Dear colleagues,
I will appreciate your help in setting the parameters to use two nodes fossil-calibration for a phylogenetic-chronogram reconstruction using BEAST.
I have the divergence time between the outgroup (two species) 43 mya and the crown group of species that I would like to date, and the divergence time of these two species in the outgroup (8.7 mya).
Is there any way to get the a posteriori mutation rate in the way I can use this value later on to estimate populations divergence time using among populations genetic distance?
Many thanks in advance for your help.
Roberto
Technically you can define more than one prior in BEAST2.
However, scientifically there might be some issues. To date your "ingroup", one callibration point might be enough 8split ingroup/outgroup). Of course it would be best to have another calibration point within the "ingroup". To calibrate the outgroup two times (split outgroup-ingroup and split of the two outgroup taxa) might bias your results. Be aware, that also sampling density as well as underlying data might bias the dating. You will find plenty of papers about that...
Thank you Artur for your answer, you are completely right, but I'm afraid I have not to many alternatives. I can just estimate the substitution rate based in nodes calibrations and use the genetic distance among populations to infer divergence. I have no calibration points for populations.
Thank you Natascha, for your answer too, maybe a figure can explain better my question. Unfortunately, I do not have calibration points within my ingroup, just for the root and for the two species forming the out group, would you recommend to use just one species as out group and calibrate just the root?
Thanks for your time in helping with this :-).
Best,
Roberto
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