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June 2014 Archives

This video is a compilation of the best clips from the 'Six-second science fair' run by GE recently. (Apparently it attracted more than 600 entries!)

Could be really interesting to set something like this as a classroom project - rapidly changing technology (including the apps) has really opened up the options :)

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If asked, "what do spiders eat?", my answer would probably include insects, spiders, other arthropods, and maybe birds. I'd never have thought of fish!

And yet it seems that fish-eating by spiders is, if not common, then not exactly rare, although other food items still account for most of the spiders' diets. In a paper just published in PLoS ONE, Nyffeler & Pusey (2014) present evidence - from an extensive literature review - for eight-legged piscivores on every continent other than Antarctica, although they're more often found in tropical & sub-tropical regions. And it seems they're not alone: the authors list a number of other arthropods with similar tastes, including water scorpions, backswimmers, caddis flies and water boatmen.

The spiders involved were mostly from the genera Dolomedes & Nilus ie they are large (as spiders go: a big female Dolomedes can have a leg-span of 6–9 cm and weigh ~0.5–2 g) and semi-aquatic, spending a lot of time at the water's edge. Here's an image of a female Dolomedes from the UK, settling in to consume a stickleback:

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Image: Nyffeler & Pusey (2014) doi:10.1371/journal.pone.0099459.g007

Incidentally, while we have spiders of this genus in New Zealand, it seems our small freshwater fish have little to worry about. Nyffeler & Pusey report that

only the largest of New Zealand's three species of Dolomedes (Dolomedes dondalei) was capable of catching fish in laboratory experiments whereas the two smaller species (Dolomedes aquaticus and Dolomedes minor) were not.

When hunting fish - & for most spiders the researchers note that fish are a relatively rare component of the diet - the arachnids seem to use touch (mechanoreception) rather than vision. They sit at the water's edge with their front pairs of legs spread out & resting on the water surface, and the others anchoring them to a rock or a plant. In some cases, especially when the water is calm, it seems that the spiders may detect their prey from ripples in the water, but in others their attack is triggered by the fish's dorsal fin actually contacting one of their legs. And while spiders usually eat other animals smaller than themselves, in the case of fishing spiders their prey may be more than twice as large as the predator, which means that there's quite a lot of effort involved in subduing dinner (usually done by biting the fish behind the head). and then dragging it out of the water to feed.

Nyffeler & Pusey cite experimental evidence showing that spider venom is quite capable of killing small fish, although it may take 20 minutes or more to do so. In the wild, that would be a long time to hang onto a wriggling fish. And why then drag it out of the water? Perhaps because the digestive enzymes injected into the prey would otherwise be diluted - remember that spiders are 'liquid feeders' who must wait until the prey's innards have been liquified by those enzymes before slurping up the resultant soup.

While the fish these spiders eat are a large prey item, & capturing them must incur some risk, the researchers argue that such hunting may well be advantageous at times when other prey items are rare. However, they conclude that

Complete piscivory is probably rare and restricted to those occasions when semi-aquatic spiders gain easy access to small fish kept at high density in artificial rearing ponds or aquaria or in small shallow waterbodies.

Owners of home aquaria and fish ponds may never view Dolomedes in quite the same way again...

Nyffeler M, Pusey BJ (2014) Fish Predation by Semi-Aquatic Spiders: A Global Pattern. PLoS ONE 9(6): e99459. doi:10.1371/journal.pone.009945

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I saw this story in the newspaper yesterday, & again today on one of the science feeds

Researchers in the US have studied the skulls of ancient human ancestors and concluded that fist-fighting may have played a role in shaping the male face.

You can read the paper itself here (Carrier & Morgan, 2014). I'm sorry, but to me it reads like a just-so story. Just because modern humans take a swing at each other from time to time, doesn't mean that this was the case for earlier hominins. The authors of the paper argue that the facial features of robust australopithecines are the result of natural selection acting through bare-fist fighting. However, they don't offer any actual evidence that this might have happened: nothing on whether paranthropine skulls show the sort of facial damage that you might expect if fighting in this way was sufficiently widespread to act as a selective force. And similarly, no real discussion of whether Paranthropus could form a fist capable of doing such damage. (The paper on Australopithecus sediba to which they refer actually describes sediba's hand as a mosaic of features.) In other words, they're making a sweeping assumption - that paranthropines routinely beat the heck out of each other - to support the a priori assumption that our own facial evolution was shaped by this.

There's also the question of whether modern human faces show much evidence of having evolved in this way; they actually seem quite prone to damage. Noses & cheekbones are rather susceptible to damage, and the bones of the cranium - thinner than those of Paranthropus - are dangerously easy to break. At the same time, according to the authors' speculative view, our hands are particularly well adapted to deliver blunt-force trauma.

This quote from the paper (emphasis mine) says it for me; we really are dealing with conjecture & imagination: 

Starting with the hand of an arboreal great ape ancestor, it is possible to imagine a number of evolutionary transformations that would have resulted in a club-like structure adapted for fighting.

Rudyard Kipling might have appreciated it - a point also made by Brian Switek in his excellent commentary over at National Geographic.

Carrier, D. & Morgan, M. (2014) Protective buttressing of the hominin face. Biological Reviews doi: 10/1111/brv.12112

 

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Definitely don't try this one at home! The changes shown in the linked video are an example of intumescence, where a substance swells when it's heated. Fascinating to watch, but since we're talking mercury fumes it's definitely not one for the classroom.

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Recently I wrote about a paper by Freeman et al: a meta-analysis looking at the impact of active learning on student success in maths, engineering, & the sciences (the 'STEM' subjects). In the same volume of PNAS is an accompanying commentary by Carl Wieman. Wieman is a physics Nobel Laureate who also leads a research group working on improving teaching & learning in maths, engineering, & the sciences (which has resulted in some interesting initiatives at other institutions). Commenting on Freeman's results, he notes that

Freeman et al. argue that it is no longer appropriate to use lecture teaching as the comparison standard, and instead, research should compare different active learning methods, because there is such overwhelming evidence that the lecture is substantially less effective. This makes both ethical and scientific sense.
Wieman goes on to say 
However, in undergraduate STEM education, we have the curious situation that, although more effective teaching methods have been overwhelmingly demonstrated, most STEM courses are still taught by lectures - the pedagogical equivalent of bloodletting. Should the goals of STEM education research be to find more effective ways for students to learn or to provide additional evidence to convince faculty and institutions to change how they are teaching?
Personally I'd go for the former; there's a wealth of information out there now. What's needed now is to somehow get more university STEM educators to engage with the scholarship of teaching & learning in their various disciplines. Now there's a challenge!
 
C.E.Wieman (2014) Large-scale comparison of science teaching methods sends clear message. PNAS published ahead of print, May 22 2014. http://www.pnas.org/cgi/doi/10.1073/pnas.1407304111
 
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There's an increasing body of literature demonstrating the benefits of active learning for tertiary students taking science subjects. This is a topic I've written about before, but I'm always interested in reading more on the subject. And let's face it, the more evidence the better, when you're wanting to get lecturers in the sciences engaged in discussion around different ways of teaching. As you'll have gathered, I find a lot of new science & education material via alerts on Facebook, as well as through the more conventional journal feeds & email alerts, and so it was with this recent paper by Scott Freeman & colleagues, which looks at the effect of active learning on student performance in science, technology, engineering and maths (STEM) classes: I saw it first described in this post1 (whence also comes the quote I've used as my title).

The paper by Freeman et al (2014) is a meta-analysis of more than 200 studies of teaching methods used in STEM classes, which included "occasional group problem-solving, worksheets or tutorials completed during class, use of personal response systems with or without peer instruction, and studio or workshop course designs" (ibid.). The impact of the various methods on student learning was measured in two ways: by comparing scores on the same or similar examinations or concept inventories; and by looking at the percentage of students who failed a course.

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