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October 2014 Archives

Evolutionary change can be fast - Peter and Rosemary Grant's long-term & ongoing research project on the Galapagos finches documented rapid responses to environmental changes, for example, as does the  recent work on cane toads in Australia. And biologists have known since Darwin's time that competition can be a strong driver of evolutionary change. (Take Gause's principle of competitive exclusion & its implications, for example.) A just-published paper about Anolis lizards demonstrates this very well (Stuart et al., 2014).

The way in which different species of this little lizard divvy up their habitat is used as an illustration of niche partitioning by many textbooks (you'll find an example here). Stuart & his co-authors describe some elegant experimental work over a period of 15 years, on artificial islands in a Florida lagoon. Initially they used six of these islands, all of which were already colonised by the green native anole, Anolis carolinensis: three of the islands acted as controls, while brown anoles from Cuba (Anolis sagrei) were introduced to the other three. The two species are described as being "very similar in habitat use and ecology", including diet, so they'd be expected to compete fairly strongly when brought together.

In other areas where the two species are found together, A.sagrei perches lower in trees than carolinensis, which left to itself would occupy most of the tree. So the prediction was that on islands where sagrei was introduced the same thing would happen: carolinensis would come to occupy a reduced niche, perching higher than the 'invader'. And this is indeed what happened, in the space of three months: 

by August 1995,on treatment islands already showed a significant perch height increase relative to controls, which was maintained through the study.

The researchers also predicted that this change in niche would be accompanied by a change in morphology; specifically, that there would be selection for larger, sticker feet in A.carolinensis, on the basis that 

[toepad] area and lamella number (body-size corrected) correlate positively with perch height among anole species, and larger and better-developed toepads improve clinging ability, permitting anoles to better grasp unstable, narrow, and smooth arboreal perches.

This prediction was tested through observations on 11 islands, five with only the native species and six with both the native and the Cuban invader. Again, carolinensis perched significantly higher in trees on islands where sagrei was also present - and on those islands carolinensis anoles also had "larger toepads and more lamellae" than were found on the same species living without the competitor (an example of character displacement) - and this happened within about 20 lizard generations.

Careful analyses allowed the researchers to rule out other explanations: 

In sum, alternative hypotheses of phenotypic plasticity, environmental heterogeneity, ecological sorting, nonrandom migration, and chance are not supported; our data suggest strongly that interactions with A. sagrei have led to evolution of adaptive toepad divergence in A. carolinensis.

So, just as with the cane toads, we are seeing rapid evolutionary change in real time.

Y.E.Stuart, T.S.Campbell, P.A.Hohenlohe, R.G.Reynolds, L.J.Revell & J.B.Losos (2014) Rapid evolution of a native species following invasion by a congener. Science 346 (6208): 463-466. doi: 10.1126/science.1257008 

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This was first posted over on TalkingTeaching.

This blog post at SkepticalScalpel really struck a chord. Entitled "Should social media accomplishments be recognised by academia", it compares the number of citations the author's received for published papers with the number of hits on a blog post reviewing original research. And finds there's no contest:

Three years ago, I wrote "Statistical vs. Clinical Significance: They Are Not the Same," which reviewed a paper on sleep apnea ...

That post has received over 13,400 page views, certainly far exceeding the number of people who have read my 97 peer-reviewed papers, case reports, review articles, book chapters, editorials, and letters to journal editors.

The SkepticalScalpel author also notes that this sort of on-line peer-review and discussion of data can have rapid, effective results:

Last year, some Australians, blogging at the Intensive Care Network, found that the number needed to treat stated in a New England Journal paper on targeted vs. universal decolonization to prevent ICU infection was wrong. They blogged about it and contacted the lead author who acknowledged the error within 11 days. It took the journal 5 months to make the correction online.

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Recently I had a blast, attending an inspirational workshop by Alan Levine (I grab professional development opportunities like these with both hands!). The workshop gave me some ideas for new things to try with my students next year, and I thought I would share the notes I made at the time (with commentary) in case there might be useful things there for others.

Alan kicked off by asking us if we knew when the internet was created (heaps of history here), by whom (I've never really understood why so many people think it was Al Gore), & for what. It was originally intended to allow scientists to better communicate with each other - but sometimes it feels as if the science is being swamped & lost in amongst everything else that's posted on the web. (A friend once said to me that one day the internet could collapse under the weight of funny cat pictures. She could be right.)

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In her book Paleofantasy, Marlene Zuk discusses cane toads (Bufo marinus) as an example of just how rapidly evolutionary processes can work. These amphibian pests were introduced into Australia in 1935 to control borer beetles in sugar cane. Unfortunately the toads never got the memo about this expectation, and have spread rapidly across the continent, damaging a range of native ecosystems as they go. (They're aided by the fact that they're toxic, killing many of the predatory animals that might otherwise eat them.)

And it's not just that the toads are and always have been fast hoppers. As this article says

When the toads were first introduced, they spread at a rate of about six miles (ten kilometers) per year. Today cane toads advance more than 31 miles (50 kilometers) annually.

In other words, they're getting faster, with animals at the 'invasion front' moving up to 1.8km in a night. (The researchers were able to measure the toads' speed by fitting them with miniature radiotransmitters, strapped to their waists.) Phillips & his colleagues (2006) point out that speed of movement in toads is correlated with leg length, and asked the question: is there a difference in average leg length between toads at the front of the amphibian wave spreading across Australia, and those at the back of the bunch? The answer:

As the toad invasion front passed our study site, we measured relative leg lengths of all toads encountered over a 10-month period. Longer-legged toads were the first to pass through, followed by shorter-legged conspecifics (order of arrival versus relative leg length: r = -0.34, n =552, P = 0.0001). Longer-legged toads therefore moved faster through the landscape.

And the evolutionary changes don't stop there. In a paper just out, Brown, Phillips & Shine (2014) describe how the animals' tendency to travel in a straight line has changed too: 

Radio-tracking of field-collected toads at a single site showed that path straightness steadily decreased over the first 10 years post-invasion.

The research team found that this behavioural change had a genetic underpinning. The progeny of toads from the invasion front moved in straighter paths than the offspring of toads from older, well-established populations to the east. In addition, "offspring exhibited similar path straightness to their parents." Brown & his colleagues concluded that

The dramatic acceleration of the cane toad invasion through tropical Australia has been driven, in part, by the evolution of a behavioural tendency towards dispersing in a straight line.

G.P.Brown, B.L.Phillips & R.Shine (2014) The straight and narrow path: the evolution of straight-line dispersal at a cane toad invasion front. Proc.R.Soc. B 281(1795) doi: 10.1098/rsph.2014.1385

B.L.Phillips, G.P.Brown, J.K.Webb & R.Shine (2006) Invasion and the evolution of speed in toads. Nature 439: 803. doi: 10.1038/439803a

Teachers: there's an open-access summary of the 2006 paper here.

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Recently some friends & I were discussing the use of what might be called 'Supplementary, Complementary, & Alternative Medicine' - a group of 'therapies' that includes (but is not limited to) things like homeopathy, reiki, acupuncture, ear candling, and cranio-sacral therapy, and for which there is little or no evidence of efficacy.

One of the reasons given by those supporting their use is a form of the 'argument from popularity' logical fallacy: 'but look at how many people use them. They can't all be wrong!' That viewpoint is exemplified here, in the claim that a large number of doctors are now recommending alternative therapies to their patients, or providing these therapies themselves. The list offered at one such practice includes

psychologists, naturopaths, nutritionists, cranio osteopaths, massage therapists, hypnotherapists, yoga practitioners, an acupuncturist and a breast thermography technician.

Now, massage, yoga (exercise), and psychology are hardly 'alternative', although including them in the list then allows one to inflate the number of people supposedly seeking out alternative health modalities. Most of the rest have been addressed far better than I could by Orac (see here, for example, and here) and the authors of the Science-Based Medicine site

But let's not get distracted. As my friend Renee said: the claim is that lots of people use these modalities, therefore they must be good; a claim supposedly supported by "the impressive statistics showing people are now willing en mass [sic] to spend their dollars on integrated health care". What we should be asking to see are the statistics showing the efficacy of such care, before we start spending any more of our scarce health dollars on it.

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A very brief post before I dive back into marking!

My friend Cathy pointed me at this short, fascinating video that shows some quirky chemistry & physics demonstrations (afficionados of Facebook will find it here). I had a couple of 'wow!' moments while watching it; science teachers will probably get the same response when sharing it with their classes.

Thanks, cathy :)

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The 'paleo' diet story on Campbell Live tonight spurred me to finish my review of one of the most entertaining popular books on genetics that I have read for some time. Entertaining, and informative, in equal measure. I wonder what author Marlene Zuk would have made of the TV story.

book cover

Marlene Zuk (2013) Paleofantasy: what evolution really tells us about sex,diet, and how we live.  Norton (New York)

ISBN 978-0-393-34792-0 (paperback)

For in that story we heard gems like this: "It's a commitment to eating food that is unadulterated, eating food in its most natural state." Paleo proponents (says the TV story) believe our most natural diet is that of our Palaeolithic cavemen ancestors. Somehow I doubt our 'cavemen' ancestors were eating avocados, beetroot, bacon or kale. (There's also an air of chemophobia, with one proponent of paleo eating stating that their diet contains "[n]othing nasty and nothing you can't pronounce" - which reminded me of the series of posters by Australian teacher James Kennedy, showing the list of chemical compounds found in natural food items: blueberries, anyone?).

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