Systematic Penguin Evolution

Posted on December 7, 2015 by Kevin Tran Lu

Contributed by: Oceana Hopkins, Arooj Khalid, Kevin Lu

The core idea of modern evolutionary theory is that all life is descended from a common ancestor. Though the theory garners much scrutiny and skepticism, it can be explained in part through the simple mechanism of natural selection. Natural selection takes advantage of the variability that exists within the genome. Random mutations that occur in the genome are behind these variations and sometimes change the fitness of an organism. Natural selection dictates that those with higher fitness survive and reproduce; thus, certain traits are selected for within the species. This process explains how gradual change occurs and how complex organisms arise from simplistic ancestors. A common misconception regarding evolution is that life evolved randomly, or by chance. This misconception could arise because of the random nature of mutations that promote variability. Though randomness is an important component to evolutionary theory, natural selection and survival of those who are more biologically fit make sure that the process is non-random.

Known for their characteristic black and white “tuxedos”, penguins are an aquatic, flightless bird found in both warm and cold climates. Because such a large part of their lives are spent in the water, certain species of penguins will only exit the water to shed their feathers or to mate. Spending nearly 75% of their lives in the water foraging for food, penguins have developed very specific traits optimized for swimming. Utilizing their strong forelimbs to propel their large bodies through the water, penguins have undergone very specific evolutionary changes that allow this mechanism to run smoothly. As discussed in Michael Habib’s paper on structural evolution, the strength of the bones in the forelimbs are significantly greater than that of birds who do not exhibit aqua-flying behavior (2009). In conjunction with increased bone density, more muscle mass also developed and aided in keeping the penguins warm in their cold feeding environment.

Closer inspection of the features that aid water-feeding behavior provides more evidence that disputes the misconception that evolution is random. As seen in 2006 by Slack and colleagues, macroevolution within penguins based on their fossils and mitochondrial genes was tracked and recorded. The evidence showed that the penguins’ bodies gradually adapted to the cold feeding environment over many generations. Additionally, researchers Thomas and colleagues observed in 2010 that cold water penguins have a flow of heat along their wings that originates from the brachial artery called the humeral plexus. This vascular countercurrent heat exchanger (CCHE) provides penguins the opportunity to forage in cold water by limiting heat loss through the flippers. Scientists identified this adaptation through fossil evidence and, upon further research, learned it evolved after penguins lost the ability of aerial flight. Researchers have proposed the CCHE evolved to help balance the energy costs of longer foraging times, since the oceans were significantly cooler than penguin body temperature. Ultimately, researchers have concluded that the humeral plexus was instrumental in allowing penguins to be water feeders in subaquatic environments.

To learn more:

Clarke, J. A., D. T. Ksepka, R. Salas-Gismondi, A. J. Altamirano, M. D. Shawkey, L. D’alba, J. Vinther, T. J. Devries, and P. Baby. “Fossil Evidence for Evolution of the Shape and Color of Penguin Feathers.”Science 330 (2010): 954-57. Print

Fordyce, R. E. and Jones, C. M. 1990. The history of penguins, and new fossil penguin material from New Zealand. Pages 419-446 in Davis, L. S. and Darby, J. D. (editors), Penguin biology. Academic Press, San Diego. 467 p.

Habib, Michael. “The Structural Mechanics And Evolution Of Aquaflying Birds.” Biological Journal of the Linnean Society 99 (2009): 687-98. Print.

Stack, Kerryn E., Craig M. Jones, Tatsuro Ando, G. L. Harrison, R. Ewan Fordyce, Ulfur Arnason, and David Penny. “Molecular Biology and Evolution.” Early Penguin Fossils, Plus Mitochondrial Genomes, Calibrate Avian Evolution. Oxford Journals, Mar. 2006. Web. 13 Nov. 2015.

Subramanian S, Beans-Pico´n G, Swaminathan SK, Millar CD, Lambert DM. 2013 Evidence for a recent origin of penguins. Biol Lett 9: 20130748. http://dx.doi.org/10.1098/rsbl.2013.0748.

Thomas, D. B., D. T. Ksepka, and R. E. Fordyce. “Penguin Heat-retention Structures Evolved in a Greenhouse Earth.” Biology Letters 7 (2010): 461-64. Print.

Out of Africa

Gallery

Posted on May 7, 2014 by Ruthe Alemu Terfie

This gallery contains 2 photos.

Contributed by Ruthe Terfie Have you ever wondered where modern humans originated? Well, if you have, you’re not alone. Many scholars in the past, and even the present, have asked the same question and debated many hypotheses. The universally accepted … Continue reading →

The Evolution of Bitter Taste

Posted on May 1, 2014 by Robert Christopher Bruner

Contributed by Jonathan Adcock, Hana Ahmed, Robert Bruner, Farhan Momin, Andrew Shibata

How Bitter Taste Works

Specialized bitter taste receptors are concentrated at the back of the tongue. Upon eating a bitter food, these receptors are activated, and and a signal is sent to to the brain that leads to the perception of a bitter taste. Bitter taste receptors are encoded by the TAS2R gene family. This family includes nearly 25 genes and psuedogenes (genes that are no longer functioning) that are concentrated in bundles on chromosomes 3, 5, and 7. Extensive studies have been performed in order to determine which molecules in bitter foods can activate these receptors. Scientists have found that many of the compounds that activate the bitter taste receptors are chemicals produced by plants. Many of these compounds were also found to be toxic and if consumed could lead to illness or death.

How Bitter Taste Evolved

Our ancestors and other animals have not always been able to taste bitter foods. The bitterness sensation is thought to have evolved 200 million years ago. The prevalent hypothesis is that bitter taste evolved by random gene mutation events which caused the formation of the TAS2R gene family and the bitter taste receptors on the tongue that could bind to toxic chemicals. Animals possessing these mutations were able to taste toxins in their food. These toxins would have tasted bad to the animal, and thus, the animal would learn to avoid the toxic food in the future. Animals with the mutations that produce the TAS2R gene family would be be better adapted to their environment because they can avoid toxic and poisonous foods that could cause sickness or death in the animal. Animals not possessing these mutations would still be susceptible to ingesting naturally occurring poisonous chemicals. Because these animals have improved survivability in comparison to other animals without the TAS2R genes, animals that could taste bitter foods would be better able to reproduce and pass the functional TAS2R genes to their offspring, who in turn would have increased survivability, be better able to reproduce and pas the TAS2R genes to their offspring. Organisms possessing the TAS2R genes have a higher fitness than organisms that do not posses this gene family. Thus, the TAS2R gene family would have been selected for via natural selection and became the ability to taste bitter foods would have become dominant in the population.

This is especially true in the case of the thyroid-inhibiting toxin, PTC. PTC is known to decrease thyroid hormone, which regulates metabolic function. PTC can also lead to liver damage and a host of other medical problems that would eventually lead to death. Being able to taste the PTC toxin would have allowed our ancestors to to avoid toxic foods that if ingested would ultimately lead to their death. Because of this, the ability to taste the PTC toxin would be passed on to the next generation and contribute to the increased fitness of the following generation. In this way, the bitter taste genes would become selected for and would become prevalent in the population.

How the Evolution of Bitter Taste Affects Me Today

Although variation in taste facilitated the evolution of primates and other animals, in modern human society it can be detrimental. With the advent of agriculture, there is less need for tasting of bitter food. Highly nutritious vegetables are known to activate the bitter taste receptors. Instead of doing their intended evolutionary job of protecting from toxic materials, the bitter taste receptors are preventing some people from getting an adequate daily amount of nutritious vegetables due to their aversive taste.

Additionally, some individuals have extremely high sensitivity to bitter tastes resulting from higher rates of expression of the TAS2R gene. These individuals are known as “supertasters”. Supertasters can be found in the highest frequency in parts of Asia, Africa, and South America. This may be because these areas originally possessed a higher concentration of toxic plants and animals in comparison to other areas. In order to compensate for the increase in potential toxins, the individuals living in this area might have benefited more from bitter taste receptors. Today, many supertasters dislike a wide variety of vegetables such as cabbage and soy, and favor sweet items over bitter vegetables. This not only leads to increased chance of obesity and diabetes, but because of the avoidance of vegetables there is increased risk for GI diseases such as colon cancer. Not all side effects are bad though. Supertasters have a higher dislike for alcohol, carbonated beverages, and smoking. Avoidance of these items is actually quite beneficial in boosting heath.

Next time you don’t feel like eating your vegetables, you can blame it on evolution!

The Plight of the Gummy Bears

Posted on April 30, 2014 by Joshua Lee

by Adrian Kinkead, Taara Rangan, Tiffany Liao, and Joshua Lee

The Basics of Gummy Bear Selection

Natural selection is a force that acts upon life on Earth, and works in tandem with evolution to produce fitter populations in a given environment. We often think of evolution as a linear phenomenon, but it is more accurate to think of it as a branching tree of trial and error. The idea that a structured process of adaptation is appealing to us; it imposes an attractive order on the natural world. But the challenges of survival are also arbitrary, meaning the strongest and the fastest don’t always have the advantage in the face of a novel threat.

Imagine a population of gummy bears, living together on their red planet.

Against this red background, the red bears are not easily seen to the eyes of the predators, but the other bears are not so lucky. Even though the red bears aren’t stronger, smarter, or faster than the others, selective pressures are random, meaning those attributes aren’t always relevant. It would follow that the majority of bears who were able to survive predation would be red.

However, life is always changing. Imagine that this red planet suddenly turned green as a forest sprang up overnight. Now, the red bears are very visible to predators. Shown no mercy, the red bear population would be easily reduced, while the green bears (who had clashed with the surface of their red planet) could blend instead.

It is easy to see natural selection as this locomotor that operates outside of the human world, but we are just as malleable to natural selection as any other species on Earth. For example, researchers at the Research Center for High Altitude Medicine found that Tibetans carry a mutation that allows them to thrive in elevations that would be burdensome on humans of other populations. When foreigners visit the summit of Mt. Everest, they must pace their elevation to allow for their blood cell count to increase in order to make up for the lower oxygen availability at that elevation. However, the observed blood cell count in Sherpas and the Tibetans remained at a baseline level. Furthermore, the study revealed that no difference in tissue oxygen concentration was observed either, despite the Sherpas and Tibetans being significantly stronger at those elevations. Researchers observed significantly higher levels of EPAS1 expression, and while the mechanism for its function is not known, they were able to confirm that this mutation accounts for the difference in physiological traits in the Tibetans and Sherpas (Simonson, et al.).

Gummy Bear Mimicry and Selection

But life isn’t just about colors. Imagine that a few of the bears developed a toxin in their bodies that cause painful stomachaches in their predators, and also produce a very bright red pigment. Predators would think twice before snatching up an easy catch of red bears and opt for other colors instead. Furthermore, the nonpoisonous red bears, despite being a duller red than their poisonous counterparts, also enjoy safety; their color is associated with discomfort and pain, causing the predators to ignore red bears altogether.

But the nonpoisonous gummy bears only receive such an advantage because the poisonous ones are so few and far between. If the poisonous ones become more numerous, predators would have an easy time of comparing the nonpoisonous red gummy bears to their brighter, redder counterparts. And so, the protection afforded to the nonpoisonous bears disappears. There may be a moment of hesitation, but predators will no doubt go back to preying on the hapless dull red gummy bears, leaving the poisonous ones alone.

This method of mimicry, known as Batesian mimicry, is not a perfect disguise however, as some predators can distinguish between dangerous and harmless prey. In a study conducted by researchers, Kraermer and Adams, they found that two salamander species, a model and mimic, would elude snake and mammal predators by color association alone. However, bird predators were able to distinguish between the palatable and toxic salamanders by their distinguishing patterns.

The organisms seen today are reflections of eons of environmental changes and selective pressures. Our DNA bears the markings and scars of cataclysmic events and relationships with other kinds of life around us. Natural selection explains the mechanism that allows organisms to evolve as a species. It acts on individuals to affect the whole, but it must be made clear that it does not evolve an individual specifically. It allows for the emergence of different attributes that can be passed on to future generations and define entire new species.

http://youtu.be/XS-pUWLtVe4

More resources on selection and mimicry can be found in:

Johnstone, Rufus A. “The Evolution of Inaccurate Mimics.” Nature 418.6897 (2002): 524-26.

Kraemer, Andrew C., and Dean C. Adams. “Predator Perception Of Batesian Mimicry And Conspicuousness In A Salamander.” Evolution 68.4 (2014): 1197-206.

Losos, Jonathan B., Thomas W. Schoener, and David A. Spiller. “Predator-induced Behaviour Shifts and Natural Selection in Field-experimental Lizard Populations.” Nature 432.7016 (2004): 505-08.

Morgans, Courtney L., and Terry J. Ord. “Natural Selection in Novel Environments: Predation Selects for Background Matching in the Body Colour of a Land Fish.” Animal Behaviour 86.6 (2013): 1241-249.

Skelhorn, J., and G. D. Ruxton. “Predators Are Less Likely to Misclassify Masquerading Prey When Their Models Are Present.” Biology Letters 6.5 (2010): 597-99. Print.

Simonson, T. S., Y. Yang, C. D. Huff, H. Yun, G. Qin, D. J. Witherspoon, Z. Bai, F. R. Lorenzo, J. Xing, L. B. Jorde, J. T. Prchal, and R. Ge. “Genetic Evidence for High-Altitude Adaptation in Tibet.” Science 329.5987 (2010): 72-75. Print.

Speed, Michael P., and Graeme D. Ruxton. “Imperfect Batesian Mimicry and the Conspicuousness Costs of Mimetic Resemblance.” The American Naturalist 176.1 (2010): E1-E14.

A Pain in the Neck: Costs of Natural Selection in Giraffes

Posted on April 27, 2014 by George Yang

Contributed by George Yang, Carl Dalmeus, and Alan Kwan

“Survival of the fittest”. The saying is used everywhere – in sports, academics, commercials, and other cultural norms. Society paints the image that the most successful people are at their physical and mental peak and have been that way since the beginning. So when survival of the fittest is mentioned in evolutionary science, many people make the common mistake of believing the fastest, biggest, and strongest organisms are the ones that survive in nature. Instead, fitness is the ability for an organism to not only survive in its environment but also successfully reproduce in the future. When facing natural selection, species may find that maintaining large morphological structures may not be the evolutionarily beneficial decision.

When people hear about giraffes, one of the first things they think of is probably their necks. Giraffes are the tallest living land animals on the planet and well-known for their long necks that stretch high over the savannas of Africa. But why exactly are the necks of giraffes so long? The most common explanation that dates back to as early as the start of the 19th century is that giraffes use their long necks to help them browse above the canopy for vegetation, which gives them an advantage over members of the same and different species. Later research found other explanations such as sexual selection (male-male combat and attracting female giraffes), increased vigilance (able to see predators from further away), and thermoregulation (increased surface area allows for greater cooling ability). For more information on a few of these hypotheses, see another recent post.

However, there are also costs associated with the long necks of giraffes. Despite having long necks, giraffes actually reach optimal feeding when their necks are bent and have the tendency to feed from low shrubs particularly during dry seasons. Longer necks would also result in enlargement of the heart, thickening of the artery walls, and higher blood pressure in order to push blood into the brain. Therefore, maintaining longer necks may be an unnecessary expenditure of energy. In addition, research suggests that giraffes with longer necks stick out from the crowd and are more likely to be subject to predation.

The long necks of giraffes is just one of many examples in nature illustrating that there are costs and benefits to most adaptations. The idea that natural selection produces perfect organisms with perfectly advantageous adaptations is just a tall tale.

For more information about the costs of selection in giraffes and other organisms, please refer to the below articles:

Cameron, E.Z. & J.T. du Troit. 2007. Winning by a neck: tall giraffes avoid competing with shorter browsers. American Naturalist 169: 130-135.

Englemoer, D.J.P., Donaldson, I., & D.E. Rozen. 2013. Conservative Sex and the Benefits of Transformation in Streptococcus pneumoniae. PLoS Pathogens 9.

Kusche, H. & A. Meyer. 2014. One cost of being gold: selective predation and implications for the maintenance of the Midas cichlid colour polymorphism (Perciformes: Cichlidae). Biological Journal of the Linnean Society 111: 350-358.

Liker, A. & T. Szekely. 2005. Mortality costs of sexual selection and parental care in natural populations of birds. Evolution 59: 890-897.

Mougeotf, F. & V. Bretagnollef. 2000. Predation as a cost of sexual communication in nocturnal seabirds: an experimental approach using acoustic signals. Animal Behavior 60: 647–656.

Simmons, R.E. & L. Scheepers. 1996. Winning by a neck: sexual selection in the evolution of giraffe. American Naturalist 148: 771-786.

Wilkinson, D.M. & G.D. Ruxton. 2012. Understanding selection for long necks in different taxa. Biological Reviews 87: 616-630.

The Origin and Early Evolutionary History of Life on Earth and the Potential Evolution of Life Elsewhere in the Solar System

Posted on April 26, 2014 by Ryan Douglas Blackwell

Contributed by Ryan Blackwell

Earth’s Age

Our planet’s approximate age is a surprisingly common misconception among the public today. Earth’s age is not in the order of thousands, hundred of thousands, or millions of years. Thanks to the efforts of modern science, we know the Earth to be around 4.6 billion years old. A less common misconception involves just how long Earth has been habitable. Conditions on Earth were not immediately suitable for life, nor did life originate late in its geologic history. Evidence suggests that the Earth was a largely inhospitable place for the first 400-600 million years of its existence. At its inception, and for a period afterwards, our planet had a molten surface under constant bombardment from meteors. Not the ideal vacation spot. Until its molten surface cooled allowing the crust to form and meteor strikes became less frequent, the development and sustenance of life would be virtually impossible. Once these extreme conditions lessened to a large enough degree, however, life could take shape. Sure enough, fossil records indicate the existence of cellular life around 3.6 billion years ago. Now you may be thinking to yourself “if life could not exist for the first 400-600 million years, the Earth is roughly 4.6 billion years old, and life does not appear until around 3.6 billion years ago, that still leaves another 400-600 million years unaccounted for.” What was occurring during this period of time you ask? The answer: chemical evolution.

Chemical Evolution

So what is chemical evolution? It is not the evolution of life. Chemical evolution is the evolution of lifeless organic matter. To be a bit more specific, chemical evolution explains the synthesis of organic matter from inorganic molecules followed by the increasing complexity of lifeless organic matter over time. The process gave rise to self-replicating molecules, provided the building blocks for life, and eventually led to the emergence of the first organisms. The appearance of self-replicating molecules is key to further chemical evolution. Self-replication inevitably gives rise to relatedness among molecules. If a cycle involved in self-replication diverges into two different cycles where one cycle produces the same molecule at a higher rate using the same materials, then this new cycle should outcompete and replace the original cycle.

Many experiments, beginning with those of Stanley Miller in 1953, have shown that given the right mix of chemicals, liquid water, and energy, simple molecules will combine and rearrange to form complex organic matter such as the amino acids essential to life. Of course these chemical ingredients had to come from somewhere. Most hypotheses for their sources fall into one of two categories: extraterrestrial or terrestrial origins. The Earth was either seeded by meteors already carrying simple organic matter (pseudo-panspermia), or organic matter formed on Earth such as around deep sea hydrothermal vents. No matter the source, once present on Earth, chemical evolution drove the synthesis of amino acids, ribose and other sugars, and other important chemical components of life from simpler ingredients, but before the emergence of more conventional deoxyribonucleic acid (DNA) based life, there existed a ribonucleic acid (RNA) world.

An RNA World

The current leading hypothesis states that RNA evolved before DNA as the primary genetic material for early life, and even before RNA there likely existed some even simpler genetic system, but we will focus on the better understood RNA system. First off, here is some preliminary information for those of you not overly familiar with DNA or RNA. At their foundations, RNA is typically composed of a single strand/chain of nucleotides whereas DNA is composed of two antiparallel strands/chains of nucleotides. A nucleotide is a nucleoside with an attached phosphate group, and a nucleoside is a nitrogenous base/nucleobase attached to a five-carbon sugar. These sugars essentially form the backbones of DNA and RNA. The five-carbon sugar that forms the backbone of RNA is ribose.

Forming RNA from the ribose produced from chemical evolution poses some problems, however. The ribose itself would have rapidly degraded if not used quickly, but the larger problem is that conditions were not conducive for the formation of nucleosides from ribose and the four canonical RNA nucleobases (adenine, guanine, cytosine, and uracil). These four nucleobases were probably not abundant on the early Earth, and conventional base pairing with the four canonical nucleobases does not occur in water, so then how could RNA exist? Another refresher for people not so familiar with DNA and RNA: a base pair is a pair of complementary nucleobases joined by weak hydrogen bonds. The inability to form base pairs may seem irrelevant in single stranded RNA, but a diverse array of RNA molecules rely on the ability of some strands to fold in on themselves and form base pairs. That aside, research shows that ribose more readily combined with likely more abundant alternative nucleobases to form nucleosides in early Earth-like conditions, and those nucleobases more readily formed base pairs in water. This suggests that the base pairs of RNA we see today (A-U and G-C) were not the same at its inception, yet early RNA likely shared similar functions with modern RNA or at least eventually evolved them.

The Final Frontier

With some of the basics on the origin and evolution of life out of the way, let us apply them to other models within our solar system.

Choose a satellite from Images 1-3, below:

I choose Titan: please scroll down to image 4

I choose Europa: please scroll down to images 5 and 6

I don’t want to participate: please scroll down to the last image

Image 4…. Welcome to Titan, or at least an artist’s impression of it. It is Saturn’s largest satellite, and it is also the only satellite with a dense, Earth-like atmosphere within our solar system. NASA’s Cassini probe has shown that seas and lakes of liquid methane dot its surface. Simulations of Titan’s chemistry indicate the presence complex organic matter making it of prime exobiological interest. These same simulations have generated solid organic matter known as tholins, which were subsequently found to have nutritious properties for specific microorganisms. Though the surface is too cold to support life, hypothetical subsurface oceans of water could be warm enough to sustain it if it existed. Alternatively, due to Titan’s unique chemistry, life with a radically different chemistry from our own could possibly evolve in such conditions.

Image 5… This is not a picture of Europa, but instead of life under the ice off the coast of McMurdo Sound, Antarctica. This image simply illustrates life that has evolved to thrive in cold water environments under the ice on Earth. Europa is one of the four Galilean moons of Jupiter. As seen in image 2, it has an outer crust composed entirely of water ice. Current models indicate that this outer crust is greater than 4km but less than 10km thick, and that it covers a 100km deep subsurface ocean of water. Despite the low temperatures, studies suggest that temperatures are high enough and enough solar energy reaches the icy moon to sustain life. Additionally the ice shell is thin enough to experience convective overturn of the surface ice. That means that oxidants and organics trapped in the ice are transported to the subsurface ocean making them available for use in chemosynthetic redox reactions at…

Image 6… Deep sea hydrothermal vents! Therefore, the development of indigenous life on Europa is considered a possibility. Again, this is not an image of Europa, but of a possibly analogous environment on Earth. Just as on Earth, deep sea hydrothermal vents could provide the organic matter and energy necessary for chemical evolution and the possible emergence of life. Given Europa’s conditions, anaerobic, archaebacteria-like organisms seem to be the most likely candidates for life. Terrestrial archaebacteria provide nice examples of what to expect.

Image 7… Oh, so you don’t feel like participating, or perhaps my writing bores you? Either way, welcome to the Moon. Since you obviously don’t care about the origins and evolution of life, you’ve been sent somewhere where life has never existed save for a few days from 1969 to 1972. Unless you’re a tardigrade (a microorganism well adapted to extreme environments and the only known animal capable of surviving the vacuum of space unprotected) you won’t have long to enjoy your solitude.

Here are some further readings if you would like more information on the subjects presented:

Brasier, Martin D., and David Wacey. “Fossils and Astrobiology: New Protocols for Cell Evolution in Deep Time.” International Journal of Astrobiology 11.04 (2012): 217-28.

Bray, Veronica J., Gareth S. Collins, Joanna V. Morgan, H. Jay Melosh, and Paul M. Schenk. “Hydrocode Simulation of Ganymede and Europa Cratering Trends – How Thick Is Europa’s Crust?” Icarus 231 (2014): 394-406.

Chen, Michael C., Brian J. Cafferty, Irena Mamajanov, Isaac Gállego, Jaheda Khanam, Ramanarayanan Krishnamurthy, and Nicholas V. Hud. “Spontaneous Prebiotic Formation of a β-Ribofuranoside That Self-Assembles with a Complementary Heterocycle.” Journal of the American Chemical Society 136.15 (2013): 5640-646.

Joyce, Gerald F. “RNA Evolution and the Origins of Life.” Nature 338.6212 (1989): 217-24.

Raulin, François. “Exo-Astrobiological Aspects of Europa and Titan: From Observations to Speculations.” Space Science Reviews 116.1-2 (2005): 471-87.

Smith, John Maynard, and Eörs Szathmáry. “Chemical Evolution.” The Major Transitions in Evolution. New York: Oxford UP, 1995. 27-37.

The Evolutionary Significance of the Narwhal’s “Tusk”

Posted on April 25, 2014 by Melissa Querrey

Contributed by Madeline Haley and Melissa Querrey

First, a short introduction to narwhals by yours truly.

https://www.youtube.com/watch?v=sCf7XQsdNtk&feature=youtu.be

The narwhal, or Monodon monoceros, is a cetacean mammal that inhabits the Arctic waters and is most commonly recognized for its large “tusk”, which closely resembles the horn of the mythical unicorn. Contrary to popular belief, this “tusk” is actually a modified tooth that forms during development from a pair of tooth buds and projects outward from the maxilla, or upper jaw. While both males and females can grow tusks, males tend to have tusks more often than females.

There has been much debate among researchers about the true function of the narwhal’s tusk. It was initially thought that the tusk was only used as an evolutionary means of self-defense and breaking the ice that covers the surface of their aquatic habitats so breaths of air can be taken. However, recent study of the anatomy of the tusk by Nweeia and colleagues revealed nerves that lead directly to the brain, giving evidence of its additional function as a sensory organ.This sensory feature serves several purposes to the narwhal by detecting changes in the external environment, such as salinity and temperature. Because these functions of the narwhal’s tusk increase its chances of survival and are retained in the population, it can be said that they are a result of natural selection.

Additionally, secondary functions of the tusk have developed due to sexual selection, which have facilitated the tusk’s persistence. Based on the discovery of broken tusk fragments and scarring, it can be inferred that male narwhals use their tusk in an aggressive fashion in order to assert sexual dominance and eventually find a mate.

While the narwhal’s tusk may seem like an obnoxious physical display, it is clear that evolutionary forces of both natural and sexual selection have driven the species to utilize its tusk in a way that enables its survival and overall individual and reproductive fitness.

Finally, check out this awesome video about narwhals.
https://www.youtube.com/watch?v=ykwqXuMPsoc

And, for more information:

Palsboll, P.J, Heide-Jorgensen, M.P, & R. Dietz. 1997. Population structure and seasonal movements of narwhals, Monodon monoceros, determined from mtDNA analysis. Heredity 78: 285-292.

Nweeia, M. T., Eichmiller, F. C., Hauschka, P. V., Donahue, G. A., Orr, J. R., Ferguson, S. H., Watt, C. A., Mead, J. G., Potter, C. W., Dietz, R., Giuseppetti, A. A., Black, S. R., Trachtenberg, A. J., & Kuo, W. P. 2014. Sensory ability in the narwhal tooth organ system. The Anatomical Record, 297: 599–617.

Nweeia, M.T., et al. 2009. Considerations of anatomy, morphology, evolution, and function for narwhal dentition. The Anatomical Record 295, 6: 1006-1016.

Silverman, H. B., & M. J. Dunbar. 1980. Aggressive tusk use by the narwhal (Monodon monoceros L.). Nature 284.5751: 57-58.

Brear, K., et al. 1993. The mechanical design of the tusk of the narwhal (Monodon nonoceros: Cetacea). Journal of Zoology 230.3: 411-423.

Mirceta, S., Signore, A.V., Burns, J.M., Cossins, A.R., Campbell, K.L., & Berenbrink, M. 2013. Evolution of Mammalian Diving Capacity Traced by Myoglobin Net Surface Charge. Science 14: 1234192

“Narwhals.” Narwhals. National Geographic, n.d. Web. 18 Apr. 2014.<http://video.nationalgeographic.com/video/narwhals?source=relatedvideo>.

Transition from Sea to Land

Posted on April 24, 2014 by Michael Ross Kaufman

Contributed by Michael Kaufman, Sterling Feeser, Cole Owens & Zach Vann

The Transition from Sea to Land

It might be shocking to hear that all of the species that inhabit land today came from ancestors that lived in the sea. In all species, mutations occur constantly by random chance. A mutation or the accumulation of many mutations can create a new physical trait whose prevalence is often determined by its ability to allow organisms to survive and reproduce. Mutations leading to traits that better allow organisms to survive and reproduce are often selected for and therefore rise in frequency with time. Because the transition from sea to land occurred, involving the accumulation of many new traits, it can be hypothesized that such land inhabiting traits provided some advantage.

One hypothesis for the nature of this advantage is the drying pond hypothesis, which suggests that droughts occurred, and fish were forced to move from one body of water to another. When a body of water dried out, the fish that already had random mutations leading to land-favoring traits were more able to reach another body of water via land and survive. Another hypothesis, the predator hypothesis, involves the idea that if species had random mutations enhancing their ability to survive on land, then they could better avoid predators. Overall, there are many hypotheses for why these traits may have been advantageous, but contradictory evidence hinders many of them, and therefore the truth behind this transitional process is still largely a mystery.

As this is one of the biggest transitions in the history of evolutionary biology, it is important to realize that drastic changes that lead to the formation of new species often involve the accumulation of many gradual mutations over time. As evidence of this, species with intermediate traits have existed. Amazingly, Tiktaalik roseae has characteristics that resemble both sea and land creatures. Tiktaalik had an intermediate structure between a fin and a limb as well as an enlarged pelvic bone compared to other fishes of the time, which is helpful for movement on land. Additionally, Tiktaalik had both gills and primitive lung structures, which were necessary to survive on both water and land respectively. Overall, the transition to land is a vitally important event that led to the development of many new species. However, because questions still remain about the certainty of the mechanistic theories, it is certain that proving exactly how and why the transition from land to sea occurred will be one of science’s greatest achievements.

“Waiting on the World to Change” Parody

In order to emphasize that natural selection acts on random mutations and is not goal oriented, we made a parody of the song “Waiting on the World to Change” by John Mayer. Species in the sea did not choose to develop land favoring characteristics; rather all they could do was “wait” for mutations to arise before selection could act.

Waiting on the World to Change (Parody)

Lyrics

The change from sea to land
Is causing lots of talk
Some species evolved to swim or stand
And over time we learned to walk
Three hundred eighty-three million years ago
A landscape was emerging
And with fins with wrists and bigger hips
A new species was diverging
So we keep on waiting
Waiting on the world to change
We keep on waiting
Waiting on the world to change
You can beat the competition
As a species in transition
So we keep on waiting
Waiting on the world to change
Under natural selection
The fittest beasts will best survive
To reproduce and pass those better genes
That helped them to stay alive
Cause you can live under the water
Breathing through a set of gills
But if lungs arise with time
You can go wherever you will
That’s why we’re waiting
Waiting on the world to change
We keep on waiting
Waiting on the world to change
It doesn’t happen cause we want it
But with time we’re counting on it
So we keep on waiting
Waiting on the world to change
Tiktaalik roseae (repeat)
And we’re still waiting
Waiting on the world to change
We keep on waiting
Waiting on the world to change
The terrestrial population
Came from countless generations
So we keep on waiting
Waiting on the world to change
We keep on waiting
Waiting on the world to change
We keep on waiting
Waiting on the world to change
Waiting on the world to change (repeat)

For More Information:

Websites
“Recent Findings:Prologue- Fish Out of Water.” Devonian Times. N.p., n.d. Web. 15 Apr. 2014.

Scientific Articles

Daeschler, E.B., Shubin, N.H., Jenkins Jr, F.A. 2006. Devonian tetrapod-like fish and the evolution of the tetrapod body plan. Nature 440: 757-763.

Hagey, L.R., et al. 2010. Diversity of Bile Salts in Fish and Amphibians: Evolution of a Complex Biochemical Pathway. Physiological and Biochemical Zoology: PBZ 83.2: 308-321.

Harzsch, S., et al. 2011. Transition from marine to terrestrial ecologies: Changes in olfactory and tritocerebral neuropils in land-living isopods. Arthropod Structure & Development 40.3: 244-257.

Kleinteich, T., et al. 2014. Anatomy, Function, and Evolution of Jaw and Hyobranchial Muscles in Cryptobranchoid Salamander Larvae. Journal of Morphology 275:230–246.

Klussmann-Kolb, Annette, et al. 2008. From sea to land and beyond – New insights into the evolution of euthyneuran Gastropoda (Mollusca). BMC Evolutionary Biology 8: 57-73.

Schoch, R.R. and Witzmann, F. 2011. Bystrow’s Paradox- gills, fossils, and the fish-to-tetrapod transition. Acta Zoologica(stockholm) 92: 251-265.

Shubin, N.H., Daeschler, E.B., Jenkins Jr, F.A. 2006. The pectoral fin of Tiktaalik roseae and the origin of the tetrapod limb. Nature 440: 764-771.

Evolution: To the Less Complex

Posted on April 23, 2014 by Mahmoud

Contributed by Mahmoud Eljalby

As organisms evolve, they become more complex, right? NO! Organisms continually evolve, this is a fact; but it is far from true to say that organisms evolve to become more complex. Some do, certainly; but others ‘lose the complexity’. Unbelievable, right?!

Well, let’s look at a couple examples. Like seafood? Let’s take a case study in fish. In 1997, researchers found that sightless A. mexicanus cavefish evolved from eyed, surface-dwelling forms! That is not all. The researchers also concluded that the loss of sight evolved independently at least three times! This shows that natural selection is strongly favoring cavefish that lost a complex trait—in this case, eyesight. The next time you eat sightless fish, you’ll know where it came from!

Not only that, but in 2012, researchers at the University of Maryland, College Park, found that natural selection favors sightless cavefish with smaller eyes. Pachón cavefish live in extremely dark environments: they live in caves. As such, having a functional eye that allows you to see in light is of no use—there is no light. Losing your ability to see, on the other hand, will give the cavefish a great advantage. The researchers found that those cavefish developed over time a non-visual sensory system: that is a sensory system that does not depend on light (and hence more useful in a cave). The genes responsible for this system were also found to indirectly promote eye regression. Through a trade-off between the evolution of a non-visual sensory system and eye regression during the adaptive evolution of the fish in the cave environment, nature was selecting for the cavefish that had the non-visual sensory system and hence had smaller eyes.

Not convinced by this example to know that evolution is not always to the more complex? Well, you can always look at many other examples, such as sightless naked mole rats and other fish species—just to name a few.

Dance changed from the 1930s to 1960s as new variations, all complex, arose. Gradually, however, dance seems to get less complex in many social settings. By 2050, will we be dancing at all?

Also, check out some of the recent research on convergence:

Rétaux S, Casane D. 2013. Evolution of eye development in the darkness of caves: adaptation, drift, or both? EvoDevo, 4:26 http://www.evodevojournal.com/content/4/1/26.

Nikitina NV, Maughan-Brown B, O’Rian MJ, Kidson SH. 2004. Postnatal Development of the Eye in the Naked Mole Rat (Heterocephalus glaber). The Anatomical Record Part A, 277A:317–337.

Peichl L, Nemec P, Burda H. 2004. Unusual cone and rood properties in subterranean African mole-rats (Rodentia, Bathyregidea). European Journal of Neuroscience 19: 1545-1558.

Durand JP. 1976. Ocular Development and Involution in the European Cave Salamander, Proteus anguinus Laurenti. Biological Bulletin, 151 (3): 450-466.

Yoshizawa M, Yamamoto Y, O’Quin KE, William R Jeffery. 2012. Evolution of an adaptive behavior and its sensory receptors promotes eye regression in blind cavefish. BMC Biology, 10:108. http://www.biomedcentral.com/1741-7007/10/108.

Bilandžija H, Ma L, Parkhurst A, Jeffery WR. 2013. A Potential Benefit of Albinism in Astyanax Cavefish: Downregulation of the oca2 Gene Increases Tyrosine and Catecholamine Levels as an Alternative to Melanin Synthesis. PLoS ONE 8(11): e80823. doi: 10.1371/journal.pone.0080823.

Evolution: A Quest for Change

Posted on April 17, 2014 by mjedrze

Contributed by Mark Jedrzejczak

https://www.youtube.com/watch?v=IVCmoPcqdEI

Ever since Morgan Freeman’s success on the Science network’s program, “Through the Wormhole” the actor has been much sought out for his iconic narrative voice and style. We are proud to present the first episode of his* most recent documentary series on the topic of macroevolution, “Evolution: A Quest for Change”.

(* well, someone that sound like him, anyway.)

The title reflects a little tongue-in-cheek on the part of the producers, since evolution is not really a quest, since quests involve a mission with an end goal. Instead, evolution is more like a knight going doing a bunch of random missions and after some time, he starts to choose those missions that get him the most princesses. Similarly, evolution is a process driven by the nonrandom selection of heritable traits that impart the best fitness. This ends up changing the gene frequencies in a population over time. On a macroscopic level, this is characterized by the evolution of a species’ gene pool as a whole, often leading to divergence and speciation. The process of macroevolution is responsible for the existence of all the organisms that ever were and will be inhabiting our pale-blue dot, planet Earth.

This documentary presents the topic of large-scale evolution, the main mechanisms that drive macro evolution, and what evidence exists for the process. At the same time, the documentary helps highlight the importance of scientific literacy, critical thinking, and smart science teaching, especially for today’s youth. Research done by Hayat Hokayem and Saouma BouJaoude (2008) on college student’s perception of evolution underscores the importance of understanding the student’s perspectives on the theory of evolution. In addition, their research suggests that accepting and working with an individual’s “cultural milieu” or worldview is the most effective method of conveying scientific ideas. An instructor simply handing a student a stack of scientific information is not good enough, especially when the latter starts reading the information with a set of presuppositions. These biases should to be understood and used as building blocks, and should not be seen as pieces that instructors need to be tear down.

A more effective way of teaching is to build upon student’s misconceptions…and also not to even use the word misconception. One study by April Cordero Maskiewicz and Jennifer Evarts Lineback (2013) advocates using students’ incorrect ideas about science as a resource for refining teaching strategies.

This documentary addresses a few of these “misconceptions”, especially a couple that were highlighted in the Maskiewicz and Lineback study. These were that ‘natural selection is trying to give what the organisms need.’ The video clearly discusses that evolution and the process of natural section have no goal or “finish line.” Another incorrect idea, taken from the “MiTEP List of Common Geoscience Misconceptions Organized by the Earth Science Literacy Principles”, that biases new students in the field of evolutionary biology, is the “young Earth” model, and this too is addressed in the video.

For more information, see:

Age of the Earth. U.S. Geological Survey. 1997. Archived from the original on 23 December 2005. Retrieved 2006-01-10.

Oberthür, T, Davis, DW, Blenkinsop, TG, Hoehndorf, A (2002). Precise U–Pb mineral ages, Rb–Sr and Sm–Nd systematics for the Great Dyke, Zimbabwe—constraints on late Archean events in the Zimbabwe craton and Limpopo belt. Precambrian Research 113 (3-4): 293–306.

Carlin, J. L. (2011) Mutations Are the Raw Materials of Evolution. Nature Education Knowledge 3(10):10.

H Su, L-J Qu, K He, Z Zhang, J Wang, Z Chen and H Gu. (2003) The Great Wall of China: a physical barrier to gene flow? Heredity. 90, 212–219.

Liman, R., Sheehy, B. & Schultz, J. (2008) Genetic Drift and Effective Population Size. Nature Education 1(3):3.

Macroevolution. Understanding Evolution. 2014. University of California Museum of Paleontology.

Hokayem, H. and BouJaoude, S. (2008), College students’ perceptions of the theory of evolution. J. Res. Sci. Teach., 45: 395–419.

April Cordero Maskiewicz and Jennifer Evarts Lineback Misconceptions Are “So Yesterday!” CBE Life Sci Educ September 4, 2013 12:352-356.

MiTEP List of Common Geoscience Misconceptions Organized by the Earth Science Literacy Principles. http://mitep.mspnet.org/media/data/MiTEP_List_of_Common_Geoscience_Misconceptions.pdf?media_000000007297.pdf

EvolutionShorts

evolution and evolutionary biologists in the natural world

Category Archives: foundations of evolution