Eggs-ceptional hatching strategyScientists have discovered that baby crocodiles talk to each other from inside their eggs in order to synchronise hatching. 29th Jun 2008 Reversing time to talk underwaterCommunications on land have come on in leaps and bounds over the last 20 or 30 years for relatively little money you can buy a phone which will transmit hundreds of thousands of characters every second, or you can buy a satellite phone which means you can talk to your mum from the middle of the Gobi desert, however underwater it isn't so easy. The problem is that because seawater conducts electricity it absorbs radio waves, this means that once you get more than a few metres under water there is no point trying to tune into your favorite radio station. 29th Jun 2008 Ancient Poet Astronomically AccurateA few weeks ago on the Naked Scientists we followed the story of the Odyssey, and how although the land has changed in the 3000 years since it was written, the poet knew his geography. Parts of the poem allowed modern scientists to locate the Island of Ithaca, even though the island has now been swallowed by it’s neighbour! 29th Jun 2008 Martian soils good for cabbages.NASA's Phoenix lander which landed almost a month ago has started giving us our best view of the Martian soil yet. 29th Jun 2008 Fastest Melting IceDoes the speed of ice melting depend on what surface it's on? We compare an ice cube on a frying pan to an ice cube on a chopping board... What you need
What to DoFeel the chopping board and the frying pan, which feels colder? Now put an ice cube on the frying pan and one on the chopping board - Which one melts first? What may HappenYou should find that the frying pan feels colder than the chopping board, and so it may be a surprise that you should find that the ice cube on the frying pan melts much more quickly than on the chopping board!
What is going on?Melting ice takes a lot of energy and this energy needs to come from somewhere. Normally this energy is released by cooling down the ice cube's surroundings, which is why you can cool a drink by putting ice cubes into it. How fast the ice cube melts depends on how fast energy can be transferred from the surroundings into the cube. Materials like metals conduct heat very well, which means that because the cube is cooler than the saucepan, heat is moved from all over the saucepan into the cube, so the cube melts quickly. So why did the pan feel cold? As it's a good conductor, it also means that if you put your warm finger on the frying pan heat is conducted out of, and away from, your finger quickly. This makes the pan feel cold. The chopping board, on the other hand, conducts heat badly, so even though there is quite a large temperature difference between the ice cube and the chopping board, relatively little heat is transferred. This means that the cube will melt slowly. It also means that heat is not transferred out of your finger quickly, and so the chopping board feels warm.
There are many applications where the conductivity of materials is very important. If you want to move heat quickly like in the bottom of a frying pan you use a good conductor like copper or aluminium. But if you want to slow the transfer of heat such as through your jacket you use an insulator, like wool.
Updating Evolution Evidence - The Peppered MothDr Remy Ware, Cambridge UniversityDave - Dr Remy Ware is from the Department of Genetics at Cambridge University where they’ve been going through the experiments that got the Peppered Moth in the textbooks. First of all, can you tell us what the original story was?
The idea was that with the industrial revolution the pollutants produce such a sulphur dioxide and soot fallout had darkened the surfaces of the trees on which these moths rest. A combination of killing off the foliose lichens on the trees and actually darkening the surfaces themselves meant that what was previously a well-camouflaged light moth on a light surface now stood out very conspicuously to predators and suffered a higher predation rate such that a new mutation causing a melanic form of the moth was at a greater advantage of being more cryptic on the surface. Following this hypothesis a chap called Bernard Kettlewell in the 1950s tried to really test what was going on here.
Remy - Simply a case of looking cryptic against your background so being light and camouflages on a light surface or being black and camouflaged on a blackened surface. Dave - So the more black ones survive the more will be in the next generation. There’ll be more and more of them around for future generations. There’s been some criticism of this experiment. What was that? Remy - Ok. This chap Kettlewell started trying to test the hypothesis of this bird predation. More recently over the past decade or so his work’s been criticised. Mainly because of issues to do with it being very artificial. What he actually did was he had an experiment in which he looked at an oak woodland in Dorset and a polluted woodland in Birmingham. He looked at the levels of predation of the different forms of the moth: the light form versus the dark form. He found a reciprocal result in his data. More of the dark form were predated upon in the lighter area. The criticism was that it was rather artificial for many reasons. Firstly he was using a mixture of lab-bred moths and wild caught moths so they may not have been behaving naturally. Also he was placing them in very conspicuous places on the tree. Dave - So naturally moths would have hidden themselves? Remy - Yeah. Later experiments would involve gluing dead moths onto the tree in positions that were rather conspicuous. We know now that moths naturally rest under twigs and under branches and things. Also he was releasing moths in very, very high densities so essentially he was creating what we would call a bird-table effect. The birds were learning that they could come to this site and they would have a good lunch straight away. It’s really these criticisms of artificiality which have been at the forefront of the arguments against the Peppered Moths case. Dave - I guess he was still showing that there was a selection pressure towards the dark ones in the dark trees and the light ones in the light trees but people weren’t entirely convinced. Remy - Yeah so whatever the criticisms are of it being artificial, it was the reciprocal nature of the results of the two areas that was so convincing. Never mind the nitty-gritty of the quantitative nature of the case, quantitatively it seemed very convincing. Subsequent evidence came from a reduction in the dark form of the moth following anti-pollution legislation later on. This was rather convincing and shows, importantly, that evolution was not a one-way process – it can go back. Dave - So you’ve now been looking at trying to fix some of the problems with this experiment to try and answer its critics. What have you been doing? Remy - Some work led by my colleague, Professor Michael Majerus, he wrote a book on melanism in 1998 addressing this point and since then had a number of criticisms. He set about systematically trying to correct the problems with the original story mainly removing these issues to do with it being a very artificial type of experiment. He tried as much as possible to make it a natural experiment. He was releasing moths in natural frequencies, very low frequencies, and this experiment took over seven years to complete because it was trying to be so realistic. Dave - Very patient! Remy - Yep! Importantly he also allowed the moths to choose their resting positions naturally. He released them overnight and allowed them to select their positions as they would do in the wild whereas Kettlewell was releasing them during the day. It was more likely they would select natural positions. Various things like this and natural density could be why it took such a long time to do. It sort of addressed each point in turn. Dave - What was the result of the experiment? Remy - Similarly to what was found by Kettlewell, again he found – this work was done in Cambridge – it was found incredibly convincingly that there was a very strong correlation between observed declines in the dark form in Cambridge between 2001 and 2008. It’s just been published now. He found there was a very close correlation between the decline of the dark form of moth during this time and the actual predation that he observed by eye. He observed various birds taking these moths from the trees, differentially with respect to colour: with respect to black form or the light form. He found a very close correlation between the predicted decline in the dark form as a result of this predation compared to what was actually observed. So it was very strong evidence that differential bird predation was responsible for this. Dave - Brilliant. Thanks very much Remy. That’s Remy Ware from Cambridge University on how experiments in evolution can themselves evolve and improve. June 2008 Evolution in the LabProfessor Richard Lenski, Michigan State UniversityProfessor Richard Lenski works at Michigan State University and in his lab he’s grown over 40,000 generations of E. coli for over twenty years. He persuaded the bacteria to evolve totally new characteristics and giving scientists new insights into how organisms adapt and change over time.
Ben - What are the advantages of using bacteria like E. coli to observe evolution in the lab? Richard - One of the advantages of bacteria is that they have such short generations. Also they have very large population sizes so in a little flask in the corner of the lab we can have millions of cells. What’s really cool to me is that we can freeze the bacteria away. That allows us to directly compare ancestral and evolved organisms. Actually comparing the living organisms is not just fossils. It’s the real-live bacteria. Imagine if we could bring Neanderthal back to life. We might try to play a game of football with the Neanderthals and we could see how the organisms in their performance, not just in their fossil morphology, but in their real performance have changed over time. Ben - What sort of evolutionary changes have you seen since your very first cell line? Richard - One of the most important changes is that the evolved bacteria are demonstrably much more fit in this environment. They actually grow twice as fast as the ancestors. When you compete them the evolved bacteria kick butt. The evolved cells are much larger. We’re looking at how they’ve changed in many other properties. In particular in the last few years we’ve been looking at how they’ve changed in the genotype. We’re actually sequencing the DNA and finding the mutations that are responsible for their adaptation. Ben - Recently you reported on a slightly more dramatic change that happened in that they seem to have been able to use a different source of food. What had happened here?
Ben - So this is one of the defining features that makes them an E. coli bacterium rather than something else. Richard - It is, pretty much. There are little grey areas around the edge that are rather technical but certainly the general property of E. coli, one of the defining characteristics by virtually all assays. For 20 years they’ve been eating their glucose and not recognising there’s an open niche, another resource in their environment. One of the twelve populations suddenly woke up, as it were, in an evolutionary sense and said, “Hmm. There’s something else to eat. There’s a desert tray around the corner after we finish our glucose.” That population evolved this new capacity to use this new carbon source as an energy source. What we’ve done has been to try to ask, “Could any of the populations have evolved that new trait at any point in the experiment?” We’ve been trying to ask if the genetic context changed so that this new phenotype became possible by virtue of the more-or-less inconsequential differences that it accumulated in one population versus the other 11 populations. We took advantage of the fact that we have all these time points frozen away in our freezer. With an extraordinarily dedicated graduate student, Zachary Blount, he essentially went back to the freezer and started the evolution experiments over from different time points along the way to the evolution of this interesting new trait. What he found was that only after a certain point in time did he ever find mutants that were able to use citrate as a carbon source. A sort of accident of the genetic changes in one line versus the other lines had opened up this door that there was another possible way of making a living in this extremely simple laboratory environment. Ben - So you need a series of smaller, seemingly irrelevant mutations in order to have this big mutation that lets you change your food source? Richard - Yes. It’s very clearly established that there were many mutations in these lines and that some subset of them that occurred in this population set up the potential to then get additional mutations that gave this very interesting new trait or phenotype. In this simple little experiment that we’ve been doing in my lab this one population of the twelve that we’ve been studying took a different road, got on a different evolutionary path and that influenced its subsequent potential. June 2008 Evolution in the Wild - Horny Soay SheepDr Alastair Wilson, Edinburgh UniversityBen - So what is it you’ve found in the Soay sheep?
Ben - So the sheep are really taking a gamble then because they know that if their horns are as big as they possibly can be then they’re more likely to have the success in later life but they are betting that their first winter will be quite a mild one? Alistair - That’s it. You can kind of think of it as different strategies so if you have a good season coming up then it’s definitely better to have gone for it in terms of growing your horns. If you get that wrong you might end up dead in which case it doesn’t matter how big your horns would have been because you’re not going to get any breeding success the next season.
Alistair - It’s a little more complicated than that but we’ve been able to find there’s genetic variation for these traits and that translates to genetic co-variation between horn growth and survival. What that means is selection is acting at the genotype. It’s not the case of a complete genetic predetermination between these genes will give you fast-growing horns and these will give you slower growing horns in that categorical way. There are some genotypes that have a tendency to go in one direction or another and it’s this genetic variation that natural selection can act on. Ben - We’ve just heard about evolution in the lab and it’s very easy in the lab to control the conditions under which your organisms are evolving. In the wild obviously you don’t have that option. You can’t say it’s going to be this temperature this winter. How do you actually study them? Alistair - It’s certainly tricky. Obviously we’ve learnt an awful lot and we continue to learn an awful lot by studying evolution in the lab. Really what we’re trying to do is tackle those problems head-on in changing environments because if we want to discover how evolution works in the real, natural world then we are going to have to work out how we’re going to change all these environmental variables – as I say temperature or population size or anything. Fortunately ecologists have been working for decades on exactly what these variables do and exactly how they affect organisms such as Soay sheep. The challenge we’re facing is perhaps trying to integrate what geneticists can do in the lab with what the ecologists are telling us and to try and integrate these sources of complexity rather than avoid them as you would do in a laboratory. Ben - Can you take a genetic profile of your population and then try and use that to estimate how well they will cope with say, a bad winter coming up. Can you actually use the genes to predict the success?
Ben - Ok. If the climate changes as we are predicting the climate should be warming up would this have an effect? Would we expect to see bigger horns on these sheep as the weather gets hotter? Alistair - Certainly a starting prediction might be that if the weather warms up we get fewer and fewer of these bad years. The net result of that is going to be that selection is always going to favour fast growth in horns rather than sometimes favouring slow growth. If that’s he case then we’re going to have an increase in, if you like, the net selection for faster growth. We would expect evolution toward faster growing horns, yes. Ben - What does this tell us about the way that selection pressures balance each other? Obviously we have the sexual selection here which is that you need to have big horns to compete with the other males around and to actually breed. We then have the external natural selection. Does one drive the other? Alistair - I guess you can look at this problem in different ways. For me, I see it all as being different components of the total selection. The key point is that selection can act in different ways through what we might call different components of fitness. Whether that be reproduction or survival in your first year versus survival in your second year. The idea really is, if we can get a handle on how these individuals are behaving throughout their whole lives across a range of environments then we can start to see how selection trades off either across different environments, different ages or through different components like survival and reproduction. We can bring all of that together to try and have an idea of the total picture. Ben - So when we say an animal is fit, and we’re looking at survival of the fittest, it could be that they are very fit in one aspect but that would, in turn, make them very unfit in another aspect. Alistair - That’s it exactly and it can be a real problem. Sometimes the things you can measure might be survival. It may be much more difficult in your system to measure the number of eggs produced or something like that. You can get quite a misleading idea of what selection is doing if you’re only looking at one aspect of fitness at a time. The challenge is to try to get a whole, complete picture of an individual’s life perhaps – how its fitness is achieved through both surviving and reproducing. June 2008 Charles Darwin - In his own words...Dr Alison Pearn, Darwin Correspondence Project & Malcolm LoveBen - It’s 150 years this week since Charles Darwin presented his ideas to the Linnean society – marking the first public outing of his theory of evolution. I went to visit Dr Alison Pearn, from Cambridge University to learn a bit more about the man behind the theory. Alison is behind the Darwin Correspondence Project, so I started by asking just what the project is…
Ben - We have the books that Darwin wrote. The books would be the distilled essence of what he wanted to communicate. Why would we need all the letters or the rough drafts? Alison - The books are meant for public consumption. They are the final, finished product. There’s a whole back-story. An extremely interesting story of how those books came into being. Darwin was not a lone genius who suddenly had an epiphany of an idea and suddenly wrote it down. Darwin was somebody who worked away for many years and in enormous detail talks about amassing great quantities of facts. He did that largely through the medium of correspondence – the medium of letters. Ben - Can we trace the development of his theories using his correspondence? Alison - To a large extent, yes we can. There were certain of his scientific colleagues with whom he did discuss ideas and certainly went into detail. In particular in correspondence with Joseph Dalton Hooker who was director of the botanic gardens at Kew and Darwin’s closest friend. And with Charles Lyell who’d been an early mentor it is possible to see Darwin begin to discuss his ideas and collecting the evidence to support the arguments he was making.
Ben - Darwin and Wallace presented their ideas together to the Linnean society in July 1858 but if the correspondence shows he was discussing aspects of it only months before, what was it that galvanised him into presenting his findings instead of the long, painstaking work he’d been doing? Alison - Well, famously it was the arrival of a letter from Alfred Russell Wallace who was out in the field in Malaysia. Wallace had also written a paper which Darwin describes as being so uncannily like his own theory. In some ways it was as if Wallace had actually seen his manuscript. He actually panicked. He immediately writes to Charles Lyell and to hooker, and is really is asking them what he should do. It’s actually Darwin’s friends who were pushing to finish in what, to him, was an unseemly hurry. When the papers were read at the Linnean Society neither Wallace nor Darwin was actually there. Wallace was still out in Malaysia and Darwin was struggling with a completely different crisis in his life. Two of his children were ill with scarlet fever. Through the detail of the letters it’s possible to see the alternating hope and despair as the children get sicker. He’s explaining to people that he can’t respond to their letters, including Hooker, who is trying to get him to publish. He’s completely distracted by the illness of his children. Just before the two papers were read at the Linnean Society his youngest child who was a baby, Charles Darwin, died.
Ben - A personal tragedy like that must have been awful for him. It must have almost made him give up. Alison - It did. It was only because it was his closest friend who had asked him to send the papers and a close friend with whom he could discuss his feeling on the death of his child that he was able to send the papers. He writes a postscript to a letter in which Darwin, as an afterthought, says I’ve just realised that you want these papers now but I dare say I don’t really care.
Ben - It was about this time that Darwin’s abstracts were presented to the Linnean society. How did he react about this. How did he feel? Alison - Personal life was still included in a very big way during this whole period. He was very concerned that the rest of the family might become sick and he writes to Hooker a few days after the paper. The first thing that he’s keen to say is that they have evacuated the children and they’ll move their daughter as soon as she’s well enough to go. Ben - Family was still at the forefront of his mind? Alison - Absolutely. In all the letters in this period once the first child has become sick it’s the family that are there first. It’s the first thing he mentions to everyone he’s writing to at this point. He does thank Hooker very sincerely for having watched his back and gone to so much trouble to make sure his name was associated with Wallace’s in writing of the papers. Although he says he’s really ashamed of himself now for having cared about whose name was given.
With many thanks to the Darwin Correspondence Project and Malcolm Love. June 2008
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