Evolution Articles

JFMcL

As Mushrooms Evolve to Live With Trees, They Give Up DNA Associated With Decomposing Cellulose

ScienceDaily (July 18, 2012) — Harvard researchers are unlocking the evolutionary secrets of one of the world's most recognizable groups of mushrooms, and to do it, they're using one of the most comprehensive fungal "family trees" ever created.


As reported in paper published July 18 in PLoS ONE, Associate Professor of Organismic and Evolutionary Biology Anne Pringle and Ben Wolfe, a Post-Doctoral Fellow in FAS Center for Systems Biology, studied the genetics of more 100 species of Amanita mushrooms -- about one-sixth of the genus' total diversity -- to create an elaborate phylogeny showing how each species is related to one another.
Arguably the most widely-recognized group of mushrooms in the world, Amanita mushrooms have appeared in popular culture ranging from Fantasia to the Super Mario Brothers video games. Though it includes a number of edible species, such as the Amanita caesarea, the group is probably best known for its many toxic species, including the death-cap mushroom.
Armed with their family tree, Pringle and Wolfe were able to determine that Amanita evolution has largely been away from species that help decompose organic material and toward those that live symbiotically on trees and their roots. More interestingly, they found that the transition came at a steep price -- the loss of the genes associated with breaking down cellulose.
"There had been earlier suggestions that this type of gene loss might be taking place, but our study is the first precise test of that hypothesis," Pringle said. "The idea makes sense -- if you're going to actively form a cooperative relationship with a tree, you probably shouldn't simultaneously be trying to break it apart and eat it. But it's a very tricky dance to form these kinds of tight, cooperative interactions, and I think this work shows there is a cost associated with that. You have to change, you have to commit, and it can become a sort of gilded cage -- these mushrooms are very successful, but they're stuck where they are."
In addition to many species which are housed in the Farlow Herbarium, located at the Harvard University Herbaria, Wolfe spent months tracking rare species in far-flung locations like London and Hawaii.
After extracting DNA from the samples, Wolfe used the genetic codes of four different genes to determine how the various species are related to one another. He then used a process called ancestral state reconstruction to show that the mushrooms have switched from being decomposers to being symbiotic with trees only once in their evolutionary history. Once the mushrooms switched to this new symbiotic lifestyle, they didn't go back to their free-living past.
Ultimately, Pringle said, the paper highlights one reason she finds such symbiotic partnerships "intrinsically interesting" -- for all their apparent benefits, the cost can be high.
"I think the really interesting thing is this idea that once you become symbiotic, some of your machinery is lost," she said. "It seems like a dead end in some ways -- you have to make this change to enter this niche, but once you're there, you can't go back -- you've lost the capacity to be free-living."
  • Journal Reference:
  1. Wolfe BE, Tulloss RE, Pringle A. The Irreversible Loss of a Decomposition Pathway Marks the Single Origin of an Ectomycorrhizal Symbiosis. PLoS ONE, 2012; 7 (7): e39597 DOI: 10.1371/journal.pone.0039597

RMG
“Discovery: Queen of Spades Key to New Evolutionary Hypothesis” Summary
http://www.nsf.gov/discoveries/disc_summ.jsp?cntn_id=124158&org=GEO (link for the article I read)
http://mbio.asm.org/content/3/3/e00099-12.full (link for the lab and commentary)
This article is about the comparison of humans and microscopic ocean plankton sharing a common trait, “that humans aren’t the only ones who can play a mean game of cards.” The scientists who developed the hypothesis described in the article are Jeffrey Morris and Richard Lenski of Michigan State University and the BEACON Center for the Study of Evolution in Action, and Erik Zinser of the University of Tennessee, Knoxville. The thought for the study came about when these men were confused with how non-symbionts got away with cutting out functions that appear to be necessary. The researchers wondered if these microbes had others do the work for them. To bring back the reference to card games, in the game of Hearts the winning strategy is to avoid the Queen of Spades, or the Black Queen. Thus, the name stuck with the notion that eliminating a necessary function confers an evolutionary advantage. These organisms simply want to lose a gene that’s a burden and have someone else pick it up; however, someone must always carry that card or the game is over and the ocean community would suffer. This hypothesis was tested on the original microbes that caused the confusion, Prochlorococcus. This particular plankton is very common in the open ocean but has a very small genome. It does not even contain the gene for catalase-peroxidase which lets microbes neutralize the damaging or cell killing compound hydrogen peroxide. Instead, it relies on other organisms to do the work. In doing so, Prochlorococcus contributes energy through photosynthesis that supports a larger community. The Black Queen Hypothesis may describe an evolutionary force responsible for the diverse, interconnected web of the oceanic world, even though it includes, in card terms, cheating.
JFMcL. Fascinating concept because it basically is creating a symbiotic relationship between two organisms through the external emnvironment!
WMWOODS
"Young People: Not As Healthy As They Seem"

http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(09)61607-X/fulltext

SUMMARY:
"Young People: Not as Healthy as They Seem"
The world has changed over the past 25 years, with the younger generation not dieing of infectious diseases, but rather more suicide and motor vehicle crashes. 25 years ago, young women married at an earlier age, increased numbers lived in rural areas, and fewer younger people went to school. In Europe the younger generation will decline and the population of younger people in Africa will increase by 2025. Global patterns also affect the health of young people, as migrations of people from different environments occur, delays in marriage, and rises in rates of education in girls. These have effected behaviors including more sexually transmitted infections and out of wedlock pregnancy and abortion. The causes of mortality vary greatly by geographical region and national and personal resources. Most deaths have behavioral causes exacerbated by national policy or failures of health service delivery systems or both. Industrialist countries, boys are 2-4 times more likely to die then women, and homicide and suicide, and injury accounts for 50%-80% of deaths. In countries where abortion is prohibited by law, mortality rates are as high as 60 out of 100,000 women. These deaths account for 25% of the adolescent mortality rate. With abortion legal, adolescent deaths lower. Differences in HIV and its transmission also pose a large effect on lives, but transmission differs upon where you live. Suicide is also a major cause of death, which ranks differently among nations. Injury for young men however remains the leading cause of deaths in every region of the world, with most deaths associated with motor vehicle accidents. In the second phase of life however, in most countries the mortality rate has dropped 30%. The enforcement of laws and road rules decreases the chances of deaths. The protective factors implement a large positive help and help protect the younger generation.
REACTION:
I believed that the facts presented in this article were very interesting, showing the change overtime of adolescent death trends and how technological advances in biology dont always stop the problem all together as other forces fill the gap.

SUMMARY BULLETS:

  • younger generation not dieing of infectious diseases, but rather more suicide and motor vehicle crashes
  • 25 years ago, young women married at an earlier age, increased numbers lived in rural areas, and fewer younger people went to school
  • Europe the younger generation will decline and the population of younger people in Africa will increase by 2025
  • Global patterns also affect the health of young people, as migrations of people from different environments occur, delays in marriage, and rises in rates of education in girls
  • These have effected behaviors including more sexually transmitted infections and out of wedlock pregnancy and abortion
  • The causes of mortality vary greatly by geographical region and national and personal resources
  • Most deaths have behavioral causes exacerbated by national policy or failures of health service delivery systems or both
  • Industrialist countries, boys are 2-4 times more likely to die then women, and homicide and suicide, and injury accounts for 50%-80% of deaths
  • In countries where abortion is prohibited by law, mortality rates are as high as 60 out of 100,000 women
  • These deaths account for 25% of the adolescent mortality rate
  • With abortion legal, adolescent deaths lower
  • Differences in HIV and its transmission also pose a large effect on lives, but transmission differs upon where you live
  • Suicide is also a major cause of death, which ranks differently among nations
  • Injury for young men however remains the leading cause of deaths in every region of the world, with most deaths associated with motor vehicle accidents
  • In the second phase of life however, in most countries the mortality rate has dropped 30%
  • The enforcement of laws and road rules decreases the chances of deaths
  • The protective factors implement a large positive help and help protect the younger generation