Mathematical model helps bridge gap between lab and 'real' world
Scientists from the UK and the US have created a mathematical model that can predict the outcome of laboratory-based biodiversity studies. Their goal was to find whether the results of biodiversity experiments conducted in miniature, man-made ecosystems can truly be applied to real-world phenomena. To find out why some places show greater biodiversity than others, one could spend decades in the field studying one part of a very complex system as it evolves. The more efficient alternative is to create mini-ecosystems in a laboratory in which many generations of bacteria may be observed in a number of situations. This simplified approach to studying biodiversity has some inherent problems, one of which is that there is a tenuous relationship between experiments in the laboratory and the broader questions they seek to address. It is hard to tell whether results are specific to one lab, or one particular experiment, or if they are 'true' and can be applied generally. Dr Laurence Hurst of the University of Bath, UK, and colleagues sought to answer this question by testing a theory called the 'geographic mosaic co-evolution hypothesis'. This states that if you have three things, namely a host, a parasite and nutrients, then you will have biodiversity. In this theory, changing one of these things will change the level of diversity: increase or decrease the nutrients given to the host and parasite, and the resulting diversity will increase or decrease accordingly. In the first part of the experiment, scientists at the University of California at Santa Cruz, US, grew a kind of bacteria (E. coli) together with a virus (T7) and observed the effect of feeding them more or less sugar over the course of 150 generations (17 days). Growing the bacteria and virus together forced them to continuously adapt to one another: three new strains of bacteria appeared as it tried to fend off the virus, and the virus mutated several times. The findings supported the geographic mosaic co-evolution hypothesis. In this system, more diversity was seen when fewer nutrients were fed into the system. In a food-rich environment, less-resistant strains were wiped out, while in a low-nutrient environment, the reduced number of virus particles allowed more bacterial strains to survive. In other words, the highest biodiversity was seen when lower levels of nutrients were fed into this mini-ecosystem. Dr Ivana Gudelj and Dr Robert Beardmore of Imperial College London, UK, then created an elegant, technically difficult mathematical model of this mini-ecosystem. 'The model was able to predict the outcome of the experiment, which was rather exciting,' Dr Hurst told CORDIS News. It predicted which bacterial strains would be the most common, and how much diversity would be seen, with increasing or decreasing amounts of sugar. The next step was to see whether the same result would be achieved when a different type of virus was used. The result was completely different: more sugar led to more diversity. The study concluded that in any given system, the genetic details of how the host and parasite interact is pivotal to whether diversity is increased or decreased with changing nutrient levels. In other words, biodiversity is not simply dependent on the availability of nutrients in an environment, rather it hinges on minute changes in the genetic makeup of its hosts and parasites. Dr Hurst explained that, 'Within the mathematical model, there is always variation. No matter where we look in the mathematical model, the diversity changes, and whether it increases or decreases depends on which bacteria or virus is being used.' What the study tells us about applying laboratory results to the field is that one cannot make assumptions about nutrient levels and biodiversity. In each ecosystem, a detailed knowledge of the genetics of the species involved is crucial for determining how nutrients will affect their evolution.
Countries
United Kingdom, United States