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A quick poll for the evolution peeps. Is fitness a phenotype?
For me "of course it isn't". Phenotype for me is the physical manifestation of the organism that determines its fitness conditional on the environment. Just like in Fisher's Geometric model - there is an underlying phenotypic space and there is a fitness function on top of it
Another way in which they are different is that I can associate fitness with an allele and measure it through the instantaneous rate of freq. change of the allele in the population. But I cannot easily associate a phenotype with an allele. Phenotype is a property of the organism.
I think that fitness is fairly easy to measure if one focuses on the genotype to fitness measurements. *However* it is very hard to associate fitness with a phenotype and extremely hard to do full mapping of genotype to phenotype to fitness. We try here: https://www.biorxiv.org/content/10.1101/2020.06.25.172197v3
Quantitative genetics muddies the waters for me bc it was developed for agriculture making fitness become virtually co-linear with the phenotype that the farmer selects on. In nature phenotype is multi-dimensional and we don't know how to map phenotype to fitness in that case.
