These chapters are rather technical and very mathematical. However, there are some interesting and general messages, that deserves to be carefully considered. Here are some questions to consider:
1. Which two main models about genetic variance have been developed and which assumptions underly them?
2. Sometimes, an initial increase in genetic variance is observed in an early stage of the selection experiment? Which of the two models can explain this, and what is the reason by behind such an increase in additive genetic variance?
3. What time frames are we talking about here we say "short-term" and "long-term"?
4. How do a/the effect size of loci and b/the number of loci affect the selection plateau?
5. How is allele frequency dynamics and hence additive genetic variance changing over time in "mixed models", i. e. genetic architectures characterized by a few loci of major effect and many loci of small effect?
Perhaps a bit out of topic, but we had a discussion on the possible explanations for why large body size is favoured in adult Medium Ground-Finches, while small body size is favoured in juveniles. Supposedly it has to do with competition. Perhaps it is an advantage for a juvenile to be small in order to be able to (partly) get into a different niche than the adults? A following question is whether this phenomenom is unique for this species? Does it occur in other environments, even mammals?
ReplyDeleteAnother discussion covered fitness surface. In the end we were a bit confused about what that really describes in practical terms?
Unfortunately, some figures (e.g. 19.2, 19.7-8, 20.4) where blank and we also thought the questions (for chapter 24-25) didn't exactly apply to what we read in chapter 19-20.
Finally, we'd like to ask if the questions for next week could be posted on Wednesday, as we intend to keep our meeting on Thursday (2nd of December)?
Daniel Bengtsson
Dear Daniel,
ReplyDeleteSorry for not posting before, but I have been away travelling for a research conference! I will post the new questions today.
Regarding your specific questions:
1. That selection often favours different trait values during different parts of the ontogeny (e. g. small body size in juvenile ground finches and large body size in adult ground finches), is often called "conflicting selection". That is very common in many animals, and might have different explanations. The suggestion that it is competition who explains the pattern in ground finches is interesting, and I have not heard it before. It certainly warrants more attention.
2. Regarding the fitness surface: I I am not sure what you mean by "practical terms", but in terms of describing and understanding natural selection on a phenotypic trait, it is certainly fundamental to know not only the INTENSITY (strength) of selection, but also the FORM (stabilizing towards a fitness peak? Disruptive selection and a fitness valley? Directional selection towards small (or large) trait values).
I am sorry for the missing pictures, we simply skipped these pictures in our discussions here. I do not think they were fundamental, as there were plenty of material in the chapters to discuss anyway.