adaptive radiation in birds

The 2005 Schol Bio paper included the following question. The three examples shown represent just some of the diversity found in bony fish. Use the diversity of the fish and/or any other named group(s) to discuss the following statement: 'Diversity is the end product of evolution.'

How do I get from that to a blog about adaptive radiation in birds? Because a number of students chose to answer the question using birds as their example. Good? No - because they chose to focus solely on the ratites, a group which they'd have studied as an example of adaptive radiation.

Now, you may think that I'm contradicting myself here. After all, I've just said that ratites show adaptive radiation. But the examiner's original example included species of fish (from memory, seahorses, flounder, and anglerfish) that differ significantly in morphology & habitat. Their expectation was that students would recognise this and select their other examples accordingly, discussing other groups with similarly high diversity in morphology & lifestyle. But ratites are actually fairly similar in body form. The examiner was, I think, hoping that students would go for the big picture: i.e. 'birds' as a whole.

And birds - the taxonomic group, Aves - do show considerable diversity. But only in some features. The fact that birds fly places considerable constraints on size & shape, for example. The upper weight limit for flight is around 15-16kg (something that was approached by NZ's own [extinct] giant eagle). Truly big birds (the ratites, for example) are those that have lost the ability to fly. And of course penguins, superbly adapted to an aquatic lifestyle, have done the same - although if you've ever visited Kelly Tarlton's, you'll have seen how they appear to 'fly' under water.

So where's the adaptive radiation in birds? Well, aside from the obvious differences in size (from hummingbirds to albatrosses), a lot of it's in their beaks and feet. Beaks shaped by natural selection to tear flesh, sip nectar, crunch nuts, filter minute algae from soda lakes or scoop fish from the sea... Feet with talons, rough scales, very long toes, webs and lobes and flaps, on legs short or stilt-like... A focus on all that - including a discussion of how natural selection operates -would have been the basis for a most interesting (& relevant) answer.

Of course, all this is really an excuse to show a holiday photo: I snapped this shoebill at the Jurong Hill Bird Park in Singapore.

good web articles on evolution issues

Here's a link to a set of articles that summarise talks on various aspects of evolution research. They're straightforward & easy to read, & should give you some interesting additional background to some recurring questions.

(pseudo)science runs amok

 Those of you who've come to one of my Scholarship preparation days may have noticed that I've got a bit of a bee in my bonnet about pseudoscience. It really annoys me when I see science being mis-used to sell a product or promote a particular point of view. A good friend of mine has just sent me one of the worst examples I've seen for a while, & I thought it could be useful to share it with you. Here's the lead-in to the article...

"Many scientists were stunned recently when it was revealed that air bubbles trapped in fossilized amber had been analyzed and found to contain oxygen levels of 38%. Yet today, it is well known that the average oxygen content of air is only 19% to 21%. In other words, since the early history of the earth, it appears there has been a whopping 50% drop in the average oxygen content of the air we breath! This discovery was particularly startling to researchers because it suggests that the human body was originally designed to grow and operate at a 50% stronger concentration of oxygen than what's currently available."

Gosh! How terrible! We're not getting enough oxygen!!!

OK, enough with the irony. But this really is a staggering misrepresentation of the facts. Yes, atmospheric oxygen levels did once reach 35-38% - in the Carboniferous period ie about 300 million years ago (relatively recently in the Earth's history - remember that this stretches back around 4.6 billion years). These high levels probably allowed the evolution of giant forms of many animals - insects and amphibians, for example.

And yes, oxygen levels have declined since then (there was a second, lower peak in the Cretaceous, about 80 mya). But they've been stable for the last 70 million years. (And in fact, with the exception of those 2 peaks, oxygen levels have been remarkably stable for the last 500 million years.) So, what about that claim that the human body was originally designed (& how I hate that term!) to grow and operate at a 50% stronger concentration of oxygen than what's currently available???

Ummm, when did humans evolve? The hominin lineage dates back only 6 million years or so. That is, we've always been exposed to an atmospheric oxygen content of 20%, throughout our evolutionary history. It's a total falsehood to suggest otherwise.

There's more. Much more. And I do intend to come back to it. But not right now - I need a sit-down and a good strong cup of tea after wading through that dreadful document!

PS a good book for you to read, if you're interested in things like oxygen levels and the role of plants in maintaining them, is this one: David Berling (2007) The Emerald Planet: how plants changed Earth's history. Oxford University Press. It's very well-written & presents a fascinating scientific story in a very accessible way. Enjoy!

coevolution of weta and fleshy fruits

Here's another paper on coevolution - this one a bit closer to home. It suggests a coevolutionary relationship between a weta species and the characteristics of many fleshy fruits of NZ plants (Burns, 2006).

Many plants rely on animals to disperse their seeds. Their seeds are often enclosed within fleshy fruits, which tend to be red or black, and which are found in easy-to-access parts of the plant (like the tips of twigs or branches). Burns points out that this doesn't apply to the fleshy fruits of many New Zealand plants - instead, they are often white, or pearly-coloured, and are tucked away inside a network of twigs. What's going on here?

Burns caught a young female ground weta in the alpine zone of Nelson Lakes National Park. He kept the insect in the lab for 2 days & collected its faeces, before releasing it into the wild in the place it was found. All the faecal matter contained seeds of mountain snowberry, Gaultheria depressa. This plant grows in a mat, with large fruit that are either red or white & tucked away within the plant canopy - they'd be hard for birds to find, for example. Other authors have suggested that this particular growth form might be linked to snowberry seed dispersal by lizards. Burns suggests that it could equally well be linked to coevolution with weta - but points out that, at the moment, supporting evidence is from one single observation. He suggests that the link could be tested by experiments looking at how much seed is dispersed by weta, lizards, & birds, and also at how well they do it - a fruitful topic for future researchers :-)

Reference: K.C. Burns (2006) Weta and the evolution of fleshy fruits in New Zealand. N.Z. Journal of Ecology 30(3): 405-406

a quote to think about

I think it was Thomas Edison who said, Genius is 1% inspiration and 99% perspiration. In other words, success (in any field) requires a lot of hard work. (True also of preparing for Scholarship exams.) Now here's another science-relevant quote...

Science isn't one success after another. It's really one success in a desert of failure (Dr Judah Folkman). Which may sound a bit harsh, but it's accurate - often, the results of the lab work you do, to test a particular hypothesis, come out negative. They don't give the predicted outcome; the experiment may not work at all. That's life. Unfortunately, that doesn't always fit well with the popular view of science, where the scientist does the experiments & Finds The Answers. (And it can be exacerbated by science publications - positive outcomes do seem more likely to get published.) I know I've said it before, but this really is an important aspect of the nature of science and it needs to be more widely recognised.

an overview of how we see ourselves

Here's something for your reading list: an excellent extended essay on how our view of human evolution, & of our place in the world, has changed over time. Enjoy!

Happy Darwin Day

Oops! I forgot... but anyway, Happy Darwin Day for the 9th of February. Charles Darwin would have been 199 years old. Next year's the 200th anniversary of his birth & also the 150th anniversary of the publication of The Origin of Species; I'll have to organise some birthday celebrations :-)

what is it with cockroaches?

I know you may read this & think I'm a bit odd... But anyway - just after the L3 exam I was talking with a student & she said, why did there have to be cockroaches in a question? My answer: why not? They're just another animal (even if many people don't like them much) & the examiner had obviously chosen this particular example to tease out understanding of evolutionary processes. (Could have been worse - they might have chosen tapeworms!)

Anyway, I did a bit of searching & found the original paper (Chinn & Gemmell, 2004). The abstract begins with the statement that [the] South Island of New Zealand offers unique opportunities to study insect evolution due to long-term physical isolation, recent alpine habitats and high levels of biotic endemism. In other words, here's an excellent opportunity to look at the potential for speciation events in a group of organisms that are isolated (no gene flow) and in a rapidly changing environment (new selection pressures). Chinn & Gemmell chose cockroaches as their study taxon & used DNA sequence data to test their hypothesis that cockroaches as a group showed rapid adaptive radiation in response to the habitat changes brought about by the formation of the Southern Alps.

Many NZ plants & animals have what are described as 'disjunct' distributions, where species of a particular genus are quite widely separated geographically. One explanation for this distribution suggests dramatic climatic and geological changes that divided habitats and generated new ones. These changes were probably due to the mountain-building event that produced the Southern Alps, an event which had a marked impact on wind and rainfall patterns (cooler & wetter on the west, warmer & drier to the east). Their effect was to kill off initially widespread plant & animal species over much of their former range, leaving the surviving populations isolated in refugia and subject to different selection pressures and the effects of genetic drift.

Chinn & Gemmell found that between 6 and 4 million years ago the ancestral cockroach (Celatoblatta) lineage split into 6, and that this correlated with the rise of the Southern Alps. Glaciation of the Alps during the Pleistocene (which had effects on both climate and landscape, and which would have further restricted the range of many species) was associated with a second, rapid round of genetic divergence. They discuss the example of C. hesperia populations: they are close genetically & seem to have moved into wet subalpine habitats fairly recently. They are also found on both sides of the Alps, which suggests dispersal through mountain passes in periods when the glaciers had receded: a suggestion supported by the authors' finding that genetic radiation of the populations occurred 1-0.5mya.

The genetic data also indicate a link between the cockroach species on Banks Peninsula and those found on the Chatham Islands. What's your suggestion for how the Chatham species got there?

Reference:

W.G. Chinn & N.J. Gemmell (2004) Adaptive radiation within New Zealand endemic species of the cockroach genus Celatoblatta Johns (Blattidae): a response to Plio-Pleistocene mountain building and climate change. Molecular Ecology 13: 1507-1518

PS Off to Paris today & Madrid on Wednesday. I've been staying near Chambéry, which is really interesting geologically - & biologically: I saw Milanese eagles up in the mountains on Thursday, & apparently somone found a cave full of cave bear skeletons in a pass up behind Chambéry.

giant fish extinctions

I mean, extinctions of giant fish, not giant extinctions of fish! This is about a paper that I read last year & put aside as a 'general interest' topic for when I was looking for something to write about.

The paper caught my eye because the title photo is of this amazing giant catfish (plus proud fisherman). It's a huge fish (they grow up to 3m long & can weigh up to 300kg) - and sadly, one which is becoming increasingly rare in its Mekong River habitat. In fact, many of the world's largest freshwater fish populations are declining, due to a combination of overfishing & degradation of their habitat through pollution and changing water use (eg damming waterways can block migration routes).

Why focus on the big ones? Stone quotes environmental scientist Thomas Lovejoy: Much like tigers on land, they are flagship species representing the wonders of life in rivers. Taking action to save these 'megafish' must entail conserving and restoring their habitat, so other fish species will benefit as well. (And it's easier to get people interested in the plight of large, exciting animals than the small, wriggly ones. Even more so when we're talking fish - people seem to be more interested when the animal is feathered or furry.) And there are social issues involved as well: the local fishing communities depend on selling the fish for their income, so how do you save the megafish (& their ecosystem) without destroying the community?

Unfortunately, for many of the fish discussed in Stone's article, scientists know very little about them. The fear is that they will become extinct even before researchers can identify what can be done to save them. Even if the species survive, sustained fishing may affect their evolution: if humans are constantly taking the largest animals, then this is placing strong selection pressure on the population: where smaller fish are surviving (being selected for), then it's their genes that will be passed on to the next generation.

Reference:

R. Stone (2007) The last of the leviathans Science 316: 1684-1688

PS This item - like the last - was brought to you from St Pierre d'Albigny in southeastern France. Ah, the joys of modern technology!

cool cephalopods

Ages ago I saw an item on TV about cuttlefish - one of the neat things I took away from it was how cuttlefish and other cephalopods (octopus & squid) use colour to communicate, and how precise their control of skin coloration is. And I would tell my students about it, but I didn't have the pictures! Well, take a look at this...

You need to watch a clip about phosphorescence in deep-sea organisms, which is itself quite fascinating, but then the speaker jumps to talking about cephalopods. And there they are - squid whose control of skin colour is so precise that a male can show a white, aggressive side to another male - while at the same time showing quite a different colour pattern on the other side of his body to the female that he's courting! And cuttlefish & octopuses that blend into their surroundings, not only mimicking the colours of the coral or algae that they're hiding amongst, but also time their movements to match the moving patterns of light & dark that waves cast on a sandy seabed.

It's enough to give you quite a different perspective on squid rings...