Wednesday, May 29, 2013

What Has No Legs And The Most Amazing Feet Ever?

This starfish photo is by Mike Murphy at Wikimedia.
We often think of echinoderms, like starfish, sand dollars, and sea urchins, as static ocean decorations. But if you watch them for long enough (or on fast-forward if you lack the patience) you will find that they have exciting motile lives. They hunt, they flee predators, and they mate. But how do they get around without any legs to stand on? Their secret is tube feet.

If you look at the underbelly of these critters, you will see lots and lots of little tubes with suction cups on the ends. These are the tube feet. Tube feet work through hydraulic pressure, the pressure created when incompressible fluids are pushed around. Tube feet extend when a muscular bulb at the top of the foot (called an ampulla) contracts, forcing water down the length of the tube. As the tube foot extends, it swings like a pendulum and then lands and plants itself on the surface. If the surface is smooth, muscles can contract causing the cup-shaped tip to form a vacuum, sticking the foot to the surface. When the ampulla relaxes, the tube foot retracts. To get around, the animal contracts and releases these ampullae in waves, causing the tube feet to extend and retract in a coordinated way that moves the animal in a particular direction (albeit very slowly). They can also use their tube feet in a coordinated way to manipulate objects, like food items.

If you take a close look at this Pycnopodia helianthoides, you can
see the structure of its tube feet. Photo by Stickpen at Wikimedia.

But tube feet aren’t just for movement! They can also be used for breathing, smelling, tasting, and even seeing! These abilities relate to the structure of the membrane in the tube feet. Echinoderms are slow moving and have a low metabolism, so they can get away with taking in oxygen and expelling carbon dioxide at low rates. The membranes in the tube feet are permeable to both of these gasses, and thus play an important role in respiration in these species. Additionally, tube feet often have chemoreceptors (receptors sensitive to smell and taste chemicals) and photoreceptors (receptors sensitive to light). It is largely through their tube feet that echinoderms perceive their world.

Echinoderm tube feet are far simpler than our own feet, with fewer muscles, no bones, and no toenails to trim. Yet their feet can look out for predator shadows, grab and taste prey and walk up walls. Sometimes, simplicity is just cooler than complexity.

Want to know more? Check these out:

1. Lesser, M., Carleton, K., Bottger, S., Barry, T., & Walker, C. (2011). Sea urchin tube feet are photosensory organs that express a rhabdomeric-like opsin and PAX6 Proceedings of the Royal Society B: Biological Sciences, 278 (1723), 3371-3379 DOI: 10.1098/rspb.2011.0336

2. Santos, R. (2005). Adhesion of echinoderm tube feet to rough surfaces Journal of Experimental Biology, 208 (13), 2555-2567 DOI: 10.1242/jeb.01683

Wednesday, May 22, 2013

Check Out My New Team-Blog, Accumulating Glitches!

I have some exciting news to share: Today is the launch day for Accumulating Glitches, a blog I am co-authoring with Sedeer el-Showk! Accumulating Glitches is one of many new science blogs launching this week at Scitable (by Nature Education), and I encourage you to check them out. (A summary of them can be found here).

In celebration of today's launch, I am sharing part of Sedeer's debut post, Do Species Really Exist?

Although these two may look like different species,
science says they are both Eclectus parrots...
But how do we determine which animals are the
same species and which are different species?
Photo by Doug Janson at Wikimedia Commons.
Faced with the rich diversity of living beings around us, humans have proven unable to resist the temptation to try to organize and categorize them. We have a natural tendency to classify things, a habit that's deeply rooted in our cognition and use of language. Our brain excels at recognizing patterns (and thus finding meaning where it doesn't exist), an ability that allows us to interact with the world using names — like "chair" — that we might be hard-pressed to properly explain. In fact, it's surprisingly difficult to define even a seemingly straightforward word like "chair" in a way that would let us recognize everything that should be included (from office chairs and recliners to stools and wheelchairs) but nothing that shouldn't (like tables, tree stumps, or other things we might decide to sit on).

Despite these difficulties, we've been classifying organisms throughout the history of human thought, from Aristotle's division between plants and animals to modern scientific nomenclature. The modern classification system is based on grouping organisms into units called 'species'; species, in turn, group together into a larger units called genus, family, order, and so on through the nested hierarchy of life. What make a species, though? Why should a particular group of organisms be thought of as a unit and given a distinct name? How do we decide which organisms make up a species?

To ponder these questions, read the rest of Sedeer's article!

Wednesday, May 15, 2013

Male Black Widows Sniff Out Femme Fatales

I am thrilled to announce that this month I am joining a new top-notch science blogging team at Scitable, Nature Education’s award-winning science education website! (But don’t worry, friends. I will continue to post here about animal physiology and behavior every Wednesday). Next week, Scitable will be launching eleven new blogs covering topics like neuroscience, genetics, oceanography, physics and more. I will be co-authoring an evolution blog called Accumulating Glitches together with Sedeer el-Showk (the author of the fantastic nature blog Inspiring Science). To celebrate the launch of these new science blogs, many of us are writing guest posts at Student Voices, another Scitable blog. What follows is the start of my guest post:

A female western black widow contemplates the tastiness
of her suitor. Photo by Davefoc at Wikimedia Commons.

Sexual reproduction is a costly affair, but the costs are not usually equal for males and females. Among animals, females generally produce larger gametes (eggs are way bigger than sperm), spend more energy gestating or incubating the young before they are born, and spend more effort caring for the young after they are born. It’s no wonder then that across animal species, females are typically more choosy of who they mate with than males are.

But what if the tables are turned and sex is more costly for males than it is for females? Such is often the case for black widow spiders, named for the females’ infamous reputation for making a post-coital snack of their mates. In such a situation where every sexual encounter is potentially the last, who would blame males for being more choosy of their mating partners? But are they?

To find out, read the rest of the post here!

And to find out more, check this out:

Johnson, J., Trubl, P., Blackmore, V., & Miles, L. (2011). Male black widows court well-fed females more than starved females: silken cues indicate sexual cannibalism risk Animal Behaviour, 82 (2), 383-390 DOI: 10.1016/j.anbehav.2011.05.018

Wednesday, May 8, 2013

Thanks Mom!

Like Mother, like baby!
Photo from
Moms give us so much more than we ever give them credit for. Biologically speaking, we all have a mom and a dad (unless you’re a flatworm or some other species that can reproduce without sex) that provide us with one of each chromosome type (our chromosomes contain our genes, commonly thought of as our “biological blueprints”). So it makes sense that we tend to think of ourselves as being half-our-mom and half-our-dad. But not so! All of us are slightly more-our-mom and slightly less-our dad.

Our genes are encoded in our DNA, which is coiled and tightly packed into dense little chromosomes. Most of our cells contain 23 different pairs of chromosomes (for a total of 46), and one from each pair comes from each parent. One of those pairs is the sex chromosomes. Individuals with two X sex chromosomes are genetically females and individuals with an X and a Y sex chromosome are genetically male. Because genetic males are the only ones with Y chromosomes, all Y chromosomes are inherited from dad. But compared to X chromosomes, Y chromosomes are piddly little things that don’t contain as many genes. So if you’re a guy, you already have more genes from mom than from dad.

In addition to our 46 chromosomes that we keep in the nucleus of each cell, we also have a tiny set of genes in another cell structure, the mitochondria. This mitochondrial DNA is only inherited from the mother, so regardless of whether you are XX or XY, you have a few more genes from mom than from dad.

Wait! My genes are where??
Your genes are lined up on the doubled-stranded DNA, which is tightly coiled and packed into
chromosomes. You have 23 different pairs of chromosomes, where one of each pair came from
mom and the other came from dad. A copy of each of these 23 pairs of chromosomes
(46 chromosomes in total) is in the nucleus of every cell you have (except for sperm or egg cells,
which only have one of each pair, or 23 chromosomes in total). Get it?
Figure adapted from an image by KES47 at Wikimedia.

But we are not simply a product of our genes. If we were, identical twins would be, well… identical. But they’re not. The slight differences between twins results from differences in how our environment interacts with our genes. (By environment, I’m not just talking about temperature and air quality, but rather all external influences). Our environment plays a big role in shaping the individuals we become, and our mothers have more effect on our environment than our fathers do. When we are developing in the womb, our moms’ bodies single-handedly provide us with nutrients, hormones, and antibodies (and sometimes pathogens). During this time, her circumstances and decisions will determine what kind of setting we are born into. After we’re born, the social interaction, nutrition, and antibodies (through breast feeding and/or vaccines) she provides will all influence our gene activity and thus how we develop. Collectively, the traits that we develop due to these factors and all mom’s other nongenetic influences are called maternal effects.

Mom gives us more genes, and has more input in determining how active each gene is. In the end, we are who we are in large part because of our moms.

So Mom, this is for you:

Happy (early) Mother’s Day!

Want to know more? Check these out:

1. BERNARDO, J. (1996). Maternal Effects in Animal Ecology Integrative and Comparative Biology, 36 (2), 83-105 DOI: 10.1093/icb/36.2.83

2. Wolf, J., & Wade, M.J. (2009). What are maternal effects (and what are they not)? Phil. Trans. R. Soc. B, 364, 1107-1115

Wednesday, May 1, 2013

The Craptastic Conversations of the Black Rhinoceros

What are you saying with your smells? Image by
Animals communicate in all kinds of ways: with vocalizations, body language, vibrations, and even odors. In fact, compared to most species, we are pathetic in our abilities to communicate with body odor. With just a whiff of eau de crotch, many animals can decipher that individual’s species, sex, age, health status, reproductive status, emotional state, and dietary history. Some species can go so far as to make out that individual’s exact identity (*Sniff Sniff* Oh! Hi Mike!).

There are a lot of advantages to using odors to communicate. For one thing, messages sent by smell are more likely to be honest than messages sent by other means. (You might be able to do a pretty good Shakira impersonation, but you can’t hide the fact that you had a tuna sandwich for lunch and haven’t brushed your teeth since). Another advantage is that unlike other signal types, an odor signal can be left behind, kind of like those sticky-notes you leave on your food in the fridge.

How do scientists know which species use odors to communicate and what information these signals contain? This investigatory process involves a lot of reasoning.

A solitary black rhino. Photo by John and Karen Hollingsworth
at the US Fish and Wildlife Service.
Wayne Linklater, Katha Mayer and Ron Swaisgood, an international team of researchers associated with Victoria University of Wellington in New Zealand, Nelson Mandela Metropolitan University in South Africa, University of Potsdam in Germany, and the San Diego Zoo Institute for Conservation Research in California, set out to test whether black rhinoceros use odor to communicate. Although rhinos lack the specialized scent glands that many smell-communicating species have, there are many reasons to suggest that they are a likely species to communicate this way.

A photo of field assistant Brayden
Crocker with rhino dung scrape mark.
Photo by Wayne Linklater.
Black rhinos are solitary. Females often have overlapping ranges, but males’ territories only overlap at their boundaries. This means that they would rarely encounter one another and would benefit from a means to leave “sticky-notes” behind to indicate where their territories are. Furthermore, despite their poor eyesight, male black rhinos have a poop-ritual in which they scrape at the ground and spread their dung. Although female rhinos don’t spread their poo, they do spray their pee when they are ready to mate.

Between 2004 and 2006, the Ezemvelo KwaZulu-Natal Wildlife Veterinary and Game-Capture Team captured a number of black rhinoceros from the Ezemvelo KwaZulu-Natal Wildlife Reserves in South Africa in order to relocate them to other reserves for conservation purposes. At this time, Wayne, Katha, and Ron collected dung from rhinos with known sexes and ages. They stored the dung in labeled plastic bags and froze them to preserve the odor freshness for a series of experiments to explore the extent of the black rhinos’ abilities to communicate with their bodily waste.

In one experiment, the researchers asked whether black rhinos could differentiate between the dung of males and females and between the dung of adults and immature subadults. They presented rhinos with the dung of young males, young females, adult males and adult females, and then measured how many times they sniffed each and how long they spent sniffing. The rhinos spent more time sniffing male dung than female dung. This means that rhino poop likely communicates the sex of the pooper. Rhinos also responded differently to adult and subadult poop, suggesting that they can tell whether the pooper is an adult or not.

In order to test whether rhinos may be able to tell the individual identity of the pooper, they did a habituation-dishabituation test. Habituation is when an animal gets used to something that happens repeatedly and stops responding to it. For example, the first time you heard Gangnam Style, you probably stopped what you were doing and maybe even learned the dance. But now it has been so ridiculously over-played that when you hear it, you just ignore it. Dishabituation happens when an animal is exposed to something slightly different and has a heightened response again. Kind of like the excitement over Psy’s new song, Gentleman, even though it sucks.

A photo of rhino performing flehmen, a behavior that helps
waft odors for better odor detection. Photo by Wayne Linklater.
Wayne, Katha, and Ron exposed rhinos to the same individual’s dung three times to see if their interest in it waned. With each presentation, the rhinos spent a little less time sniffing it. When the researchers put poop from a different rhino (that was the same sex and age as the first pooper) in front of them, their interest returned. This suggests that rhinos can tell the individual identity of the pooper from his/her poop.

But can rhinos use their poop like “sticky-notes”? The researchers aged dung for 1, 4, 16 and 32 days and put them in front of rhinos to smell. Their response was the same, no matter how old the dung was. This indicates that rhinos can spread their poop to leave an “I was here” message for at least a month.

As fun as it may be to spend years studying rhinoceros poop, there are some important uses for research like this. Black rhinos are critically endangered, largely due to hunting, poaching and habitat loss. In fact, Mozambique's Limpopo National Park declared the last of their rhino population killed as recently as last month. Conservation efforts such as captive breeding programs and reintroductions have helped in several areas, but have not been enough to sustain the populations. Conservationists could apply this knowledge of how rhinoceros use dung odors to communicate to these breeding and reintroduction efforts in order to make them considerably more successful.

Want to know more? Check this out:

Linklater, W., Mayer, K., & Swaisgood, R. (2013). Chemical signals of age, sex and identity in black rhinoceros Animal Behaviour, 85 (3), 671-677 DOI: 10.1016/j.anbehav.2012.12.034