Phylogram from Bayesian analyses depicting the evolutionary relationships among the genes encoding receptors for GnRH and other peptides. Two amphioxus sequences, A and B, differ by a single amino acid; thus, only one was included in the analysis. Colored backgrounds emphasize strongly-supported, monophyletic subfamilies of GnRH receptors. Symbols indicate three categories of support value: triangles, posterior probability of 0.90-0.95; squares, posterior probability of 0.95-0.99; circles, posterior probability of 1.0. ACPR = adipokinetic hormone/corazonin-related peptide receptor; AKHR = adipokinetic hormone receptor; CRZR = corazonin receptor; OTR = oxytocin receptor; V1bR = type 1b vasopressin receptor. The scale bar depicts a branch length corresponding to 0.3 amino acid substitutions per site. Latin names of species and accession numbers for sequences are provided in Additional file 1: Table S1.