How to calculate Fst from AMOVA

Question

I calculated an AMOVA from a genind object, with one hierarchical factor. In the table I obtain there are SSD values (for my grouping factor,"Error" and total) and sigma2 values (for my grouping factor and "Error")

I have two questions:

What does "error" stand for?
How do I calculate Fst? Which values do I have to use?

A genind object in R is an object which contains allelic information about a set of individuals.
This is the table that I get:

Analysis of Molecular Variance

Call: amova(formula = plantula.dist ~ g, nperm = 100)  

           SSD         MSD  df  
g     354992.9 354992.9297   1  
Error 310814.9    693.7834 448 
Total 665807.9   1482.8683 449 

Variance components:  
       sigma2 P.value  
g     1574.69       0  
Error  693.78         

Variance coefficients:  
       a   
224.9956

Welcome to Bioinformatics! Could you please clarify what is a geneind object? And could you provide the exact output of the table? (If you provide how you get that table that would probably be also helpful to answer you) — llrs, Jun 08 '17 at 12:35
I tried to insert the table, though I can't quite format it right... sorry, I'm still figuring this out! — Beatrice Baldi, Jun 08 '17 at 12:59
Please also indicate the non-standard packages you are using. I’m assuming amova comes from ‹pegas›? — Konrad Rudolph, Jun 08 '17 at 13:05
Yes @Llopis I mean fixation index, and yes Konard Rudolph, the amova I am using is from the package pegas. Sorry for not specifying! — Beatrice Baldi, Jun 08 '17 at 13:19

score 1 · Accepted Answer · answered Jun 09 '17 at 07:07

1

Error is the estimation that can't be fitted by your parameters (in this case g). The amova function in pegas package does the following:

This function performs a hierarchical analysis of molecular variance as described in Excoffier et al. (1992). This implementation accepts any number of hierarchical levels

And as per the definition of Fixation index, you need the variance in the frequency of the allele between different subpopulations, weighted by the sizes of the subpopulations, the variance of the allelic state in the total population. Which is not provided by amova. Thus you cannot compute the fixation index from amova results.

answered Jun 09 '17 at 07:07

llrs

4,693
1
18
42

That's what I thought. Thank you for confirming it. And thanks for the explanation for error! – Beatrice Baldi Jun 10 '17 at 09:19
@BeatriceBaldi if this answers your question, you can mark as solved by checking the tick at the left of the answer. This way you let others know that this problem is solved – llrs Jun 10 '17 at 10:48

How to calculate Fst from AMOVA

1 Answers1