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Posts Tagged evolution

an entertaining take on plants & plant cells Alison Campbell Mar 02

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The new semester kicks off tomorrow & right now I'm adding resources to my first-year bio moodle page & running through the powerpoints for the week's lectures. After a couple of introductory sessions we're diving into the section of the class that focuses on plants, and I'm giving some serious thought to how I present that material given that it looks like more than half the class didn't study the relevant year 12 Achievement Standard. 

So among other things I've looked around for some engaging short videos on plant biology, and I found this one (part of what looks like a great sequence, which I've bookmarked for future use): 

OK, I know the humour might not appeal to everyone, & he does speak rather fast at times, but the presenter's engaging, the graphics are good & the key points are emphasised and repeated – a nice little primer for my class to watch for homework as preparation for making sense of plants.

kiwi evolution – a new take on an icon’s ancient past Alison Campbell Dec 18

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‘The’ kiwi (Apteryx spp.) has always been a bit of an enigma, not least for the fact that it lays an absolutely enormous egg in comparison to its body size. In one of the essays in his book Bully for Brontosaurus (1991), Stephen Jay Gould argued that this differential in egg/body size was due to the impact of scaling: kiwi, he believed, had ‘downsized’ from a moa-like ancestor but had retained the large moa-type egg. This idea was quite widely accepted, even though later genetic evidence indicated that kiwi were in fact more closely related to the Australian emu than to NZ’s now-extinct moa. But new research suggests quite a different evolutionary trajectory – and I rather suspect that Gould, great scientist that he was, would be delighted to see his hypothesis robustly challenged :)

The research reported in this news article from scoop.co.nz will be published in the Proceedings of the 8th International meeting of the Society of Avian Palaeontology and Evolution – you’ll find the abstracts of the conference papers here. A newly-described fossil, from what’s known as the ‘St Bathans fauna’ of Central Otago turns out to be a new genus and species of kiwi, but a tiny one by today’s standards. Paul Scofield, one of the paper’s authors, is quoted in the scoop report as saying that

[this] fossil from the early Miocene, about 20 million years ago, shows us that it’s a tiny bird about one third the size of a small kiwi today. It suggests the opposite [to Gould's hypothesis] is, in fact, the case – that the kiwi has developed towards a larger size, a trend that is seen in many birds from the early Miocene.

So, how would an ancestral kiwi have arrived in New Zealand? The suggestion is that they flew. This is based on the evidence that a) kiwi and emu are more closely related than kiwi and moa and b) the emu-ish early kiwi arrived here after NZ and Australia were separated by the developing Tasman Sea.

Finding the wing bones of this new fossil species would help to confirm/deny this proposal. Although – having read the abstracts for the conference, I can’t help wondering if a proxy might be the size of a part of the brain known as the ‘cerebellar flocculus’, as suggested in another presentation by Walsh et al. It’s an intriguing possibility, anyway! And I’m wondering – how may we then explain that anomalous kiwi egg?

I’ll look forward to getting hold of a copy of the paper by Worthy and his colleagues, once it’s published.

 

Gould, S.J., (1991) Of kiwi eggs and the Liberty Bell, pp 109-123 in Bully for Brontosaurus. Penguin Books, London. 

Walsh, S., Iwaniuk, A., Knoll, M., Bourdon, E., Barrett, P., Milner, A., Abel, R., & Dello Sterpaio, P. (2012) Can the size of the avian cerebellar flocculus be used as a proxy of flying ability in extinct birds? 8th Internat. SAPE Meeting, 11.-16. June 2012 Naturhistorisches Museum Wien

Worthy, T.H., Tennyson, A.J.D., Salisbury, S., Hand, S.J., & Scofield, R.P. (2012) A fossil kiwi (Apterygiformes) from the early Miocene St Bathans fauna, New Zealand. 8th Internat. SAPE Meeting, 11.-16. June 2012 Naturhistorisches Museum Wien

selecting for maladaptive behaviour Alison Campbell Dec 13

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One of the questions that often comes up in my first-year bio classes relates to natural selection and human evolution. Does the fact that modern medical science keeps alive people who in previous centuries might have died, mean that we’re countering the effects of natural selection? As you can imagine, this generates quite a lot of interesting discussion that spans ethical issues as well as the obvious biological ones.

Next year I think I’ll give the class a new paper to read: one that examines such a question in the context of the Chatham Island black robins (Petroica traversi) (Massaro et al, 2013).

As many New Zealand biology students may know, by 1980 the breeding population of this little bird was reduced to a single pair, in a total population of seven. Things were not looking good, but dedicated conservation workers – led by the late Don Merton (there’s a lovely obituary for him here) – managed to turn things around by careful management of the population, including fostering the robin’s first clutches under another species (thus inducing the robins to lay again), and translocating the small population from Little Mangere Island to the better habitat on Mangere Island. However, it seems that at the same time, the conservationists were also unwittingly selecting for a distinctly maladaptive behaviour – that of laying eggs that were left teetering on the very brim of the nest.

After that initial bottleneck event the population slowly started to recover. However, the researchers working with them noticed that in 1984 one of the five breeding females laid a sinlge egg were laid at the edge of her nest, with more females following suit in subsequent years. Left alone the eggs didn’t hatch, mainly because they weren’t incubated (although I suspect some could simply fall off the edge). The obvious thing to do was to reposition the eggs in the nest, & this resulted in an increased in chicks hatched & subsequently fledged. However, Massaro & her colleagues report that by 1989 18 of the 35 females (51%) were ‘edge-layers’, a behaviour that would leave the population completely reliant on human intervention if edge-laying continued to spread.

The research team suspected that this was an example of inherited rather than learned behaviour, and hypothesised that

[if] rim-laying [had] a genetic basis, and its spread [had] been facilitated by human intervention through egg repositioning, the frequency of this trait would be predicted to decrease following cessation of intervention.
Conservation workers stopped moving rim eggs in 1990, which then meant that the researchers could subsequently compare data sets:
we therefore compared egg-laying data from three years before cessation of repositioning (1987–89) with a three year period almost two decades after management stopped (2007–09)

and found that the number of rim eggs being laid decreased significantly between those two periods. They next looked at the many years’ worth of data to see if the ‘rim-laying’ behaviour had any effect on individuals’ evolutionary fitness, and discovered that

[when] rim eggs were not repositioned, females that laid rim eggs had significantly reduced clutch sizes (i.e. number of eggs laid inside nests that were incubated), and decreased hatching and breeding success compared to normal-laying females, demonstrating that rim laying substantially reduces fitness.
The final step was to confirm that this maladaptive behaviour did have a genetic underpinning. This part of the study was aided by the fact that there’s an extensive genetic pedigree available for this closely-studied species. Examining that pedigree, Massaro & her co-workers found that a) the behaviour first showed up in the grand-daughters of the ‘founding’ female, ‘Old Blue’; and b) that the population was highly inbred. A detailed analysis of the pedigree led them to determine that the rim-laying trait was an autosomal dominant trait that’s inherited in a Mendelian manner (ie no evidence of sex-linkage). Their final message:
This episode yields an important lesson for conservation biology: fixation of maladaptive traits could render small threatened populations completely dependent on humans for reproduction, irreversibly compromising the long term viability of populations humanity seeks to conserve.

 

You’ll also find information on the study here on the University of Canterbury website.

Massaro M., Sainudiin, R., Merton, D., Briskie JV, Poole, AM, Hale ML (2013) Human-Assisted Spread of a Maladaptive Behavior in a Critically Endangered Bird. PLoS ONE 8(12): e79066. doi: 10.1371/journal.pone.0079066

 

a glorious (but deadly) cephalopod Alison Campbell Nov 18

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Every now & then the husband goes on a fossil-fossicking expedition, in order to add to his collection of things long dead & turned to stone. There are a number of good sites in the Waikato region, and one of them has yielded quite a few belemnite remains: specifically, the bullet-shaped fossilised internal shells of one group of cephalopods. Plus he’s also found a few rather lovely ammonites, though nothing on the same scale as a giant specimen found near Kawhia Harbour in 1977. (Apparently the largest of all was found in Germany – its shell, if uncoiled, would be close to 11m long!).

The evolutionary history of cephalopods spans around 500 million years, and there’s a good overview of this on the UCMP(Berkeley) evolution website. I hadn’t visited this part of their site before, but was directed there by PZ Myers (who else?) & his use of this stunning image – too beautiful not to share :)

Beautiful, but deadly:

These little molluscs – members of the largest species grow to be about 15 cm long, head tip to tentacle tip – produce two different venoms. One, they use in hunting their usual prey1 of crabs and shrimps; the other is released when the animals are alarmed or agitated. While people certainly report blue-ringed octopus bites, it seems that the toxin may also be secreted directly into the water: the author of this website reports feeling localised neurological symptoms after putting his hand into a tank of seawater that had been used to transport a largish specimen. The venom contains the poison tetrodotoxin (TTH)2, also produced by a range of other organisms including a genus of newts, some harlequin frogs, snails, and worms from a number of different phyla. And, of course, the pufferfish, whose family name (Tetraodontidae) gives us the name of the toxin.

This poses an interesting question: why would members of so many different phyla evolve the same poison? It turns out that it’s not actually the animals who make the TTH: the job’s done by colonies of symbiotic bacteria living in their poison glands. Life really is more complex and more complicated than we can imagine.

1  Sometimes, the prey fights back:

2 It’s been suggested that TTH is the mysterious ingredient supposedly used in zombifying people – you’ll find an interesting discussion of this idea here on HowStuffWorks.

a creeping assassin Alison Campbell Nov 04

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The daughter & her friends play Assassin’s Creed from time to time. This little arachnid would fit right in:

Photo: Jeremy Miller

For this is an assassin spider, one of a number of species (in the superfamily Palpiamanoidea) that prey on other spiders.

The assassin spiders have a long history: a combination of fossil & DNA evidence suggests that they go to before the supercontinent Gondwana began to break up under the slow but irresistable influence of plate tectonics. While there’s one fossil found in what’s now the northern hemisphere, all living species are found south of the equator, in Madagascar, South Africa, and Australia.

These strange little creatures are only a couple of millimetres long, but have a set of adaptations that allow them to strike their prey from a (reasonably!) safe distance. Their fang-tipped jaws are enormous – in the image above, the jaws holding the spider’s meal are about the length of the animal’s abdomen. The long ‘neck’ is an extension of the cephalothorax – the first of the 2 major sections of a spider’s body (the other is the abdomen, or opisthoma). The combination of neck & jaws means an assassin spider can impale another spider before the latter is within range to strike back. That’s after they’ve found their prospective dinner by following lines of thread it’s left behind, using their very long forelegs (which may also be used to lure the prey closer.

Which is probably quite enough for those of you who aren’t fond of spiders, not even itsy little 2mm-long spiders. But for those who want to find out more, try this video:

teach creationism, undermine science Alison Campbell Sep 23

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Every now & then I’ve had someone say to me that there’s no harm in children hearing about ‘other ways of knowing’ about the world during their time at school, so why am I worried about creationism being delivered in the classroom?

Well, first up, my concerns – & those of most of my colleagues – centre less on whether teaching creationism/intelligent design is bringing religion into the science classroom1, & more on how well such teaching prepares students for understanding and participating in biology in the 21st century. For example, if a school can make statements like this:

It is important that children and adults are clear that there is one universal truth. There can only be one truthful explanation for origins that means that all other explanations are wrong. Truth is truth. Biblical truth, scientific truth, mathematical truth, and historical truth are in harmony2.

and go on to list the “commonly accepted science we believe in”, then their students are not gaining any real understanding of the nature of science. And the statements regarding the science curriculum that I’ve linked to above indicate that it’s not just biology with which the school community has an issue. Physics, geology, cosmology: all have significant sections listed under “commonly accepted ‘science’ we do not believe in”3. (Did you notice the quote marks around that second mention of science?)

Science isn’t a belief system, & while people are entitled to their own opinions they are not entitled to their own facts. Any school science curriculum that picks & chooses what is taught on the basis of belief is delivering (to quote my friend David Winter) “a pathetic caricature of actual science, … undermin[ing] science as a method for understanding the world and leav[ing] the kids that learned it very poorly prepared to do biology in the 21st century.” Or indeed, to engage with pretty much any science, in terms of understanding how science is done and its relevance to our daily lives. And if we’re not concerned about that lack of science literacy, well, we should be.

 

although I do think this is a problem too.

2 with the subtext that the first ‘truth’ takes precedence.

Taken to its extreme, the belief system promoted in teaching creationism as science can result in statements such as this:

We believe Earth and its ecosystems – created by God’s intelligent design and infinite power and sustained by His faithful providence – are robust, resilient, self-regulating, and self-correcting, admirably suited for human flourishing…

…We deny that Earth and its ecosystems are the fragile and unstable products of chance, and particularly that Earth’s climate system is vulnerable to dangerous alteration because of miniscule changes in atmospheric chemistry.

This does not look like a recipe for good environmental management to me.

 

charter schools can teach creationism after all Alison Campbell Sep 19

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I first wrote about charter schools just over a year ago. At the time I was commenting on statements that such schools would be able to employ as teachers people who lacked teaching qualifications, wondering how that could sit with the Minister's statements around achieving quality teaching practice. But I also noted concerns that charter (oops, 'partnership') schools could set their own curricula, as this would have the potential to expand the number of schools teaching creationism in their 'science' classes.

Well, now the list of the first 5 charter schools has been published: two of those schools is described (in the linked article) as intending to "emphasise Christian values in its teaching." By itself that =/= creationism in the classroom – but yesterday Radio New Zealand's Checkpoint program (17 September 2013) reported that the school's offerings will probably include just that: 

In addition the prinicipal has reportedly said that the school will teach "Christian theory on the origin of the planet." 

And today we're told (via RNZ

The Education Minister has conceded there's nothing to prevent two of New Zealand's first charter schools teaching creationism alongside the national curriculum.

Two of the five publicly-funded private schools, Rise Up and South Auckland Middle School, have contracts that allow a Christian focus.

The minister, Hekia Parata, said on Tuesday that none of the five schools would teach creationism alongside or instead of evolutionary theory.

But on Thursday she told the House two of the schools will offer religious education alongside the curriculum.

Ms Parata did not specify how the two would be differentiated in the classroom.

South Auckland Middle School has told Radio New Zealand it plans to teach a number of theories about the origins of life, including intelligent design and evolution.

Point 1 (trivial, perhaps?): South Auckland Middle School needs to look into just what constitutes a theory in science. (Hint: a theory is a coherent explanation for a large body of facts. "A designer diddit" does not remotely approach that.)

Point 2 (not trivial at all): Why do people responsible for leading education in this country think it acceptable for students to learn nonscience in 'science' classes? After all, the Prime Minister has commented on "the importance of science to this country." Evolution underpins all of modern biology so how, exactly, does actively misinforming students about this core concept prepare those who want to work in biology later? Nor does teaching pseudoscience sit well with the increased emphasis on 'nature of science' in the NZ Curriculum.

This is really, really disappointing. We already have 'special character' schools which teach creationism in their classrooms (see here, here and here, for example). It's irking in the extreme that state funding will be used to support the same in the new charter schools.

bicep-flexing & s*xual selection Alison Campbell Aug 09

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When I was a kid, we’d all look forward to Friday evenings – because Dad & Grandma would come back from town with the weekly supply of comics. The ads in the back were almost as good as the cartoons, although we were very disappointed to find out that sea monkeys were definitely not as advertised! I also remember regular ads featuring a poor weedy guy who, having had sand kicked in his face by various over-muscled bullies, followed the instructions of various manly authorities and ended up developing his own set of biceps, triceps, washboard abs & all the rest: all the better to impress the girls at the beach.

I was reminded of all this earlier this week when I noticed a Facebook report on bicep-flexing in male kangaroos, based on this 2013 paper in the Biological Journal of the Linnaean Society. (It’s behind a paywall, alas, but you should be able to read the abstract.)

As Darwin recognised, at least some of the physical differences between males and females may be the result of competition: think showy male peacocks and their relatively dowdy mates, for example. This competition may be directly between males, as they try to gain access to females – an example of this would be elephant seals, where the males battle each other to become ‘beach-masters’, and the winners gain access to females coming ashore on their beaches. In this case, selection favours male strength. In other cases females select males to mate with on the basis of some attribute – perhaps the brightest plumage, or the loudest song.

As Warburton & her colleagues point out, these different forms of sexual selection are not mutually exclusive, & it’s sometimes hard to tease out which has the greatest impact on a species’ characteristics. They decided to investigate sexual selection in a large species of marsupial, the western grey kangaroo (Macropus fuliginosa), a polygynous species where males tend to have greater development of the chest & arm muscles. It’s fairly clear that in large kangaroos & wallabies, male reproductive success is linked to body size, which in turn is linked to social status: “the large males… gain an exclusive consort relationship with oestrous females”. Larger males have larger home ranges and so may have more chance to find and mate with females, and in addition genetic data suggest that

alpha males may be able to outcompete and exclude smaller males from access to females.

But how to tell if the larger arm & chest musculature of males is down to sexual selection, or simply a factor of differences in overall body size? You measure some kangaroos (in this case, purchased from pet food manufacturers. Poor Skippy!) This allowed the research team to look at the slope of trait size (eg bicep size) against body size:

When the slope of a trait size against body size is ‘isometric’, the relative trait size is constant across a range of body sizes. Where the trait size decreases with body size, the slope shows ‘negative allometry’ and where the trait size increases with body size the slope shows positive allometry. A trait that is positively allometric is therefore relatively larger, in proportion to body size, in larger individuals. If this relationship differs between the sexes, then it can be interpreted that there is differential selective pressure acting on males and females as they grow larger.

While the numbers involved were fairly low (13 males and 15 females), the team ensured they had a range of body sizes. (I’m guessing the fact that that body mass was estimated from measurements of the thigh bone rather than directly, by weighing, reflects a lack of scales big enough to plonk an entire kangaroo corpse onto.)

The results? Male kangaroos had larger (“more exaggerated”) forelimbs, and more variability in muscle mass, than females. Both of these suggest that sexual selection might be acting on forelimb size, and it’s likely to be through male-male competition. This is because male kangaroos use their forelimbs to push or wrestle with their opponents as they fight to determine their place in the social hierarchy. There’s also a suggestion that the larger male muscles

may also be an important aspect of visual signalling (presumably of potential fighting ability) and dominant males will frequently adopt poses which best display their muscularity and size.

So perhaps there’s also potentially an element of female choice: those exaggerated biceps may attract admiring female glances (or at least, allow them to appraise a male’s genetic quality), rather than being simply a part of the roo equivalent of sand-kicking.

N.M.Warburton, P.W.Bateman & P.A.Fleming (2013) Sexual selection on forelimb muscles of western grey kangaroos (Skippy was clearly a female). Biological Journal of the Linnean Society 109(4): 923-931

have you heard of a pyrosome? Alison Campbell Aug 02

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“Have you heard of a pyrosome?” asks Carin Bondar.

My immediate answer was, no; no, I haven’t – but you know me, I’m always curious :) Turns out that pyrosomes – which look almost other-worldly in the video below – are colonial tunicates: the same taxonomic group as the perhaps-more-familiar sea squirts. And that means that they’re in the same phylum as us, for both tunicates and mammals are chordates.

These are adult seasquirts (image from reefbuilders.com).

They’re filter-feeders, sucking water in through a siphon and extracting all the edible bits & pieces using a mesh-like filtering system (that in evolutionary terms is homologous to fish gills), before squirting the water back into the ocean. True, they don’t look anything like the more familiar chordates (e.g. fish, amphibians, reptiles, birds & mammals), but at the embryonic stage all these groups have some features in common: a hollow dorsal nerve chord; a stiff notochord – which gives our phylum its name – running the length of the body; a tail that extends beyond the anus; and a system of pharyngeal pouches. These last become the filter-feeding mechanism in tunicates and give rise to the gills – and the gill bars that support them – in fish. In mammals the pouches are homologous to the various glands found in the neck, while the same tissues that formed gill bars in fish are involved in trachea and larynx formation. 

And this amazing creature is a pyrosome. It’s about 20m long and is a colony of tunicates, each one sucking water in through its ‘mouth’, filtering out its dinner, and expelling the water into the cavity running the length of the organism. You can see this happening later in the video. Ultimately the water leaves through a single opening at one end, & this means that the pyrosome is capable of moving under its own – albeit very slow – steam.

I do love finding out new stuff!

the male himalayan monal – an absolutely gorgeous bird Alison Campbell Jul 23

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Another for the ‘gosh, isn’t this beautiful?!’ files: the Himalayan Monal (the national bird of Nepal).

(Image via Facebook: Tambako the Jaguar; Flickr — with Robin SubbaSarvesh Wangawad,Jeriko AngueRoberto DelapisaJonas MgrNeelesh SuryavanshiShashank Asai,Sushant Bhujel and Pabitra Lamichhane.)

This stunning bird (Lophophorus impejanus) is a type of pheasant, and like other pheasants the species is strongly sexually dimorphic: the males are dressed in gorgeous irisdescent plumage, while the females’ plumage is dark brown apart for white patches on throat & rump, & the same bright blue circle round the eyes.

Such marked differences between the sexes are often due to intersexual selection, with females acting as the agents of selection & choosing their mates on the basis of physical appearance, or other attributes that give information on the male’s quality. The monal is a stand-out example of the eventual outcome.

Strongly dimorphic species are often polygamous – more usually polygynous, with dominant males mating with several females during the breeding season; phalaropes, however, are polyandrous, with the more brightly-coloured female laying eggs in the nests of several males and leaving them to incubate alone. In species where there’s little dimorphism, it’s often associated with monogamous breeding patterns, & as a general rule the type of breeding pattern in a given species is linked to the species’ ecology.

 

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