The Mount Mulanje Pygmy Chameleon

DSCF7127 - pygmy chameleon small
Rescuing the Mulanje Pygmy Chameleon from the path.
Christine Cambrook | CC BY-NC-SA 4.0

By far the rarest animal that I have encountered during my time in Mozambique has been the Mount Mulanje Pygmy Chameleon, Rhampholeon platyceps. A stunning little creature, it is endemic to the Mulanje massif, only being found in the southern and eastern-facing mid and high altitude evergreen forest of the massif. This includes the Ruo Gorge, where we came across the little guy (or possibly girl) above. Unfortunately its forest habitat remains only in fragmented patches and, due to its restricted range and the high threat of deforestation, it is declared Endangered by the IUCN Red List. We were lucky that this individual was crossing the path in front of us.
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What can a blind cavefish tell us about circadian clocks?

Circadian clocks and a revolving planet go hand-in-hand. But why so many plants and animals have a circadian clock from an evolutionary perspective is relatively unknown. One way to find out is to study animals that live in non-rhythmic environments. And at the end of 2013, my team published a study on exactly that: the circadian clock of the Mexican blind cavefish, Astyanax mexicanus, from data collected in the laboratory and in the fishes’ natural habitat. We showed that these cavefish fish shows wonderful daily patterns of behaviour and gene expression, confirming that it has a functional circadian clock.

Continue reading “What can a blind cavefish tell us about circadian clocks?”

Parasitoid wasps and GM butterflies

A parasitoid wasp parasitising a caterpillar
A parasitoid wasp parasitising a caterpillar. USDA photo by Scott Bauer

Foreign pieces of DNA are found in the genomes of many animals – these ‘Genomic parasites‘ are pure, genome hopping pieces of DNA code which embed their lifecycle within the DNA in our own cells. You could call this genomic parasitisation a form of genetic modification, just as scientists in labs the world over use simple molecular biology techniques to insert useful genes into genomes to better understand biological processes. However, most of the time, genomic parasites like transposons have no function in their hosts and simply hitch along for the ride, reproducing as the host reproduces. This doesn’t fit our usual understanding of the meaning of genetic modification, which involves humans and active manipulation of the genome, in most cases to improve it.

However, a recent piece of research shows another form of natural genetic modification which also doesn’t involve humans – and this form does affect the life of the host and can confer some advantage. Continue reading “Parasitoid wasps and GM butterflies”

Why does Mozambique have a picture of a coelacanth on one of its coins?

Like the currency of many African countries, the notes and coins of Mozambique feature images of some of the majestic animals of Africa: the elephant, the rhino, the lion. But one Mozambican coin features a rather more obscure animal, the coelacanth.

A Mozambican 2 Meticais coin
A Mozambican 2 Meticais coin
CC-BY-SA 4.0 Andrew Beale

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Colourful Chameleons and Stripy Zebras – The Coolest Animals in Africa

You can say all you like about lions or elephants being the coolest animals in Africa. They are awesome for sure but they’re not quite the top. I suggest that that title goes to the chameleon and the zebra.

Why? They are just so unique: one changes colour as much as a fashion model, and the other has a coat pattern unlike any other mammal. And thanks to two papers released this year, we’ve begun to understand a bit more about their unique skin.

In the space of a few seconds, this guy went from brick (https://instagram.com/p/wEsq3JRnsn/?modal=true) coloured to plant (https://instagram.com/p/wEsT9RRnqJ/?modal=true) coloured as he attempted to blend in. Credit: @joannefbeale (https://instagram.com/joannefbeale/)
In the space of a few seconds, this guy went from brick to plant coloured as he attempted to blend in. Credit: @joannefbeale

Continue reading “Colourful Chameleons and Stripy Zebras – The Coolest Animals in Africa”

Mosquitos – fine-tuned by evolution to preferentially feed on humans

Would you look at that! The story of mosquitos, cheese and body odour has taken another leap into scientific respectability with a paper being published in the pinnacle of journals, Nature. “Evolution of mosquito preference for humans linked to an odorant receptor” by McBride and colleagues was published towards the end of last year and looks at how the domestic form of the mosquito Aedes aegypti has evolved striking evolutionary adaptations that help it to find, bite, and spread disease to humans.

Aedes aegypti during a human blood meal.
By James Gathany [Public domain], via Wikimedia Commons
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Plants, polyploidy and producing new species

Modern wheat. A product of polyploidy.
CC Wheat field / Weizenfeld II | Christian Schnettelker

When I talk about my career and my interest in evolutionary biology, I often get asked, “How do you actually get new species?”. It’s not a stupid question; for people without a background in biology it really is very hard to imagine how the diversity of life we see today has formed from the types of ancient creatures we find in the fossil record. I normally look to my favourite fish, the Mexican blind cavefish, or point out the variety that can be produced in the single species of dog, or mention horizontal gene transfer to confer antibacterial resistance in bacteria, to show how even small changes can result in quite big differences in a species. Add to that vast amounts of time and it becomes a little easier to imagine the “hedge” of life taking shape.

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The physics of human walking and considering the wider picture

Gorilla walking like a man. CC talkrational.org
A gorilla walking like a man. Photo by talkrational.org is licensed under CC BY 2.0

Impulsive ankle push-off powers leg swing in human walking
Susanne W. Lipfert, Michael Günther, Daniel Renjewski, and Andre Seyfarth
J Exp Biol 2014 217:1218-1228.

I love papers like this. The extreme level of detail people go to in the quest to discover is fascinating. The question that always comes to my mind is “What made them decide to research this in the first place?” Was it through trying to understand more about where humans come from or was it purely a mathematical and physical curiosity about how we walk? The beauty of science is that it is allowed to be curiosity driven – just like those papers and pieces of research which made it into the IgNobel Awards and have ended up being pivotal in their respective fields.

“Impulsive ankle push-off powers leg swing in human walking” is a rather complicated paper, full of mathematical terminology and notation, but if you can get through the equations you’ll discover a story that shows how human walking has been fine-tuned, linking this physical paper to fundamental questions of human origins. Continue reading “The physics of human walking and considering the wider picture”

Why have a circadian clock?

Almost every animal and plant on the planet has a circadian clock, even those that live in the depths of the sea and deep underground in caves.

The presence of clocks in almost all life-forms implies that it is a helpful or advantageous characteristic, an evolutionary adaptation, serving to improve the fitness of the organism. This argument makes apparent sense but, without testable hypotheses, has little to support it.

Two main hypotheses have been formed to explain the evolutionary benefit of having a circadian clock. The first is known as the External Synchronisation hypothesis – that the benefit to the circadian clock lies in being coordinated with the external environment, for example, the predictable daily change in light and dark that we call day and night. The second is the Internal Synchronisation hypothesis – here the clock benefits an organism by allowing it organise physiological processes in time in order to avoid conflict between incompatible processes, for example separating the process of photosynthesis from that of nitrogen fixation in the case heterocystous cyanobacteria.

These two hypotheses aren’t mutually exclusive. The internal synchronisation hypothesis doesn’t necessarily require a 24 hour clock; plenty of other periods would suit. But, timing pressure placed on an animal from the external environment could force biological processes to fit within the 24 hour day, for example, the reactions for photosynthesis. These are only necessary in the day when it is light. But since nitrogen fixation and photosynthesis are incompatible, nitrogen fixation gets restricted to the night and internal organisation has been forced on an animal from external pressure. Once established, internal synchronisation could become independent of external pressures. Perhaps, in the origin of circadian timing systems, external synchronisation came first and internal synchronisation second, but now, either one serves as a selective advantage. So, though the two hypotheses propose reasons for selective advantage a circadian clock might give to an organism, and therefore why Clocks may have evolved in the first place, arguments are complicated as whether these are the original selective pressure that formed a circadian timing system.

How might we test which which hypothesis is most important today? One way is to look at animals that live in non-rhythmic environments, those that do not experience the regular and predictable cycle of day and night. These animals offer the chance to directly test the first, external synchrony, hypothesis, since in a non-rhythmic environment, there is no need to synchronise to an absent cycle. 

The deep sea and caves are two environments that fit this description. Interestingly, most studies on organisms that live there give at least some hints that circadian clocks are present and working even here. Although, there are many difficulties interpreting and comparing this research due to the various experimental conditions used, this general observation lends weight to the internal synchronisation hypothesis – in the absence of a no cycling external environment, a ticking clock must be being used for something else, and internal synchrony is the most obvious.

My PhD research looked at one organism that lives in the depths of caves and is highly adapted to life there: the Mexican blind cavefish, Astyanax mexicanus. This fish shows wonderful daily patterns of behaviour and gene expression, confirming that it has a functional circadian clock. It also shows some interesting quirks, which give some insight into why an animal that lives in the dark and has done so for tens to hundreds of thousands of years might keep a system that generates 24 hours rhythms in physiology and behaviour.