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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

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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

Following the April Fools’ tradition, there have been a number of animal-related spoofs released on April 1st in recent years. Here are the few I’ve spotted:

– Gorillas at Port Lympne wild animal park have their behavioural enrichment taken to new levels by the introduction of iPads.

– Maintenance workers at the Tower of London unearth what could be a unicorn skeleton.

– Do you want to know what your pet is saying? Use the handy Google Translate app.

And my all-time favourite – flying penguins; you’ve got to love the BBC’s special effects team for their ingenuity [you can also click through to another video showing how they made the penguins fly]

If you know of any others, it would be great to hear about them!

Asian elephant (thanks to Kabacchi)Behaviourally, wild elephants perform many actions that suggest cooperation among their herd, such as looking after other mothers’ calves, helping herd members out of mud and other sticky situations, and collectively protecting the herd’s calves against predator attacks. Proving elephants cooperate with each other experimentally, however, is difficult – not least because elephants are huge and potentially dangerous animals to be doing experiments with!

In this week’s PNAS, Joshua Plotnik and his fellow researchers devised a clever experiment with Asian elephants, Elephas maximus, at the Thai Elephant Convservation Center. Adapting a test previously used with chimpanzees, the researchers provided pairs of elephants with a challenge – a table with food on it lay behind a net just out of the elephants’ reach, but a rope had been curled around the table and one end of this rope lay in front of each elephant. If just one elephant pulled their rope end, the rope pulled free of the table and so neither elephant got the food, however, if both elephants pulled their rope simultaneously, the table was pulled towards them and they were rewarded by being able to reach the food.

The research demonstrated that not only did the elephants quickly learn this task, they also learned to wait by their rope for their partner to be released before pulling on the rope (up to 45 seconds after their own release and access to the rope).  In addition, two elephants devised their own method for getting the food; one would wait for his partner to be released – but he waited by the partner elephant not by the experimental apparatus. The second worked out that she could stand on her end of the rope and the other elephant would then do all the pulling!  Finally, in control trials, where one elephant’s rope was out of their reach (i.e. the task was impossible), the elephants gave up before, or soon after, their partner gave up, suggesting that they recognised it was their partner and not just tension on the rope that they required to complete the task.

Although this behaviour perhaps does not sound that impressive to us humans, it is in fact pretty unusual for the animal kingdom. Humans are masters of cooperation with peers, but most other animals cannot coordinate their behaviour to work as a team to gain a reward (examples of animals that can include apes, dolphins, and domestic dogs). In similar experiments to this, for example, rooks (Corvus frugilegus) did not wait for their partner if the partner’s release was delayed. The elephants’ ability to learn this type and level of cooperation between two individuals, therefore, puts their cooperation skill level on a par with chimpanzees.

Reference

JM Plotnik, R Lair, W Suphachoksahakun, FBM de Waal. 2011. Elephants know when they need a helping trunk in a cooperative task. PNAS 108(12): 5116-5121

Further Information

Asian elephants:
The Encylopedia of the Earth
WWF
National Geographic

Cooperative behaviour:
Game theory and the Prisoner’s Dilemma
Cooperative behaviour meshes with evolutionary theory – SciencDaily
How did cooperative behaviour evolve? – Science 

Squid (not the correct species, but gives you an idea! Thanks to Dan Hershman)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.

Flounder (thanks to jurvetson)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.

Squid (thanks to icelight)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  

This fortnight’s highlight is a collection of photos by the Smithsonian Institute taken by scientists using camera-traps. Camera-traps are an important tool in zoology research nowadays. Essentially a camera-trap is an infra-red (or, less usually, pressure pad) triggered camera (sometimes pair of cameras) set up across a trail or at a place where the target animal is likely to pass (such as a scent-marking point, salt lick, or waterhole) that takes a photo automatically when an animal breaks the infra-red beam (or stands on the pressure pad). They allow scientists to see rare and cryptic (camouflaged) animals, to make population estimations of animals in dense habitat such as rainforests where you don’t usually see the animals, and to prove that certain species are present or using particular habitats. And as a nice bonus, you get some interesting and beautiful photos of some of the rarer and more secretive animals on our planet.