Songbird Duets

Are you and your significant other perfectly synchronized to sing in sweet, sweet harmony?  A paper published recently by Eric Fortune and colleagues in the journal Science has shown that couples of one species of songbird called the plain-tailed wren (Pheugopedius euophrys) do just that.  Plain-tailed wrens live in bamboo thickets in the Andes in South America.  In most species of songbirds only the male birds sing and they perform their song to attract females and defend their territory.  What is unique about the plain tailed wrens is that both males and females sing in a duet.  They alternate singing parts (or syllables) of the song so that it sounds like the whole song was produced by only one bird.  This takes remarkable coordination between the male and female birds.  Males and females each produced the same syllables whether singing together or alone but when both partners sang together they adjusted the amount of time between syllables to coordinate with their partner indicating that they were listening to both their own voice and their partner's during singing.  It appears that the females may be largely responsible for keeping the song on track.  Male songs were more variable and sometimes males would stop singing prematurely but the female would continue the song allowing the male to rejoin her.  The researchers recorded the activity of neurons in region of the brain that drives the motor output of the song called HVC.  In most birds this region of the brain will respond to auditory playback only of the song it actually produces.  In duetting wrens, however, the neurons responded best to playback of the duet song in its entirety even though each wren only produces half of the song.  The exact function of the duet is unknown, though it is thought to play a role in territory defense.  Could it be that the females are choosing males based on their ability to listen to and synchronize with her?  Regardless this is an intriguing example in which these birds brains have become adapted not only to produce complicated vocalizations but also to precisely coordinate with a partner.

A shortage of scientists?

I was just listening to the slate political gabfest and they were discussing Florida Governor Rick Scott's comment that he thinks that state funded colleges should shift funds away from degrees like psychology and anthropology and shift funding to subjects such as science and engineering, because there are more job opportunities in those fields.  David Plotz was arguing that maybe we should shift funding for undergraduate education to science since we're talking about allocating taxpayer dollars and we want to have the greatest benefit for society.  There is much to argue about the intrinsic value of a balanced liberal arts education and the depth and creativity that a variety of disciplines contribute to society.  However, I would like to challenge the second half of this assumption.  Are there REALLY more jobs available in science?  Where are they?  Are we really seeing that there are lots of great science jobs and not enough people to fill them?  From where I'm sitting this certainly doesn't appear to be the case.

I would argue that if there is a diminishment of science in this country that it is not a pipeline problem, at least not in biology.  There are 1,000s of scientists called postdoctoral researchers many with  a decade or more of experience toiling away for very little pay just waiting for their potential to be tapped.  Biologists who complete a Ph.D. face stiff competition for only a few academic jobs and the funding to support independent research through the National Institutes of Health and National Science Foundation has been shrinking or holding steady.  This article from Science Insider states that the funding rate for grant proposals will likely fall below 20% in 2011.  These low funding rates have an especially grim impact on young scientists; this is the money that science professors use to fund graduate students and postdocs to work in their lab.  On top of that the few postdocs lucky enough to find a job in academia will have trouble getting their research programs off the ground.  If the United States wants to promote science breakthroughs we need to commit to funding scientific research.

Maybe you would argue that funding academic research is not promoting the kind of science that we want.  There are many arguments for the necessity of basic research; biotech and other companies participating in research that can contribute to human well-being rely on the discoveries made in the course of pursuing of scientific questions that may not initially seem directly applicable.  Aside from this I know many postdoctoral researchers who enjoy benchwork and would be happy to leave academia for a steady paycheck, some choice in their location and to continue doing what they love.  Is there a way the U.S. could invest in creating more jobs for people with Ph.D.s to work on the nation's scientific problems outside of the university system?  I have to say, the way it is now, I would not necessarily suggest that a student pursue science as career unless they were really passionate about it.  I am not arguing that science education is not important but what does it mean to encourage more undergraduates to study science if we as a society are not willing to invest in scientific research for the long term?

Pardon me, are you still using that shell?

One animal that is common in tidepools the world over are hermit crabs.  Peering into a tidepool you might see a snail that appears to be scurrying around sideways and then you'll see the little eyes and legs peeping out.  A hermit crab!  Unlike other crabs, hermit crabs have a soft, curled up abdomen that must be protected and hermit crabs depend on using snail shells as their little house.  Crabs (and all other arthropods) must shed their shell in a process called molting in order to grow and hermit crabs undergo an additional danger because as they grow they need to find new shells.  A hermit crab is always on the lookout for a new and better shell.  What are the chances of finding a shell of exactly the right size?  Since every hermit crab is looking a slightly bigger shell when one hermit crab changes shells then this will vacate a shell that is suitable for another, slightly smaller, hermit crab.  In the wild hermit crabs have been observed participating in an amazing behavior called a vacancy chain in which they will line up in order of size in order to take advantage of a new shell.  How does this come about?  For one thing the smell of dead or dying snails or other hermit crabs have been shown to attract hermit crabs resulting in several hermit crabs congregating and competing for new shells.  Hermit crabs will fight for shells by pushing each other with their claws.  Rotjan et al. (2010) reported in Behavioral Ecology that when hermit crabs are living in high density they will exhibit several interesting behaviors that lead to the establishment of a line organized by size to facilitate an orderly change into new shells.  For example a hermit crab that encounters a shell that is too large for it to inhabit comfortably will wait within the area of that shell for up to an hour.  This behavior increases the chances that other hermit crabs will show up allowing the waiting hermit crab to acquire a shell of the appropriate size.  In addition, in the presence of a large shell multiple hermit crabs will participate in a behavior called "piggybacking."  A crab will grab onto the back of crab slightly larger than itself.  Once a crab large enough take advantage of the new shell arrives then the hermit crabs form a line in order of size.  When the largest crab moves into the new shell then the next largest crab moves into the now vacant shell and so on down the line until the very smallest shell is left behind.  I find this to be a fascinating and surprisingly efficient way for everyone to get a new, bigger house!

Tidepools!

Last week I participated in Marine Biology camp for high school students in Bodega Bay California.  Students collected animals from the tidepools and mudflats, took them back to the lab to observe them and then designed and conducted their own experiments.  It's so fun to get the chance to approach science again from this basic level of fascination and curiosity which is what drove me to study biology in the first place.  Some of my earliest memories are of exploring the tidepools of Islesboro, Maine finding muscles, barnacles, green sea urchins, brittle stars and crabs.  I would collect shells and seaglass which seemed like mysterious gifts from an unknown world.

Rocky Intertidal habitat in Big Sur, California.  Picture by Vanessa Miller-Sims

Tidepools are special place at the interface of land and sea and the organisms that live there must deal with living in an ephemeral habitat that is constantly changing in both time and space.  The intertidal zone is defined is the area that is out of the water at low tide but completely covered at high tide. Organisms living in this environment are exposed to wave action, changes in temperature and salinity, exposure to air and sun in addition to competition for space with other organisms and predation.  The intertidal is divided into zones depending on how much of the time the organisms that live there are submerged.  Organisms that live in the highest part of the intertidal zone are submerged for the least amount of time and must have adaptations to avoid drying out while the lowest part of the intertidal is submerged most of the time and thus provides the most stable habitat.

Barnacles in Garrapata State Park in Big Sur.  Picture by Vanessa Miller-Sims

These barnacles are not covered by water and as you can see they are closed fast to keep them from drying out.  When the tide rises and they are once again covered they will open up and feed on small particles suspended in the water.

Big Sur Tidepool. Picture by Vanessa Miller-Sims

A look into a submerged tidepool shows anemones snails and coralline algae.

A good read for lovers of Monterey Bay

I just finished reading a book called The Death and Life of Monterey Bay A Story of Revival by Stephen R. Palumbi and Carolyn Sotka.  It was a fun, interesting and quick read that I would definitely recommend to anyone who has visited and been enchanted by Monterey Bay or who is interested in marine conservation.  The first time I visited Monterey and Pacific Grove I immediately experienced it as a magical place full of history as a seaside fishing town and replete with natural beauty and sea critters.  The Monterey Bay Aquarium does an amazing job of showcasing the diverse and plentiful marine life of Monterey Bay and I love gazing out watching the sea otters float on their backs in the kelp.  The aquarium is built within an old cannery building on Cannery Row and I had known that the canneries once fished almost unfathomable numbers of sardines out of the bay before the fishery collapsed.  However, before reading this book I had not fully understood the extent of the environmental devastation that Monterey Bay had endured.  During the course of the 19th and first half of the 20th century the bay's resources were exploited one by one.  First the otters were hunted to the brink of extinction (and were in fact thought to be completely extinct), followed by California gray whales and abalone.  By the time the canneries started up the bay was already a greatly changed place.  The canneries not only fished out the sardines but also released large amounts of pollution into the bay and apparently the rocky shore was covered in rotting fish and flies.  Today Monterey Bay is an uplifting testament to the fact nature can regain a foothold when we leave a place alone and implement smart management.  The biggest change to Monterey Bay has been the return of the sea otters which have allowed kelp forests to flourish by keeping herbivorous sea urchin and abalone at bay.  The kelp in turn provides habitat for numerous fish species and allows a whole ecosystem to flourish.  The book tells the story of the rise and fall of Monterey Bay and the characters that have inhabited its shores over the course of the last 200 years.  

Keep those mozzies (mosquitoes) away!

Mosquitoes are a fact of life in the summertime but have you ever wondered how they track us down so quickly?  We've all had the experience where we're enjoying a nice summertime picnic and as soon as dusk arrives the mosquitoes show up one by one and start attacking.  How do they find us so quickly?  Mosquitoes are attracted to carbon dioxide, which seems a little unfair.  We release carbon dioxide every time we breathe out and to be even more tricky mosquitoes are specifically attracted to intermittent pulses of carbon dioxide.  Mosquitoes can follow carbon dioxide odor upstream to it's source (us).  This is always particularly clear to me when I am camping and I wake up in the morning to see both the condensation on the tent surfaced caused by my breath and the mosquitoes longingly pressed up against the screen of the tent.

Picture by JJ Harrison found on Wikipedia.org

Mosquitoes and other animals (including us) perceive a smell when small molecules in the air bind to a receptor and activate an olfactory neuron which then passes the message on to the brain.  Mosquitoes and other bugs have these receptors on an antennule on their head.  Receptors bind molecules based on their shape and chemical composition.  Most receptors are not perfect if a molecule is similar in shape to the intended molecule or present in a high concentration then it too will bind to the receptor.  A recent paper published in Nature (474:87-91) looked for molecules that would bind to the mosquito carbon dioxide receptor thus confusing the mosquito and limiting its ability to find us.  The scientists recorded the activity of the carbon dioxide receptor neuron and found one compound which activated the receptor for an unusually long period of time.  Such strong long-term activation of the carbon dioxide receptor could disable the response olfactory receptor neuron to carbon dioxide and should limit the mosquitoes' ability to track the carbon dioxide odor.  This is in fact what the researchers found; mosquitoes were placed in a wind tunnel with carbon dioxide being released from an air cylinder.  Fewer of the mosquitoes that were treated with molecule that activated the carbon dioxide receptor were able to find the carbon dioxide source and those that did took longer.  We can't stop breathing so it's a relief by blocking the ability of mosquitoes to detect and track carbon dioxide we may be able to hide our distinctive long range scent.

Stickleback Evolution

Sticklebacks are an excellent species for studying how populations adapt to their local environment through natural selection because nature has done an experiment for us.  The oldest (ancestral) population of sticklebacks is a marine form that spends most of its life in the sea and returns to freshwater to breed.  Just over 10,000 years ago much of North America was covered with ice and as this ice receded lakes were formed.  At that time different populations of marine sticklebacks found their way to and colonized freshwater lakes, these populations underwent rapid adaptation to the freshwater environment.  For example fish in freshwater lakes tended to lose the spines on their pelvis and the armor plates usually found in marine fish.  This resulted in fish from freshwater populations looking remarkably similar to each other even though each population is more closely related to the marine population than to each other.  This phenomenon of populations that live in similar environments developing similar morphological (body shape and structure) characteristics is called parallel evolution. 

Natural selection works because individuals that are better adapted to their habitat live longer and have more offspring than those that are poorly adapted.  However, in order for natural selection to act there must be variation in the natural population.  Where do the morphological characteristics seen in the freshwater populations come from?  The body plan of every organism is encoded in its DNA; genes are regions of the DNA that encode proteins.  Every aspect of an organism's anatomy, physiology and behavior is dependent on the structure of these proteins and where and when they are expressed.   Variation could result from differences in the DNA sequence of a gene itself which would alter the structure of the protein.  However changing the structure of a protein is likely to diminish or even inactivate its function.  Most proteins (and thus genes) act in many different parts of the body and at different times; changes that broadly disrupt protein function are likely to do more harm than good.  On the other hand changes in the regulatory regions of DNA control where, when and how much of a protein is expressed will result in smaller, more targeted changes.  Differences in these regulatory parts of the genome may have the specific types of effects that we see in stickleback populations and allow for rapid adaptation.  This is exactly what researchers in Dr. David Kingsley's lab at Stanford University have found.  They were able to locate specific genes that account for morphological differences between populations however in each case genetic differences were found not in the gene region that determines the structure of the protein but rather in regulatory regions that control when and where the gene is expressed.  This is an exciting result that shows that variation in a single region of DNA can have a big effect on the morphology of a particular body part without causing overall deleterious effects.  This type of genetic variation would allow for the rapid adaption to new environments seen in stickleback populations and could eventually lead to the creation of new species.

Isolation and Adaptation

Biologists agree that the huge diversity of species seen on earth have evolved from a common ancestor through the process of natural selection.  However the details of how this occurs have been hotly debated.  How do populations of organisms adapt to their local environment?  How are new species formed?  One theory called gradualism (which was the mechanism initially proposed by Darwin) suggests that adaptive changes occur in incremental steps.  So for example, if a bird had a short beak which was well adapted to environment A and some individuals from that population suddenly found themselves in environment B (lets just say that it is and island and there no subsequent contact between the two populations) and environment B favors individuals with long beaks then there will be natural variation of beak length within the population and those individuals with longer beaks will survive better and produce more offspring.  Over many generations mean beak length will become longer and longer until eventually population B have longer beaks than population A.  Such differences between populations could be modulated by relatively small changes in a large number of genes.  One question is whether adaptive changes can also occur on a more rapid timescale.  Examination of the fossil record indicates that in many cases a species changes very little over time and speciation events are relatively rapid (on a geological time scale) leading to an idea called punctuated equilibrium.  One question is whether traits instead of shifting gradually through intermediate stages can be changed directly from one state to another.  Using the previous example immediately after the birds from environment A colonized environment B the vast majority of birds would have relatively short beaks but a few individuals would have substantially longer beaks creating a bimodal distribution of beak size.  The longer beaked individuals would survive better and produce more offspring and over time the majority of individuals in population B would have long beaks.  In this case beak length would likely be controlled by a small number genes such that changing the regulation of one or a few genes would result in large changes in the size of the beak. 

Stickleback fish have provided a great natural experiment for studying evolutionary mechanisms.  The marine form of sticklebacks have invaded many North American lakes in separate colonization events.  Once a stickleback population becomes established in the lake environment several adaptions occur including a loss of armor plates and reduction of the pelvis.  Comparing marine and freshwater populations has allowed evolutionary biologists to observe how these fish adapt to their new environment and in some cases discover the underlying genetic mechanisms.

Tomorrow: What do sticklebacks have to tell us about the mechanisms of adaptive change?

Threespine stickleback (Gasterosteus aculeatus)