‘Shark Men’ series returns

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.

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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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Research News: Predicting sea turtle nest predation

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.

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  

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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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Animal April Fools’ Hoaxes

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!

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