Posts Tagged ‘Evolution’

At The Water’s Edge/Carl Zimmer

April 13, 2009

tiktaalik_phylo

Written in large, friendly, ocean-blue letters on the cover of “At the Water’s Edge” by Carl Zimmer are the words:

FISH WITH FINGERS,

WHALES WITH LEGS,

and How Life Came Ashore but

Then Went Back to Sea Again”聽

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Monday Organism – Axolotl/Ambystoma mexicanum

March 16, 2009

250px-axolotl

Ambystoma mexicanum is binomial for Axolotl, or “tiger salamander”. This amiable amphibian is typically found in Mexico (what is it with me and Mexican organisms?), and is widely used in scientific research since its embryos are rather transparent, making it ideal for researchers in developmental biology.

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Is Evolutionary Theory Useless?

March 5, 2009

The latest rant by Michael Egnor, the ID-creationist neurosurgeon with a surname that simply demands snarky puns, has got me thinking not so much about the crux of his graphic tantrum (“There’s lots of idiots like me! *thumps chest* and we’ll kick your ass!”) – but about something he wrote that’s quite superfluous to Egnor’s petulant ravings:

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Monday (paleo)Organism – Indohyus

February 16, 2009

indohyus500.jpg

Due to the current fossil whale craze, I’ve decided to dedicate this week’s Monday Organism to another famous fossil related to whales. Well, I say “related to whales”, and this much is true for any ancient organism, but the truth is, Indohyus is really, if anything, only a sister taxon to ancient cetaceans – it’s unlikely that whales descended from Indohyus directly.

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Yet Another “Mother Whale Fossil Found With Fossil Fetus” Post

February 4, 2009

maiacetus

Not what you might call a typical “Yet another X” line, I know. I wanted to write a post about the matter this morning, and in the interim, I found out that pretty much half of scienceblogs wrote eloquent, descriptive and fascinating posts about this.

So, just to mention this to anyone who’s not an avid scienceblogs reader – a new fossil found in Pakistan of a protocetid (ancient whale). Finding a well-preserved fossil of a transitional form is amazing already, but, and this is the kicker:

The fossil was of a female pregnant whale, and contained a fossilised fetus in it.

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Monday Organism – Mexican Tetra

January 19, 2009
Blind cave fish, A. mexicanus

Blind cave fish, A. mexicanus

Astyanax mexicanus, or “blind cave fish”, as it is commonly known, is an evolutionary wonder. The tetra lives freshwater rivers in Mexico, particulary in dark caves in which eyesight is redundant.

The most fascinating aspect of the blind cave fish, as the name implies, is its characteristic lack of eyes.

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Monday (Paleo)Organism – Ambulocetus natans : The Walking Whale That Swims

January 12, 2009

evi_amulocetus_large1

Ambulocetus natans, a long-extinct species of cetacean from the Eocene (about 59-60 mya) and creationist nightmare extraordinaire, is one of the most fascinating fossil species known. Ambulocetus natans literally means “The walking whale that swims”, so as to provide an uppercut reply to any creationist who ignorantly inquires: “What I don’t see in the fossil record is walking whales that swim!”.

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Monday Organism – Platypus!

January 5, 2009

Anyone with even a slight penchant for biology must know of this peculiar creature: The Platypus.

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Monday Organism: To Everything, Fern, Fern, Fern

December 8, 2008

hi-fern-forest-2

Back in the old forum days, I used to write on specific organisms frequently. Now that I’m doing Botany, I think this little spot would be missing a lot if I didn’t give some spotlight to the greater picture, especially in regard to groups of organisms most of us take for granted, such as plants.

This last week brought us undergrads face-to-face , for the first time,聽 with real hardcore terrestrial plants, and the first such plants were a group of organisms called Ferns.

Even though I’m alt-tabbing the wiki article for fact verification (and digging up fun facts as well), I can, sans wiki, sum up聽 what are the interesting differences between Ferns and all the other plant taxa we’ve learnt of so far.

Ferns are similar to mosses in some respects, and like mosses and all evolutionary descendants of mosses, they’re embryonic plants, with distinct sporophytic stages that develops from a protected embryo that is grown and shielded within the parent fern.

Ferns actually have independent sporophytic stages, which is a bit odd. Flowering plants don’t have that, and neither do mosses (which can be very roughly considered the evolutionary “befores and afters” of Ferns). In mosses, the sporophyte is, if not completely “parasitic” on top of the gametophyte, is still an attached (above-ground) outgrowth of it.

In flowering plants, the gametophyte is situated atop the sporophyte, which is the reverse for mosses. I won’t get any deeper into that, since I haven’t studied about them yet 馃檪

Ferns are distinguished in the plant kingdom as the first truly Vascular Plants. It’s not that more primitive plants don’t have some means of relaying organic material and water around the body of the plant, but in Ferns, we witness the first instance of complex, all-body vascular organs, namely, the Xylem and the Phloem. The X and P are just fancy words for “tube for shifting organic compounds” and “tube for shifting water”, respectively. As the first hardcore terrestrial plants, vascular organs are a must-have adaptation. Growing taller is a logistic nightmare, but with the enormous selection pressure on short plants that compete on the same sunlight, it’s a must. It’s a good evolutionary explanation for why those Ferns went through all the trouble, and this is actually a distinguishing feature in Ferns: they’re specialists. Their penchant for being taller is just the tip of the iceberg (they’re also adapted to hostile habitats, habitats which constrain the flowering plants but not Ferns).

The most revealing innovation in Ferns is the organ that most of us seem to readily associate with plants: Leaves.

To begin with, I was simply delighted to finally understand what this organ actually is. Up until next week, leaves to me, as they are to most laymen, were simply “green bits on them flowers and whatnot”. There’s more to that, or merely, a more accurate description. Leaves are firstly defined as the photosynthetic organs. In short, what the mouth does for heterotrophs like us, the leaves do for autotrophs like plants. In short, it’s the plant’s way of getting chow. Up until now, photosynthesis wasn’t confined to specialized organs, and hence, leaves are聽 truly a hallmark of evolutionary innovation.

As an aside, it’s interesting to note that evolutionary innovations are often a precursor to two things:
A.Enormous comparative fitness (evolutionarily-speaking, as opposed to simpler organisms)
B.An evolutionary dead-end. Jacks-of-all-trades have more “promotion possibilities” than “Masters-of-one-trade”. This is why bacteria outlived many metazoa (and will probably outlast us!)

Since I’m an evolution afficionado, I want to have the finishing part of this post to focus on some interesting evolutionary tale, but I think I can combine that with some cool info on Ferns in general. What I mean by that is that you can actually see for yourself the evolutionary “nodes” in Fern evolution by observing the various stages of leaf evolution.
Like Is said, leaves are the photosynthetic organs of plants, but leaves haven’t sprouted de novo out of ancient moss-like thalluses (even though even weeds have leaflike apparatuses).

The first instance of leaves comes in the shape of protophylls (ancient leaves). Protophylls are nothing but dandruff like scales without any actual vascular tubes for carrying the photosynthetic products to the body of the plant. Since the protophylls are usually small and aggregate, this is not a big problem, and obviously this is an ample condition for evolutionary advance: now that we have the specialization in order, all we have to do is grow some tubes. 馃檪

Psilotum - a protophyllic fern

Psilotum - a protophyllic fern

The second and third stages of leaf evolution are very similar: Microphylls and Macrophylls. The noted difference between the two is that microphylls have only one artery-like tube and macrophylls have a branching like web of vascular tubes. It’s quite easy to imagine how one evolved to the other, but not so easy to come up with how protophylls evolved into either, or should I say, to one and then the other. 馃檪

Lycopodium - a microphyllic fern

Lycopodium - a microphyllic fern

So, yet again, we come across an oft-taken-for-granted plant group and find that it tells us fascinating evolutionary stories. Mainly, that those cheeky bastards are opportunistic little buggers that probably gave us the precursors for modern plants, meaning that Shakespeare and other like-minded cupid-heads should give them some credit. The true journey to dry land starts with Ferns, and so the true evolution for the plants we hold as familiar starts with them.




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Monday Organism (Yes, I’m Aware It’s Sunday) – Cyanobacteria

November 30, 2008

On most Sundays, I won’t be around to post, except in the evening, half-brain dead from ISL class. Anyhow, I’m a day off to recuperate from last week, so I have time to post my very first “Monday Organism”, and a day early, at that!

Since this is the first weekly organism, I think it’s appropriate to explain why there is, in fact, a weekly organism. Since this blog is about biology, it’d be mighty improper unless it had聽 periodical items about animals, don’t you think? I mean, come on, it’s no use running a blog about biology without fluffy animals in it (or angry wobbly ones or, well, extremely tiny ones).

Also, the Monday Organism is sometimes going to be about higher taxa as well (usually very high taxa, mainly to illustrate an interesting point about evolutionary biology)

The first Monday Organism is actually not an Organism, but a Phylum: Cyanobacteria.

c810x2cyanobacteria

Cyanobacteria literally means “blue bacteria”, but they’re actually called “blue algae” in Hebrew. The wiki on Cyanobacteria states that the taxonomy of Cyanobacteria is under revision, which is no surprise. In class, this group was even (I think most appropriately) called “Cyanophyta”, meaning “blue algae”.

Cyanobacteria are a fascinating group, and their existence is sound evidence for various evolutionary theories, the most important one is probably the evolution of the chloroplast organelle, the organelle in plant cells in which photosynthesis occurs.

The truly amazing thing about Cyanobacteria is the fact that they’re actually prokaryotes (having no distinct cell nuclei), and yet, they have photosynthetic pigments in their cells which are used to produce organic material by absorbing light energy from the sun. This means, in effect, that Cyanobacteria are the evolutionary precursor for the eukaryotic plants.

While it is obvious that all algae are commonly related, the truly interesting characteristics of Cyanobacteria are the ones that point out to the evolution of plant organelles. When I first learnt about Endosymbiont theory, I was plainly told that “endosymbiont bacteria eventually became permanent organelles”. Now these endosymbiont bacteria have a name: Cyanobacteria. In fact, the evidence shows that the Cyanobacteria themselves evolved into the chloroplast, and it is quite possible that every plant cell is, in a way, a symbiotic colony of eukaryotes and prokaryotic photosynthetic bacteria!

Obviously, the radiation of photosynthetic taxa is prolific enough to rule out such a simplistic story, but the evidence shows similar genetic and biochemical traits in modern day chloroplasts and in the makeup of Cyanobacteria. Since this isn’t an encyclopedic article and I rather focus only on one interesting concept at the time, I’ll give just one example for “evidence” of the common descent of CB and chloroplasts :聽 the genetic makeup of chloroplast DNA (yes, they have their own DNA and they replicate on their own!) is similar to Cyanobacteria DNA. This alone is solid evidence for common descent for the two.

There’s lots of special cases of endosymbiosis that show not-so-common descent, but rather “common descents”, but I’ll leave that to the avid reader.

The main point of this post is not so much to tell about CB anatomy (warning: other posts might deal with interesting anatomy and physiology!), rather it is to illustrate classic tools in evolutionary research: genetic, anatomical, biochemical and physiological comparison as instruments for detecting common descent. It’s a crucial way of thinking in all of biology, and it highlights the sometimes elusive practical value in evolutionary theory: knowing the genetic relationship between different taxa can be critical in any biological endeavor. If one seeks to find antibiotic weaponry against infection and disease, knowing the culprit’s phylogeny can be of tremendous use, and phylogeny is best derived from the comparative tools I’ve briefly illustrated here.