Posts Tagged scholarship biology

how biology teachers can respond to intelligent design Alison Campbell Mar 17

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Creationism is a recurring issue for teachers of biology. It can come in many forms (eg young-Earth creationism, old-Earth creationism, & so on) but – despite what many ‘IDers’ would say – its most recent incarnation is as intelligent Design ‘theory’, or IDT. (I use the quote marks advisedly; Intelligent Design doesn’t offer any evidence that can be explained by a coherent scientific theory, instead preferring to generate a false dichotomy between IDT and evolution: if evolution is wrong about ‘x’, then IDT is correct.) While IDT received a resounding defeat in the Dover trial of 2005, it continues to be promoted around the world as a ’scientific’ alternative to evolution.

Anyway, a colleague has just sent me Jim Mackenzie’s paper, How biology teachers can respond to Intelligent Design, which I thought I’d talk about here. As Mackenzie says, a significant number of authors have already argued convincingly that IDT is bankrupt as far as scientific theories are concerned. He proposes several strategies that science teachers can use in dealing with attempts to introduce IDT into their classrooms, and comments that it’s possible to use these with younger children. I think this is particularly useful given that the 2010 NZ science curriculum makes evolution an organising theme for biology (aka the ‘Living World’) from the earliest years of primary schooling. Mackenzie’s strategies are drawn from a case dating back more than 20 years, from an attempt to mandate the teaching of creation ’science’ – surely an oxymoron - in Arkansas schools. I found this a little surprising given the more recent Dover case, but then it is all creationism under the skin, despite attempts by various ID proponents to claim otherwise.

Just as in Dover, the Arkansas attempt to insert creationism into school curricula claimed that there was strong scientific evidence in support of doing so. The case went to court. In his decision, Judge Overton noted that teachers given the job of producing a curriculum for teaching biology from a creation ’science’ viewpoint could not find any scientific articles in its support. Not one. There was simply no creationism research available to make this a viable alternative to evolution.

Mackenzie suggests that teachers wishing to show that ID is outside science should use a ‘wide’ definition of science. He argues that definitions of science allowing only ‘natural’ (as opposed to supernatural) explanations are too narrow & risk being accused of excluding ‘too much’. He then goes on to state that this definition is ‘inoperative [in any case] because once an explanation comes to be incorporated into science it is seen as natural and matrialist, even if had previously seemed not to be’, & gives Newton’s theory of gravity as an example. Gravitational theory was originally viewed as magical or occult, but because it allowed accurate predications, was eventually accepted. Well & good, but the suggestion that if scientists accepted IDT as scientific, its arguments might be accepted as Newton’s were seems to me to be drawing a long bow. There are many reasons why scientists have already rejected IDT as non-scientific, as Mackenzie himself admits. It is, however, useful to emphasise, as he does, that even when the bar of what is considered ’science’ is set very low, IDT fails to clear it. There is still no ID research published in scientific journals that clearly presents evidence in support of ID (attempting to show that evolution can’t explain something, & claiming that as evidence ‘for’ ID, doesn’t count.)

The second strategy is to make it clear that religion is not the enemy of science. Part of the reason for excludng creationism from US schools lies in the constitutional separation of religion and the State. Show a particular standpoint is religious & it can’t be taught in schools in the USA. That’s not the case in many other places, & here in NZ it’s possible to present religious instruction in state schools, provided parents have the opportunity to opt out. The problem here, as recent mailouts to science departments have shown, begins when attempts are made to present a particular religous viewpoint in the guise of science. (I thought the Ministry of Education’s response to this was a bit of a cop-out: saying that parents can withdraw their children from religous education ignores the fact that this stuff was being sent to science teachers with the obvious hope that it would be incorporated into science classes.)

Nonetheless this is a key point – there’s nothing to be gained, if the question of creationism is raised in a science class, in ridiculing religion. Religious beliefs are often strongly held & denigrating them won’t do anything to convince a student (or their parents) of the validity of evolution & is more likely to set them at loggerheads with the teacher. A more useful strategy might be to point out that major religious leaders – including the last Pope – have indicated that there is no conflict between faith and science on this matter.

Mackenzie’s third key statement is that ’science teachers should trust their own expertise’ – and this means bringing that expertise to the fore. We’re all aware (or we should be!) that in science theories are constantly being tested, added to, modified. There’s much about the current state of evolutionary biology that Charles Darwin would never have recognised: Mendelian genetics, the concept of genetic drift, punctuated equilibrium, horizontal gene transfer… All these new ideas have been tested empirically & subsequently become an established part of evolutionary biology (& after that, they make it into the textbooks). There’s a very strong case to be made for us to talk about all this with our students, rather than treating it all as a fait accompli. As Mackenzie says, ‘[t]here may always be new ideas, new evidence, and every scientific conclusion is open to revision.’ How better to give students an understanding of this key aspect of the nature of science?

And finally, he suggests that ‘alternative theories should not be excluded.’ Well, I’m fine with that, as far as it goes – & as long as we are talking about ‘theory’ in the scientific sense. But what Mackenzie really means is that, faced with a request to include ID in the classroom, teachers should respond that they would intend to look at a wider range of alternative perspectives . This of course assumes that teachers are aware of that range, and are confident in their ability to explain why they do not constitute a scientific explanation for life’s diversity. And that there is actually time in the full-on classroom day to do this approach justice.

J.Mackenzie (2010) How biology teachers can respond to Intelligent Design. Cambridge Journal of Evolution 40(1): 53-67. DOI: 10.1080/03057640903567039

how do we teach students to question what we say? Alison Campbell Mar 14

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This is a re-post of something I’ve written for Talking Teaching. I’ve reproduced it here because I think the notion of teaching things like critical thinking & the nature of science are just as relevant here as they are in a discussion about teaching itself.

I’ve just been reading a post by Tim Kreider, over at Science-Based Medicine. Tim’s talking about the learning experiences of medical students, but a particular phrase caught my eye. I”m reproducing it here because I think it can be applied much more widely: students are in the habit of transcribing and commiting to memory everything uttered by the professors who grade them.

I’ve seen this happen myself. I remember talking with a class about fungi & saying that while most fungi are saprophytes (consuming dead material), some are predatory. And they all (well, all those I could see, anyway) wrote this down unquestioningly. ‘Hang on a minute,’ I said; ‘does this sound likely to you?’ They agreed that no, it didn’t really, it didn’t match with what they already knew about fungi. ‘Well then,’ I said; ‘why didn’t any of you call me on it?’ ‘Because,’ they said, ‘you wouldn’t tell us anything incorrect, would you?’ Which showed a touching faith but also a worrying lack of willingness to question things that didn’t sound right.

(Just as an aside: This was amply demonstrated one year when my class was sitting a lab test. One of the questions asked students to label a section of plant tissue, selecting their labels from a list that I provided. It happened to be April 1st – so I included the word ‘aardvark’ in that list. Rather worringly, about 30% of the class used it for a label – & when asked why they said well, it didn’t sound right, but they just knew I wouldn’t have used a word that didn’t belong… And not one of them questioned it at the time.)

Now, in his SBM post, Tim makes the point that med students in their pre-clinical training have to learn so much content that there isn’t a lot of room for rigorous skepticism (but make no mistake, he’s still arguing of the need to teach critical thinking). And I agree, there is factual content that I want my students to be able to remember (& my colleagues teaching at 2nd-year would like it too!) But at some point we must surely also want our students to develop a healthy skepticism: the ability to think critically about what they’re hearing & learning.  And I certainly don’t like the idea that my science students might regard me as infallible. Not least because that’s not a particularly good model for what science is like. They need to know that scientists can & and do make mistakes, get things wrong, interpret data in ways that subsequently (in the light of further data) turn out to be inaccurate. And they need to feel confident that it’s OK to ask questions. The thing is, how best to get this across?

Speaking for myself, I’m a firm believer in modelling this for my students. If I’m asked a question to which I don’t know the answer, I’ll tell them so, up front. But then I’ll say, but I can hypothesise about this – here’s what the answer might be, & here’s my evidence for thinking this. (If the classroom has web access – & most of ours do these days, we’ll often go on to check what I’ve said on the spot.) If it turns out that I’m wrong (which happens quite a lot, then that’s fine, & we’ve all learned something new.

Plus, I actively encourage questioning during my lectures. (Pop quizzes & concept maps are good for encouraging the sort of conversations that lead to this.) Sure, I mightn’t get through as much content as if I didn’t do this, but the students’ learning experience is surely going to be a better one if they can follow up on things on the spot. And hopefully they learn from this that it really is OK to ask questions :-)

And – I’m all for telling stories. How better to help students learn about the nature of science than to use a narrative approach that lets them see how scientists viewed the world at some past point in time, & how science has led to a change in - or a reaffirmation of – that perspective?

writing that essay Alison Campbell Mar 09

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Found this today (while procrastinating…)

funny graphs and charts

Now, while the cartoon is funny, the message is not (& hopefully some of my first-year students are reading this – pay attention, guys!). Leaving an assignment to the last minute is not a good strategy for success – not in science, & not in any other area either.

It means you’ll do a rush job, so your formatting, spelling, grammar & so on are likely to suffer. And these do matter, because you’re essentially attempting to communicate with the reader about your understanding of a topic & how you write is part of that. (I’ve had students use – repeatedly, within an assigment – the wrong technical term in a way that makes me wonder if they actually understand what they’re writing about.)

It means you’ll be last to the library & so may miss out on that crucial book; of course, access to on-line journals has changed that more than a little. But if you’re not confident about what you’re searching for, leaving things until the last minute will make it that much less likely that you’ll find that perfect reference (remembering that you actually have to read them as well!). Wikipedia doesn’t count.

it means you probably won’t proof-read your work properly. So you may not pick up the fact that you haven’t properly cited a reference (or haven’t included that source in your References section). Or that you’ve missed out a whole paragraph that presents the crucial information supporting your argument. Or – eek! – that you haven’t actually answered the question at all.

It means you probably won’t have crafted a really good essay. (Trust me on this – I’ve seen an awful lot of them.

And, when crunch time comes & you haven’t finished writing, going to your teachers & saying ‘I ran out of time’ is unlikley to be viewed with favour… I wouldn’t advise trying the following, either.

the age of mammals Alison Campbell Mar 06

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The last 65 million years have sometimes been called ‘the Age of Mammals’ (although I’m inclined to think it should be the Age of Insects, or perhaps – as it’s always been – the Age of Bacteria; after all, in terms of sheer number of individuals, bacteria have got to be the dominant life form on the planet…). This gives the impression that mammals are a relatively recent evolutionary novelty.  But just how old is this class of organisms? Just what is the ‘age’ of the mammals?

Mammals began to diversify after the mass extinction event that marks the boundary between two geological ‘periods’ (the Cretaceous & Tertiary) and which carried off a large number of species, most notably the dinosaurs. But they’ve been around for much longer. Much, much longer – the mammal family tree has its roots way back in the Carboniferous, 350-270 million years ago.

Not that those ancestors wandering through the swampy Carboniferous forests would have looked like the mammals of today. Scientists call these ancestral beasts, ’mammal-like reptiles’ ie they were reptiles, but with some mammal-like features, including features of their skulls. Modern mammals, those early mammal-like reptiles, and everything in between, are described as synapsids.

  

Amniote skull types. a) Anapsid eg turtles b) Synapsid eg mammals c) Euryapsid eg ichthyosaurs & plesiosaurs d) Diapsid eg dinosaurs & birds. (NB the ‘amniotes’ are the reptiles, birds, & mammals – all produce an amniotic egg with a number of membranes associated with the yolk & developing embryo.)
 
The synapsid skull (b) has a single opening in the external bone layer, behind the eye – these diagrams can be a bit confusing & certainly my students sometimes find them so; it looks like the hole might go through from one side of the skull to the other, but in fact that’s not so.
 
Early synapsid reptiles roamed the Earth from the Carboniferous period until the Jurassic, and at one time were the dominant land animals. Many groups of these early reptiles were not in our direct lineage; one group that was, was the pelycosaurs - which included the fearsome predator Dimetrodon. (The name Dimetrodon means ‘two kinds of teeth’ – this is significant as most reptiles have a single type of teeth in their mouths, while modern mammals have 3-4.) One group of pelycosaurs evolved into the mammal-like  ’therapsids’, a group that included Thrinaxodon, and the therapsids in turn produced a number of descendant groups. One of them, the cynodonts, was on the line to modern mammals (but not, as it turns out, directly linked to them). 
 
By the way, it’s actually rather difficult to define a clear instant at which an animal becomes a ‘mammal’, rather than a ‘mammal-like reptile’! Therapsids have a number of mammal-like features: compared to the sprawling stance of reptiles, they held their legs more underneath the body (making locomotion more efficient); they had a distinct neck; their mouths contained several different types of teeth – something described as heterodonty; the beginnings of a secondary palate began to separate the airway from the mouth; and one of the bones in the lower jaw (the dentary) was enlarged compared to that in reptiles. But they definitely weren’t mammals.
 
Many therapsids became extinct during the mass extinction event that marked the end of the Permian, around 225 mya. (Incidentally, this was one of the greatest mass extinctions in terms of species lost – David Raup & Jack Sepkoski estimated that up to 94% of all species then alive, died in the end-Permian event. On the mammalian side the survivors included cynodonts like the herbivorous dicynodont Lystrosaurus (the distribution of Lystrosaurus fossils provided early evidence in support of the concept of continental drift) and the carnivorous ‘theriodonts’. The latter were similar to wolves in size, with large serrated canine teeth and skull modifications that provided larger jaw muscle attachment points.
 
During the Triassic cynodonts gradually became more & more like ’true’ mammals. Eventually their lower jaws comprised just a single bone (called the ‘dentary’ because it bears the teeth). Along with this came a change in the way the jaw articulated with the skull (& associated changes in the tiny bones of the inner ear). Another feature was the obvious presence of a diaphragm. OK, you say – this is so unlikely to fossilise, so how can you say this? The evidence lies in the lack of ribs attached to the lumbar vertebrae (the ones that form the ’small’ of your back) – in modern mammals the diaphram is attached to the lower edge of the ribcage, & there are no lumbar ribs. The therapsid Thrinaxodon didn’t have lumbar ribs either, so the diaphragm must have been an early evolutionary innovation in the proto-mammal lineage.

And these beasts were probably furry :-)  Cynodont jawbones are perforated by small holes, similar to those which in modern mammals carry nerves and blood vessels to the whiskers, which implies furriness. (Cuddliness would be highly unlikely!) And a wonderful fossil from the Jurassic, Castorocauda, includes direct evidence of fur. Not only this, but a range of features tell us that Castorocauda spent a lot of time in the water. So, an immediate predecessor of modern mammals swam in the streams that T.rex would have splashed through: the earliest evidence yet of an aquatic mammal.

But the origins of ‘true’ (modern) mammals remains a bit murky. This isn’t helped by the fact that many of the early forms are known mainly by their teeth. (I’m sure it’s been said by someone before, but you could jokingly say that the evolution of mammals is traced through the matings of teeth with teeth…).So to get back to that original question: what is the age of the mammals? The answer has to be – it depends on how you define them :-) 

how i became a science teacher Alison Campbell Feb 20

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I’ve been reflecting on my teaching career lately, partly because I have to write a teaching portfolio. It occurred to me that talking about how I came to be where I am now might perhaps be interesting to some of you who are thinking about your future. In my experience, at least, things don’t always go according to plan :-) & it pays to be flexible.

With both parents working in science-related fields (mum a biology teacher, dad a technical officer for a government department) I suppose at least one of we four children was always going to be a scientist. By the time I was 7 or 8, I’d decided to be a doctor. I read mum’s biology books (well, OK, I looked at the pictures) & thought, as probably most kids who contemplate a career in medicine do, how neat it would be having a job helping people get well. A bit later on, though – maybe after mum showed me a dissection – it struck me that while it while it was probably fairly straightforward to open somebody up, putting everything back together so that it was still all in working order was a big ask. I crossed medicine off the list.

I studied the the sciences at school (and maths, & languages & geography up till the end of 5th form [year 11]), but didn’t really focus on a career until – I think – the beginning of year 13. With mum as my example, I decided on teaching (she’d moved into a teaching career relatively late in life). Way back then the government provided studentships to aspiring teachers: you got a rather decent monthly allowance for the duration of your studies, & in return you were expected to take up a teaching job at the end of your time at university. After an interview, I was awarded a studentship & trotted off to Massey to study biology.

Things began to unravel at the edges when I was invited to study for Honours, at the end of my 2nd year at Massey. This meant a further 2 years of study, which the Ministry of Education (who held my purse-strings) was quite happy with. But part of the final Hons year is your dissertation, where you spend a reasonable amount of time on a research study. I chose to look at mallard ducks – their behaviour was pretty well-described, but I wanted to know if there were any differences between the behaviour of mallards on the local lake (Centennial Lagoon) and a smaller population on a country pond. (There were.) I quite liked doing the research, & towards the end of that year I was asked if I’d like to work towards a PhD. Hmmm, teaching or study, study or teaching?

Study won out, & I went on to spend a further 3 years or so looking at the behaviour of black swans on a Manawatu dune lake. Mind you, I was also ‘teaching’ in the sense of demonstrating in undergraduate lab classes, but teaching as a career seemed a bit more distant. However, when I graduated I wasn’t immediately able to get into any research positions, and without that happening we weren’t going to leave Palmerston North as my husband had a secure & stimulating job there. So I applied for – and won! – a position as ‘assistant biology teacher’ at Palmerston North Girls’ High, & that was it. I was totally hooked on teaching. (I still am.) I loved, & love, the interactions with students, & also I get a real buzz from those times when you see something ‘click’ with a student.

(At this point I have to say that I really do think that good teachers are born as well as made. I took 4 extramural papers at ‘TColl’ while I was teaching, and after passing them & putting in another couple of years in the classroom I received my Trained Teachers Certificate. But still, a lot of what ‘worked’ for me in the classroom still seems to me to be instinctive.)

Anyway, after 8 years in secondary classrooms (& with our family expanded to include our 2 children), I ended up going back to Massey as a senior tutor. And I’ve remained in tertiary classrooms ever since. I have to say, I think I’m really lucky to have that secondary teacher training & experience – it’s given me an insight into the prior learning experiences of new students coming into my first-year lectures & lab classes. At the same time, the things I do with & for secondary teachers helps me to understand the classroom practices & processes that work for them & with which ‘my’ students will be familiar with when they join me at Waikato. And it’s also what got me into writing this blog – it’s a way of giving something back to those teachers, maybe encouraging their students to think more critically & read more deeply in the scientific literature, and hopefully helping to inspire their own journeys in science.

Because it is an ongoing journey, & I think that’s something you shouldn’t lose sight of – that you may end up in unexpected places in your passage through life :-)

breadth vs depth Alison Campbell Feb 11

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One of the conflicts faced by probably every classroom teacher is the one between the amount of material one has to teach (& the students to learn about) and the time available. I face it myself: huge (though also very good) textbook, requests from my colleagues to make sure that the first-year course adequately prepares students to take second-year papers, students coming in with a range of backgrounds & prior experiences of biology – & a 12-week semester in which to accommodate it all. Reflecting on my teaching practice over the last several years in our A semester intro bio paper, I think I probably teach less content, less detail, than when I started in this particular paper, but have more of a focus on identifying (& dealing in depth with) big, or key, ideas. As you’ve probably guessed from my posts, I encourage my students to think critically about what they’re learning, and to gain an understanding of how those ideas & concepts relate to each other. And of course I’d like all my students to view science as fascinating, fun, useful, & relevant to them in their daily lives…

So of course I was interested in a paper by Marc Schwartz & his colleagues, entitled Depth versus breadth: how content coverage in high school science courses relates to later success in college science coursework. How would their findings relate to my own teaching approach? (And, is what I do in the classroom supported by empirical data, or is it a case of intuition & experience leading me up the garden path?) In a survey of 8310 students taking first-year biology, chemistry, & physics courses, the authors fround that students who said they’d spent at least a month studying at least one major topic in depth, while at high school, received higher grades in their university science classes than students who hadn’t done (or didn’t remember!) doing any in-depth work. Interesting! The team also looked at the outcomes for students who reported having broad high school classes that covered something on all major topics. The results here were equally interesting – these students didn’t seem to have any advantage over students who hadn’t ’studied everything’ in physics & chemistry, & were at ‘a significant disadvantage in biology’.

Presumably students spending a month or so on a single topic can really come to a good understanding of the area, mastering key concepts & able to understand how it all fits together. Taking a ‘deep learning’ approach, in other words.  In classrooms where there’s a drive to cover everything, it could well be that many students cope with the huge volume of material by using learning approaches that could be called ’shallow’ – rote learning techniques, for example, that don’t really aid a thorough understanding. (All this, of course, assumes that the tertiary assessment practices these students are encountering reward those taking the ‘deep’ learning approach to their studies…) And those with the learning skills developed by taking a deep learning approach to one topic can then apply those to the new material they learn in the following year, enhancing their learning outccomes there as well.

I guess my fondness for trying to focus on teaching methods that encourage ‘deep’ learning reflects my own philosophy that there is simply too much information potentially available. In ‘the old days’ it was probably quite possible to teach a subject such as any one of the sciences in fairly comprehensive breadth. But since then, particularly with the advent of modern technology, there’s been something of an explosion of knowledge. I know some of my students are quite daunted by the sheer size (& volume of content) of our textbook (the excellent Campbell [no relation!} & Reece). For me, & my colleagues in first-year biology, the question is, how to include it all? And,  should we cover it all? Schwartz et al quote another author as saying that '[to] be successful [in their learning], students need carefully structured experiences, scaffolded support from teachers, and opportunities for sustained engagement with the same set of ideas over extended periods of time." That ’sustained engagement’ part is the tricky one, when you’re teaching a ’service’ course that’s intended to prepare students for a range of paper options in their next year of study. I try to manage it by identifying common themes (eg the need for gas exchange, internal transport, energy) that apply across the living world, & tying things to those, so the themes recur even if the material attached to them is novel. But it’s a testing balancing act, nonetheless… Nice to know that at least one research paper suggests that I’m on the right track :-)

M.S.Schwartz, P.M.Sadler, G.Sonnert & R.H.Tai (2009) Depth versus breadth: how content coverage in high-school science courses relates to later success in college science coursework. Science Education 93: 798-826 doi 10.1002/sce.20328

procrastination – something to avoid Alison Campbell Jan 16

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I’ll be using this lolcat in my classes for sure :-)

funny pictures of cats with captions

And seeing it spurred me to write a bit about studying at university, for those of you who’ll be heading that way this year. Namely, that it’s not like being at school.

At uni, you’re expected to take responsibility for your own learning. You’re not going to be chased up to come to class, for example. (Having said that, I do e-mail to anyone who’s missed two or more lab classes, asking what the story is.) Although you shouldn’t take that as licence to wag lectures – too much goes on in them that you can’t really afford to miss. Most lecturers will probably provide their first-year students with study guide notes, but the lecture itself is more than going over those notes. They’ll be put in context; there’ll be interesting little anecdotes, quizzes, all sorts of stuff.

And you certainly shouldn’t miss a lab class without good reason. They’re an essential part of the paper, & if you miss more than 1-2 without providing a medical certificate or some other documentation, you may end up failing the course. Not a good thing at all. In fact, failing to attend a compulsory class, or hand in a compulsory item of assessment, might have the same result. If you know in advance that you’re going to be away, or that you need an extension on an assignment (for a good reason! "I didn’t get around to starting it until last night…" is unlikely to be viewed with any degree of sympathy), then talk with your lecturer or tutor & see what can be done. I’ll do all that I can to help someone who comes to me early when they recognise that they need help, but there’s next to nothing I can do for someone who turns up at my office for the first time, the week before the final exam.

Which I guess brings me to the point of the lolcat – don’t procrastinate. Manage your time properly. Make lists. Plan ahead. Don’t leave things till the last minute. The potential penalties for not doing this can be quite severe. Our registrar & I are working on approving enrolments at the moment (in fact, both of us were in the office for most of today, which is a bit dire on a lovely sunny Saturday!), and every so often a ‘re-entry appeal’ crops up. These are from people who, for whatever reason, have failed more than a certain proportion of their year’s program of study, & so are not automatically eligible to return to the university. Some are on medical grounds – but in all too many of these appeals the reason given for failing is along the lines of ‘I didn’t manage my time &/or workload properly’, often accompanied by ‘I didn’t ask for help when I should have’. If someone in this position is given re-entry, then they’ll have to repeat the papers that they failed or, if they change programs, take different ones at the same level. There’s a big cost in this, in both money & time – it may extend the time taken to complete the degree by up to a year, & that’s a lot of fees & student loans.

Procrastination can be expensive. Don’t do it.

gannet monogamy model moot Alison Campbell Dec 01

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When you studied animal behaviour in year 13 you probably learned about the different mating systems: polygamy (polygyny & polyandry), promiscuity – & monogamy: a bond between a single male & a single female. You may also have heard that in some species, such as swans, that bond is life-long.

It turns out things are more complex than that. My first inkling of this came back when I was working on the literature survey for my PhD on behaviour in black swans, & found (rather to my surprise – I was probably too naive for my own good back then) that swans indulged in some definitely non-standard breeding practices, with more than one paper describing a menage a trois (one female, 2 males). Cuckoldry wasn’t unknown, either. Plus, our own stitchbirds are known to practice polyandry, polygyny, and monogamy as well; homosexuality’s been documented in a large number of animal species; & of course there’s that recent example of oral sex in fruit bats. Anyway, the concept of variations on monogamy in swans got me thinking & I realised that for monogamy the idea of life-long fidelity probably didn’t hold either – after all, if your current partner is incapable of producing offspring, or turns out to be a lousy parent, it’s probably worth your while (in genetic & evolutionary terms) to divorce them & find a new one. Plus, if one partner dies, the other is unlikely to sit around doing nothing (in the reproductive sense) for the rest of their life. But it wasn’t something I investigated further at the time.

A new paper by Stefanie Ismar & her colleagues (Ismar et al. 2009 – based on Ismar’s PhD research) looks at the frequency & costs of divorce in Australasian gannets. (Not the costs of a settlement – the reproductive & hence evolutionary costs!). Gannets have long been another example of life-long fidelity in animals. They nest in large colonies (the best-known in New Zealand are probably those at Cape Kidnappers & Muriwai beach) & are highly territorial within those colonies, aggressively defending the small area immediately around their nest site. Each breeding season the males arrive at the breeding colony first, re-establishing their territories & waiting for the females to turn up – the birds are philopatric, which means that they are strongly attached to the colony where they were hatched & will return there to breed themselves. Although this set-up is described as monogamous, Ismar et al. cite genetic research showing at least some chicks have ‘extra-pair parentage’ – they’re produced by matings between one partner & an outsider (I’d suggest sneaky copulations between the female & a roaming, possibly neighbouring, male, as it would be harder for a strange female to come in & lay eggs in an established pair’s nest).

The study population comprised individually-banded gannets in part of the Cape Kidnappers colony. Ismar recorded the presence/absence of individuals, the presence of pair bonds, & the reproductive success of breeding pairs (where possible comparing her data with those from previous breeding seasons). From this the team was able to determine if members of a pair had divorced (one living with a new partner but the previous mate also present in the colony) or if a mate had been lost (ie didn’t reappear at all in the subsequent breeding season).

They found that divorce rates ranged between 40-43% – so much for gannets faithful unto death :-) This sounds high – were the birds accruing any reproductive advantage through their fickleness? Well, over the 2-year study period, pairs that remained together had significantly higher reproductive success (they fledged more chicks) than individuals who’d lost a mate & subsequently re-mated. Similarly, divorcees fledged fewer chicks than birds who retained their mates from the previous season (although the difference was statistically significant only for the 2008-09 season). These results suggest that there’s a benefit to sticking with the same mate when you can, perhaps because it takes a bit of experience to learn to cooperate with a partner in rearing the chicks. This would explain why first-time breeding pairs often have a lower breeding success than long-established pairs.

So why the high divorce rate? The researchers suggest that this may reflect delays in partners arriving at the colony. A bird who waits too long for their beloved to turn up may end up not breeding at all, so divorce could represent a compromise that offers at least a chance of reproductive success (the entertainingly-named ‘musical chairs hypothesis’). However, it’s still too early to completely rule out the idea of divorce as a way of minimising mate incompatibility, or perhaps minimising inbreeding  - as the authors say, more research is needed to unweave the ecological & behavioural determinants of breeding success in long-lived seabirds. 

Ismar, S., Daniel, C., Stephenson, B., & Hauber, M. (2009). Mate replacement entails a fitness cost for a socially monogamous seabird Naturwissenschaften DOI: 10.1007/s00114-009-0618-6

whence the nucleus? Alison Campbell Nov 22

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One of the deepest divisions among living things is the split between prokaryote and eukaryote cells. In eukaryote cells, the chromosomes are enveloped in a layer of phospholipids – these cells have a ‘true’ nucleus surrounded by a nuclear membrane, something that’s absent from prokaryotes. And there are other differences: eukaryotes either have, or have had, mitochondria (tiny organelles where aerobic respiration occurs) and plants & algae also have chloroplasts, & there’s a lot of other cellular infrastructure besides. Now, we teach students about the origins of mitochondria & chloroplasts (most likely by the process of endosymbiosis, first put forward as an explanation by Lynn Margulis), but what about that nucleus?

There have been various hypotheses put forward to explain the origin of the eukaryote nucleus. One is that the chromosomes of the ‘pre-eukaryote’ were somehow surrounded by a section of the cell membrane. Certainly some prokaryotes have extensive infoldings of the cell membrane, but if this hypothesis was correct it should mean that the nuclear membrane is a single continuous sheet of phospholipid bilayer, & it’s not.

As well as ‘how’, scientists have also tried to answer the ‘why’ question – just why do eukaryotes surround their chromosomes in a membrane. The usual answer – the one I was taught – is that this protects the nuclear contents; against what, we weren’t told. If a nucleus is so useful, why did this structure never evolve in bacteria? Reading Nick Lane’s Life Ascending pointed me in the direction of another possible answer, first proposed in 2006 by Koonin & Martin.

Introns are non-coding sequences. apparently the molecular corpses of jumping genes, found within eukaryote genes. ‘Active’ jumping genes are able to cut themselves out of a sequence of DNA using what could be described as molecular scissors, & reinsert a copy of themselves somewhere else. Introns have lost this ability to cut themselves out of a gene, but the cell must do so in order to remove these non-coding sequences prior to the process of translation & production of a functional protein. It seems that eukaryote cells do this using the same molecular scissors as jumping genes, modifying messenger RNA sequences by ’splicing’ out the introns. However, this process takes time (Martin & Koonin, 2006).

In general, prokaryotes don’t have introns. A piece of prokaryote mRNA will be translated into a protein almost as fast as the mRNA is itself being produced, because DNA, mRNA, and everything else needed to manufacture proteins are all in very close proximity within the cell. It’s suggested that eukaryotes acquired introns very early on, picking them up from their new endosymbionts, the mitochondria. Supporting this hypothesis, the presumed bacterial ancestors of mitochondria do have a particular type of intron; and Martin & Koonin note that the evolutionary relationships of the proteins associated with the nuclear membrane also suggest that this membrane formed in cells that already contained mitochondria.

The presence of introns would have presented significant problems for the early eukaryote cells. Because RNA splicing is relatively slow, if mRNA was translated into proteins as soon as the mRNA was produced, many of those proteins would be faulty because they’d be produced by translating the ‘wrong’ intron information as well as the ‘right’ information encoded in the functional part of the gene (the exons). Any cell with structural features that provided at least some separation of transcription & translation would thus be at a selective advantage, because they wouldn’t be wasting energy in producing faulty proteins . Martin & Koonin are suggesting that the nuclear membrane evolved in response to this selection pressure, providing a mechanism to separate the two processes – production of mRNA & production of proteins – to give sufficient time for the introns to be splieced out before the assembly of a protein could begin. It’s a fascinating hypothesis, although only time (& lots of research) will tell us if it’s a good model for the origin of the eukaryote nucleus.

(NB introns aren’t always spliced out in the same way every time a gene is expressed. This underlies the fact that, while the human genome contains around 25,000 genes, our cells can contain 60,000+ diffierent proteins!)

W,Martin & E.V.Koonin (2006) Introns and the origin of nucleus-cytosol compartmentalisation. Nature 440: 41-45. doi:10.1038/nature04531

PS below is a good explanation of how & why introns are spliced out (there is a large range of excellent science videos at the site this came from):

 

a guest post from an olympian Alison Campbell Nov 17

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Last week I attended the launch of Science OlympiaNZ, a charitable trust set up as an umbrella group to support New Zealand’s various International Science Olympiad programs (& very generously supported by the Todd Foundation). Among the speakers was Max, a member of this year’s highly successful NZ International Biology Olympiad team. Max gave a great speech, & I enjoyed it so much that I asked if he would allow me to post it here as a guest blog. And he did! Thanks, Max!!

I thought I’d start by explaining exactly what the International Biology Olympiad is, as I’ll admit I didn’t really know until last year. Firstly it’s international, as in 230 participants from over 60 countries, from Azerbaijan to Vietnam. Secondly, it’s to do with biology, the study of living things. Lastly, it is an Olympiad, which is sort of like the Olympics except that we were armed with calculators, scalpels and microscopes rather than shotputs, javelins, or ping pong bats. Instead of having rippling muscular bodies that epitomised human perfection, ours were often weedy, pimply & four-eyed. Instead of determining superiority by who could bench-press the most or flatten the other in an arm-wrestle, greatness was a measure of how many decimal places you could recite pi to (in my case 3.14 but I managed to beat most of them in an arm wrestle!). It was exams rather than sport, brains over brawn. A different kind of perfection, but no less elegant or respectable.

While there were many differences between the Olympiad and the Olympics, there were several similarities that should not be overlooked.

Firstly, the competitors at the IBO were elite, talented and driven. Just to get there they had to have won their own national Oympiads, and had not travelled half-way around the world to enjoy Japan’s excellent sushi; they were there to win. For example, the American team has over 20,000 students competing for just 4 spots on the team, while rumour has it that in China the IBO students get plucked from school at a very young age and are specifically groomed for the IBo at some sort of institution, where they learn about the birds and the bees in far too much detail for a five-year-old. Many teams receive scholarships to whatever university they choose.

Furthermore, the competition itself is intense. This is a test that has to differentiate between the smartest students in the world. It is almost a guarantee that you walk out of the exam feeling like a wreck. They purposely don’t give you enough time and questions are diabolical. Most students in the Olympiad are used to acing the tests they get at school, and then they get hit with a test in which 50% is a respectable score. It is also physically exhausting, with 6 hours of practical exam in one day, and 5 hours theory in another. The practical reminded me of a horror movie. We performed such tasks as dissecting caterpillars that we assumed were dead but which started wriggling violently when we started pulling their intestines out. We had to pull the heads off flies and grind up and study the paste. And at one stage the guy next to me badly cut his hand, splurting blood everywhere as medics stitched it up, while I was trying REALLY hard not to get distracted! We also spent time staining seeds, using a spectrometer to observe enzyme activity, used a microscope A LOT, DNA electrophoresis, chromatography, and the list goes on.

But perhaps the best thing about the Olympiad is also one of the best things about the Olympics. It has an amazing ability to unite and bring people together. People were hanging together from China and Taiwan, India and Pakistan, and the USA was even getting on well with the rest of the world. I was being a bit harsh earlier in this talk when I said that everyone there was geeks; there were actually some really interesting, articulate, and surprisingly normal people. The competition cultivated great friendships amongst people who shared the same passion, and now I can say I know people from Harvard, Yale, Cambridge, Oxford, and probably a few future Nobel laureates and the dud who will cure cancer. It is amazing to think what a network of the best biological minds in the world is capable of.

So how did I go? Firstly, as is probably quite obvious by now, my practical section was horrible. I tried a few sly shortcuts that should have paid off due to the intense time pressure, but they backfired badly. I knew I had to do really well in the theory to have any chance of getting a medal, which was quite worrying because I am usually way better at practicals than the theory. In the end, my theory did go quite well and I got a bronze medal. This statement makes me seem freakishly brilliant, as in 3rd best in the world, right? Well… not quite. The medal system works on a percentage basis, with the top 10% getting a Gold, next 20% getting Silver and next 30% getting Bronze. I finished 103 out of roughly 230 people, which was a performance I am very happy with. The people there were so amazingly smart I would have been glad to beat a single one of them, let alone over half of the competitors. My experience at the Olympiad reminds me of the Olympic creed:

The most important thing in the Olympic Games is not to win but to take part, just as the most important thing in life is not the trumph but the struggle. The essential thing is not to have conquered but to have fought well.

Finally I’d like to thank my sponsors and the volunteers at NZIBO who made this trip possible. If you hadn’t helped out I could have missed out on the trip of a lifetime, and a bullet train to the forefront of world science. I am truly indebted to you and if you ever need a good doctor (or perhaps engineer? I haven’t quite decided yet) you know where to look. 

 

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