Scientific models are used by researchers in order to understand interactions that are going on around us all the time. They are like microscopes – but rather than observing objects and structures, they focus on specific processes. Models are built from the ground up from mathematical rules that we infer from studying ecosystems, and they allow us to run and re-run experiments to gain understanding, in a way which is not possible using other methods.
I’ve managed to reproduce many of the patterns of co-evolution between the hosts and parasites in the red king model by tweaking the parameters, but the points at which certain patterns emerge is very difficult to pin down. I thought a good way to start building an understanding of this would be to pick random parameter settings (within viable limits) and ‘sweep’ paths between them – looking for any sudden points of change, for example:
This is a row of simulations which are each run for 600 timesteps, with time running downwards. The parasite is red and the host is blue, and both organism types are overlayed so you can see them reacting to each other through time. Each run has a slightly different parameter setting, gradually changing between two settings as endpoints. Halfway through there is a sudden state change – from being unstable it suddenly locks into a stable situation on the right hand side.
I’ve actually mainly been exploring this through sound so far – I’ve built a setup where the trait values are fed into additive synthesis (adding sine waves together). It seems appropriate to keep the audio technique as direct as possible at this stage so any underlying signals are not lost. Here is another parameter sweep image (100 simulations) and the sonified version, which comprises 2500 simulations, overlapped to increase sound density.
You can hear quite a few shifts and discontinuities between different branching patterns that emerge at different points – writing this I realise an animated version might be a good idea to try too.
Stereo is done by slightly changing one parameter (the host tradeoff curve) across the left and right channels – so it gives the changes a sense of direction, and you are actually hearing 5000 simulations being run in total, in both ears. All the code so far (very experimental at present) is here. The next thing to do is to take a step back and think about the best way to invite people in to experience this strange world.
Here are some more tests:
A new project begins, on the subject of ecology and evolution of infectious disease. This one is a little different from a lot of Foam Kernow’s citizen science projects in that the subject is theoretical research – and involves mathematical simulations of populations of co-evolving organisms, rather than the direct study of real ones in field sites etc.
The simulation, or model, we are working with is concerned with the co-evolution of parasites and their hosts. Just as in more commonly known simulations of predators and prey, there are complex relationships between hosts and parasites – for example if parasites become too successful and aggressive the hosts start to die out, in turn reducing the parasite populations. Hosts can evolve to resist infection, but this has an overhead that starts to become a disadvantage when most of a population is free of parasites again.
Example evolution processes with different host/parasite trade-offs.
Over time these relationships shift and change, and this happens in different patterns depending on the starting conditions. Little is known about the categorisation of these patterns, or even the range of relationships possible. The models used to simulate them are still a research topic in their own right, so in this project we are hoping to explore different ways people can both control a simulation (perhaps with an element of visual live programming), and also experience the results in a number of ways – via a sonifications, or game world. The eventual, ambitious aim – is to provide a way for people to feedback their discoveries into the research.
As part of this year’s Fascinate festival we took over the bar at Falmouth’s Poly with visualisations of the camouflage pattern evolution process from the egglab game.
This was a chance to do some detective work on the massive amount of genetic programming data we’ve amassed over the last few months, figure out ways to visualise it and create large prints of the egg pattern generation process. I selected family trees of eggs where mutations caused new features that made them difficult for people to spot, and thus resulted in large numbers of descendants. Then I printed examples of the eggs at different stages to see how they progressed through the generations.
We also ran the egglab game in the gallery on a touch screen which accidentally coincided with some great coverage in the Guardian and Popular Science, but the game kept running (most of the time) despite this.
The Poly (or Royal Cornwall Polytechnic Society) was really the perfect place for this exhibition, with its 175 year history of promoting scientists, engineers and artists and encouraging innovation by getting them together in different ways. Today this seems very modern (and would be given one of our grand titles like ‘cross-displinary’) but it’s quite something to see that in a lot of ways the separation between these areas is currently bigger than it ever has been, and all the more urgent because of this. The Poly has some good claims to fame, being the first place Alfred Nobel demonstrated nitro‐glycerine in 1865! Here are some pages from the 1914 report, a feel for what was going on a century ago amongst other radical world changes:
Some hungry butterfly hunters making evolution happen at the Summer Science exhibition last week. Thank goodness for multitouch!
I’ve been working lately with the Heliconius research group at the University of Cambridge on a game to explain the evolution of mimicry in butterfly wing patterns. It’s for use at the Summer Science Exhibition at the Royal Society in London, where it’ll be run on a large touch screen for school children and visiting academics to play.
The game models biological processes for education purposes (as opposed to the genetic programming as used on the camouflage egg game), and the process of testing this, and deciding what simplifications are required has become a fascinating part of the design process.
In biosciences, genetics are modelled as frequencies of specific alleles in a given population. An allele is a choice (a bit like a switch) encoded by a gene, so a population can be represented as a list of genes where each gene is a list of frequencies of each allele. In this case the genetics consists of choices of wing patterns. The game is designed to demonstrate the evolution of an edible species mimicking a toxic one – we’ll be publishing the game after the event. A disclaimer, my terminology is probably misaligned in the following code, still working on that.
;; an allele is just a string id and a probability value
(define (allele id probability)
(list id probability))
;; a gene is simply a list of alleles
;; return the id of an allele chosen based on probability
(define (gene-express gene)
(let ((v (rndf)))
(lambda (allele r)
(let ((segment (+ (car r) (allele-probability allele))))
(if (and (not (cadr r))
(< v segment))
(list segment allele)
(list segment (cadr r)))))
(list 0 #f)
;; a chromosome is simple list of genes
;; returns a list of allele ids from the chromosome based on probability
(define (chromosome-express chromo)
(map gene-express chromo))
When an individual is removed from the population, we need to adjust the probabilities by subtracting based on the genetics of the eaten individual, and the adding to the other alleles to keep the probabilities summing to one:
;; prevents the probability from 'fixing' at 0% or 100%
(define (calc-decrease p)
(* (min p (- 1 p)) allele-decrease))
;; remove this genome from the population
(define (gene-remove-expression gene genome)
(let ((dec (calc-decrease (allele-probability (car gene)))))
(let ((inc (allele-increase dec (length gene))))
(if (eq? (allele-id allele) genome)
allele (- (allele-probability allele) dec))
allele (+ (allele-probability allele) inc))))
9,000 players, 20,000 games played and 400,000 tested egg patterns later we have over 30 generations complete on most of our artificial egg populations. The overall average egg difficulty has risen from about 0.4 seconds at the start to 2.5 seconds.
Thank you to everyone who contributed their time to playing the game! We spawned 4 brand new populations last week, and we’ll continue running the game for a while yet.
In the meantime, I’ve started working on ways to visualise the 500Mb of pattern generating code that we’ve evolved so far – here are all the eggs for one of the 20 populations, each row is a generation of 127 eggs starting at the top and ordered in fitness score from left to right:
This tree is perhaps more useful. The ancestor egg at the top is the first generation and you can see how mutations happen and successful variants get selected.
I’m swatting up on my scratch skills for the first codeclub at Troon Primary School in Cambourne tomorrow afternoon! It’s exciting to finally head to the frontlines of algorithmic literacy in education.
Also on Wednesday I present at talk about FoAM and cross-disciplinary working at Exeter University’s Biomedical Informatics Hub, I’ll be talking about Borrowed Scenery, The Lobster DorisMap, Hapstar and Lirec, specifically concentrating on things that happen when people work together across many disciplines.
Some examples of graphs that scientists have created and published using Hapstar, all these images were taken from the papers that cite the hapstar publication, with links to them below. I think the range of representations of this genetic information indicate some exciting new directions we can take the software in. There are also some possibilities regarding the minimum spanning tree, finding ways to visualise and explore the range of possible MST’s for a given graph.
IVENS, ABF, et al. “Reproduction and dispersal in an ant‐associated root aphid community.” Molecular Ecology (2012).
Wielstra, Ben, and Jan Arntzen. “Postglacial species displacement in Triturus newts deduced from asymmetrically introgressed mitochondrial DNA and ecological niche models.” BMC Evolutionary Biology 12.1 (2012): 161.
Kesäniemi, J. E., Rawson, P. D., Lindsay, S. M. and Knott, K. E. (2012), Phylogenetic analysis of cryptic speciation in the polychaete Pygospio elegans. Ecology and Evolution, 2: 994–1007. doi: 10.1002/ece3.226
Vos M, Quince C, Pijl AS, de Hollander M, Kowalchuk GA (2012) A Comparison of rpoB and 16S rRNA as Markers in Pyrosequencing Studies of Bacterial Diversity. PLoS ONE 7(2): e30600. doi:10.1371/journal.pone.0030600
Hapstar is released, and now has it’s own website. Here’s a screenshot of an example haplotype network of human and neanderthal DNA sequences.
Hapstar is the new name for my little bioinformatics project, visualising population structure from differences between genetic sequences. The last few days I’ve done a lot of work on the GUI, allowing you to drag nodes around by hand, zoom in and out and navigate the graph. Also quite a bit of graph theory, validating the input graphs by detecting if they are a single connected component – or contain isolated graphs. It’s already been used to produce figures for an upcoming publication, so hopefully I can show some real examples soon.