Fig. 1.

SPR and MIP genes occur in most sequenced insect genomes, whereas SP and Dup99B orthologs are detected only in small groups of Drosophila genus. The presence of corresponding orthologs was revealed by BLAST analysis on the corresponding genome assemblies and is indicated by + (presence) or − (absence). The phylogram showing relationships among insect species was adopted and modified from http://flybase.org/blast/. ^aThe presence of SPR and MIP genes in Aplysia californica were inferred from the identification of corresponding ESTs from a CNS-specific cDNA library (39).