Former SNP leadership candidate Ash Regan has resigned from the party to join Alex Salmond's Alba party.
Alba said her decision came after increasing disillusionment with the SNP's leadership and its "wavering commitment" to Scottish independence.
Ms Regan, 49, was elected as SNP MSP for Edinburgh Eastern at the last election and becomes the Alba party's first representative at Holyrood.
She came third in the SNP leadership contest won by Humza Yousaf in March.
The first minister said she should now do the "honourable thing" and step down as an MSP to allow a by-election.
Mr Yousaf said: "I can tell you categorically that the reason she's in that parliament is because she had the SNP logo next to her name on the ballot paper."
He told BBC Scotland she was "not a particularly great loss" to the party.
More here https://www.bbc.co.uk/news/uk-scotland-67248844