… bridging the gap
Jun 15th, 2009 by Neil Greenspan
Biological evolution is, obviously, a historical (i.e., time-dependent) process. However, the importance to evolution of dynamics occurring on multiple time scales is still being delineated. Continue Reading »
Jun 7th, 2009 by The Editors
In a new PLoS Biology article, Read, Lynch and Thomas combine two facts and evolutionary thinking to propose a creative and surprising solution to insecticide resistance and malaria transmission.
The facts are:
1. Mosquitoes develop resistance to new insecticides quickly; finding new agents is not like to solve the problem.
2. Most mosquitoes die well before the 10-14 days needed to contract and transmit malaria.
They suggest that low doses of a late life acting insecticide could shape a shorter mosquito life span that would dramatically decrease malaria transmission. This strategy would also slow the development of resistance to the insecticide. They note the risk that this would select for faster development in Plasmodium, but suggest that fitness trade-offs might slow this evolution.
They offer a mathematical model. They also offer a very practical suggestion: screen insecticides to identify those that act late in the mosquito’s life span.
Source: Read AF, Lynch PA, Thomas MB (2009) How to Make Evolution-Proof Insecticides for Malaria Control. PLoS Biol 7(4): e1000058. doi:10.1371/journal.pbio.1000058
An article in the April, 2009 issue of Evolution, offers provocative support for George Williams’s 1957 prediction that decreased extrinsic mortality rates will select for slower rates of aging. The article compares data from subsistence and European societies in the past 200 years, and concludes that selection may have slowed aging rates in just 10 generations, and it may account for differences in aging rates in different populations. The multiple measures of aging rates are a strength of the article, but they also add complexity that makes interpretation of the results challenging, as the authors note.
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Has Actuarial Aging “Slowed” Over the Past 250 Years?
A Comparison of Small-Scale Subsistence Populations and European Cohorts
Michael Gurven and Andrew Fenelon
Evolution 63(4):1017-1035. 2009
doi: 10.1111/j.1558-5646.2008.00592.x
Williams’s 1957 hypothesis famously argues that higher age-independent, or ‘extrinsic,’ mortality should select for faster rates of senescence. Long-lived species should therefore show relatively few deaths from extrinsic causes such as predation and starvation. Theoretical explorations and empirical tests of Williams’s hypothesis have flourished in the past decade but it has not yet been tested empirically among humans. We test Williams’s hypothesis using mortality data from subsistence populations and from historical cohorts from Sweden and England/Wales, and examine whether rates of actuarial aging declined over the past two centuries. We employ three aging measures: mortality rate doubling time (MRDT), Ricklefs’s ω, and the slope of mortality hazard from ages 60–70, m′50–70, and model mortality using both Weibull and Gompertz-Makeham hazard models. We find that (1) actuarial aging in subsistence societies is similar to that of early Europe, (2) actuarial senescence has slowed in later European cohorts, (3) reductions in extrinsic mortality associate with slower actuarial aging in longitudinal samples, and (4) men senesce more rapidly than women, especially in later cohorts. To interpret these results, we attempt to bridge population-based evolutionary analysis with individual-level proximate mechanisms.
May 14th, 2009 by Neil Greenspan
There are few examples of the power of natural selection more globally relevant than those pertaining to the influenza A viruses, which, along with the influenza B and C viruses, constitute the orthomyxoviruses. Influenza A viruses kill thousands of people every year and infect numerous species in addition to humans. Virtually any person is potentially susceptible to infection, as the antibodies elicited by natural exposure in one year typically protect much less effectively against the viruses circulating in the next or subsequent years. Continue Reading »
May 8th, 2009 by Bernard Crespi
Mouse ‘models’ for psychiatric disorders, strains of mice genetically engineered by ‘knocking out’ a specific gene that mediates expression of the disorder, provide invaluable information regarding the genetic, developmental, physiological, and neurological causes of mental diseases in humans. One of the first mouse models relevant to autism was generated via knockout of a gene called FMR1, whose loss of function in humans causes an autistic spectrum condition called Fragile X syndrome (Kooy et al. 1996; Hagerman et al. 2009).
Amazingly, such mice can now be ‘rescued’ - that is - restored to essentially normal function for cognitive tasks that were formerly much impaired, via treatment with drugs that down-regulate one of their brain receptors for glutamate, called mGLUR5 (Dölen et al. 2007; Hagerman et al. 2009). Fragile X mice can also be rescued by knocking out one copy of the actual gene that codes for mGLUR5, which reduces the brain’s production of this receptor and thus mimics the impact of pharmaceutical treatment (Dölen et al. 2007). Continue Reading »
May 8th, 2009 by The Editors
The University of Michigan School of Public Health is offering a one-week, one credit course from July 27-31 on Evolutionary Epidemiology (EPID 788) taught by Betsy Foxman and Randolph Nesse. For details and an application, click above. For the course description, click “continue reading.”
May 1st, 2009 by Carl Bergstrom
Hedging against Antiviral Resistance During the Next Current Influenza Pandemic
Commentary on: J.T. Wu, G.M. Leung, M. Lipsitch, B. S. Cooper, and S. Riley 2009. Hedging against Antiviral Resistance during the Next Influenza Pandemic Using Small Stockpiles of an Alternative Chemotherapy. PloS Medicine. Online ahead of print 4/30/09. http://www.plos.org/press/plme-06-05-wu.pdf
Eight days ago we received the first reports of a half-dozen infections in Texas and California patients by a swine-derived strain of influenza A H1N1; these reports were accompanied by speculation that these case might be related to a cluster of atypical pneumonia cases in Mexico City. Only eight days later, we now are looking at hundreds of confirmed cases, and presumably thousands of total cases, distributed throughout the US and Mexico, with additional confirmed cases in multiple regions of Europe, Asia, and Oceana. The World Health Organization has raised the pandemic alert level from phase 3 to phase 5 (widespread human infection), and pandemic plans are being put into operation around the globe.
The point is that things move extremely fast in the early phases of an epidemic - and at the same, early decisions about plans to control or mitigate the epidemic can cast a very long shadow with respect to the ultimate trajectory that the epidemic takes. Yesterday, PloS Medicine released an advance copy of a paper by Wu et al., written prior to the current situation but uncannily relevant to the current pandemic control process.
Using a set of simulation models, the authors show that the choice of which antivirals to use early in an influenza pandemic can have dramatic consequences for the evolution and spread of antiviral resistance Continue Reading »
Apr 23rd, 2009 by Neil Greenspan
This week marks the 35th anniversary of the landmark paper, in Nature [248:701-702, 1974, April 19], by Rolf Zinkernagel and Peter Doherty that established the principle that T lymphocytes [murine cytotoxic T lymphocytes (CTL) in this study] exhibit specificity for both the nominal antigen (e.g. a gene product derived from a pathogen such as HIV-1 or influenza virus) and a self-major histocompatibility complex (MHC) molecule, a phenomenon that became known as “MHC restriction.” Zinkernagel and Doherty showed that only CTL from mice immunized with lymphocytic choriomeningitis virus (LCMV) and sharing MHC alleles with radioactively-labeled target cells could effectively lyse those target cells after they had been infected with LCMV. One element that made this discovery particularly noteworthy was that in a subsequent publication in Lancet [1975 Jun 28;1(7922):1406-1409], the two immunologists used MHC restriction to explain the high degree of polymorphism already documented for murine and human class I MHC loci.
In this context, it is of interest that a recent paper by Kawashima et al., in Nature [2009 Apr 2;458(7238):641-645], offers impressive evidence that the evolution of HIV-1 is shaped by the prevalence of particular human gene products, the HLA class I molecules encoded at the HLA-B locus. Continue Reading »
Apr 10th, 2009 by The Editors
This week’s Science has an extensive review of the National Academy Sackler Colloquium on Evolution in Health and Medicine. Elizabeth Pennisi packs many examples into just a few paragraphs and gives a vivid sense for the excitement of the meeting and its possible future impact. She contrasts the active participation of physicians at this meeting with their near-absence at first meeting for the field, actually organized by Steven Stearns, who also edited the foundation text in the field, Evolution in Health and Disease, and, with Jacob Koella, a second edition, now available from Oxford University Press. Pennisi’s article does a fine job of emphasizing the importance of evolutionary biology for medicine, and also the many challenges faced by Dean’s who must cope with an already over-crowded curriculum. Continue Reading »
Apr 8th, 2009 by The Editors
The National Academy of Sciences webpage has just posted an interview with Peter Ellison about the recent Sackler Symposium Evolution in Health and Medicine. Audio recordings of all the talks with slides will be available on the web after a few weeks; in the meanwhile, Ellison’s talk gives an overview of what turned out to be a remarkable meeting. A highlight was when Jeffrey Flier, Dean of Harvard Medical School, addressed Elllison and suggested they collaborate immediately to figure out strategies for bringing more evolutionary biology into the Harvard curriculum. Several other exchanges also revealed new enthusiasm for ensuring that doctors and medical researchers are provided with the full range of evolutionary knowledge. The payoffs such knowledge offers were illustrated, sometimes dramatically, by many of the presentations on specific scientific topics.
Unless otherwise noted, original content on the Evolution & Medicine Review is licensed under a Creative Commons Attribution 3.0 Licence.
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