It doesn’t add up

first_imgAn important new finding by Harvard researchers indicates that cellular mutations responsible for an organism’s successful adaptation do not, when combined over time, provide as much benefit as they would individually be expected to provide.The study from the laboratory of Christopher Marx, an associate professor in the Department of Organismic and Evolutionary Biology (OEB), is one of two investigations with identical approaches and equivalent results that are being published in Friday’s (June 3) issue  of the journal Science. The other paper comes from the lab of Tim Cooper, an assistant professor in the University of Houston’s Department of Biology and Biochemistry.Hsin-Hung Chou, a postdoctoral fellow in Marx’s lab, is the first author on the Harvard paper.Although the Harvard and Houston groups each studied a different bacterium that evolved in different conditions, the patterns they uncovered were the same: The more fit the strain was before introducing the beneficial mutation in question, the less further improvement was conferred.Marx and Cooper, who are both colleagues and friends, submitted their work simultaneously to Science this past February, asking that the journal consider their manuscripts jointly. “We independently came to the same remarkable punch line with completely different model systems. We thus feel that this congruence of results adds substantial strength to the suggestion of generality from our findings,” they wrote in their joint submission letter to Science. The two research groups posit that their findings help explain the “deceleration of population adaptation” over time.Although the papers of Marx and Cooper came to remarkably similar conclusions, they contrasted strongly with analogous studies looking at mutational combinations within single proteins. For example, an earlier paper from the laboratory of Daniel Hartl, Higgins Professor of Biology in OEB, showed that mutations within the enzyme that provides resistance to penicillins interacted with each other violently. The same mutation could be tremendously beneficial if partnered with some mutations, and quite deleterious when grouped with others. These interactions would greatly constrict which paths for improvement can be driven by natural selection.In their letter to Science, Marx and Cooper wrote that “our papers are critical because they paint … [a] picture that suggests that adaptation involving the wider context of whole genome networks may behave entirely differently than adaptation of proteins.  Interactions between beneficial mutations are common but seldom impose hard limits on the mutational transitions that can be selected. This result has broad implications for understanding the trends and causes of fitness landscapes.“Any finding in experimental evolution establishes rigorously what can happen; when results are repeated across systems it suggests that this might actually be what does happen in nature.  Indeed, this simple effect of mutation interactions on the form of the fitness landscape may provide a new ‘predictability’ to evolutionary biology,” they wrote.The editors of Science apparently agreed with Marx and Cooper, and not only are the papers being published in the same issue of the journal, Science is also publishing a commentary on the papers titled “Evolutionary Sum Is Less Than Its Parts.”Earlier studies of evolutionary mutations in individual proteins, and preliminary studies done in Marx’s lab had shown that mutation was order dependent, that the order of changes over time had a controlling effect upon the end result. “But our work and the other new work being published shows a different picture throughout the cell,” Marx said. “We found that all positive mutations are always good, but the amount that they’re good becomes less and less over generations.”One of the exciting things about doing this kind of science, Marx said, is that it demonstrates that evolution is something that can be studied with microbes in the laboratory, and on the timeline of a graduate career. This allows questions of broad interest in natural systems to be addressed experimentally.“Our ultimate goal,” Marx said, “is to find out why this happens. We need to be able to understand these interactions in order ultimately to be able to take advantage of them.”last_img read more

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Guyana police killings prompt calls for inquiry

first_img 17 Views   no discussions Tweet Share NewsRegional Guyana police killings prompt calls for inquiry by: – July 20, 2012 Sharecenter_img Sharing is caring! Share Home Affairs and National Security Minister Clement Rohee (L) allegedly instructed Police Commissioner Leroy Brummell (R) to fire at protestorsGEORGETOWN, Guyana — The shooting to death by police of three unarmed protestors in Guyana’s mining town of Linden on Wednesday has prompted widespread calls for a government inquiry into the incident.The three shooting victims were part of a large demonstration protesting a 50 percent increase in electricity rates. Protestors reportedly blocked the Wismar Bridge, which facilitates vehicular traffic to and from the country’s vast and natural resources rich hinterland region. This prompted riot police sent in from Georgetown to fire teargas and rubber bullets. Protestors responded by throwing stones and teargas canisters back at police, who responded with live rounds, killing three and wounding dozens. Calling for a Commission of Inquiry into the shooting, Rickford Burke, president of the New York-based Caribbean Guyana Institute for Democracy (CGID), said, “These killings are a wanton slaughter of African-Guyanese by Guyana police. The peoples of the Caribbean region must express outrage at these killings and solidarity with the black population in Guyana.”Sharma Solomon, regional chairman of Region Ten – Upper Demerara/Berbice, the geographic and local government administration with jurisdiction over Linden, on Wednesday confirmed that three males have been killed, including Ron Somerset, a Guyana Defense Force officer. Solomon also confirmed several injuries and said many were admitted to hospital. Demerara Waves news service has quoted the chairman as saying the town was “in pandemonium.”Burke said the buck stopped at President Donald Ramotar and Home Affairs and National Security Minister Clement Rohee who allegedly instructed Police Commissioner Leroy Brummell to fire at protestors. He also urged opposition leader Brigadier David Granger to be more assertive, saying, “I hope Mr Granger as leader of the party that is the political representative of the people of Linden will relinquish his non-confrontational posture and adopt political measures to wrest from the government a genuine account of the chain of command and who issued the orders to shoot. He must also understand that his supporters expect him to ensure criminal prosecutions must be a consequence of any inquiry or a term of resolution of this horrific incident.” Late Wednesday night several government buildings were reportedly ablaze, including the offices of the government’s Inland Revenue Department. Prime Minister Samuel Hinds further angered residents with a statement condemning the protest and expressing regret at the disruption of business. He made no reference to the killings nor offered any form of condolences. The police have issued a statement calling for calm and the government on Thursday announced that the military has been called out to patrol the town. Ramotar scheduled an emergency meeting with Granger, who made an emergency visit to Linden on Wednesday night. He visited shooting victims at the McKenzie hospital as well as grieving relatives of those killed. Granger said on Thursday that country’s commissioner of police should immediately be suspended.Meanwhile, Ramotar said he regrets the deaths and injuries caused by the shootings and that authorities will open an investigation once calm is restored to the area. Caribbean News Nowlast_img read more

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