Monday, January 17, 2011
Sunday, January 16, 2011
In a perhaps apocryphal story the biologist J. B. S. Haldane (of population genetics fame) was asked what he could intuit about The Creator from his works after years of study. He replied "He has an inordinate fondness for beetles." The reason why becomes clear when you look at the numbers of described species found on our planet. There are roughly 250,000 species of plants that have been formally described compared to 350,000 species of beetle. This number is always growing and many speculate that it could eventually reach over a million species.
So what I began wondering this morning is why. Many disproportionately specious groups have powered flight (the insects when compared to other arthropods are much more specious, the same is true of birds and bats when compared to their closest relatives) but powered flight is a shared characteristic of beetles and other insect groups. So I went searching and found a partial answer on the website of UC Berkley's Museum of Paleontology which focuses on teaching evolution.
It seems that more beetles, compared to their closest relatives, feed on angiosperms (flowering plants). The theory goes that when angiosperms first began evolving more beetles than other insect groups began to use these new organisms as food. When you compare lineages of beetles that feed on angiosperms to their closest relatives that do not you see a clear pattern: the families that feed on angiosperms are much more specious. But again...why?
The answers are still not clear but scientist have put forth at least one good theory. Basically the idea is that the angiosperms are not providing a single new niche but a whole host of them by containing a number of new food sources: root, seed, leaf, fruit, etc. By being the first insects to "colonize" these new niches they were able to undergo an "adaptive radiation" across all available food sources. The theory is similar to the rapid speciation of cichlid fish whose mouth parts evolved rapidly to take advantage of available food in what might otherwise have been a single niche.
Evans, Arthur V. and Charles L. Bellany (1996). An Inordinate Fondness for Beetles. Henry Holt and Company Inc. NY, NY.
Understanding Evolution: http://evolution.berkeley.edu/
Wednesday, January 12, 2011
Tuesday, January 11, 2011
There are just so many reasons cephalopods are amazing. They change color and shape and they were for a very long time one of the oceans' greatest predators. Another really awesome and bizarre thing about them has to do with something called convergence.
In evolutionary biology convergence is when we find two organisms that are not closely related phylogenetically with the same morphology or behavior. One of my favorite examples are icthyosaurs and dolphins. Ichthyosaurs were marine reptiles that lived about the time of the dinosaurs. Here's an image: http://www.google.com/imgres?imgurl=http://www.sedgwickmuseum.org/education/downloads/ichthyosaur.jpg&imgrefurl=http://www.sedgwickmuseum.org/education/gallery.html&h=864&w=1772&sz=220&tbnid=xx1gNAc8VpX3gM:&tbnh=73&tbnw=150&prev=/images%3Fq%3Dichthyosaur&zoom=1&q=ichthyosaur&hl=en&usg=__i4eg6bdQuh8Eq1nGf0n3zTqQyP0=&sa=X&ei=xcIsTY_9LYSs8AbaopGRCQ&ved=0CEQQ9QEwBg
They looked quite a bit like dolphins, or they did as far as we can tell from the fossil record. The reason why? They occupied the same niche, or the same role in the ecosystem. They were fairly large marine predators that ate primarily fish. So the needs and selection pressures that applied to icthyosaurs were more or less the same as they were for dolphins. Same selection pressures, same shape more or less.
So the weird thing about cephalopds is that there are three major ways that they are convergent with us, and vertebrates in general. The first is a closed circulatory system. They have a system of hearts and closed blood vessels. Most invertebrates just have an open body cavity and the oxygen carrying fluid just sort of washes around inside the animal. This change to a closed system may not seem like much but it is much more efficient and has allowed for the evolution of the second convergent feature.
Cephalopods are the most intelligent of invertebrates and likewise they have the largest brain compared to body size. This would not have been possible without the efficiency of a closed circulatory system. And not only does their brain contain a whole lot more neurons than most other invertebrates, it is also arranged into function specific "lobes" just like our brains. (Quick tangent: each of an octopus's arms has its own neurology such that an arm can be doing something productive without the octopus's brain knowing about it. Imagine your hands making a PB+J until suddenly you look down, delighted. Sandwich time! says the brain.)
The final and most complex form of convergence found in cephalopods are their eyes. Vertebrates have extremely complex eyes that allow us to do really cool things like focusing. We probably all take it for granted but most invertebrates see the world only in a blur of grays. For them detecting motion is far more important than what the actual object looks like close up so the need to focus has never really come up. For reasons that are still debated (oh, you scientists, constantly debating) there were selection pressures on cephalopods for them to develop a more complex "camera" eye. Most cephalopods still cannot see color but they have very good vision both close range and long distance. And they are able to focus to work out finer details than most invertebrates.
So the next time someone asks you (and I know they will) why cephalopods are so cool you can confidently answer: cephalopods are just like us! They have a closed circulatory system! How neat is that!?
And, as always, my neurons. Thank you, neurons!
Tuesday, January 4, 2011
After twenty something years of reading about the Pleistocene, the Carboniferous and perhaps the better recognized Jurassic (it's got its own park!) and Triassic I'm finally starting to make sense of it all. The difficulty with remembering the time of these eras and what went on during them is mostly that they deal with time in millions of years which is all but completely baffling to the human brain. We have difficulty making sense of decades sometimes so when you put things in the perspective of geological time it can be really tough to grasp.
But I want to introduce you all to the Cambrian. In my humble opinion this period may win the prize for most interesting geological time (wow, I think I really just out nerded myself) for a couple of reasons. First, this period is where nearly every phylum that exists on earth evolved. We often talk about certain groups of animals being more or less ancient than others but in reality they mostly started here. There are a few exceptions such as jellies and sponges but nearly everyone else originated in the Cambrian. In the early 1900s a fossil bed in Canada now known as the Burgess Shale was discovered that began the study of what we call the "Cambrian Explosion," a huge increase in the amount of large shelled animals.
The other thing about the Cambrian is that the top predators of the time, besides the Terror Shrimp Anomalocaris, were the Ammonites, a group of (you guessed it) cephalopods. These ancient ancestors of squids and octopuses looked a little more like we imagine a mollusk with a spiral shell protecting their soft bodies. Here's an image from wikimedia: http://en.wikipedia.org/wiki/File:Asteroceras_BW.jpg.
Because there were no jawed animals yet, the cephalopods had pretty much free reign over the Cambrian sea food. Yum!
There is still a family of cephalopods today that retains the shell, the Chambered Nautilus, but most other cephalopods have lost their external shell. However both squids and cuttlefish in addition to several other orders of cephalopod such as the spirula have an internal shell.
And of course, the whole cambrian sea was littered with trilobites and opabinia. What a time it must have been to be extant.
I saw that name and...well I just had to share...
Plus it's an ancestor of Limulus, everyone's favorite chelicerate.
What? It's just my favorite chelicerate? Hrmm...
Monday, January 3, 2011
Cephalopods are an order of mollusks containing squids, octopuses, cuttlefish and kin. The name means "head footed" and comes from the fact that these animals have their arms (or feet) near their mouth and eyes (or head).
Besides horseshoe crabs cephalopods are probably the world's coolest animals. I think that's been scientifically documented. Why, you ask? Well, observe:
Both of these octopuses are utilizing (probably the coolest) common feature of cephalopods. They have specialized cells in their skin called chromatophores that allow them to change both the color and texture of their skin. Funny thing is that cephalopods, as far as I know, are all color blind. So how in the heck do they know what colors to change?
Well new research has shown that they actually have opsin in their skin. Opsin is a molecule that resides in our retinas. When light waves strike the molecule it changes shape and this change begins the neural cascade that results in perception. Instead of having their surroundings taken in by the eye, processed by the brain and then translated to their skin cephalopods' skin are taking in the surroundings directly and changing in response.
Stay tuned for more cephalopod posts coming up this month!