mechanisms mediating individual interactions

[bobweek]

ben asked me to draft up a summary of commonly used mechanisms mediating interactions in coevolutionary models and how they might be implemented in eidos. after some careful thinking, i concluded that this functionality would be best left as user-defined. instead, i think a class of recipes demonstrating how these models can be implemented would be most effective to aid researchers interested in using slim to study coevolution. more thoughts in the attached document. interspp-intxns.pdf

[petrelharp]

Thanks for the writeup! A question: you've got tables with values of α for the "interaction table"; what's the range of meanings for α? (It's usually just affecting "fitness", abstractly defined, right?)

[bobweek]

happy to be helpful :) α is typically thought of as a probability of interaction "success" (or probability of encounter depending on the model/perspective) as a function of genotypes or phenotypes. for phenotypic mechanisms, α might be considered the degree to which the interaction occurs instead of the probability of a binary outcome (like "how much grass did the cow eat?" instead of "what is the probability of the cow eating this grass?").

there is another step that needs to be taken "after" α to map the results to fitness effects (which would determine whether the interaction is an antagonism, mutualism, etc). there are many ways this can be done. one approach would be add s*α (with s a selection parameter) to the individuals baseline fitness to determine their fitness after the interaction. in this case a positive s means a successful interaction benefits the focal individual while a negative s induces a cost on the individual. if s is positive for both species, the interaction is a mutualism, etc. another approach is to consider multiplicative fitness effects. it's also possible to set this mapping up so the type of interaction evolves depending on relative trait distributions or allele frequencies of the two species. i can go into further details if there's interest.

[petrelharp]

I wonder if it'd be helpful to have a list of examples of biological mechanisms mediating interactions?

[bobweek]

sure!

• the mam model has been used to explain the genomic basis of an interaction between a daphnia and a bacteria - luijckx2013
• the gfg model has been used to explain the genomic basis of an interaction between a flax and a rust fungus - brown2011
• the trait matching model has motivation from many sources.
• one being the antagonism between a warbler and a brood parasitic cuckoo. in this case the trait-matching model might explain two components of the interaction. 1) coloration of the cuckoo egg must match that of the warbler to trick it and 2) song of the cuckoo offspring must match that of the warbler also to trick it. - davies1991
• another is the timing of flowering and the emergence of pollinators
• the trait-differences model has been used to explain the phenotypic interface of the interaction between a camellia fruit and a parasitic weevil - toju2006
• the trait-differences model may also explain the phenotypic interface of a pollination-based mutualism - pauw2009

[bhaller]

Hi @bobweek and @petrelharp. This is all very interesting. Would you like to develop an example recipe (or two) for the SLiM manual demonstrating these techniques with simple multispecies models, Bob? That might be quite useful to folks. If you're interested, don't launch into doing it quite yet, but just let me know you're interested, and I'll ping you when things are ready for that to happen – probably just a few days, but I want to get a few ducks in a row first. :->

[bobweek]

Yes, I'm interested! :)

[bhaller]

OK, between @bobweek and myself we have now got recipe 19.6 that is trait-matching, and recipe 19.7 that is matching-allele. That doesn't show every enumerated possibility, but I think it gestures sufficiently towards how to write these types of models, perhaps. I think I will therefore close this issue. However, there will probably need to be a couple more recipes in the manual to show how to do different types of ecological interactions beyond parasitoids and parasites, and maybe they should also show different styles of genetic interaction, just for the variety of it. So I'll likely be consulting your writeup again in future; thanks for that, it's quite clarifying!