The relationship between intron length and the level of divergence between D. melanogaster and D. simulans for the combined dataset of 225 introns. A significantly negative correlation is found for all introns (Spearman correlation coefficient R
= -0.388, P < 10-4), first introns (R
= -0.451, P < 10-4) and non-first introns (R
= -0.304, P < 10-4).