Natural Computation Seminar Series.

Monday, 16th October 2006. 2pm - 6pm. UG 04 Learning Resources Centre. Birmingham University. Birmingham.

(Take the train to University Station. Turn Right and its the first building on your left after the canal).

 

Artificial selection has been practiced for centuries to shape the properties of individual organisms, providing Darwin with a powerful argument for his theory of natural selection. Several new experiments show that whole ecosystems can also be shaped by artificial selection procedures. Ecosystems initiated in the laboratory vary phenotypically and a proportion of the variation is heritable, despite the fact that the ecosystems initially are composed of thousands of species and millions of individuals. Artificial ecosystem selection can be used for practical purposes; illustrates an important role for complex interactions in evolution; and challenges a widespread belief that selection is most effective at lower levels of the biological hierarchy. (Adapted from Swenson and Sloan-Wilson, PNAS, 2000).

Program.

2pm Alex Penn (CCNR, University of Sussex/University of Southampton). An Introduction to Ecosystem Selection.

 

Ecosystem selection is an exciting and controversial new area of research with connections to some of the most fundamental questions in evolutionary biology and ecology today. A response to artificial selection on the level of whole microbial communities was demonstrated experimentally by Swenson, Wilson et al (1,2), but these experiments shed no light on the mechanisms by which it occurred. Are higher-level processes additional to individual selection occurring? The question remains: Can a multi-species community or ecosystem possess the qualities to act as a level of selection, or even potentially a level of inheritance in its own right? If so, what could this tell us about the first evolutionary units, major transitions in evolution and the origin of new forms and levels of heredity (3)? By forcing us to reconsider the operation of selection on a previously "un-selected" level, artificial ecosystem selection experiments provide an ideal test bed for questions about at what levels, on what sources of variation and how selection can act. In addition to this theoretical interest, ecosystem selection is of direct practical relevance. If higher-level selection does occur in natural ecosystems, there could certainly be implications for the evolution of ecosystem function which merit exploration. The possibility also exists of using artificial evolution techniques to produce microbial ecosystems "designed" for specific purposes such as bioremediation or production of useful compounds.

In this talk I will present a general introduction to theoretical and experimental work in this newly developing field, exploring artificial selection experiments, in their capacity as model systems and their potential to evolve useful bespoke communities; and the potential for ecosystem selection to occur "in the wild". I will discuss the concepts of variation, heredity, and phenotype in the ecosystem context, along with possible mechanisms via which ecological systems could satisfy these criteria. It has been suggested that possible novel sources of higher-level heritable variation, qualitatively different to those which exist at the individual level, could exist in ecological systems, and I will present some simple models which demonstrate these dynamics (4,5). These possibilities bear interesting comparison to the origin of new levels of inheritance during major transitions in evolution.

I will also present the results of the first field-trial of this technique, practical experiments on using ecosystem selection to improve the growth of Lens culinaris in a semi-arid environment with degraded soil (6). It is hoped that the ecosystem selection technique can be developed as a tool to "design" bespoke ecosystems for practical applications in bioremediation, agriculture and waste treatment and I will discuss further practical projects in development in some of these areas.

1. Swenson, W. and Wilson, D.S. and Elias, R. (2000) "Artificial Ecosystem Selection". PNAS, 97: 9110
2. Swenson, W. and Arendt, J. and Wilson, D.S. (2000), "Artificial selection of microbial ecosystems for 3-chloroaniline biodegradation", Environ. Mirobiol., 2: 9365

1. Maynard Smith J. and Szathmary, E. (1995), "Major Transitions in Evolution", Spektrum.

1. Penn, A.S. (2003) "Modelling Artificial Ecosystem Selection: a preliminary investigation", In proc. Advances in Artificial Life, 7th European Conference, ECAL 2003.

1. Penn, A. and Harvey, I. (2004), "The role of non-genetic change in the heritability, variation, and response to selection of artificially selected ecosystems", In proc. Artificial Life IX: Proceedings of the Ninth International Conference on the Simulation and Synthesis of Life.

1.   Penn, A. (2006) "Ecosystem Selection: Simulation, Experiment and Theory" D.Phil. Thesis, University of Sussex.

 

3.00pm Joel Peck. (Center for the Study of Evolution). What is it for? Darwinian processes in ecosystem evolution.

It is clear that modern eukaryotes arose from a combination of two organisms that co-occurred in some ancient ecosystem. Less extreme examples of mutualism are common. With facts like this in mind, some researchers have suggested that is may sometimes be useful to think about certain ecosystems as if they were part of a population of ecosystems, and that natural selection can act on variation among ecosystems. This idea leads to the questions such as: (1) What biological processes could lead to natural selection on ecosystems? And (2) How we would know if ecosystems were responding to natural selection? This talk will provide a few ideas about how appropriate answers to these questions might be produced. A critique will be presented of a relatively well-known model related to ecosystem selection (by D.S. Wilson in Ecology, 1992). Some preliminary results from a new model of ecosystem selection will also be presented. This model has the advantage of providing a very simple version of a realistic mechanism of ecosystem selection. It also allows for the occurrence of mutualistic interactions, which are common in nature, but can not be studied with the Lotka-Volterra equations commonly used in ecosystem modelling.

4.00pm Hywel Williams. (Earth Systems Modeling Group, University of East Anglia) Artificial ecosystem selection in a simulated microbial microcosm

Recent work with microbial communities has demonstrated an adaptive response to artificial selection at the level of the ecosystem
. However, the reasons for this response are not clear and there is some uncertainty concerning the level at which adaptation occurs: does the artificial selection scheme implicitly select for traits of a single species or are higher-level community traits the subject of selection? Here we present an individual-based evolutionary simulation model of microbial ecology in which artificial selection experiments similar to those reported by Swenson and Sloan-Wilson are performed, and where a similar response to artificial ecosystem selection is observed. We find that the response to artificial ecosystem selection is a robust phenomenon that occurs even when strong individual-level selection pressure acts independently on related traits. The size of the community response to selection depends inversely on the duration of the period between artificial selection events, which is explained by the occurrence of individual-level mutation and relaxation towards the non-selected ecological state during the inter-selection event period. The rate of relaxation depends on the rate of individual-level mutation during reproduction. The ecological function of a selected microbial ecology is found to be a complex function of community activity and abiotic factors, and we show that in many cases the community response to selection cannot be decomposed into the responses of individual species. Our findings also cast doubt on the possibility of developing generally applicable microbial communities for the degradation of environmental
pollutants.

 

5pm. Chrisantha Fernando. (School of Computer Science, Birmingham University). Chemical Evolution by Natural Selection.

 

We propose that chemical evolution can take place by natural selection if a geophysical process is capable of heterotrophic formation of liposomes that grow at some base rate, divide by external agitation, and are subject to stochastic chemical avalanches, in the absence of genes or any modular heredity. We model this process using simple hill-climbing, and an artificial chemistry that is unique in exhibiting conservation of mass and conservation of energy. Selection at the liposome level results in the stabilization of rarely occurring molecular autocatalysts that either catalyse or are consumed in reactions that confer liposome level fitness; typically they contribute in parallel to an increasingly conserved intermediary metabolism. Loss of competing autocatalysts can sometimes be adaptive. Steady-state energy flux by the individual increases due to the energetic demands of memory, i.e. maintaining variations in the chemical network, and of growth. Typically self-organizing principles such as those proposed by Kauffman, Fontana, and Morowitz have been hypothesised as a mechanism of chemical evolution, rather than chemical evolution by natural selection. We reject those notions as either logically flawed or at best insufficient in the absence of natural selection. Finally, a stochastic population using a simplified variation operator shows the sufficient conditions for achieving chemical evolution by natural selection using an outline experimental protocol.

6pm. Drinks at Staff House followed by Dinner.