Figure 4.

Intergenic spacer (IGS) size index (i.e., weighted average length) based on Southern Blot hybridization in females of 29 species of the Drosophilinae subfamily. Cladogram of phylogenetic relationships among species groups is based on Remsen and O'Grady [31]. Relationships within species groups are based on: melanogaster group [32]; virilis group [33, 34]; obscura group relationships [35]; and willistoni group [36]. Numbers above nodes indicate approximate date of divergence (in million years) based on Tamura et al. [19], unless otherwise noted. ¹ based on divergence of the melanogaster subgroup versus the montium and ananassae subgroups [19]; ² based on Pitnick et al. [18]; ³ based on Russo et al. [27].