Dodos on a Diet

Have you ever thought a photograph made you look fat? Well spare a thought for the Dodo. According to French researchers, portraits of Dodos (Raphus cucullatus) painted by seventeenth century artists may have added quite a few kilos. In fact, some seventeenth century estimates may have doubled the birds’ weight!

A seventeenth century image of a Dodo, painted by an unknown artist.

Using measurements taken from preserved Dodo skeletons, the French team estimated the average weight of an adult Dodo at 10.2kg. In comparison, seventeenth century eyewitnesses suggested the birds weighed as much as 22.7kg (or 50lb). Contemporary paintings often show the birds as large, rotund animals, but the French researchers suggest that this was either because they were exaggerated by the artists, pictures of overfed birds, or the birds were puffing out their feathers in a display of some kind.

To derive their svelt estimate, the researchers measured the lengths of the Dodo skeletons’ femur, tibiotarsus and tarsometatarsus bones. The result was lower than other modern attempts to gauge the mass of the Dodo.

As we’ve seen many times on Hypothesis Now, using preserved remains and fossils to investigate extinct animals can only tell us so much. Given some commentators believe the Earth is in the midst of a sixth mass extinction, this just reinforces the urgent need for conservation of species and entire ecosystems. Once they’re gone, we lose vital information about our world, and there’s no way to get it back.

Incidentally, the researchers here aren’t the only ones that thinks the Dodo could lose a few kilos. A new gallery opening on the 21st January at the Natural History Museum in London will show a seventeenth century painting next to a modern image painted by one of the palaeontologists at the museum. You can find further details of the exhibition here.

Paper reference: Angst, D., Buffetaut, E., & Abourachid, A. (2011) The end of the fat dodo? A new mass estimate for Raphus cucullatus. Naturwissenschaften. On-line first 15th January 2011. DOI: 10.1007/s00114-010-0759-7

Cold weather causes female butterflies to act like males

In the animal kingdom, men usually have to persuade, cajole or bribe their way into a lady’s favour, which means the males of many species cultivate gaudy displays to attract the females’ attention. Yet for one species of butterfly, the situation is sometimes reversed. Some female squinting bush brown butterflies (Bicyclus anynana) spend their time frantically displaying the bright eye-spot patterns on their wings to as many males as they can find in the hope of attracting a mate.

A female Bicyclus anynana showing off her eye-spots. Image: William H. Piel and Antonia Monteiro/Courtesy of Yale University

The role reversal only happens when females are exposed to cold temperatures as caterpillars. According to researchers from Yale University in the USA, the behaviour change helps the female butterflies survive in difficult times: a female who manages to persuade a male to mate with her also receives a parcel of nutrients from the male, increasing her life span. This is particularly important during the cold season, when it is harder for the butterflies to reproduce successfully.

In contrast, the males’ life span is reduced once they give up their nutrient package, so they will very carefully pick the best females. In this case, the ‘best’ is the one with the brightest eye-spot patterns on her wings.

The reason males of most species regularly have to compete for the affection of females is that, usually, mating is cheap for males. Sperm are small and easy to manufacture in their millions, so males can mate with any and every female they find. On the other hand, the female’s eggs need a lot of resources to produce and nurture, so she has to make sure they are fertilised by only the fittest males around. Effectively, the females are a valuable resource over which the males must compete for access.

Very occasionally, however, these roles are reversed. The best-known example of this is sea-horses, where the male becomes pregnant and expends most of the effort required to raise the young. He therefore takes much more care over who he mates with. In the case of the squinting bush brown butterflies, a female who can persuade a male to give up his nutrient-rich gift will live longer. Suddenly the males become the valuable resource, and a prize worth fighting for.

Reference:  Prudic K.L., Jeon, C., Cao, H., & Monteiro, A. (2011) Developmental Plasticity in Sexual Roles of Butterfly Species Drives Mutual Sexual Ornamentation. Science. 331 (6013). pp. 73-75. DOI: 10.1126/science.1197114

The woman who knows no fear

Fear keeps us alive; it primes our bodies to help us avoid or confront danger, and has been described as one of our ‘basic emotions’. But where does fear come from, and what would life be like if one were completely fearless?

Scared of snakes such as this Spotted Python? Image: Wikimedia/Vicki Nunn

American researchers have recently had the chance to find out. They have been studying a woman, known as ‘SM’, with a rare condition which means part of her brain called the amygdala doesn’t work. She is also incapable of experiencing fear, although she can feel the full range of other emotions. The finding supports the idea that the amygdala is responsible for our fear response.

According to the lead author of the study, “Because SM is missing her amygdala, she is also missing the ability to detect and avoid danger in the world. It is quite remarkable that she is still alive.”

To test her fear response, SM was exposed to fearful stimuli such as snakes and spiders, a haunted house and horror films and her response monitored. SM never showed a fear response, and never reported feeling afraid.

Most surprisingly, this even applied when she was holding animals that she claimed to be afraid of. According to the researchers, SM was happy to handle the animals, and was confused by her own behaviour when the researchers pointed out that she had said she was afraid of such creatures.

What about this kimura spider? Image: Aiko Tanikawa/Wikimedia

But what can come from the study of someone such as SM? Potentially, the findings could help doctors treat anxiety disorders. The researchers are also involved with helping soldiers suffering from post traumatic stress disorder – an anxiety disorder caused by experience of a traumatic event. Understanding where fear comes from could one day help doctors treat PTSD by switching off or reducing the fear response that causes the disorder.

The study also demonstrates the importance of small-scale case studies in science. Whereas experiments including large numbers of people and statistically significant results rightly play a major role in much scientific research, there is still a role for smaller studies.

This is particularly true in psychology and other social sciences, where it is impossible or unethical to experimentally modify the participants – no researcher would ever consider deliberately creating brain lesions in people to learn about their brain structure! In these cases, study of rare cases such as SM can allow researchers to access information they cannot learn through other methods.

 

Feinstein, J.S., Adolphs,R.,  Damasio, A., & Tranel, D., The Human Amygdala and the Induction and Experience of Fear, Current Biology, In Press. Available online 16 December 2010. DOI: 10.1016/j.cub.2010.11.042.

Fossils created by a breath of wind

Researchers have found that an icy wind may ultimately have been responsible for the creation of astoundingly well-preserved fossils found in the Soom Shale in South Africa.

A modern glacier in Africa - does this look dusty to you? Image: John Spooner/Wikimedia

The rocks in the Soom Shale contain exceptionally well-preserved fossils of aquatic animals that show not only bones and shells, but muscles and other soft bits, which very rarely fossilise. But how can a gust of wind fossilise so many creatures in such exquisite detail?

According to research conducted by scientists at the University of Leicester, UK, the wind created the perfect conditions for fossilisation. It deposited great swathes of nutrient-rich dust, blown from a nearby glacier, onto the surface of the shallow sea that covered the Soom Shale region 435 million years ago. The nutrients stimulated the growth of algae called phytoplankton near the surface of the water. This died and sank into the depths, where it rotted, using up all of the oxygen.

In these ‘anoxic’, or oxygen-free, conditions, the bodies of the sea creatures that inhabited the region could lay undisturbed by scavengers or bacteria. Their soft tissues such as muscles were left intact long enough to leave faint impressions in the sediment that entombed them.

It was the microscopic structure of this sediment that led the researchers to make their discovery. They found that the sediment here contained large grains mixed in with the expected fine-grained marine sediment. They realised that these large grains must have been blown into the sea from the glacier, and that this would also have brought a supply of nutrients to the sea.

Of the many ancient creatures that dwelled in the shallow sea, some of the most interesting are the conodonts. These were eel-like animals that possessed a notochord – a stiffening rod along their back. The evolution of the notochord was an early step in the evolution of all vertebrates, including ourselves.

Paper Reference: Gabbott, S.E., Zalasiewicz, J., Aldridge, R.J. & Theron, H. 2010. Eolian input into the Late Ordovician postglacial Soom Shale, South Africa. Geology 38, pp 1103-1106. doi: 10.1130/G31426.1

‘Polka-dot’ termite mounds support thriving ecosystems

The regular polka-dot pattern of termite mounds on the savannah of central Kenya supports a great abundance of plant and animal life – more than the region could support without the termites. The discovery, made by American and Belgian scientists, suggests regular patterns like this are so beneficial we should expect to see them in many other ecosystems.

The red dots are termite mounds. Image: Robert M. Pringle/Plos Biology

While studying geckos on the African savannah, the scientists noticed that the lizards tended to congregate around the sprawling termite mounds. Looking more closely, they discovered that it wasn’t just lizards that preferred the mounds – they were covered in a dense layer of plants and animals. The numbers of plants and animals decreased as the scientists moved further away from the mound, suggesting the mounds were responsible for supporting a thriving local ecosystem, but how do they do so?

The scientists aren’t sure. They think the termites, which create elaborate nests up to ten metres across, alter the soil structure by mixing in larger particles of soil. This helps water filter down to plant roots. The termites also seem to stir into the soil more nutrients such as phosphates and nitrogen, which plants need to grow. Increasing the number of plants boosts herbivore and insect numbers, which draws in predators like the geckos.

It doesn’t stop there. The regular spacing of the termite mounds across vast swathes of savannah support a much more productive ecosystem on a much larger scale. The regular spacing means no area is very far from a mound and its life-supporting effects, so the entire ecosystem can be more productive.

The findings should also be useful in completely different environments: conservation work to restore coral reefs or forests can use the idea of regular ‘polka-dot’ spacing to ensure that the fragile ecosystems are as strong as possible while they recover.

Paper Reference: Pringle RM,  Doak DF,  Brody AK,  Jocqué R,  Palmer TM, (2010) Spatial Pattern Enhances Ecosystem Functioning in an African Savanna. PLoS Biology, 8(5). e1000377. doi:10.1371/journal.pbio.100037