Friday, August 24, 2012

Accessible Research: Hummingbirds!

One of my favorite parts of being in Berkeley is listening for, and trying to catch a glimpse of hummingbirds. The ones near our apartment have a beautiful twitter/tweet that is very distinct, but finding where it is coming from can sometimes be challenging.

I recently had the fortune to come upon a hummingbird catching a snack:

Hummingbird eating (middle of the picture). Berkeley, CA. Aug 2012.
This second picture is so neat to me, because it was taken at just the right time so you can see the wings in motion.
Hummingbird in flight (middle of the picture). Berkeley, CA. Aug 2012.

I've been studying genome sequences, and I thought, surely, by now, there must be a hummingbird genome sequence. Well, there may be one in the works, but the closest I could find was a paper from 2009, and so I figured I could sum it up here for you all

There are many reasons why it would be useful to be able to study hummingbird genomes including their amazing evolutionary adaptations for hover flight, and, it's just awesome that they are just so very small, and have super teeny-tiny eggs, for a bird:

Elephant bird, ostrich, and hummingbird eggs by Frans Lanting.

So, here is your brain tidbit for tonight:

The smallest avian genomes are found in hummingbirds


Hummingbird hover flight is thought to take up a lot of energy. Cells that are smaller tend to be more efficient at exchanging gas. And, smaller cells are correlated with smaller genome sizes. So, it was thought that hummingbirds should have smaller cells, and also smaller genomes relative to other birds.

One can measure the size of a genome using... okay, I try to avoid technical jargon here, but I just have to tell you. The name of the technique is: Feulgen image analysis densitometry. Whoa! Please read the link if you want more details, but the quick and dirty is that this method uses a dye to color the nucleus (where the DNA resides) of the cells of the species you are interested in, and then compares the size and density to the size and density of the nucleus of a species with a known genome size. For example, say you come to me with 100 silver coins, and want to know much silver is in each coin, but didn't have the money/time/experience/ability to analyze each coin and figure out exactly how much silver is in it. I could take a silver coin from my pocket, one that I know how much silver is in it, and use that as a standard for comparison. For each of your coins, I can estimate approximately how much silver is in it, by determining how much larger or smaller that coin is relative to my coin. (Note, the coin example doesn't take into account density, but hey, if it were a perfect analogy, it wouldn't be an analogy.)

The researchers measured the genome sizes of 37 (THIRTY-SEVEN!) hummingbird species, and observed that the size of hummingbird genomes is, indeed, reduced relative to chicken. They also conclude that this reduction happened in the common ancestor of all hummingbirds, which might indicate that the common ancestor also had high metabolic function, and perhaps was also small. Cool. They also found that four tropical hummingbirds did not have smaller genome sizes, and think that this might be due to the particular environments they live in.

So, it seems that constantly spending a lot of energy might lead to having smaller cells and, consequently, smaller genomes. It will be great to have a hummingbird genome someday to figure out which parts of the genome are different (and which might have been lost) relative to other, larger birds.

And, because it's just fun, I want to end by sharing that the authors mention, hummingbirds have the largest relative heart and lung volumes of any vertebrates, not just birds (Suarez et al. 1991Suarez 1992). Awesome!

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