In all trials of civil actions before a circuit judge, or an associate circuit judge sitting as a circuit judge, a jury shall consist of twelve persons selected pursuant to sections 494.400 to 494.505, unless all parties agree on a lesser number, but not less than eight, in which case the number of veniremen shall be reduced accordingly. Three-fourths or more jurors may return a lawful verdict. All verdicts shall be signed by each juror who agrees to the verdict.