Specifying source-sink populations

[ortego....@gmail.com]

Hi Laurent,

I think I have a trivial question. I am using Fastsimcoal to test different models of population divergence using RadSeq data and a folded SFS. My question is: Does it matters which populations are specified as sink/source in the .tpl file? Here you are a simple example (models 1 and 2 only differ in the lines specifying the historical events, the “topology” is the same in both models, they only differ in the populations that are specified as sink or source):

**Model 1**

//Number of population samples
3
//Population effective sizes (number of genes)
4225
NPOP1
NPOP2
//Samples sizes
30
30
30
//Growth rates : negative growth implies population expansion
0
0
0
//Number of migration matrices : 0 implies no migration between demes
2
//Migration matrix 0
0 MIG1 MIG2
MIG3 0 MIG4
MIG5 MIG6 0
//Migration matrix 1
0 0 0
0 0 0
0 0 0
//historical event: time, source, sink, migrants, new deme size, new growth rate, migration matrix index
2 historical event
TDIV1 0 1 1 RESIZE1 0 1
TDIV2 1 2 1 RESIZE2 0 1
//Number of independent loci [chromosome]
1 0
//Per chromosome: Number of contiguous linkage Block: a block is a set of contiguous loci
1
//per Block:data type, number of loci, per generation recombination and mutation rates and optional parameters
FREQ 1 0 5.9e-8 OUTEXP

**Model 2**

//Number of population samples
3
//Population effective sizes (number of genes)
4225
NPOP1
NPOP2
//Samples sizes
30
30
30
//Growth rates : negative growth implies population expansion
0
0
0
//Number of migration matrices : 0 implies no migration between demes
2
//Migration matrix 0
0 MIG1 MIG2
MIG3 0 MIG4
MIG5 MIG6 0
//Migration matrix 1
0 0 0
0 0 0
0 0 0
//historical event: time, source, sink, migrants, new deme size, new growth rate, migration matrix index
2 historical event
TDIV1 1 0 1 RESIZE1 0 1
TDIV2 0 2 1 RESIZE2 0 1
//Number of independent loci [chromosome]
1 0
//Per chromosome: Number of contiguous linkage Block: a block is a set of contiguous loci
1
//per Block:data type, number of loci, per generation recombination and mutation rates and optional parameters
FREQ 1 0 5.9e-8 OUTEXP

Does it make biological sense to test these two models? In other words, it is theoretically possible that they yield different results? I get similar results in terms of parameter estimates and likelihood, but I want to know if it really makes sense to test them or if they just represent the same demographic process (i.e. they are the same and indistinguishable model).

Thank you very much in advance!

Best
Joaquín

[Laurent Excoffier]

No it should not matter which one is the source