal. Bolas spiders, by contrast, produce imitation female moth pheromones that lure male moths close enough to the spider to be caught.

An Australian research team has shown that assassin bugs of the species Stenolemus bituberus use two separate techniques to catch their spider prey. When stalking, the bug will slowly creep towards the spider until it is in striking distance. Its second technique is very different – the assassin bug will lure the spider to approach within striking distance by plucking the spider’s web threads, pretending to be prey caught in the spider’s web.

By comparing examples of web vibrations made by the assassin bugs to those made by actual struggling prey, falling leaves (which elicited no response from the spiders), and courting male spiders (which prompted the females to take up a mating position), the study demonstrated that the bugs specifically imitate the vibrations made by struggling prey. Spiders can be a dangerous prey that can counter-attack and eat the assassin bug instead, and high-frequency vibrations can lead to a fast, aggressive approach by the spider that could endanger the assassin bug. By mimicking weakly struggling prey using low-frequency vibrations instead, the assassin bug lures the spider into a slower, less dangerous (to the bug) approach by the spider that enables the bug to effectively draw the spider within attacking range for an easy arachnid meal.

Reference

Wignall AE and Taylor PW. 2010. Assassin bug uses aggressive mimicry to lure spider prey. Proceedings of the Royal Society B doi: 10.1098/rspb.2010.2060

Further Info

Angler fish
– National Geographic
– Sea and Sky
– Arkive

Bolas spiders
– University of Kentucky
– Video of the spider lassoing prey (not for arachnophobes!)

Assassin bugs

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