Coevolution Theory: Autumn Leaves

Lac Du Flambeau, Wisconsin, USA

Photo by: Cindy Brintnall

Autumn Leaves: A Theory in Coevolution

Good Evening readers! 

As autumn is in full swing here in Australia, I can't help but miss all the bright colors I get to see back home during this season. I wanted to find a way to incorporate it into my studies, and it turns out, there is science behind it (who knew), AND it is relatable to coevolution! Consequently, this week I will be discussing a theory behind why the colors change in the fall. It turns out, it may be all because of bugs.

 The most popular belief today is that the bright autumn colors are just a result of cell deterioration in deciduous trees (Archetti, 2000). However, Archetti states that the trees might change color due an adaptive change driven by coevolution between insects and trees.

The theory states that the bright colors of the trees signal their fitness and soundness, and parasites will then pass the healthy-looking trees over as hosts. The advantage to the trees is less parasites and eggs laid on it, and the advantage to parasites is that they can more easily choose a suitable host.

According to Archetti, this theory follows the rules of Amotz Zahavi's "Handicap Principle." This means that the trees have evolutionarily adapted to use an expensive and honest signaling system. Trees in poor health cannot afford to produce such flamboyant signals, and fail to ward off the preying parasites. The Handicap Principle is usually used as an example in sexual selection, such as when fitter male birds have longer or brighter feathers that can hinder them, but their expense also rewards them. This is true with the trees as well, because the trees who can "afford" the price of brighter colors are the ones who will receive less damage by the parasites.

However, there are a few issues with this theory.
- The system would hold up under "normal" systems, but in a particularly poor or particluarly good year, it wouldn't work.
- Insects are known to favor the color yellow
-Aphid and other termites' migrations do not take place in the short leaf-change timespan  (Wilkinson, 2002)


What do you think? The idea has yet to have overwhelming empirical evidence, but it does have some merit. Let me know, as always,  in the comments below!

Thanks for tuning in, and have a phenomenal week!


D



References:

Archetti, M. (2000). The origin of autumn colours by coevolution. Journal of Theoretical Biology, 205(4), 625-630.

Wilkinson, D. M., Sherratt, T. N., Phillip, D. M., Wratten, S. D., Dixon, A. F., & Young, A. J. (2002). The adaptive significance of autumn leaf colours. Oikos, 99(2), 402-407.

Coevolution and Pollination

Coevolution and Pollination:

Ophrys : Bee Orchids

Hello readers,

Today the topic is Coevolution and Pollination, and I am going to introduce to to a fascinating Genus of plants called Ophrys, or "bee orchids."

The Bee orchids depend on bees for pollination, so evolutionarily, they had to evolve ways to keep the bees interested and ensure pollination. This should not come as a surprise considering that many plants attract bees to cross pollinate, however, the mechanism this genus uses is quite interesting.

Rather than evolving for  just smell or color, bee orchids actually evolved to display a flower in the same shape as the bee itself. The floral mimicry is a tactic to encourage a process known as pseudocopulation. This is when a male bee, seeing what he thinks is a female, will land, attempt to mate, and pollinate the flower. The flower is not only in the shape of the bee, but also releases mimic pheromones, called allomones, that smell like a female.

During pseudocopulation, pollen will stick to the bees head or abdomen. This pollen will travel on the bee until it becomes attracted to another "mate," where pollen exchange can occur and pollination will happen. 

I find this story of coevolution particularly interesting, and it brings up many evolutionary questions. Because the bee orchid species depends entirely on the bee, it has devoloped use of deception to suit its purpose. But once the bee has been duped, it may not revisit the flower or the same type of plant again. Do you think this species would have increased its success by developing some other traits? 

The coevolution is an extreme example of mutualism, because the bees need flowers just as the flowers need bees. However, mimicry is typically seen in coevolution between prey-predator animals. Do you think the bee orchids are trying to out compete other plants? Or are they just mutual-beneficiaries-turned-frenemies?  Do coevolutionary "arms races" occur between mutualistic species?

Please discuss in the comments below! I would love to hear what you think. 

Thanks for reading, and have a phenomenal day! 

D

Sources:

Borg-Karlson, A. K. (1990). Chemical and ethological studies of pollination in the genus Ophrys (Orchidaceae). Phytochemistry, 29(5), 1359-1387.

Schiestl, F. P. (2005). On the success of a swindle: pollination by deception in orchids. Naturwissenschaften, 92(6), 255-264.

(http://news.stanford.edu/news/2010/april/gifs/australia_fire_news.jpg)

Hey Folks!


The co-evolutionary issue at hand today has quite the Aussie spirit to it. This is a story about the coevolution of Australia's wildlife, particularly kangaroos, with a changing environment due to humans.

Aboriginals have been using brush fires as a form of hunting for thousands of years, to capture lizards in the winter. Scientists believe that these practices lead to the success of some animals over others. For example, the small fires burned down the grass, and exposed the small patches of land to more easily spot lizard mounds and other prey for foragers.

Over time, species evolved to adapt and even become dependent on the small fires that the aboriginals used. The patches left by burning left areas of old and new vegetation, which benefitted species like kangaroos, that could hide from predators in the old vegetation and use new growth patches as a food source. The kangaroo populations actually decline in areas outside the areas affected by human fire.

These ecological benefits of the fires set by Martu peoples highlights what might be an unintentional sustainable practice. Although setting the grasslands on fire may sound like the opposite of helping an ecosystem, the blazes are smaller than those caused naturally by lightning, and the controlled fires may actually prevent massive destructive fires from sweeping over a larger area.

Australia has been seeing a decline of mammals, and it may be due to a removal of practices like the aboriginal burning regimes and other human intervention, such as introduced species. The reinstallation of these fires might be able to save several species of animals native to this habitat and adapted to the occasional small fires.

This is a story of removing an element that one species has coevolved to. When a rapid change occurs  (like removing the fire mosaic), the small, fire-adapted mammals are exposed to different conditions, that put pressure on their life habits and expose them to dangers like large widespread bush fires.



Thanks for reading today!

Can you think of any other instances in which animals coevolved to a human activity that was eventually stopped? Let me know in the comments below!


Thanks and have a great day!


D



Resource:

Codding, B. F., Bird, R. B., Kauhanen, P. G., & Bird, D. W. (2014). Conservation or Co-evolution? Intermediate Levels of Aboriginal Burning and Hunting Have Positive Effects on Kangaroo Populations in Western Australia. Human Ecology, 42(5), 659-669.

Happy Easter,  Folks!



 So far, we've covered two types of coevolution. Predator and prey, as with the snake and lizard, and host and symbiont, as with the wolves & humans. Today, we will discuss a third type: host and parasite evolution.

  http://www.evolbio.mpg.de/15867/header_image.jpg

Host-parasite coevolution refers to complementary genetic change of two opponents driven by mutual selective pressure. Both species are constantly trying to get the better of each other, but reciprocal adaptations make it almost impossible for one side to get the upper hand.

Host-parasite evolution is important across a range of fields including wildlife ecology and agriculture. but perhaps one of its most outstanding features, is that it is opening a door to studying disease in the medical field.

Many fatal human diseases like influenza, AIDs, and malaria have been known to be constantly evolving, and thereby evading the treatments or vaccinations against them. Scientists want to further understand the intricacies of the interactions of diseases with the human immune system and their coevolution patterns to be able to make effective more effective treatment and perhaps an innovative solution to protect human lives.

The problem is that studying and validating coevolution with disease is a difficult thing to do. Demonstrating co-evolution is difficult because the world of science has inadequate "understanding of either the genetics or molecular basis of the host–pathogen interaction; involve-ment of polygenic traits; fitness constraints on these traits, including constraints imposed by simultaneous interactions with multiple hosts or multiple pathogens; phenotypic plasticity; and the long time scales involved" (Woodhouse et al 2002). So what are the solutions? Find concrete evidence of human-pathogen coevolution, of course. But to do this there need to be new modern approaches to how we search for  and detect coevolution. Woodhouse et al suggests that one way to do this is to look to the molecules for clues. That is, search for changes in each species' genes that are involved in interaction between the two. Reciprocal polymorphisms in the genes could provide evidence that the host and pathogen are coevolving and reacting to the other's adaptations over time. 

I brought this to you readers because I am interested to know...

 Do you think humans can "win" over pathogens by science and wit alone? 

Will understanding the interactive foundations of host and pathogen and consequent adaptations be a savior? What will this mean for the future of medicine or pathology?

Do medical "solutions" just drive disease to evolve faster and become more dangerous?


Overall, I think that our understanding needs to be deeper in this matter if we want to help save more lives in the present. That said, I'm not sure if humans are tempting nature or fate by trying to win an evolutionary battle thats been raging for thousands of years. Falsely thinking we have rid the world of a disease could make us more susceptible to an adaptation or mutation in the disease in the future. There is no doubt that there are some incredible medical innovations waiting to be invented.


Thanks for reading and comment below what YOU think on the matter. 

Have a great week,  

D

 

Reference:

Woolhouse, M. E., Webster, J. P., Domingo, E., Charlesworth, B., & Levin, B. R. (2002). Biological and biomedical implications of the co-evolution of pathogens and their hosts. Nature genetics, 32(4), 569-577.

Hello Readers! Hope your weekend is going phenomenal!

Today I want to talk about coevolution in predator and prey. Unlike mutualistic coevolution, where species evolve to actively benefit each other, predator-prey coevolution is an "arms race." This means each species is trying to evolve faster and better ways to either attack or escape. In the end, the prey that has the best escape tactics passes on its genes, and the predators most successful at ambush also survives to pass on its genes. This locks in a never ending process of predator and prey trying to best each other, and gives science some cool adaptations to watch evolve.

Some prey species have evolved flashy characteristics to escape predators such as camouflage, mimicry, and warning coloration. But visual displays don't work for every species. Some animals have to evolve their senses as well. The velvet gecko, (Oedura lesueurii) has had to evolve its sharp chemosensory skills in order to survive the wrath of its mortal enemy, the broadheaded snake (Hoplocephalus bungaroides) (Downs & Shine, 1998).

                           Fig. 1a                                            Fig. 1b

                            

Figure 1a: The velvet gecko(Oedura lesueurii). http://www.arod.com.au/arod/pictures/squamata/gekkonidae/amalosia/Amalosia-lesueurii-thumb.jpg
Figure 1b: The broacheaded snake (Hoplocephalus bungaroides)  http://cdn1.arkive.org/media/1D/1DF710F3-9E7F-42FA-885C-B58FC330E80F/Presentation.Large/Broad-headed-snake.jpg


In their study, Downs and Shine have found that the velvet gecko is so tuned into the chemical scent of the broadheaded snake, that they did not respond to the scent of a related snake that does not predate on geckos. This means that their chemosensory skills may have evolved as a direct response by predation pressure from the snake species.

The snake uses an ambush tactic by laying in crevices and rocks waiting for an unsuspecting gecko to crawl into their trap. The snakes can spend up to 4 weeks waiting for dinner to come along. This may seem a disadvantage compared to other predators who actively seek their prey, but to get a sharp sensing velvet gecko, the snakes have to be tricker. Researchers think that the snake lies in wait for so long so that it does not risk spreading its scent for the gecko to pick up. This behavior would be the "arms race" response to the gecko's evolved chemosensory skill. In the experiment, the geckos all avoided crevices fully scented with the broached smell, but some individuals fell for the partially scented ones, meaning that the lie and wait method may be advantageous for the snake.

The geckos ability to sense the snakes is an example selective advantage, because sharp individuals are able to avoid scented crevices and the awaiting predators.


If the arms race is truly what drove these changes in behavior and sensing, the cost may have been greater to the snake. According to Downes & Shine, the lie and wait tactic may have put a strain on the reproductive and ecological habits of the snake species. This predatory behavior may have lead the snakes to a low reproduction rate, and threaten the species' success in the future. If this species where to fail in response to an arms race, has the prey won? Has any species ever "won" an arms race?

If you have any example of a cool "arms race" situation or want to discuss this post, feel free to comment below!


Thanks for reading, and have a good week! :)

D



Resource:

DOWNES, S., & SHINE, R. (1998). Sedentary snakes and gullible geckos: predator–prey coevolution in nocturnal rock-dwelling reptiles. Animal Behaviour, 55(5), 1373-1385.

Hello, Readers!

This week I am going to introduce you to a new kind of co-evolution, and it is much smaller than the wolves I discussed last time...

We are going into the sexual organs of mice, to learn about coevolution between gametes. While this sounds a little far-fetched, a study published in 2014 found that mice gametes co-evolve over generations, fighting a microscopic arms race with each other. Over 24 generations, researchers found that female mice that evolved in a polygamous program had "more defensive ova" than the females evolved under a monogamous system.

This study is interesting because it proves that sexual competition isn't just between males and females, or males and males, but between the sperm and egg. The female defense is driven by sperm competition, and acts by the use of a sperm barrier that can intercept or moderate sperm entrance. Sperm competition was seen after 8 generations of mice, when the male mice would output more sperm with a higher motility. Females eggs that were evolved under polygamous regimes were less likely to get fertilized than the eggs from monogamous regimes in a controlled test. While lower sperm defense can be a positive in monogamy, ova defenses can be beneficial in an environment with high sperm availability. This is because the female then is able to be fertilized by the mate that has the most competitive or fit sperm. This is an evolutionary advantage to the female, who can then have the fittest offspring. This  "postcopulatory sexual selection" may be able to explain asymmetry in fertilization rates when comparing different populations. Firman et al. also suggests that competition like this may also lead to genetic divergence in populations, eventually making the 2 populations impossible to breed due to reproductive isolation.

The researchers were able to study just the gamete integration using in vitro fertilization. 

This study is interesting to me, because it makes me wonder about all the other species that have gametes that are coevolving and competing with one another, especially mammals. Coevolution is an incredible thing to see among whole organisms, but between mere cells? That is something beyond cool. No matter how small, life finds a way to compete for the #1 spot. 

Thoughts? Please share below. I'd love to hear what you think of the smallest layer of sexual competition and coevolution!

Have a good week,

D

Reference:

Firman, R. C., Gomendio, M., Roldan, E. R., & Simmons, L. W. (2014). The coevolution of ova defensiveness with sperm competitiveness in house mice. The American Naturalist, 183(4), 565-572.

                                                                   

                                                             http://disqussion.club/wp-content/uploads/2014/08/dog-wolf.jpg

Hey Folks!

     Welcome to my first official blogpost. Today I'll talk about something everyone can relate to in the world of coevolution, and that's dogs! Human's best friend wasn't always in our backyards and on our couches, they may have actually coevolved with us. You definitely wouldn't find a pack of wild pugs somewhere in the forest, so how did our furry friends come to be? Where did they come from?

                                           

     As you might have gathered, humans didn't suddenly find an island of dogs and form a magical partnership in the ancient past. Dogs actually descended from wolves, particularly European wolves (Thalmann et al 2013). It was generally thought that the domestication of dogs occurred 11,000 to 16,000 years ago, but more recent DNA evidence using fossils suggests that domestic dogs could've had multiple origins, and could've been domesticated as far back as 135,000 years ago (Vilá et al 1997). Whether its tens of thousands or hundreds of thousands of years, we've been hanging around dogs a very long time, and there is evidence that we have, and continue, to coevolve with our beloved companions.

                                                         

                                        https://gollygeedotorg1.files.wordpress.com/2013/01/dog_history_tree.jpg?w=540&h=366

      Schleidt & Shalter (2003) suggest an alternative hypothesis to the popular belief that we domesticated wolves after the agricultural evolution. They state that the canids used to follow herds of ungulates and feed on the weak, old, and sick individuals. At this time, early humans were hunters and gathers, and adapted to life on the savanna. Schliedt & Shalter claim that at this time, some early humans adopted the lifestyle of the canids, following herding animals for food. They joined the wolves as mutual predators. Early humans and canids, therefore, would have had their first contact as mutual predators, and coevolved together from that point, to eventually become loyal servants and friends of our modern human race. As human skill diversified, the ways in which dogs aided us did as well, from herding creatures to seeing eye dogs.

                                           https://s-media-cache-ak0.pinimg.com/originals/66/45/82/66458285b557eb7c9a2c6fb2017105ac.jpg
   
      Additionally, humans and dogs may have similarly evolved genetically as we faced the same ecological pressures together. After sequencing the genomes of several dogs and wolves, researchers found that certain genes may have indeed evolved parallel to each other over time (Wang et al 2013). this is known as convergent evolution. Genes that were under positive selection pressure at the time for canines were the same as some that were positively selected for in humans. Genes involved in processes like metabolism, serotonin levels,  and even cancer were evolving parallel between our 2 species. Wang and his team think that both species may have been evolving in response to a pressure in their environment such as overcrowding. The genetic change in serotonin levels may be associated with the need for less aggression to live in a crowded environment. This study suggests that studying dogs might shed light on human evolution as well as human disease and neurological disorders.


      But really, are we all that surprised by this? We always knew our pups were special. They are always great listeners & understand us like nothing else. No seriously, there is science behind that! In a study done in 2001, dogs were tested on the ability to pick up social cues of humans, and dogs were better than chimpanzees! They have the same ability as a small child to pick up on communications like gazing, head nodding, and pointing  (Soproni et al 2001). This could be because dogs have learned to pick up on human signals over time, because it can benefit them. For example, when you drop a piece of food on the floor and are to lazy to clean it up, your best friend will be your living vacuum at the point of a finger! Mutual benefits for both parties.

                                          http://www.adogsdayout.com/wp-content/uploads/2012/07/Dogs1.jpg

   No matter how long we guess we've been connected or whether we evolved together by convergent evolution or coevolution, we already knew that our pups hold a special place in our hearts and minds. Go home and give your pooch a pat for dealing with us all these years, and a treat to thank them for choosing us.


Here's a bonus picture of me and my pup, just to show off how lucky I am :)

Enjoy your weekend, and I would love feedback on my first post!

Thanks for stopping by,

D




References:

Schleidt, W. M., & Shalter, M. D. (2003). Co-evolution of humans and canids. Evol. Cogn, 9, 57-72.

Soproni, K., Miklósi, Á., Topál, J., & Csányi, V. (2001). Comprehension of human communicative signs in pet dogs (Canis familiaris). Journal of Comparative Psychology, 115(2), 122.

Thalmann, O., Shapiro, B., Cui, P., Schuenemann, V. J., Sawyer, S. K., Greenfield, D. L., ... & Wayne, R. K. (2013). Complete mitochondrial genomes of ancient canids suggest a European origin of domestic dogs. Science, 342(6160), 871-874.

Vilà, C., Savolainen, P., Maldonado, J. E., Amorim, I. R., Rice, J. E., Honeycutt, R. L., ... & Wayne, R. K. (1997). Multiple and ancient origins of the domestic dog. Science, 276(5319), 1687-1689.

Wang, G. D., Zhai, W., Yang, H. C., Fan, R. X., Cao, X., Zhong, L., ... & Zhang, Y. P. (2013). The genomics of selection in dogs and the parallel evolution between dogs and humans. Nature communications, 4, 1860.