Saturday, October 18, 2008

Toad dissection

I decided to photograph and talk about a toad dissection I did this week. Some people (Lorelei?) might not want to see these pictures. A few of the Queenslanders amongst you are likely to have done a toad dissection at school. I wish I could preface this entry with some illuminating comment on the ethics of dissection, but in order to do this sort of thing I try not to think too hard about the morals of what I'm doing. Sometimes I feel a sympathetic pain in the same body part as the part of the animal I'm cutting. I am a hypocrite. But enough of my moral flabbiness, and on with the toad.

Here's my toad. I picked it out of the other toads in the tub because it was a very pretty shade of pale yellow. It's illegal to breed cane toads, so the toads we used were captured in Northern Queensland and crated down.

This is always the saddest part of the dissection.

Once I've made the first cut it's easier to think of the toad as a specimen, and not an animal. Here (above) I've cut through the skin to reveal the abdominal muscles. Toads have no external genitalia (both sexes have a multi-purpose cloaca), so it's only once you get inside that you can tell what sex it is. This is a male toad, because it has a vocal sac. You can see the vocal sac in the photo immediately above. It's the black-and-white flecked section of skin beneath the lower jaw.

These pictures were taken after I cut through the muscle layer. The internal organs are known collectively as the viscera. In the above picture, where the chest muscles and vocal sac have been severed, you can see the white roof of the toad's mouth.

Here's a close-up of the viscera. The following organs are visible:

Lungs: the pale yellow, honey-comb sacs on either side of the body. As well as breathing with their lungs, toads can breathe and absorb water through their skin.

Heart: dark red, in the centre of the chest.

Stomach: pale pink tube on the lower right hand side of the photo. It is attached the small intestine, which is the thinner, coiled tube.

As it turned out, there was something wrong with my toad. The large grey ball in the middle of the viscera is the gall bladder, which is abnormally enlarged. Normally the toad's liver would be dark brown-red and cover a large portion of the viscera. However, this toad's liver is visible as the two shrunken, pale brown masses on either side of the gall bladder. Humans with poor liver function can have a yellow complection. Maybe the yellow colouring I initially took to be the sign of a particularly beautiful toad was actually a result of liver disease. The demonstrator told me that if my toad was a human, it would be an alcoholic.

At this point my camera ran out out of batteries, so I can't show you the toad's kidneys, which were located under the rest of the viscera, or its internal testes, which are small yellow things that sit above the kidneys. Neither can I show you inside its heart, which I had to remove, slice through and put in a petri dish. Underneath the viscera I could see the toad's backbone sitting against its skin. I ran out of time to draw the nervous system, so I wanted to take the toad home in my lunchbox to finish the prac, but the demonstrator wouldn't let me.

Next week I'm doing a pigeon.

Monday, October 13, 2008

To Pea or not to Pea

Here are the names of some plants we had to identify on our ecology excursion. I like a good latin name, but sometimes you can't beat a common name for whimsy.

screw fern
pithy sword sedge
wire rapier sedge
red beaks
milky beauty-heads
common billy-buttons
creeping cudweed
button everlasting
twin-flower beard-heath
common raspwort
slender dodder-laurel
coarse dodder-laurel
love creeper
horny conebush

It's nice to know, though, that even scientific names are not above being a wee bit twee. Note the obtuse angles in the leaves of this plant, the common flat-pea. The plant's scientific name is Platylobium obtusangulum.

Thursday, September 25, 2008

Having the Slime of my Life: defensive reflexes in Myxiniformes

Some animals have unfortunate names.

The dik dik, for example.

Or the nudibranch.

Other animals not only have a funny name, but remind us that nature is not always beautiful. The naked mole rat springs to mind.

But my favourite animal in the aforementioned category is the hagfish. Hagfish resemble the earliest fish in that they have no lower jaw. Instead, they tear pieces off polychaete worms and dead fish. I am not sure whether it's their gummy, left-my false-teeth-out style of eating that gives them the name 'hags', but it seems appropriate.

Hagfish are also known, charmingly, as slime hags, due to their numerous mucus glands. This is what my textbook has to say about hagfish:

"A disturbed hagfish can produce enormous volumes of protective mucus; once released from the body, the mucus expands very rapidly and can completely fill a bucket containing the hagfish within minutes."

Disappointingly, it seems that there is no such creature as a fagfish, with whom these slimy, disturbed hags would presumably form a symbiotic relationship.

Monday, September 8, 2008

Fish fingers: Acanthostega and tetrapod evolution

This handsome devil is Acanthostega. One of my lecturers refers to him as 'friend Acanthostega', and, for reasons I will explain, I have come to think of Acanthostega as a friend.
There are no photos to show you, because Acanthostega has been dead for approximately 365 million years.

A cultural theory enthusiast might say that Acanthostega inhabited the liminal zone. A normal person might say that he was a half-fish, half reptile who lived in a swamp. When you hear about creatures crawling out of the primeval soup, it's Acanthostega who did the crawling.

As you can see, Acanthostega's limbs sit a little awkwardly on his body. This is because limbs have only just been invented. Acanthostega's predecessors were fish with fins. He was probably not mobile on land, but could use his legs to brace himself against aquatic plants, and push up out of the mud.

Early limb-bearing creatures like Acanthostega usually had six to eight digits on each hand. It was only later in evolutionary history that most animals settled on five digits as the optimal number.

Of all the species that have ever existed, it is estimated that 99% are extinct. It's sad to think of the last Acanthostega sinking lifelessly into the Upper Devonian mud. However, there is a happy ending. Limbs proved to be a very successful evolutionary strategy. Acanthostega is not just a friend, but a relative. It seems (my textbook is not explicit on this) that his descendants include ourselves!

Sunday, August 17, 2008

If an animal mates with another species of animal, is it still bestiality?: Onychophorans and outbreeding depression.

I promised more obscure invertebrates, so here is an onychophoran. Onychophorans are forest leaf litter dwellers. I have never seen one, but I live in hope. Their common-or-garden name, velvet worms, seems to suggest that holding one would feel like being stroked with a piece of velvet. As a presumptive scientist, I have qualms about using a word like 'cute', but look at those little antennae. I'm only human!

Onychophorans are also wonderful because they are freaks. I have a soft spot for animals who exist in distant, unclassifiable, evolutionary backwaters. Onychophorans appear to be related to both insects and annelid worms, but cannot be classified as either. They exist in a phylum all of their own. To put this in perspective, human beings are in the phylum Chordata, along with (more or less) everything else that has a backbone. The phylum Onychophora contains only onychophorans. 

Germaine Greer reputedly remarked the other day that she was an animal. Perhaps Germaine should consider becoming an invertebrate. In the tradition of female-dominated ant, bee and termite societies, and female praying mantises who devour their mates after sex, some onychophorans live under a rigid matriarchal hierarchy. 

The Australian species Euperipatoides rowelli commonly lives in a social group of up to 15 females, males and young. They hunt as a pack, immobilising their prey with a sticky secretion of mucus. The group observes a strict hierarchy in the order in which they feed. The dominant female feeds first, followed by other females, then the males and young. According to biologists who made this discovery, 'hierarchy within the group is established by aggressive-dominant and passive-subordinate behaviours'. At least there are no passive-aggressive onychophorans. 

Aggressive behaviour consists of kicking, biting, chasing and climbing on other individuals. Passive behaviour involves running away or allowing oneself to be climbed on. Females are commonly larger than males, and this may explain their higher status. Onychophorans of this species have been observed running their antennae over others' backs, perhaps to estimate their size and social status. 

However, while it's a dog-eat-dog world inside the onychophoran pack, they close ranks against outsiders. To quote the aforementioned biologists, 'E. rowelli from different groups, ie. from different logs, are met with intense agression'. Perhaps Germaine is right. It seems all too easy to draw parallels with the human condition. Personally, when I see someone from a different log, I can barely contain myself. But first I run my antennae over their back, just in case. 

Unfortunately for onychophorans, fragmentation of their habitat means it's sometimes difficult to find a mate, so they resort not to inbreeding, but to outbreeding. To explain by way of analogy, onychophorans are not like the hillbilly who marries his cousin, but the hillbilly who marries his goat. Unable to find a mate of the same species, they will breed with a different species of onychophoran. As with many cross-species matings, the resulting offspring often have fertility problems, as well as unusual numbers of legs. 

Tuesday, August 12, 2008

God scribbled a penis on the ocean floor: the discovery of Riftia pachyptila

Invertebrates are animals that have no backbone. (Actually, to be technically correct, they have no dorsal notochord, but I want this blog to be intellectually light weight, so let's say the first definition is okay.)

Some invertebrates have captured the popular imagination. There are childrens' films featuring ants and bees. There are no childrens' films that feature cute, talking digenean flukes. You might dress your kid in a T-shirt with a picture of a butterfly. You would not dress her in a shirt with a picture of a tapeworm. Or, for that matter, a nematode, a nemertean, or a nudibranch.

Pycogonids are related to spiders, but Incy Wincy pycogonid never climbed up the water spout. A vestimentiferan never flew away home to find her children missing and her house on fire.

Maybe this is because having your house on fire is a pretty normal state of affairs for vestimentiferans. These animals live around hydrothermal vents on the ocean floor. At great depths, molten rock released below the earth's surface causes hot water to flow up into the ocean.

Before 1977, no one knew vestimentiferans existed. Scientists who were conducting an oceanographic survey from a navy submarine unexpectedly discovered unfamiliar worm-like creatures living around vents at a depth of 2500 metres.

Vestimentiferans live inside a hard tube. They have no mouth or gut. Instead, they are filled with bacteria. The hydrothermal vents release sulphur, which the bacteria digest to produce energy. (This is highly unusual, as most living things have to obtain energy either from eating someone else or from photosynthesis.) The vestimentiferan can then digest the bacteria.

In the words of our normally serious and world-weary lecturer, they are 'easy to remember for the exam because they're the ones that look like a giant penis'. Giant is the right word. Vestimentiferans grow to be 2.5 metres long.

More deeply unpopular invertebrate friends to come!

Saturday, July 26, 2008

You're an Ugly Mole: the cryptic lifestyle of Notoryctes typhlops

As we all know, Australian mammals are shameless media tarts. But not marsupial moles. Marsupial moles live in the central Australian desert. Because they are rare and live underground, almost nothing is known about their behaviour or life cycles.

As you can see from the pictures, they look just like Mr. Mole from Wind in the Willows, if he was an albino with a backwards-facing pouch and no eyeballs.

Marsupial moles' underground lifestyles have made sight unnecessary, so over many generations their eyes have degenerated. They have small lenses left in their skin where their eyes would originally have been. They also have no external ears.

Anyone who has ever worn a pair of girls' togs to the beach would know about that annoying pocket-like bit in the groin that seems especially designed to fill up with sand. Marsupial moles don't have this problem. The entrance to a marsupial moles' pouch faces backwards so that when the mole burrows through sand, its pouch is not filled up with grit.

Friday, July 25, 2008

Stop, or my Epitoke Will Shoot!: Polychaete Reproduction

Sexual reproduction can be a bitch. The medical expenses, the ballooning uterus, the risk of disease. When it comes to reproduction without the hazards, polychaete worms have it made.

Polychaetes (pronounced poly-keets) are a type of annelid, and so are related to earthworms and leeches. They live in the ocean, and often have spectacular facial tentacles. Some are free-living, while others live in tubes and have fan-like tentacles to catch food. Ancestral earthworms probably resembled free-living polychaetes, but they lost their tentacles when they moved onto land and started burrowing underground.

If you were one of a few peculiar species of polychaete, having a baby would be a breeze. The hard work would be done for you by a specially adapted clone. At a certain point in your adulthood, you would notice a small version of yourself sprouting from your rear end. This individual would be your 'epitoke'. You would referred to as the 'atoke'.

You may have several epitokes joined in a line behind you. They would be genetically identical to you, but have features that would make them better suited to sexual reproduction. Polychaete epitokes have specialised structures for swimming. Their guts degenerate to make room for vast quantities of eggs or sperm. In human terms, your epitoke would be just like you, but with perkier breasts, a larger penis, wittier conversation and a better car.

When they were large enough, your epitokes would break off from your body and swim up into the ocean. They would brave predation from other animals (or the humiliations of the speed dating scene) in order to release what are genetically your sperm or eggs into the water. You could stay at home watching television and making cups of tea, knowing that a superior version of yourself was out doing all the hard work. With any luck, the ocean would soon be filled with your larvae, even though you had no hand in producing them directly.

And if your epitoke was eaten by a fish (or limped home emotionally crippled from a failed marriage to someone who turned out to be a lady-boy) you could always sprout another one.

Polychaetes are not the only animals to bud off a clone of themselves for sexual reproduction. In some classes of jellyfish, the jellies you see floating in the ocean are only half the story. They have budded off a body form known as a polyp, which is attached to the bottom of the ocean. The floating form of the jellyfish is called a medusa. It's the sexy one. Like the epitoke, it goes around releasing sperm and eggs into the water. Polyps prefer to stay in.

If you want to make this interactive, perhaps we can all take a moment to ask ourselves: in the great ocean of life, am I an atoke or an epitoke? Actually, maybe not. I enjoy anthropomorphism as much as the next person, but sometimes biology hits a little too close to home.

Thursday, July 24, 2008

My Cousin is a Slime Mould OR Phylogenetic Relationships With Particular Attention to Homo Sapiens

The most exciting thing about biology is discovering who you are related to. My human ancestors are a supremely undistinguished bunch of agricultural labourers. My animal, plant, fungal and protistan relatives are a lot more exciting. 

Knowing who your relatives are is useful for serious scientific endeavours like working out how closely you are related to your pet. For example, Romy is more closely related to Coalface (a rabbit) than I am to Gerald (a llama). 

It's also possible to work out how closely you are related to  your meal. Obviously, I am more related to the cheese I ate for lunch (derived from a cow, a fellow mammal), than to the tuna I ate yesterday. I am less related to the mushrooms I will eat tomorrow, but more closely related to them than I am to the seaweed I ate in a noodle soup the other week. I am probably more closely related to the seaweed than to the broccoli I ate the other day. I am only distantly related to the bacteria in yoghurt, which makes me think that moving onto a a high-bacteria diet is the only way to end all this disgusting cannibalism. 

I'd like to show how we are related to everything,  but I'll start close to home. Here's a picture of all the mammals (or maybe not, I can't seem to get pictures to stay up). You can read the tree like you would a human family tree, with the branches representing divergence from a common ancestor. The closer we are on the tree, the more closely we are related. 

Humans are over with the apes and monkeys in PRIMATES. As you can see, our closest relatives are not clever elephants, graceful antelope, or generous organ-donating pigs, but TREE SHREWS. There is a tree shrew in the Melbourne museum. It looks like a rat. Our next closest cousins are bats and gliding lemurs. Thankfully, primates are only distantly related to the CETACEA (whales and dolphins). You already know how I feel about those guys. 


Friday, March 7, 2008

When your mouth is your anus is your vagina: reproduction in phylum Porifera

Orifices are sophisticated inventions. Having a hole for every function is the mark of a recently-evolved animal. More ancient animals like birds and reptiles have a cloaca, which is an opening used for both defecation and reproduction. 

Even having a digestive tract with two ends is a complicated arrangement. Animals like jellyfish, corals and sponges, who were the earliest evolved animals, have a large body cavity with just one opening leading to the outside environment. They eat, shit and have sex using the one hole. 

Sponges reproduce sexually by shooting their sperm into the water. (Copulation is a land animal invention, developed to cope with the lack of a hospitable, moist environment and free transport provided by the ocean. In light of this, a uterus can be thought of as a mini, internal, ocean substitute.) Each sponge hopes (metaphorically, sponges have no brain) that its drifting sperm will be 'eaten' by another sponge. If one's vagina doubles as one's mouth, there is a danger that the sperm will not be used to make baby sponges, and instead be digested as a nutritious food source. Happily, sponge cells are capable of telling the difference between food and the sperm of other sponges. 

Sunday, March 2, 2008

Why Anna Should Probably Not Sleep With Her Brother OR Consanguinous Matings and Darwinian Fitness

I've always assumed jokes about inbred, two headed, Tasmanian congenital idiots were exaggerations. Apparently not. The statistics on inbreeding are quite frightening. 

Amongst live births resulting from incest, 6/18 children die in infancy or childhood, and 3/18 have intellectual disabilities. 

Here are some statistics on the offspring of first cousins, compared to the children of unrelated parents: 

Trait Unrelated 1st cousins

stillbirth and neonatal death* 4% 11%
major congenital malformation 1% 1.7%
genetic abnormality 7.9% 18.8%
mental deficiency 1.3% 5.5%
recessive muscular dystrophy 0.0034% 0.051%
*1941 figures

So perhaps it's wise to think twice before taking a plunge into the shallow end of the gene pool. Your sibling may be intelligent and attractive, but chances are your resulting daughter-niece or son-nephew will not be.

Whales: Neo-cons of the Sea OR Cetacean Phylogeny and Convergent Evolution

Every now and then life throws up an evolutionary backslider: a creature who, having successfully evolved into a new way of life, turns around and evolves right back into something that resembles its primitive ancestor. 

The ancestors of tree kangaroos (inhabitants of PNG and far North Queensland) evolved from mammals who came down from the trees and adapted to life on the ground. Then, at some point, they began to re-adapt themselves to life in the trees, taking their big, ungainly, land-adapted feet with them. 

Whales have taken things a step further. The ancestors of whales were land dwelling mammals with limbs and toenails, or possibly hoofs. Life had emerged from the ocean 400 million years ago, and was ticking along nicely for more than 300 million years before these ancestral whales decided it would be a bright idea to crawl back into the primal soup. At this point, they grew their limbs back into flippers and went back to live in the ocean like a bunch of fat, bloated fish. 

How, whales, is this a positive lifestyle choice? You are now WARM BLOODED creatures who live in a FREEZING OCEAN. You're the size of a TRUCK and you eat things that are the size of a FULL STOP. You breathe AIR and live UNDER WATER. And you wonder why Japanese people want to kill you!