Monthly Archives: April 2014

Venom Variation

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Contributed by Annelise Bonvillian, Cherisma Patel and Liz Pinkerton

I introduce to you two rattlesnakes. I think they’re generally friendly but they could also be planning to maim me. You just never know with venomous snakes. 

Judging by their appearance, you’d think both rattlesnakes were of the same species. You’d be right, being the clever person you are. They are in fact part of the same subspecies of Southern Pacific Rattlesnake (Crotalus oreganus helleri).

These C. o. helleri rattlesnakes are venomous. Before we dive into their story, let’s explain venom.

Venom Across The Tree of Life

Many animals have evolved venom for protection or to help them capture prey. We, unfortunately have not.

There are also a wide range of structures for delivering venom, such as the cute little fangs in these rattlesnakes.

The interesting thing is, similar types of venom have evolved in completely unrelated species. This is not because all venomous species evolved from one super venomous ancestor or because the venomous critters of the world get together to talk strategy.

Evolution of venom is a solid example of convergent evolution in which organisms that are not very closely related independently evolve similar traits due to similar environmental pressures. The proteins in the toxin end up acting on the same physiological molecule by chance. Most venoms involve disrupting major physiological pathways that are accessible by the bloodstream, especially the hemostatic and neurological systems. Damaging these systems would efficiently cripple any prey or potential predator.

Back to the Rattlesnakes

Getting back to our original C. o. helleri rattlesnakes, you’d think it might be true that they’d have the same type of venom because they’re of the same subspecies, right?

In fact, these two rattlesnakes are very closely related, but the populations that live in the mountains have a distinctly different venom than those that live in the desert.

Distribution of Crotalus oreganus

Distribution of Crotalus oreganus

A research team from the University of Queensland studied the variation between rattlesnakes in the mountainous area of Idyllwild, California and those in the desert of Phelan, California. The extent of venom variation is surprising for two populations because the two areas are relatively close together geographically.

The venom of the desert-dwelling rattlesnake contains proteins that break down blood vessels and prevent clotting.

This venom is slow acting. It is described as haemotoxic and would lead to uncontrollable bleeding. Neat!

Its close relative in the mountains is equally as morbid. The mountain populations have proteins in their venom that stop nerves from sending signals to the muscles.

This venom is fast acting. It is described as neurotoxic and results in paralysis. Sweet!

The venoms are completely different even though these two populations are from the same subspecies.

In fact, venom can vary between species, subspecies, individuals, sexes, and ages. Another research team from the Biomedical Institute of Valencia that loves poisonous reptiles just as much as the the previous one studied venom variability in Mojave rattlesnakes in Arizona. They found that you were 10 times more likely to die from a bite in one county than another. Here, the severity, not the type, of venom was what varied.

So, getting back to our C. o. helleri rattlesnakes (don’t worry, we love you best), here’s another question: which would be better to have in the snake’s arsenal? The fast acting neurotoxin venom or the slow acting haemotoxin?

Evolution, the lovely process that developed these fine creatures is NOT about having the best of a trait. The fitness of a certain trait is relative. What is good for one population might not necessarily be the best for another. Based on where they live, different venom types might be more beneficial in capturing prey or warding off predators.

So why would it be more beneficial for the mountain rattlesnake to have a faster acting venom?

Researchers suspect that environmental differences between these two populations of rattlesnake are likely to have promoted the huge variation in venom between the two.

If the mountain rattlesnake’s venom was slow acting the, prey could hide before the venom had properly incapacitated it.

And venom isn’t cheap. Creating venom costs a lot of energy and wasting it time and time again would be a shame. Natural selection would thus lead to a venom composition that would reduce metabolic cost. Natural selection is the process by which organisms that have higher fitness and are more adapted to their environment tend to produce more offspring and survive.

Now, in the desert, rattlesnakes don’t have to worry as much about their prey hiding before they can get to them. They might not have evolved the quicker neurotoxic venom because there was no selective pressure to have their venom be fast acting.

As with most things in this incomprehensible universe, we are not sure if the desert dwelling Southern Pacific rattlesnake maintains its haemotoxic venom due to lack of selection pressure. Or perhaps somehow the snakes have co-evolved with their prey and the haemotoxic venom is just the most efficient one for the prey type.

All in all, it’s important to realize that evolution isn’t a race where the end goal is to have the best of something. Traits change randomly due to mutations, and factors such as the environment or prey type select for variations that are most beneficial for survival.

In related news, using the vast powers of human intelligence to learn from the natural world, snake venom is being adapted to heal instead of hurt. Venom works in the same way as many medicines, and the enzymes in venom are being modified to affect disease processes.

One specific example includes the using ACE inhibitors in Brazilian pit viper venom to prevent hypertension.

However, with the decline of snake diversity due to environmental degradation, the diversity of venom and its medical potential is decreasing.The fact that venom from various snakes can be used to target certain  diseases is a very important implication for evolutionary medicine. Population divergence in snakes increases the potential for variation in venom type, which can ultimately increase the antidotes possible for fighting certain diseases.

So why research things like rattlesnake venom? Not only is the subject wildly fascinating, but unraveling the complexities of snake venom can help humans better counter its life-threatening effects and can also promote the development of new medicines. In conclusion,  though we may be terrified of you, dear rattlesnakes and other venomous denizens of this world, we’d also like to say thanks. May you continue to amaze us.

Check out these sites for more information:

Caswell, Nocholas R., Wolfgang Wuster, Freek J. Vink, Robert A. Harrison, and Bryan G. Fry. 2012. Complex cocktails: the evolutionary novelty of venoms Trends in Ecology and Evolution.

Holland, Jennifer S. 2013. Venom: The Bite That Heals. National Geographic: The New Age of Exploration. http://ngm.nationalgeographic.com/2013/02/125-venom/holland-text

Kartik Sunagara, Eivind A.B. Undheimc, Holger Scheibd, Eric C.K. Grene, Chip Cochrane, Carl E. Persone, Ivan Koludarovc, Wayne Kellne, William K. Hayese, Glenn F. Kingd, Agosthino Antunesa, Bryan Grieg Fry. Intraspecific venom variation in the medically significant Southern Pacific Rattlesnake (Crotalus oreganus helleri): Biodiscovery, clinical and evolutionary implications. 2014. Journal of Proteomics. http://www.sciencedirect.com/science/article/pii/S1874391914000256

Massey DJ, Calvete JJ, Sánchez EE, Sanz L, Richards K, Curtis R, Boesen K. 2012. Venom variability and envenoming severity outcomes of the Crotalus scutulatus scutulatus (Mojave rattlesnake) from Southern Arizona. Journal of Proteomics. http://www.ncbi.nlm.nih.gov/pubmed/22446891

Yong, Ed. 2014. Rattlesnakes Two Hours Apart Pack Totally Different Venoms. National Geographic: Phenomena. Online. http://phenomena.nationalgeographic.com/2014/01/27/rattlesnakes-two-hours-apart-pack-totally-different-venoms/

Zimmer, Carl. 2013. On the Origin of Venom. National Geographic: Phenomena. Online. http://phenomena.nationalgeographic.com/2013/01/09/on-the-origin-of-venom/

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

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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.

Sexual Evolution of the Cuttlefish

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Contributed by Carolyn Barnett, Justin Kim and Mimi Wang

Remember your mom telling you that cheaters never win? Well, she needs to take another look at nature and receive a lesson from the spectacular cuttlefish. Through sexual selection, smaller male cuttlefish, aptly called “sneaker males” have evolved an alternate mating system allowing them to successfully compete with the larger males for mating time. Specifically, the sneaker males take on female coloration, hide their masculine fourth arms, and hold the rest of their arms in the posture of an egg-laying female, in a bid to sidle up to a guarded female.

cuttlefish displays

Cuttlefish display strategies. In the left panel, a sneaker male (center) displays towards the female on the right while not displaying towards the male on his left. In the right panel, there are males on three sides. Rather than try to appear like a female to all of them, the sneaker males chooses to fully display.

Because the sneaker cuttlefish use bright colors to conceal their male features, they are able to avoid aggression from the larger males and increase their chance of mating. Males who know that they can’t win in display or physical combat will sometimes display the brown and white pattern of the female while two other males are fighting over a female.  This allows him to get close to the female and slip her a sperm sac while the other guys are fighting!

Females are the deciding factor on whether or not to accept the males’ advances. In a fertilization study with the cuttlefish, the researchers observed that mimickers succeeded in fertilizing females 60 percent of the time, meaning that this method actually works.

This novel mating system is driven by sexual selection, which is not another term for natural selection. Sexual selection only deals with the driving forces of individuals to increase their reproduction rate, usually by whatever means necessary. In some cases, although the evolved feature may increase their reproduction rate, it can negatively affect their survival. Sneaker cuttlefish use more energy to keep their physical appearance and are more visible in the ocean, which can lead to decreased survival. This disproves the misconception that natural selection works only for the good of the species. If sexual selection allows the animal to reproduce more, the animal accepts that he may have a lower chance of survival.

You may have heard that a big part of evolution is that only the strongest, and largest amongst the population can survive. These cuttlefish show us that you don’t have to be big or strong, you just need to be smarter than the other guys and be fit enough.

For more information, see…

1. It pays to cheat: tactical deception in a cephalopod social signaling system Brown, Garwood, Williamson http://171.66.127.192/content/8/5/729.full

2. Adaptive Coloration in Young Cuttlefish (Sepia Officinalis L.): The Morphology and Development of Body Patterns and Their Relation to Behaviour R. T. Hanlon and J. B. Messenger Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences Vol. 320, No. 1200 (Aug. 12, 1988) (pp. 437-487) Page Count: 69 http://www.jstor.org/stable/info/2396667#bibInfo

3. Female impersonation as an alternative reproductive strategy in giant cuttlefish Mark D Norman*, Julian Finn† and Tom Tregenza‡ http://rspb.royalsocietypublishing.org/content/266/1426/1347.short#cited-by

4. Principal features of the mating system of a large spawning aggregation of the giant Australian cuttlefish Sepia apama (Mollusca: Cephalopoda) K. Hall, R. Hanlon http://link.springer.com/article/10.1007/s00227-001-0718-0#

5. Female Choice of Males in Cuttlefish (Mollusca: Cephalopoda) Jean Geary Boal Behaviour, Vol. 134, No. 13/14 (Nov., 1997), pp. 975-988 Published by: BRILL Article Stable URL: http://www.jstor.org/stable/4535485

6. Behavioural and genetic assessment of reproductive success in a spawning aggregation of the Australian giant cuttlefish, Sepia apama Marie-José Naud ,Roger T. Hanlon†, Karina C. Hall‡, Paul W. Shaw§, Jonathan N. Havenhand http://www.sciencedirect.com/science/article/pii/S0003347204000387

 

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

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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”

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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>.

 

 

Hummingbirds Debunk Misconceptions in Evolution

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by Randolf Lee and Nick Mirza
humminbird2What are some of the things that come to mind upon hearing the word “fitness?” The immediate reaction is to think of how fitness applies to humans – strength, speed, and agility are commonly associated with fitness. These traits constitute a rather narrow definition of fitness; in the context of biology, fitness takes on a much broader definition to include any traits that increase reproductive success. In practice, fitness appears in an incredibly wide variety of forms, many of which defy the common conceptions of what it means to be fit.

Hummingbirds are an excellent example of organisms whose evolution contradicts conventional notions of what it means to be “fit”. The blazing fast speeds at which hummingbirds flap their wings give them remarkable flying abilities. This comes at a high cost: hummingbirds have a huge metabolic demand relative to their size. In other words, a huge amount of energy is needed to sustain hummingbird flight. It might seem that the high metabolic demand caused by hummingbirds’ flight mechanics would favor the evolution of slower wing speeds. This does not appear to be the case. Instead, one of the ways that hummingbirds compensate for the high metabolic demand of their wing flapping is by reducing metabolic demand in an entirely different realm: DNA. Current research suggests that natural selection has favored smaller genome sizes in hummingbirds (and other avian species). Smaller genomes require less energy during replication and maintenance, meaning precious resources can be used by flight muscles. This budgeting of energy consumption allows hummingbirds to maintain their stunning flight abilities without sacrificing other physical abilities or raising their already high caloric demand. The reduction of genome size is probably not among the first things that come to mind when thinking about evolutionary adaptation and fitness. One commonly held belief regarding evolution is that complexity and fitness go hand-in-hand; it would therefore be assumed that large and highly complex genomes would result in higher fitness. Hummingbirds demonstrate that this is not the case, and that fitness is manifested in a variety of ways.

Hummingbird evolution is also an excellent example of speciation caused by isolation of populations from one another. There are about 350 identified hummingbird species, all of whom live in the Americas. A considerable number of these species are found in the Andes Mountains. Contemporary research suggests that as parts of the Andes gradually rose in elevation (due to tectonic shifting), hummingbird populations were forcibly separated, which eventually led to speciation. More specifically, the genus Adelomyia split into several species due to uplift in the northern reaches of the Andes.

For more information see:

Chaves, J. A., Weir, J. T., & Smith, T. B. (2011). Diversification in Adelomyia hummingbirds follows Andean uplift. Molecular Ecology, 20,21.

Chaves, J. A., & Smith, T. B. (2011). Evolutionary patterns of diversification in the Andean hummingbird genus Adelomyia. Molecular Phylogenetics and Evolution, 60,2.

Gonzlez, C., Ornelas, J. F., & Gutierrez-Rodriguez, C. (2011). Selection and geographic isolation influence hummingbird speciation: Genetic, acoustic and morphological divergence in the wedge-tailed sabrewing (Campylopterus curvipennis). BMC Evolutionary Biology, 11, 1.

Kirchman, J. J., Witt, C. C., McGuire, J. A., & Graves, G. R. (2010). DNA from a 100-year-old holotype confirms the validity of a potentially extinct hummingbird species. Biology Letters, 6, 1, 112-5.

Parra, J., McGuire, J. A., & Graham, C. (2010). Incorporating clade identity in analyses of phylogenetic community structure: an example with hummingbirds. The American Naturalist, 176, 5.

Wright, N. A., Gregory, T. R., & Witt, C. C. (2014). Metabolic ‘engines’ of flight drive genome size reduction in birds. Proceedings of the Royal Society of Biological Sciences, 281.

A Jurassic Park for Real?

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Contributed by Tianai Sun and Weili Qu

The mysterious dinosaurs in movies or museums must have amazed you. But have you ever thought about keeping a real pet dinosaur? Good news: it could happen! One of the major misconceptions about evolution is that since evolution occurs slowly, humans cannot influence it. However, modern genetic tools enable humans to accelerate, decelerate, or redirect evolution. To aid the study of evolution, some scientists long to study living dinosaurs. Unfortunately, they went extinct 66 million years ago. To bring back dinosaurs would require abundant dinosaur DNA, which is rare, and more advanced genetic tools than are currently available. Lacking the crucial raw materials, is it possible that we can transform current animals into dinosaurs? Believe it or not, scientists may answer, “chickens!”

It is hard to imagine the transition from chicken to dinosaur, for they are drastically different in both size and appearance. However, a decade ago, Dr. Vargas from Universidad de Chile and his colleagues found that chicken embryos follow the same pattern of digit development as dinosaurs, even though they differ morphologically. This provides strong evidence that dinosaurs are authentic ancestors of chickens. As a result, chickens are an ideal model to be modified into dinosaurs.

Although chickens are closely related to dinosaurs, their major differences, including the “beak” shape and tail length, still induce difficulties in the process of transformation. How exactly could scientists solve these issues?

Chickens and birds have beaks with vestigial snouts, while alligators possess well developed snouts on their upper jaw. They, however, share similar developmental processes. Recently, by manipulating chicken embryos, Dr. Arhat Abzhanov successfully generated a modified chicken whose beak was similar to an alligator’s snout. Given that the snouts of alligators are morphologically similar to that of dinosaurs, this groundbreaking achievement brings us one step closer. Similarly, scientists are endeavoring to identify genes that control tail development in order to extend the tail of chickens, mimicking the tail of a dinosaur. If this goal is achieved, the creation of “chickenosaurus” as well as the realization of the Jurassic Park could be within reach in the future. Regardless of whether this happens, we will gain fundamental insights into how developmental patterns evolve.

More broadly, advanced scientific developments provide humans with the ability to explore the world. Genetic tools are widely used in biological research and are surprisingly effective in bringing about novel knowledge. While evolution often occurs slowly, the idea that humans cannot impact evolution due to its slow rate is incorrect, exemplified by the attempt to recreate features of extinct dinosaurs through genetic approaches. So, don’t be disappointed if scientists are unable to bring the amazing dinosaurs back to you, for even simply recreating specific phenotypes of dinosaurs in model systems enlightens our understanding of dinosaur evolution.

To see how a chicken could be transformed to have a dinosaur-like snout, claw and tail, check out the video below:

For More Information…

1.Ted Talk: Jack Horner: Building a dinosaur from a chicken http://www.ted.com/talks/jack_horner_building_a_dinosaur_from_a_chicken#t-143965

2.Horner, J. R. 2001. Dinosaurs under the big sky (p. 195). Missoula: Mountain Press Publishing Company.

3.Grossi, B., Iriarte-Díaz, J., Larach, O., Canals, M., & Vásquez, R. A. 2014. Walking Like Dinosaurs: Chickens with Artificial Tails Provide Clues about Non-Avian Theropod Locomotion. PloS ONE, 9(2), e88458.

4.Carrano, M.T., Biewener, A.A. 1999. Experimental Alteration of Limb Posture in the Chicken (Gallus gallus) and Its Bearing on the Use of Birds as Analogs for Dinosaur Locomotion. JOURNAL OF MORPHOLOGY, 240:237–249.

5.Vargas, A.O., Fallon, J.F. 2005. Birds Have Dinosaur Wings: The Molecular Evidence. JOURNAL OF EXPERIMENTAL ZOOLOGY (MOL DEV EVOL) 304B:86–90.

6.Carrano, M. T. 1998. Locomotion in non-avian dinosaurs: integrating data from hindlimb kinematics, in vivo strains, and bone morphology. Paleobiology Vol.24, No. 4, pp. 450-469.

7.Padian, K., Horner, J. R. 2011. The evolution of ‘bizarre structures’ in dinosaurs: biomechanics, sexual selection, social selection or species recognition?. Journal of Zoology, 283: 3–17.

Evolution of Eusociality

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by Lingshan Chen

EusocialView Original Graphic

Eusociality is a sociobiological phenomenon in which adult members are divided into reproductive and non-reproductive castes and have overlapping generations of parent and offspring. The reproductive caste contains only one or a few members of the entire colony and is responsible for producing all the offspring. Conversely, the non-reproductive caste is composed of the majority of the colony. They cooperatively raise the young and otherwise provide and protect the colony. This extreme form of altruism and social life has long perplexed scientists as it contradicts the intrinsic selfishness displayed by organisms.

Although some mammals are eusocial, the majority of eusocial species belong to  the phylum Arthropoda and order Hymenoptera, most commonly seen in bees, wasps, and ants.  There are several advantages of the organized structure of eusociality. Resources such as food, territory, and protection are maximized in comparison to solitary individuals.

For example, the leaf-cutter bee, Megachile rotunda, is a solitary species. These bees reproduce, forage, and raise eggs individually. Each female leaf-cutter bee adult must cut leaves to build nests for each egg. Inside each nest, the female must provide pollen and nectar to feed the larvae. When the bee leaves to forage for food, the nests are left unprotected. In contrast, honey bees have a queen that lays many eggs each day to populate the colony. Worker bees are sterile and provide food and protection for juvenile siblings. Though many honey bees are not reproducing, the productiveness and safety of the colony as a whole has increased.

If eusociality is advantageous, why is it so rare? To investigate this question, we can look at the origin of eusociality. Evolutionary theories propose that at first, solitary organisms group together for mutual benefits. In Hymenoptera, eusociality may have arisen because relatedness between individuals is maximized because of their reproduction method. In this system, fitness benefits from related individuals are a lot greater than the cost to the individual. An intermediate step occurs when workers develop the choice to stay and help with the colony or start their own colony. Other theories also suggest that eusocial evolution follows a series of stages that start with the formation of groups between related or unrelated individuals that must persist. For the group to remain cohesive, the acquisition of pre-adaptive traits such as nest building are necessary. Following this stage, eusocial genes emerge through mutation or recombination. As a result of multiple driving forces, primitive eusocial colonies reach a transition stage termed the  “point of no return”, during which different castes develop and maintain morphological differences, and evolve into advanced eusociality.

For more information please see the following papers:

Bang, A., & R. Gadagkar. 2012. Reproductive queue without overt conflict in the primitive eusocial wasp Ropalidia marginata. PNAS 109:14494-14499.

Dolezal, A.G., Flores, K.B., Traynor, K.S., & G.V. Amdam. 2013. “The evolution and development of eusocial insect behavior.” Advances in Evolutionary Developmental Biology (2013): 37-57

Grüter, C., Menezes, C., Imperatriz-Fonseca, V.L., & F. L. W. Ratnieks. 2012. A morphologically specialized soldier caste improves colony defense in a neotropical eusocial bee. PNAS 109 (4) 1182-1186.

Nowak, M.A., Tarnita, C.E., & E.O. Wilson. 2010. The evolution of eusociality. Nature 466(26) 1057-1062.

Plowes, N. 2010. An Introduction to Eusociality. Nature Education Knowledge 3(10): 7

Richards, M. H., Wettberg, E.J., & A. C. Rutgers. 2003. A novel social polymorphism in a primitively eusocial bee. PNAS 100 (12) :7175-7180.

Rueffler, C., Hermisson, J. & G.P. Wagner. 2012. Evolution of functional specialization and division of labor. PNAS 109(6) E326-E335.

Strassmann, J.E., Queller, D.C., Avise, J.C., & F. J.Ayala. 2011.  In the Light of Evolution V: Cooperation and Conflict Sackler Colloquium – Introduction. PNAS 109 10787-10791.

Wilson, E.O. & B. Hölldobler. 2005. Eusociolity: Origin and consequences. PNAS 102(38) 13367-13371.

Transition from Sea to Land

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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

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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.