Yes, yes, I know it is usually the Friday documentary, but, with everything getting back into a rhythm after New Year, I thought a nice Sunday relaxing one would be ideal.
This is a BBC one from late last year, about the life cycle of stars. I started watching it last night, aiming to fall asleep to it, but had to stay awake to the end!
Astronomy is not usually something I post about, as it is not a subject I know much about, but, this one was fascinating!
Enjoy!
So, I have linked a couple of documentaries in this series, How the Earth made us, the Deep, and Water. This week the documentary is about how fire and heat from within the earth has shaped our societies
The last post about Life on Earth was about Cowries, and I said that this time I would write about some of the ways they have been part of human society for a very long time.
Cowries as we saw, have very shiny, smooth shells, and this has led to them being used a currency throughout both ancient history, and modern times:
This is a species called Monetaria moneta, which looks like this:
Monetaria moneta (also called Cyprea moneta). Image from Gastropods.com
As you may have noticed, the name of this animal sounds a lot like the word “money”, and in fact, this particular Cowry, and one or two other species, have been used historically as currency.
In China, they were used as currency from at least 1200 BC, and the Chinese Han character for money is the same character as for sea shell.
Cowrie shells from ca 900 BC, image from University of Maine
They were also used in Bengal in India as currency, and widely used throughout the Asia-Pacific region.
They were extensively used in the Maldives
Many African nations also used shells as currency, and during the slave trade era, Europeans would use cowrie shells in exchange for slaves, and there was a trade in cowrie shells between Asia and Europe for use in Africa. Excavations of sites in the USA have uncovered cowrie shells in both the slave houses, and the houses of people who were involved in the slave trade (See further reading).
The use of shells as currency within Africa continued until the early 20th century, and in Ghana, some of their coins display cowrie shells as the image on one side.
20 Cedis coin from Ghana, image from the British Museum
Mondays post will be staying within Molluscs, but moving on to another amazing animal!
Further Reading:
http://www.britishmuseum.org/pdf/MoneyInAfrica_Presentation.pdf
http://www.britishmuseum.org/explore/highlights/highlight_objects/cm/c/cowrie_shells.aspx
http://www.computersmiths.com/chineseinvention/coins.htm
http://www.conchsoc.org/interests/shell-money.php
http://www.conchsoc.org/pages/MW_6_p19-21a.pdf
http://www.monticello.org/site/research-and-collections/cowrie-shell
As I mentioned last week, I have an exam on Wednesday, so am doing some final revision today and tomorrow, so no long posts til Wednesday.
On Wednesday I will be picking up with the story of life on earth, but until then, I wanted to share this documentary.
It is another BBC one (I have a thing for their awesome documentaries), and is on the topic of human evolution.
It is part of a series called “The Origins of Us”, and this episode is about our bones.
I hope you find it as interesting as I did. Alice Roberts, the presenter is one of my favourite presenters of anthropology type documentaries.
I do not usually post twice in one day, but this is far too cool to not post about:
There is a phenomena in nature known as gynandromorphy, which means that an organism displays both male and female characteristics. This is different from hermaphroditism, which only refers to the sexual organs.
This appears to be mostly within insects, but some crustaceans have been found to have it too…This post is not about those, but these pictures of butterflies illustrate what it means (image from wikipedia):
That is interesting, I can hear you saying, but is it worth another post on a Sunday?
Well….you might not think that butterflies are cool enough for that, but, I think this is extra awesome:
Gynandromorphy in chickens. Image from Nature.com
The REALLY cool thing about this is not just that it is a half male, half female chicken, but what this tells us about how chickens sexual characteristics are determined.
In humans, our male, or female characteristics are determined by our hormones when we hit puberty. There are variations within each sex, with some men being extremely hairy, others who are almost hairless, likewise with women, as well as our overall body shape.
In chickens (and possibly other birds) the sexual characteristics of the animal appears to be determined primarily by the chromosomes, instead of by hormones (so in humans, it would be XX or XY, there are variations on this, but that is a whole other post).
This image illustrates the differences between how chickens and humans develop sexual characteristics (Full link to article in references)
Differences in how mammals and chickens determine sexual characteristics. Image from Not Exactly Rocket Science
Bilateral Gynandromorphy is usually seen in insects, and is down to the way that their cells are determined during development, and I will try to explain. This is a bit complicated, but it is due to at which stage of division after fertilisation the gynandromorphy occurs. Early on in development, between 8 and 64 cells into division (see references for info) if a chromosome (X or Y in humans) is left behind in the nucleus after division, this leads to a 50/50 bilateral gynandromorphy This is because early cell division determines the left and right sides of an organism.
Mosaic gynandromorphy occurs when a chromosome is left behind more than once during the developmental process.
The strange thing with birds appears to be that even though the gynandromorph chickens have a mix of chromosomes (Z or W in chickens) throughout their body (This was tested by tagging the chromosomes with a fluorescent molecule), one side had more female cells and one had more male cells.
Further testing showed another anomaly between birds and mammals. In mammals, if you put an XY cell (male) into an XX environment (say, an ovary), the male cell will become a functioning part of that region, and act like the other cells around it in response to sex hormones, however, when this occurs in a bird, the cells continue their original sex designation. So, when researchers put a lot of ZW (Female) cells into a ZZ environment, and subjected them to the hormones, the cells continued to produce female enzymes, and female structures.
As that was quite technical, I will end with some cool pictures of this, including one where the difference is not immediately obvious (all images from Dalton State College):
Butterfly bilateral gynandromorph
Bilateral Gynandromorph, slightly female on left back wing (the grey)
Moth (Malacosoma disstria) bilateral gynandromorph. The female half is the left side.
References/Further Reading
http://www.daltonstate.edu/galeps/Gynandromorphs.htm
http://www.nature.com/news/2010/100310/full/news.2010.114.html
http://www.vims.edu/newsandevents/topstories/archives/2005/dual_sex_crab.php
Apologies for the lack of posts this week, I am in the middle of exams at the moment, but hope to have the 2nd post on brachiopods up at the weekend.
So, the documentary I have for you today is “How the earth made us” Episode 1: Deep Earth
I mentioned last week that I also love geology, this programme is about how the geological processes of the Earth have played a role in human civilisation throughout history. Later episodes cover atmospheric conditions, climate, water and fire (volcanos).
For me, this series combines so many aspects of natural science that I love. I wanted to go into Climate Science, but, Atmospheric Physics has a LOT of very scary maths in it, although I love the complexity…I have had to promise that I am not going to do stormchasing if I ever go to the USA, or at least dont tell people til after I do it! I also have a crazy fascination with volcanos, and again, have been asked to not mention it if I am going clambering up the side of the volcano when I go travelling!
So, without further ado, Dr Iain Stewart with How the Earth made us. Enjoy!
Last time I said I would move on from worms today, but I thought that I should at least cover the creatures alive today that resemble those which made the fossil burrows I showed last time, and talk a bit about the links between flatworms, and the worms I will cover today, so one more post on worms (for now!)
So, without further ado (cue drum roll), let me introduce you to the subject of my post today, Nemertea (not to be confused with Nematodes, which are something completely different)
This, is a Nemertea (also known as Ribbon Worms):
Basiodiscus mexicanus. Image from UCMP Berkeley
Not all of them are this pretty, a lot of them are dull coloured, and some look like this:
Lineus longissimus, the Giant Ribbon Worm (or Bootlace Worm). Image from seawater.no
The species shown above, Lineus longissimus is one of the longest creatures in the world! It is usually 5-15m long, but has been reported up to 60m long! In contrast to its length, it is usually 5mm or so wide!
It is extremely common in the UK, and can be found wrapped around the bases of algae, or appearing to have tied itself in knots in shallow pools.
Another Lineus longissimus, this time curled up around itself. Image from MarLin (Marine Life Information Network)
This is a video of one moving around, so you can see how they move differently to the flatworms we looked at before
So, why am I showing you pictures of a slightly gross looking creature? (I cannot decide whether I find them fascinating or gross…maybe they can be both)
Well, this phylum of organisms used to be thought to be directly related to the flatworms we covered previously, but now they are thought to have arisen separately, whereas flatworms and Cnidaria are thought to have evolved from one ancestral species, with one line of descendants becoming the radial corals and jellyfish, and another heading off to become the flatworms, with the bilateral symmetry.
The latest research, looking at both genetics, and how cells develop within an organism (cell lineage) appears to show that they are not related to flatworms, but nevertheless, they have some similar features, as well as some which are more evolved, and one very unique feature.
Lets start with what they have in common, and work out from there.
They have bilateral symmetry, and a triploblast body (the three levels of cell within the body) both of which we first saw in the flatworms. (See here for the diagrams from that post)
They do not have a body cavity as such, so they are usually classified as acoelomate, but they have a special structure, which we will get to shortly, and so there is discussion about whether this is a body cavity or not.
The image below is a diagram of a Nemertea, and hopefully you can see the similarities to the cross section of the flatworms here
Nemertea cross sectional diagram. Image from North Carolina State University: Agriculture & Life Sciences
Here is a cross-section of a flatworm for easier comparison:
Acoelomate cross section. Image from University of Illinois Chicago
Nemertea also have the protonephridia that flatworm have (the flame cells which act as a simple excretory system), and they are able to reproduce both asexually, and sexually, also like the flatworms.
So, they have a few features in common, what do they have different?
Firstly, they have an exit to their digestive system (you can see this at the bottom of the picture above). This means that solid waste does not exit through the same orifice as food goes in by. They therefore have a complete digestive system, although still a very simple digestive system, without the liver, kidneys and other organs which we have. Apart from the obvious yuk factor to only having one way in and out for food and waste, what is the advantage of having two ends to your digestive system?
Well, firstly, I do not think animals are bothered by the yuk factor in the way we are, but there is a very clear advantage to having both a mouth, and an anus. The advantage is, simply, that you can eat and excrete simultaneously, which means having a complete digestive system is more efficient.
Another important development is that Nemerteans have what is known as a closed loop blood-vascular system. In flatworms, oxygen and other nutrients are distributed by diffusion (remember how they had a digestive system spread all through their body). Nemerteans have dedicated blood vessels to transport nutrients around their systems.
Nemertean Circulatory System. Image from North Carolina State University
Finally, I said that Nemerteans have a unique feature, and now I will see if I can explain this, because it is very weird, and very cool, and quite gross at the same time.
Nemerteans have something called an eversible proboscis. Eversible means something that can be turned inside out, and a proboscis is something which sticks out from a head, so an elephant has a proboscis, usually called its trunk. Butterflies have a proboscis, it is the straw-like organ similar to a tongue which they stick into flowers to suck up nectar.
So, Nemerteans have a body part which is turned inside out, and comes from their head….sounds weird, but what exactly does it mean? In the image below, the proboscis is shown inside the body, and is the dark line running the length of the body.
Diagram showing the proboscis of a Nemertea, running the length of the body. Image from bumblebee.org
This proboscis lies within a cavity in the body, above the digestive cavity, known as the rhynchocoel. It is because of this cavity that the discussion arises about whether Nemerteans are acoelomate or coelomate.
The proboscis itself is a hollow tube of muscle, and the image below shows it being stored in the body, and after being everted (turned inside out)
Proboscis of a Nemertean. Image from Cabrillo College
So, how does the proboscis get from the inside to the outside, and what is the point of it?
There is fluid in the cavity where the proboscis lies, and when the animal runs into prey (quite literally sometimes, as some species are not very good at finding their way around), muscles at the back of the cavity contract, and this causes an increase in pressure in the cavity, which forces the proboscis out of the body. There is a spike on the end of the proboscis, and this is stabbed into the prey, whilst the proboscis itself coils around the prey.
The proboscis also has toxic slime (mucus) on it, and this goes into the prey. Some of these toxins are the same as in the puffer fish (tetrodotoxin), so very effective! The proboscis is then pulled back into the body, bringing the prey with it, this brings it towards the mouth (the opening under the head), and it is then swallowed whole.
I think the description might seem a bit confusing, so this video hopefully makes it clearer (also take a look at the length of the proboscis relative to the length of the animal).
I did say I thought they were both gross and fascinating…
Next post will be away from worms, I promise!
References and further reading:
Phylogenetic position of Nemertea derived from Phylogenomic Data -Struck & Fisse 2008: http://mbe.oxfordjournals.org/content/25/4/728.full
Progress in Nemertean Biology: Development and Biology – Turbeville 2002 http://intl-icb.oxfordjournals.org/content/42/3/692.full
Information on Cell Lineage – Chisholm 2001: http://bio.research.ucsc.edu/people/chisholm/lab%20PDFs/Cell%20Lineage%20(EoG).pdf
Today I began writing a post which turned out to need a lot more research than I originally planned, and to need a lot of re-wording so it does not sound too boring, so, instead of a Friday post, I am going to link to another awesome documentary.
This one is David Attenboroughs First Life, and it is a bit of an update on Life on Earth, which is the series I am working through for these posts. It is well worth watching, and I hope you enjoy it as much as I do (I have watched most of these documentaries at least 5 or 6 times, as each time I notice something I did not see last time I watched it)
One final thought before I link the video. When I was getting these DVDs, I noticed that an entire DVD set of say, Life on Earth, costs about the same as a movie. Now, maybe I am strange, but I think that a documentary series is far better value than a single movie. I usually get my DVDs from the Amazon BBC site, so maybe prices are different elsewhere, but for me, they are great value.
After being a bit technical last post, today will be more visual I hope! I am hoping that I can show you some very interesting things today about Turbellaria, and hopefully something you had no idea about, but will find fascinating. Apologies for not posting this yesterday, I was trying to track down some good videos and images.
So, lets start out with moving around. As I mentioned in my last post, Turbellaria are mobile organisms. Although jellyfish and medusa stages of the Cnidaria are not sessile (stationary), they do not really move, they are more carried around by currents within the water (This is called passive locomotion). So, another step forward that Turbellaria make is being more in control of their movements (Active locomotion).
Being more mobile may have led to the cephalization that I mentioned last time, as in order to move, you need to see, or sense, where you are going, and so sensory organs became located at the front end of the organisms. Many species of Turbellaria have light sensitive spots on their front end (these are called ocelli), and some have small flaps sticking out of the side of their heads, which look like little ears, but are usually chemo-receptors (in us, we have our taste buds and our sense of smell as chemo-receptor)
A Turbellarian (Sabussowia ronaldi) with the eyespots visible (the dark spots). Image from wikipedia
So, now they can see, at least a little bit, where they are going, how do they move where they want to go?
Many Turbellarians move by moving their muscles (and in smaller species, cilia) in an undulating motion (like ripples moving along their body), and sliding over mucus which they secrete (A bit like snails, but more wiggly!). There are some species however, which swim, and they do this in the same manner as the ones which wriggle along the sea floor or ground, by waves of muscle contraction. I think this looks really fun, and beautiful, so here is a video of a marine flatworm swimming.
Now, to get a little bit stranger, once they get where they want to go, how do they eat, and what do they do with their food?
As I mentioned last post, Turbellaria have blind guts, that is, there is only one entrance and exit. This does not mean that absolutely everything which is taken in and not used comes back out the same way, although the majority of it does, as we shall see shortly. Turbellaria, and their phylum Platyhelminthes, are the first organisms we encounter which have excretory organs. In humans, these would be things like kidneys, which filter out waste products from our blood.
Turbellaria have nothing as complex as our kidneys, but they do have what are known as protonephridia. These are effectively tubes which are closed at one end, and have small holes which draw fluids in from the body. They have special cells called flame cells, which have flagella attached to them (flagella are structures extending from a cell, which often move in a whip-like motion, which is where they get their name. Flagellum is Latin for whip. These are often used for movement in bacteria) These beat, and move fluids down into the open end of the tube, where they are moved along with the help of cilia, and the tube opens out at the edge of the body. These protonephridia are used for something called osmoregulation which is mostly removing excess fluids from the organism, although small amounts of ammonia are also removed.
Protonephrida. The blue arrows indicate where fluids enter near the flame cells, which beat and move the fluids down the tubes so they can leave the body at the surface. Image from Biology 8th Edition: Campbell & Reece via College of DuPage
Turbellaria are carnivorous, and feed on things such as small crustaceans (crabs are crustaceans), insects, and very small organisms called rotifers. The cool thing about Turbellarian feeding is not what they eat, but how they eat it.
The image below is the general anatomy of a Turbellarian, it shows some of the structures I have already mentioned, including the eyespot, and the brain-like collection of nerves at the front end, and the protonephridia, and some parts that we will come to in a bit, however, the part we are interested in now is the tube sticking out on the underside, labelled as “pharynx”.
General anatomy of a Turbellarian. Image from Geochembio.com
The image below more clearly illustrates the location of the pharynx. In humans, our pharynx is the tube which runs from our mouth down towards our stomach, behind our larynx (the tube which we breath through).
Diagram of a Turbellarian, showing the pharynx, and gastrovascular cavity. In humans, the gastrovascular cavity is our stomach and intestines. Image from DuPage college, and Biology 8th Edition: Campbell and Reece
So, the pharynx in turbellaria is a tube which can be pushed out of a hole in the underside. As these do not have teeth, or a mouth for holding food and starting digestion as we do (food begins to be digested within our mouths, before we swallow it), turbellaria instead have digestive juices come directly out of their pharynx onto their food, which begins to digest it, and it is then sucked back up into the pharynx, where it goes to the cavities within the organism for digestion to be finished. Undigested food is excreted back through the mouth.
The video below shows a pharynx extended from a turbellarian ready for feeding (at around 0.27 seconds), as well as some of the other features I have mentioned in this post.
I said at the beginning of the post that I would show you some things that you probably didn’t know, and this is where I do that, I hope you find this next section as interesting and weird as I do!
Turbellaria are able to reproduce both sexually, and asexually. When they reproduce asexually, they usually divide themselves in two behind their pharynx, then each new animal regrows the parts that it is missing, so one part grows a new head end, and one grows a new tail end, some divide themselves lengthwise to reproduce asexually. This in itself is fairly cool, as asexual reproduction is usually confined to much smaller organisms.
However, the really cool part is when they reproduce sexually. If you look at the detailed diagram of the anatomy above, you can see that it has various genital organs. The image below shows this in clearer detail
General body plan of a Turbellarian. Image from Southwest Tennessee Community College
In the image above, you can see that the animal has both a penis, and a genital pore, as well as testes, oviducts and ovaries. This means that Turbellarians are hermaphrodites, having both male and female genitals. This is useful from an evolutionary perspective, as it means that if you encounter another of your species, you are able to reproduce. In humans, in order to reproduce, we need someone of the opposite sex, whereas Turbellarians just need to bump into another of their own species.
So, when they bump into each other, do they both fertilise each other, or how do they decide which one is going to be receiving the sperm?
Well…this is where it gets weird. Flatworms do something called penis fencing, yes…you read that right.. (This is part of the reason I was delayed making this post, I had to find a video which clearly showed this occuring, and internet searching “penis fencing” can lead to some…strange results!)
Basically, both flatworm extend their penises, and they have a fight with them, and try to insert theirs into their opponents genital pore. Unfortunately, they are not always very good with their aim, and tend to stab each other quite a bit in the process! I think the video below illustrates this much better than I can with words.
I hope you found this as interesting as I did researching this!
Next post will be moving a bit further up the evolutionary tree.
It is taking a bit longer than I thought to source material for my next post, so, here is a documentary I have been watching these past few days. It goes some way to explain the reasons why I do the subject I do (Environmental Biology). For me, it is all about finding the connections between organisms in an ecosystem, and the presenter of this documentary shares my enthusiasm for these links between animals and plants.
The documentary is Secrets of our living planet, from the BBC, presented by Chris Packham, and I have chosen Episode 3, on the seasonal northern forests. This is the climate zone I am most familiar with, although this documentary focuses on North American forests, the forests are not so different from the ones in the region I live in (Northern Europe), although North America has far cooler wildlife, and WAY bigger forests!
If you have an hour to spare, grab a cup of tea/coffee, and sit down and watch this, if you like David Attenborough documentaries, you will like this, it is a bit more in depth than Attenborough, and is really fascinating, especially if you have never looked at these connections before.
I have also put a short second video up because, well, it is awesome, and even though it looks really insane, I would love to be able to do this! Having said that, I would need some serious breathing exercises before attempting it I think, even if I knew what I was doing! It is Jeb Corliss base-jumping/gliding, and I want one of those squirrel suits!
Normal posting will resume on Monday!
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by May K.
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