Transcript diversity reflects deleterious RNA processing errors shaped by population size in metazoans

Alternative transcription initiation, splicing and polyadenylation generate extensive transcript diversity in eukaryotes, but its evolutionary significance has been disputed. This study analyses 166 transcriptomes across 75 metazoan species to show that transcript diversity generally decreases with effective population size, supporting the view that most transcript diversity reflects deleterious RNA processing errors rather than adaptive functions.