All posts by Alun Salt

About Alun Salt

When he's not the web developer for AoB Blog, Alun Salt researches something that could be mistaken for the archaeology of science. His current research is about whether there's such a thing as scientific heritage and if there is how would you recognise it?

How American should an American Chestnut be?

The American Chestnut used to rule the forests of North America. However in the early 20th century a blight almost wiped them out. Billions of trees were killed and all that remain are a few thousand in isolated stands. Scientists have found possible defences against the blight, but both methods will change what the American Chestnut will be in the 22nd century.

Inoculating a chestnut with a slurry of hypovirus.

Inoculating a chestnut with a slurry of hypovirus. Photo: Wisconsin Department of Natural Resources / Flickr.

It’s hard to be certain how many American Chestnut, Castanea dentata, trees there were in the USA before the 20th century. There was no urgent need to count them until it was obvious they were dying en masse, and by then it was too late. The killer was Cryphonectria parasitica.

C. parasitica arrived some time after 1900. It’s fungus that likes to enter via wounds in a tree and grow in or under the bark. There it grows as a canker around the stem. As it grows it releases oxalic acid, killing plant cells. When the canker surrounds the stem there’s no way for food to pass the stem and everything upwards dies.

It’s thought that the fungus arrived with Asian chestnuts. The Asian chestnuts have evolved along with the blight over millions of years, so they’re much less susceptible to it. The American Chestnut had about forty years to adapt. It’s now functionally extinct. As it stands it has no future. However, it might return with some help. Asian chestnuts have some genes that give it resistance to the blight. If the few remaining American chestnuts could be cross-bred with them, then they too might have resistance.

If you cross and American and Asian chestnut then you end up with something half-American and half-Asian. Cross that with another American tree and you get something three-quarters American. At the moment the hybrid trees are one-sixteenth Asian and fifteen-sixteenths American. Is that American enough? Who gets to say how good is good enough?

Blythe et al. have a paper recently published in Restoration Ecology: Selection, caching, and consumption of hardwood seeds by forest rodents: implications for restoration of American chestnut. As the title suggests, she and her team have put the hybrid trees to the test, by seeing how rodents react to the chestnuts.

They compared the hybrid chestnuts with American chestnuts and other nuts and seeds found in American forests. The hybrid chestnuts might look convincing to humans, but there was a preference for the American chestnuts over the hybrids from the rodents. Another puzzling feature was that they scattered the hybrid chestnuts over a wider range than the American chestnuts. The hybrids were eaten, but they’re not a straight substitute for American chestnuts. Blythe et al. conclude that the hybrid chestnut trees are not the ecological equivalent of the American chestnut trees.

But hybrids are not the only hope for the American Chestnut.

Another solution is genetic engineering. The problem is the tree cannot cope with oxalic acid. If they could get the genes to cope, then the tree could be almost entirely as it was before. Wheat has those genes. If they could be pasted into the chestnut it wouldn’t kill the fungus, but it would enable the tree to live with it. Blythe et al. say that a GM chestnut would be more likely to be an ecological equivalent, but they also warn that for social reasons there could be resistance to planting GM American chestnuts instead of the hybrids.

Another possibility would be that there isn’t just one solution, but both hybrids and GM trees could mixed plantations to restore forests.

It raises a question that follows a lot of de-extinction proposals, who is the ecological restoration for? Is it to restore the damage done to an ecosystem, or is it more a statement about how people feel about an ecosystem? The hybrid chestnuts might be different, but if de-extinction is a social process and less a matter of ecology, then maybe the public will decide that hybrid chestnuts are American enough.

Blythe, R. M., Lichti, N. I., Smyser, T. J., & Swihart, R. K. (2015). Selection, caching, and consumption of hardwood seeds by forest rodents: implications for restoration of American chestnut. Restoration Ecology.

Trees? Tibetan dendrochronologists don’t need trees!

Everyone knows that you can age a tree by counting its rings, and the width of those rings is a record of climate. But do you need trees to track the climate?

Tree rings

Tree rings. Photo: Katy / Flickr.

Climate isn’t the same everywhere. The forthcoming El Niño event threatens parts of the world with droughts and other parts with floods. So in recreating models of past climates it’s helpful to be able to check your work against a wide data set.

Dendrochronology, the study of tree rings, is a useful tool for doing this. A tree has annual growth and it’s visibly marked in the structure of the tree, making rings as the trunk grows bigger. The width of these rings is a record of the climate for that year. During a wet year a tree may be able to put on more growth than during a drought. So take a sample from a trees and the rings give you a very tight match between the year and its climate.

Of course, that does mean you’re reliant on the area you’re looking at having trees.

Eryuan Liang and Dieter Eckstein have looked at the Tibetan plateau, where there are few trees, and thhey’ve found an alternative. They published a paper in Annals of Botany, Dendrochronological potential of the alpine shrub Rhododendron nivale on the south-eastern Tibetan Plateau, where they showed shrubs could be used instead.

Liang and Eckstein took samples from by the Zuoqiupu Glacier, between 4250 and 4500 metres above sea level. There air pressure at that height is so low that there’s a good chance you’d pass out without acclimatisation. They deliberately went this high, as human activity has affected the plants lower down. Rhododendrons are firewood, so the climate record could literally go up in smoke.

Rhododendron rings

(A) Cross-section of the oldest snowy rhododendron at the study site. The well-defined annual growth rings are shown in (B) and details of the wood anatomy in (C). Scale bar = 5 mm. Photos: Liang and Eckstein (2009).

You can see Liang and Eckstein found well-defined annual rings, and also no rotten core to the stem. They found the rings were wide enough to make dendrochronology practical.

They were also able to correlate the ring patterns in the rhododendrons with the rings in Georgei firs, so it looked like the rings were a reliable ecological indicator. The key period for ring width was the mean minimum temperature in July and in the November before. With rhododendrons being widespread in the Tibetan Plateau, they looked like a good source for climate data.

Interesting, but this was all in a paper in 2009, why does it matter now?

Liang and Eckstein got rings as far back as sixty years. It proved the concept, but it was limited in use. Now they’ve co-authored another paper, and the record goes back a lot further. The paper is Up to 400-year-old Rhododendron shrubs on the southeastern Tibetan Plateau: prospects for shrub-based dendrochronology (subscription required) in the journal Boreas.

This new study uses Rhododendron aganniphum. The plants in the new sample sites had a correlation with the July temperatures, but the relationship to the November temperatures seems a bit more murky. However, the samples they found enabled them to build one sequence from the year 1670 and four more from the eighteenth century. It seems more work could help flesh out the changing climate of the Himalayas.

Liang, E., & Eckstein, D. (2009). Dendrochronological potential of the alpine shrub Rhododendron nivale on the south-eastern Tibetan Plateau. Annals of Botany, 104(4), 665-670. DOI: 10.1093/aob/mcp158

Lu, X., Camarero, J. J., Wang, Y., Liang, E., & Eckstein, D. (2015). Up to 400‐year‐old Rhododendron shrubs on the southeastern Tibetan Plateau: prospects for shrub‐based dendrochronology. Boreas. DOI:10.1111/bor.12122

#SciFund is running a masterclass in poster design

Grab Attention

If you’re attending a conference any time soon, then you may want to look at #SciFund’s new course Mastering the art of poster design. Unlike MOOCs you do have to pay for this, but what you get for $50 is a five week course between Jun 7 and July 11, 2005.

If you want to see if if the course is likely to help you, you can get a preview of sorts. One of the course tutors is Zen Faulkes, who runs the Better Posters weblog. You can scroll through and read his critiques of other posters.

Like the FutureLearn courses, we have no affiliation with #SciFund, so you’ll need to contact them to register.

Drinking in the name of SCIENCE!

Pint of Science I’m used to Science driving people to drink, but next week it’s hoped that drink will drive people to Science. The Pint of Science festival is happening next week in Australia, France, Ireland, Italy, Spain, UK, USA and Berlin, Germany and São Carlos, Brazil. It’s the third iteration of the event, following work by Michael Motskin and Praveen Paul at Imperial College, London, to talk to people affected by Parkinson’s, Alzheimer’s, motor neurone disease and multiple sclerosis about their research.

Exactly what’s on depends on where you are. So if you’re in Los Angeles you can check out the Physics of Kung Fu Panda one night, while New York has a slate of talks, including Kevin Griffin on DIY Tree Science. In Brazil you get many mathematical talks, including Matemática e beleza. So, if you live somewhere where there’s a few events locally, it might well be worth looking around to see what’s on.

If you’d like to see if there’s something on near you, you can visit the website to find out. If there’s nothing near you, there are some soundfiles of recent talks below.

Science, Politics and Evidence

Polling station

X marks the spot.

I write a few of these posts in advance. So this is being written the day before the General Election in the UK to come out the day after the election. I don’t know who has won at the moment, but if predictions are right it’s possible no one will know who’s won for a week or so after the result. We’re politically plural in the AoB Blog office so there’ll be a mix of emotions. For some of us it’ll be a day of exasperation or frustration, while the people who voted for the losers will deal with it in their own way.

But it’s not a foregone conclusion that politicians have to be disappointing.

Back in March last year a group of scientists decided that politicians could make better decisions if they had access to independent information. Instead of just setting up a unit, they chose to speak to politicians first to find out what would be most useful to them. They also wanted to know the best way an Evidence Information Service could deliver that information.

To get that information, they went to the public to ask for help. The idea was that each constituency would have its own champion who would interview an MP, and local representative for the devolved governments. I took part and spoke to my local MP and AM (Assembly Member) with a structured set of interview questions. The aim was to write a paper based on those responses. You can see the draft online.

Impressively, they’ve also released their raw data. Their conclusion is that the politicians who met with interviewers showed their human side in responding to questions. I don’t feel I can say exactly what my MP and AM said without breaching confidentiality, but I was impressed with both of them. It seems around the UK, politicians of all parties would like access to independent scientific information.

For most of the results announced today the winner will have been voted in by an overwhelming minority. Regardless of who wins, it would be helpful for the representatives to have somewhere they can get scientific information. Chris Chambers et al. might have a way to aid policymakers, even if the election results mean they’re not the ones I want.

You can read more about the proposed Evidence Information Service at the Guardian.

Biodiversity flourishes in an ancient rubbish tip

The preservation of archeological sites does not always overlap with the conservation of biodiversity. At the most basic level, the United Nations Educational, Scientific, and Cultural Organization separates cultural heritage sites and natural heritage sites: Of 981 heritage sites, 759 are cultural, 193 natural, and only 29 (2.65%) have mixed properties ( Cultural conservation and biodiversity conservation have overlapped in the sustainable use of natural resources (Timmer and Juma 2005), but shared targets of elevated conservation importance for both archeological and biodiversity priorities are still few.

Roots at Ta Prohm

Ta Prohm. Photo: Andrea Schaffer / Flickr.

The first archaeological dig I worked on, I could probably have used a little less biodiversity. Or at least fewer horseflies. And fewer trees. The site was a Gallo-Roman farmstead in what had become a forest. The roots of the trees were pulling apart the remains of the building. However, the trunks were thick and the roots had come to support parts of the walls, even as they were prising the bricks apart. A similar effect is even more visible in places like Ta Prohm. For archaeologists the natural environment can be a pest.

In their paper Biodiversity and Archeological Conservation Connected: Aragonite Shell Middens Increase Plant Diversity, Vanderplank et al. point out that an archaeological site is not always good news for biodiversity as humans tend to clear sites of anything they think gets in the way. Finding a site where the conservation priorities for archaeology assist biodiversity is rare, but it seems to be the case in Baja California.

Clam shell midden

Clam piles in Baja California Sur. Photo Sam Beebe / Flickr.

The archaeological sites might look dull at first sight. They’re piles of shells. In fact they’re piles and piles of shells. Masses of them. Once someone had eaten what was inside, the shell could be thrown away, so you get what are effectively rubbish dumps. One of the surprises about them is how old they are. The earliest sites are around ten thousand years old. This dates from close after the arrival of humans in the landscape Another surprise is how many people made the middens. Not as many as you might think.

It’s thought the groups of people occupying places would have been fairly small, maybe around thirty people closely connected as a family. They’d forage on the shore for food and move inland when the season was right to take advantage of food sources there. For small groups to make mounds this big, they’d have to be eating shellfish for a long time. Dates from the shells show this is what happened, with some sites being in use till the arrival of Europeans.

With occupation going on for so long, it’s not surprising that it has an effect, almost like geology and this is what Vanderplank et al. have found. Shells are becoming part of the local geology, in particular clam shells which degrade comparatively quickly compared to other species hunted for food. Vanderplank et al. decided to test to see if plant biodiversity could be an indicator of archaeological remains. The targets were middens by Colonet and San Quintín, Mexico.

It would have been neat if they could have shown a simple relationship between middens and biodiversity. Sadly, life’s not so considerate. There was quite a bit of difference in species between the two sites. They found that middens increased biodiversity at San Quintín, while biodiversity was greater away from the middens at Colonet.

While that’s slightly annoying, it shouldn’t be surprising. Obviously the local species will vary with the environment. Around San Quintín, the land is low-lying and often floods. The leaching of calcium from the shells allows plants to thrive that otherwise would not grow in the saline soils around the middens. Colonet had much less saline soils, so the effect there was somewhat different.

Vanderplank et al. argue that the effect of these middens makes them a marker of the Anthropocene. This is a proposed geological age that reflects humanity’s effect on the environment. Vanderplank et al’s paper would put the start of the Anthropocene somewhat early, but with things like the Ruddiman Hypothesis it’s not wildly out of step with some academics.

It certainly opens the possibility of using botanical survey as a means for prospecting for archaeological sites, not just in Mexico, but anywhere where humanity has had a major impact on sites.

Vanderplank S.E., Mata S. & Ezcurra E. (2014). Biodiversity and Archeological Conservation Connected: Aragonite Shell Middens Increase Plant Diversity, BioScience, 64 (3) 202-209. DOI:

The European Space Agency is offering a free course on climate observation


If you ever wonder where climate data comes from then ESA, the European Space Agency, might have the course for you. Monitoring Climate from Space is a free online course that looks at Earth Observation. The variety of instruments in space, and their wide coverage of the planet is creating an awful lot of data. How can you pull it all together to get a clear view of what’s happening? Over the five weeks they’ll cover Earth Observation from the basics to a look at how the various climate models are made.

The course is the product of CCI, the Climate Change Initiative, one of ESA’s many units and delivered by FutureLearn.

If space isn’t you’re thing and you’re looking for something closer to home then there’s also courses coming up on Our Hungry Planet: Agriculture, People and Food Security and Soils: Introducing the World Beneath Our Feet.

If you’re planning to take one of these courses, why not let us know below?

For one flower, bad hair days are the best days

If you want to please Leucospermum arenarium (Proteaceae) you’d better leave brushes and combs alone, as it has an unusual way to get pollinated.

Leucospermum arenarium in the field and one of its pollinators, Gerbillurus paeba. Photo Johnson and Pauw.

Leucospermum arenarium in the field and one of its pollinators, Gerbillurus paeba. Photo Johnson and Pauw.

Plenty of plants are pollinated on the wind, or via currents in water. Others get some help. Insects are favourite, but plants are known to use birds and bats to carry pollen from one flower to another. What doesn’t happen very often is pollination by a rodent. To begin with people thought rodent pollination was just the flowers getting lucky on occasion, but more research has shown there is more going on than that, and that some plants have adapted to attract rodents. One might be L. arenarium the subject of a paper in Annals of Botany by Christopher Michael Johnson and Anton Pauw.

One adaptation Johnson and Pauw mention is a new word to me, geoflory. These are flowers on, or close to the ground. The proximity to the ground makes them accessible to rodents, or so the explanation goes. Johnson and Pauw point out that rodents can climb, and will if they think the trip is worth the effort.

Another adaptation they look for in a rodent-pollinated plant is in the nectar. If the flower is going to work then it can’t be destroyed by a rodent visiting it for food. It might deposit pollen on the rodent as it gets demolished, but it won’t be in a position to receive pollen from other plants. So L. arenarium must be doing something interesting with its nectar, if it’s getting rodents to pollinate it.

To examine the pollination in action Johnson and Pauw staked out some flowers in one of areas you can find them in South Africa. By day they kept their distance and watched. For the night, they baited traps and waited to see who came to forage.

The day results probably took a lot of patience:

Diurnal observations recorded no bird visitors and only nine insect individuals (six Hymenoptera, two Coleoptera, one Diptera) visiting L. arenarium flowers during 22·5 h of observation.

That’s less than one every couple of hours. I’m not sure I could concentrate to observe the insects at that rate. I’d be wanting to read a book, which isn’t a good idea when you’re supposed to be watching the flowers. When the insects did arrive, they didn’t carry off any pollen. The traps caught rodents. Gerbillurus paeba, the hairy-footed gerbil and Rhabdomys pumilio, the striped field mouse were caught with pollen about them.

Fortunately they didn’t have to rely just on chance observations. They also bagged some flowers, so they could only self pollinate and caged some flowers, so only insects could get in. Then they caged some flowers with doors for the rodents to get in. The bagged and caged flowers didn’t produce many seeds. It was only when rodents could access the flowers that the plants produced many seeds.

The plants protected their flowers by producing a sugary nectar that was channeled to the petals so the rodents didn’t have to take the flower apart to get it.

So there is little doubt the flowers are getting pollen on to the rodents, but there is another problem they face.

If you try sticking things to a mammal’s fur they’re not going to be happy. It doesn’t matter if you douse a rodent in pollen, if it’s not going to stay there. Does it?

Johnson and Pauw examined the foreheads of gerbils that came to visit the flowers. They also examined their faeces. Sure enough they found that a lot more pollen had been through the gerbil than stuck to the outside.

What they propose is that grooming is bad news for the flowers, and there won’t be a lot of long term carrying of pollen. However some rodents might be fussier about their fur than others. If that’s the case then it would be interesting to see if G. paeba and R. pumilio are less worried about looking good compared to other rodents in the area when they’re out foraging.

There’s certainly a big cost to the flower to use rodents to pollinate. I wonder if the specialism makes the rodents very good at delivering the pollen to the right flower, in much the same way that some orchids will specialise with a pollinator to ensure accurate delivery for pollen.

You can now pick up the paper free from Annals of Botany. You can also pick up an older paper co-authored by Anton Pauw, if you’re interested in rodent pollination, from the American Journal of Botany, Rodent pollination in the African lily Massonia depressa (Hyacinthaceae).

Johnson C.M. & A. (2014). Adaptation for rodent pollination in Leucospermum arenarium (Proteaceae) despite rapid pollen loss during grooming, Annals of Botany, 113 (6) 931-938. DOI:

We need Oddballs not Lunatics

Attack of the Dream Stealers!

When I can’t find a suitable image, I go to the Pulp-O-Mizer

Flipping through back issues of BioScience to see what’s now free access, I found an interesting editorial, Oddball Science: Why Studies of Unusual Evolutionary Phenomena Are Crucial.

Science funding decisions are increasingly at risk of becoming politicized, and reductions in basic science funding are often justified as eliminating wasteful government spending.

It’s apt in the UK at the moment as cuts are a hot topic for the general election here, though science less so.

The examples it highlights, like snail sex, are easy to mock if you don’t know anything about the research, but Brennan et al. make the point that it’s actually the weirdness of what is studied that can make it easier to learn something. If extreme conditions highlight new questions, then it seems we need more oddballs not less.

Ecologists make their own flowers to study moths

Thanks to JSTOR Global Plants for pointing to an interesting paper in Functional Ecology, Shape matters: corolla curvature improves nectar discovery in the hawkmoth Manduca sexta.

Hawkmoth, Manduca sexta

Hawkmoth, Manduca sexta. Photo by Pondhawk/Flickr

The research looks at how the the 3D structure of a flower helps guide hawkmoths towards nectar. Scents and sight can guide a pollinator, but to what extent does the physical form aid a visitor? Campos et al. compared trumpet-shaped flowers against flatter flowers. There’s quite a few ideas of how the mechanical properties of a flower work with pollinators. There’s the shape, and also the internal structure such as grooves in the interior that can act as guides. What is significant and what is not?

The Campos paper is novel because they have found a way to control for these features. Actually finding flowers with all the relevant factors controlled for would either be near impossible or else very impossible. Instead the team printed them.

I hadn’t thought at all about 3D printing for Botany, until I listened to to documentary on 3D Bioprinting, a couple of weeks ago (BBC Radio, available worldwide). In fact flowers seem to be just one of many things that botanists could use 3D printing for.

The ‘flowers’ look very minimalist interpretations of flowers, so people who know more about the mechanics of flowers than me can debate to what extent the approximation is useful. In many ways the simplistic shapes give very clear parameters that can be tested. Another feature is that they’re monochrome. This is because of the limitations of 3D printing. The shapes are built from layers of plastic and each layer has its own colour, so it may well be a limitation for a while yet.

As well as demonstrating that botanists can make physical structures and vary them to test hypotheses, 3D printing also bodes well for replication. A factor in replicating experiments is the equipment. How trumpet-shaped is trumpet shape? Having a stored plan means that other scientists could download and run their own variations on published experiments.

I’m now wondering what could happen if you could combine TreeSketch with 3D Printing.

Campos E.O., Bradshaw Jr H.D. & Daniel T.L. (2015). Shape matters: corolla curvature improves nectar discovery in the hawkmoth Manduca sexta, Functional Ecology, 29 (4) 462-468. DOI: 10.1111/1365-2435.12378