Cell Population Evolution

We have learned that evolution occurs at the population level, and that natural selection occurs at the individual level. The evolution of an individual is not possible, but what about the evolution in an individual? The evolution of populations of an individual's cells can lead recovery like in the case of the young boy who suffered from adenosine deaminase deficiency, but the more common case presented in the textbook is the development of cancer.
Cancer cells arise from a cell that has a high number of mutations, according to the Cancer Genome Project cancer cells on average have 60 or more mutations. The older a cancer cell is the more mutations it will accumulate because the tumor population will begin from a single cell with low genetic diversity. The cancer cells develop their mutation through microevolution but after the mutations are present there are environmental pressures and other natural forces that act as natural selective forces inside the body. The cancer cells can undergo its own form of genetic drift called metastasis, which is when a cancer cell migrates to another part of the body. We have looked at another case where there has been an evolution inside of a person when looking at HIV, and like with HIV some scientists say that future treatments of cancer need to anticipate the evolution of the cancer cells to the selective force or treatment. The authors of one paper say that the best treatment will use the natural selection process to direct the cancer away from a resistant form.
http://www.sciencedaily.com/releases/2013/01/130122101454.htm
http://www.nature.com/scitable/topicpage/cell-division-and-cancer-14046590
http://www.sciencedaily.com/releases/2012/06/120621101905.htm

Attack of the killer fungus

Cordyceps is a genus of ascomycete fungus that feeds on insects and arthropods. An illustration of this is in our textbook on page 542, figure 14.13. The most common of species of the genus Cordyceps is Cordyceps sinensis is also known as the "caterpillar fungus." Upon doing research for this topic, I could not find a basic overview of the genus Cordyceps, so I will briefly discuss some of the species.
Cordyceps sinensis is found on the Tibetan Plateau and preys on ghost moths primarily. Spores will infect the host while they are underground larvae, then germinate, ultimately killing and mummifying the host. Eventually a fruiting body will burst from the host. The fruiting body is an ascocarp and usually grows up to 10 cm long and .5 cm wide. They are usually orange and can be brown as well.
Cordyceps militaris is parasitic on buried larvae and pupae pf insects and grows alone usually in summer and fall. It is widely distrubuted in North America and is most popular in the Rocky Mountains. The fruiting body is about 2 to 8 cm long and can be up to .5 cm wide. It is club shaped with the top wider than the base. Described as orange and often curved, it narrows at the base and arises from the buried pupa or larvae.

There are more than 400 species of Cordyceps. They can take many different shapes and sizes and infect numerous hosts. The mind blowing video below describes in detail how Cordyceps affects a hosts. Imagine if this fungus could somehow become so advanced that it could infect humans. It would be something straight out of a science fiction horror movie!

For more information on Cordyceps check these websites out:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3175130/

http://en.wikipedia.org/wiki/Ophiocordyceps_sinensis

Sperm Competition

The male's reproductive success isn't just based on the ability to mate with a female. It goes from direct male to male competition to sperm competition. If a female mates with two or more males, the male whose sperm reaches the eggs first or reaches the most eggs will have a higher reproductive success. Various species have developed adaptations or traits that could give them an advantage over another male. One trait that can be seen in the Mediterranean fruit fly is the production of large ejaculates. The more sperm the fly produces the greater probability that some of its sperm reaches the female's eggs. The larger the ejaculates the greater probability the fly has of reproductive success. Some males take a more direct route to insure their reproductive success. He will guard his mate to insure that no other male will mate with his female. Some spiders deposit a copulatory plug into the female. This plug insures that the female cannot mate with any other mate. Other adaptations include prolong copulation, applying pheromones, or barbed horns on the penis. The barbed horn adaptation is seen in damselflies. Scientists have studied these adaptations and they have shown to be very successful. They are sharp needle-like spikes coming off of the male’s penis. Their job is to scoop the sperm out of the female from her previous mates. This insures that his sperm is only competing against few or no other mates. Often though multiple males can impregnate the female. This produces offspring with different fathers at the same time. An animal’s main goal is to produce viable offspring. Many species have gained adaptations to help them better accomplish this goal. Some of these adaptations can be seen when comparing sperm competition among males. These adaptations enable males to insure that they have a high reproductive success.

For more information:

http://faculty.vassar.edu/suter/1websites/bejohns/mateselection/files/sperm_comp.htm

http://www.life.umd.edu/faculty/wilkinson/honr278c/PDF/Wigby04.pdf

Sexual selection and the roles of males and females

So far we have learned how natural selection impacts various things in the environment. However, there are certain environmental aspects that natural selection cannot explain. Sexual dimorphism is the difference in the males and females of a species. Natural selection cannot explain these differences between sexes and Darwin was puzzled by the occurrence. Sexual dimorphism can be the difference in size, coloring, or body structure between the sexes. One example is the cardinal. The females are a dull brownish color, while their male counterparts are a vibrant red. Male birds of paradise, on the other hand, are known for their elaborate feathers and strange mating dances. Females are much less ornate and do not perform these elaborate dances. Males and females play different roles in taking care of the offspring. This is otherwise known as parental investment. Parental investment is the time and energy spent to take care of the offspring as well as to create the actual offspring. A trade off is seen when comparing parental investment techniques. The more energy and time the parent spends on the offspring the higher potential for reproductive success it has. However, the more time spent on the offspring, the parent’s remaining reproductive success decreases. Many species have zero parental care and they produce mass amounts of offspring to better the chance that some will survive to reproduce. Females, in the majority of the species, are the ones that expend the most energy to take care of the offspring. Comparing male to female potential reproductive success vary from species to species. Species either have high parental care and few offspring or many offspring with little parental care. Mammals usually care for their offspring for many months while many insects just produce mass amounts of offspring with no parental care.

http://quantumbiologist.wordpress.com/page/2/

For More Information:

http://www.nature.com/scitable/knowledge/library/sexual-selection-13255240

http://beheco.oxfordjournals.org/content/11/2/161.full

The Trade-Off Hypothesis

The evolution of virulence has 3 different modes and hypotheses. The first is coincidental mode. This hypothesis says that the virulence is not the target of selection but it is a coincidence or by product of selection on other traits. The second is the short-sighted hypothesis. In this hypothesis the fitness in the host is increased but the ability of transmission to a new host is less likely. The third hypothesis is the trade-off. This hypothesis is where there is a trade-off between killing their host and also increasing their ability of transmission.

There are many examples of the trade-off hypothesis but the book shows one example of a pathogenic fungus that kills an insect and sprouts from it. I found this interesting for a fungus to kill its host but it is actuallly quite common. An interesting exmple is the zombie carpenter ant that has fallen victim to the fungus in the family Cordyceps. The fungus releases chemicals that exert a mind control over the ant. The ant climbs a plant and latches it mandibles at the stem of the leaf. This becomes the ants resting place, because the stalk of the fungus sprouts out of the ants head. The fungus kills its host but in the process it increases its potential of transmission by exerting its mind control.
 
http://neurophilosophy.wordpress.com/2006/11/20/brainwashed-by-a-parasite/
http://www.forensicgenealogy.info/contest_171_results.html

Kin selection

Kin selection is simply changes in gene frequencies across generations that are driven in part by interactions between related individuals, and it is also known as the theory of social evolution. Many cases of evolution can be studied by examining how someones relatives can influence another persons fitness. You can see many examples of this in animals and in humans. Eusociality (true sociality) is used to describe social systems with three characteristics: an overlap in generations between parents and their offspring, cooperative child care, specialized heredity of non-reproductive individuals. A great example of kin selected traits can be seen in monkey communities. Data shows that maternal kin, kin related to by mothers, behaved more preferentially towards each other. However, once kin was beyond half-siblings or further relatives, this dropped significantly. Alarm calls in ground squirrels is another example. While they may alert others of the same species of danger, they draw attention to the caller and expose it to increased risk of predation. It has been observed that calls occurred most frequently when the caller had relatives nearby. This is a fascinating example because it is as if they are looking out for their family members. A similar example can be seen in the courtship behavior of the wild turkey.  A subordinate turkey may help his dominant brother put on an impressive team display that is only of direct benefit to the dominant member. Let me give you a question a think about. If your mother, sister, brother, father, even grandfather, what have you, was in need of something, for this example we will say help moving from an old home to a brand new home, but oh darn on this same weekend your best friend is having their birthday party! Which would you choose? Me personally, I would choose helping my family member. Because (as bad as it sounds) family is more important. Studies have been done on this, and the majority of people will help a kin relative opposed to their non kin friend. Studies have demonstrated that relatedness is often important for human altruism (unselfish regard for or devotion to the welfare of others) in that humans are inclined to behave more altruistically toward kin than toward unrelated individuals. Many people choose to live near relatives, exchange sizable gifts with relatives, and favor relatives in wills in proportion to their relatedness. Chapter 12 was an interesting chapter to read because my family is very important to me. I was raised in a southern family, and I know that no matter what challenges I go through in life, my family will always be there for me. I knew this occurred in humans off course, but it is assuring and compelling that it also occurs in animals.
This video explains kin selection and gives many good examples of altruism:

Also, check out these links for more information on kin selection:

http://link.springer.com/article/10.1007%2FBF01065540?LI=true

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/K/KinSelection.html