Rehnuma Tabassum
Freshman
School of Life Sciences
Independent University, Bangladesh
August 19th, 2017
What selective forces govern evolution? There are many answers to this, and it often boils down to adaptations that confer individuals with reproductive and survival advantages. The Red Queen hypothesis provides an elegant model for how organisms adapt to survive that focuses on coevolution between different organisms that drives innovation and adaptation. It was proposed by Leigh Van Valen in 1973, and describes evolutionary arms races like that between hosts and parasites, where host and parasite constantly try to evolve new strategies to attack and defend against each other.
The name of the hypothesis came from the sequel to Lewis Carroll’s Alice in Wonderland, entitled Through the Looking Glass, in which there is a scene with Alice and the Red Queen constantly running just to remain in the same spot. How does this apply to biology? Let’s go through an extreme example. If a parasite species evolves an adaptation to infect and kill its host, most or all of the host species would be expected to die as the parasite spreads through the population. However, if a few of the host individuals turn out to be immune to the parasite, those individuals would become common and multiply. At this point, the parasite would be under pressure as it would be running out of hosts to infect. If any individual parasite then evolves a new adaptation to infect the now immune host, it would spread through the host population again to restart the cycle. The host and the parasite are constantly co-evolving, or in other words, locked in an arms race. Thus, they remain in the same position relative to each other. This is the reason it was named the Red Queen Hypothesis. Parasites do not have to kill; any reduction in the reproductive fitness of hosts would reproduce these dynamics by selecting for more immune hosts.
The Red Queen hypothesis has been used to try to answer several important questions in evolution [1]. For instance, it has been used to explain the relatively constant extinction rates (proportion of a large group, such as mammals, that goes extinct over a period of time) across groups of organisms that have existed for different amounts of time. Constant extinction rates mean that organisms do not keep getting better adapted with time. This is consistent with coevolution with parasites in which organisms must keep adapting to stay in the same position (of adaptedness), and failure to respond to the parasite’s next innovation could result in extinction at any step.
The Red Queen also provides an explanation for the evolution of sex. This is an important question because asexual reproduction ensures passage of more of an organism's genes (100%!) compared to just half by sexual reproduction. The reproductive instinct is largely a product of our innate drive to pass on our genes. So why have sex and pass on just half? Well it turns out that sexual species have much better chances of survival than asexual species under adverse conditions as there is greater diversity in the population as a result of recombination of genes and traits. And parasites provide the most immediate and ubiquitous selective pressures in the environment of hosts, and are thus thought to have been important in the evolution of sex.
Freshman
School of Life Sciences
Independent University, Bangladesh
August 19th, 2017
What selective forces govern evolution? There are many answers to this, and it often boils down to adaptations that confer individuals with reproductive and survival advantages. The Red Queen hypothesis provides an elegant model for how organisms adapt to survive that focuses on coevolution between different organisms that drives innovation and adaptation. It was proposed by Leigh Van Valen in 1973, and describes evolutionary arms races like that between hosts and parasites, where host and parasite constantly try to evolve new strategies to attack and defend against each other.
The name of the hypothesis came from the sequel to Lewis Carroll’s Alice in Wonderland, entitled Through the Looking Glass, in which there is a scene with Alice and the Red Queen constantly running just to remain in the same spot. How does this apply to biology? Let’s go through an extreme example. If a parasite species evolves an adaptation to infect and kill its host, most or all of the host species would be expected to die as the parasite spreads through the population. However, if a few of the host individuals turn out to be immune to the parasite, those individuals would become common and multiply. At this point, the parasite would be under pressure as it would be running out of hosts to infect. If any individual parasite then evolves a new adaptation to infect the now immune host, it would spread through the host population again to restart the cycle. The host and the parasite are constantly co-evolving, or in other words, locked in an arms race. Thus, they remain in the same position relative to each other. This is the reason it was named the Red Queen Hypothesis. Parasites do not have to kill; any reduction in the reproductive fitness of hosts would reproduce these dynamics by selecting for more immune hosts.
Computer simulation of Red Queen dynamics. Indiana University
The Red Queen hypothesis has been used to try to answer several important questions in evolution [1]. For instance, it has been used to explain the relatively constant extinction rates (proportion of a large group, such as mammals, that goes extinct over a period of time) across groups of organisms that have existed for different amounts of time. Constant extinction rates mean that organisms do not keep getting better adapted with time. This is consistent with coevolution with parasites in which organisms must keep adapting to stay in the same position (of adaptedness), and failure to respond to the parasite’s next innovation could result in extinction at any step.
The Red Queen also provides an explanation for the evolution of sex. This is an important question because asexual reproduction ensures passage of more of an organism's genes (100%!) compared to just half by sexual reproduction. The reproductive instinct is largely a product of our innate drive to pass on our genes. So why have sex and pass on just half? Well it turns out that sexual species have much better chances of survival than asexual species under adverse conditions as there is greater diversity in the population as a result of recombination of genes and traits. And parasites provide the most immediate and ubiquitous selective pressures in the environment of hosts, and are thus thought to have been important in the evolution of sex.
Sexual reproduction thrives in the presence of parasites, as described in the text. Kimberly Battista
The advantage of sexual reproduction has been observed in various studies. One study compared sexual and asexual snail lineages (in a species that was capable of both) in an environment that contained natural parasites [2]. Among asexually reproducing snails, the dominant clonal variants were replaced by clonal variants that were initially rare as the parasites adapted to infect the common variants. The sexually reproducing snails persisted through the study without such replacement, evidently harboring sufficient diversity to keep the parasites from wiping out large fractions of the population. This supported the hypothesis that sexual reproduction can provide an advantage in the battle against coevolving parasites.
Not only are parasites present everywhere, they tend to reproduce very quickly and hence can adapt quickly too. In regard to that, the Red Queen hypothesis can also be used to explain the evolution of adaptive immunity, in which the immune system responds anew every time a new parasite or bacteria attacks our body by learning and remembering how to fight that specific pathogen. Because larger mammals like humans have long generation times, the adaptive immune system provides a means of countering the rapidly evolving pathogens in the environment.
It is important to note that there are probably many other factors that shaped the course of evolution, but the Red Queen hypothesis provides a useful model for addressing several basic questions in evolution, and has been supported by numerous evidence-based approaches.
Bibliography:
[1] M. A. Brockhurst, T. Chapman, K. C. King, J. E. Mank, S. Paterson, and G. D. D. Hurst, “Running with the Red Queen: the role of biotic conflicts in evolution,” Proc. Biol. Sci., vol. 281, no. 1797, p. 20141382, Dec. 2014.
[2] J. Jokela, M. F. Dybdahl, and C. M. Lively, “The Maintenance of Sex, Clonal Dynamics, and Host‐Parasite Coevolution in a Mixed Population of Sexual and Asexual Snails.,” Am. Nat., vol. 174, no. S1, pp. S43–S53, Jul. 2009.
Not only are parasites present everywhere, they tend to reproduce very quickly and hence can adapt quickly too. In regard to that, the Red Queen hypothesis can also be used to explain the evolution of adaptive immunity, in which the immune system responds anew every time a new parasite or bacteria attacks our body by learning and remembering how to fight that specific pathogen. Because larger mammals like humans have long generation times, the adaptive immune system provides a means of countering the rapidly evolving pathogens in the environment.
It is important to note that there are probably many other factors that shaped the course of evolution, but the Red Queen hypothesis provides a useful model for addressing several basic questions in evolution, and has been supported by numerous evidence-based approaches.
Bibliography:
[1] M. A. Brockhurst, T. Chapman, K. C. King, J. E. Mank, S. Paterson, and G. D. D. Hurst, “Running with the Red Queen: the role of biotic conflicts in evolution,” Proc. Biol. Sci., vol. 281, no. 1797, p. 20141382, Dec. 2014.
[2] J. Jokela, M. F. Dybdahl, and C. M. Lively, “The Maintenance of Sex, Clonal Dynamics, and Host‐Parasite Coevolution in a Mixed Population of Sexual and Asexual Snails.,” Am. Nat., vol. 174, no. S1, pp. S43–S53, Jul. 2009.
Rehnuma is a first-year student in the Microbiology department. She writes:
"I am a person who is always positive when it comes to learning something different or knowing something unknown about our existence. I have always wanted to be a great scientist, like Robert Hooke and others who have changed our way of thinking about life and life-forms .Of course I'm nowhere close to these people yet, but my dream is alive."
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