Wednesday, 24 March 2010

The Russians are coming?

The Muscovy duck - surely this must be an immigrant to Brazil right? Maybe from Moscow? After all there are feral populations around Britain and they can withstand pretty cold temperatures (down to -12). The gourmets amongst you may know it as the Barbary duck, which means it comes from North Africa? Wrong again! It's actually a native of South and Central America, the name deriving from their "musky" smell, as described by the famous biologist Linnaeus. They seem to be pretty easy to domesticate, and were farmed all over Latin America before the Spaniards arrived.

Quite large for a duck, they do apparently make a good meal, with a strong flavoured meat. Ironically, this has probably helped it as a species, as populations have been imported to North America, Asia and Europe, and subsequently become feral. They can cross breed with local Mallards, and although the offspring are sterile this has been encouraged by duck farmers, for two very different reasons. Firstly, crosses grow fast like Mallards, and large like Muscovies. Secondly, for the Jewish market. Now, I am open to correction on this, but as I understand it........ the Torah lists those foods which are kosher, and only these can be eaten, and this does not include ducks. However, there is a dispensation for animals that have been eaten historically, which covers Mallards, and those domestic ducks derived from them. South American Muscovies weren't eaten by ancient Israelites BUT, if crossed with Mallards the offspring are, sort of, Mallards. Apparently, there is a long running discussion about this.

I've got rather a soft spot for Muscovies as they form one of my earliest memories, on a little pond in Norfolk. So perhaps I'll stop talking about eating them, and talk about biology instead. They eat plant life, insects, and small fish if they can catch them, and domestic ones are said to be great for removing insects and weeds from a garden, and even mice apparently. They live in small groups of 4-12 rather than pairs, and are pretty polygamous, both reasons why they domesticate so well, and lay huge clutches of eggs, 8 to 16. The drake won't incubate the eggs, but he will hang around and protect the ducklings, and Muscovy drakes can be quite aggressive.

So, the Muscovy duck. A duck of the world, but not from Muscovy.

Wednesday, 17 March 2010

Fever in the forest - addendum

Lots of good questions! Thanks guys, it´s really nice to get feedback.

Steve, from what I know, Aedes aegypti can feed during the day, but they are more active around dusk. It´s complicated though, as Vitoria is being invaded by another species that can transmit Dengue, Aedes albopictus, and this is around all day. Worse still, it´s very nervous and flits away before finishing a good meal, so it has to bite lots of people.

I'm not sure that socks give you such immunity! Mosquitoes hunt you down by first following a trail of CO2, which is why some buzz around your face, and then smelling your sweat, which means exposed skin. Now, feet can be quite a potent source of er, odours, and the skin on the side is quite thin, hairless and easy to penetrate, so they make a good target, but not the only one. To diverge slightly, there was a famous experiment showing Limburger cheese as a good mosquito attractant, as the smell is similar to unwashed feet!

Bec, I know it sounds bizarre, but it might actually work! It is female mosquitoes that do the biting, and it´s only males that are released, after being sterilised. They mate with the females and produce infertile eggs (so you do get bitten now, just less in the future). This technique has been used to control insect pests like the Screw worm fly, or Mexican fruit flies, and in theory you don´t need any pesticides, but the problems are....
a) there is a high start up cost, you have to release lots of mossies, and sterilising them by radiation is fairly sophisticated
b) unless you live on an island, there will always be an influx of mosquitoes from outside. You just have to keep releasing indefinitely.
Still, it´s possible.

Mynah, I don´t know! They found antibodies, and virus gene sequence, but whether the bats, rodents etc would be a reservoir of infections for humans isn´t clear. In fact, what might be happening is that Dengue is evolving into Bat Dengue, Mouse Dengue etc, which wouldn´t be a problem (well, not for us).

Thanks again for the feedback!

Saturday, 13 March 2010

Fever in the Forest

Now and again through the evening calm comes the sound of a powerful petrol motor, and soon afterwards the streets are filled with a thick grey cloud. This is insecticide, and they are fumigating against the mosquito Aedes aegypti. Aedes is one of the banes of mankind, in many ways, but the worry here is Dengue fever.

Dengue is a virus, and causes fever, joint pains and, even sometimes hemorrhage and death. It is incredibly common in tropical regions around the world, with about 50 million cases a year. You can´t catch it by shaking hands, or sneezing or eating the wrong foods, it has to be transmitted blood to blood, which in practice means the bite of a female mosquito of the Aedes genus. Hence the attempt to eradicate this little pest.

But does this really have anything to do with the Mata Atlantica? It´s not just the mosquito bite that causes a disease, there has to have been someone infectious to infect the insect. Or something infectious. Some animals act as reservoirs for human diseases, the sylvan equivalent of typhoid Mary. Yellow fever, for example, is notorious for infecting primate populations, so lumberjacks clearing forest are often particularly at risk.

In the Americas at least, that was thought not to be the case with Dengue, not least because it is not native here. It was brought over with slaves from Africa and immigrants from Asia, and so is not adapted for local wildlife. However, recent research in French Guyana, the French colony north of Brazil, found viral RNA in quite a few animals, including rodents, marsupials and bats. Several of these, such as the mouse opossum Marmosa murina are found in the Mata Atlantica and the presence of virus in their systems suggests that it is adapting. This is bad news for attempts to eradicate the disease.

Saturday, 6 March 2010

The Crocodile Butterfly

A little while ago a strange report appeared in the local paper here......

A building worker had found a huge insect with a crocodile like head. This turned out to be jacare - borboleta, or "crocodile butterfly" (Fulgora lanternaria). You can easily see how it got it's name, but infact it's not a butterfly, and it cannot bite you. Nocturnal, the jacare - borboleta feeds on nectar and fruit and is completely harmless to humans.

The large, conspicuous, head is in fact hollow and can be used as a drum, "headbanging" trees. It may also be a way of scaring off predators, just as the wings have large eye patterns which are flashed if danger threatens.

Being large, nocturnal and, well, weird, a number of myths have built up around F. lanternaria. The English name is the "lantern fly", and it was believed to be luminous, but in fact there is no evidence that this is so. In Brazil it was believed that the head was poison tipped, and any animal, touched by it would fall down dead.

In Colombia and Venezuela, it is claimed that if bitten by one, you must have sex within 24 hours or die a horrible death. As I said, it's actually impossible to be bitten, but it does raise an interesting image of a patient arriving at Casualty.