Fig. 3

Expansion of heat shock protein 70 (HSP70) genes has occurred in bivalve genomes. a Genes that contain conserved Pfam domains related to heat shock chaperones. See also Additional file 1: Table S4. b Unrooted maximum likelihood molecular phylogeny of HSP70 domain sequences of selected animal genomes. The blue area highlights a group of predominantly bivalve genes. Protein sequences of Pinctada fucata and Crassostrea gigas are marked with purple and green lines, respectively. Thick purple and green lines indicate that the clade comprises only one bivalve species, suggesting lineage-specific gene expansion. Yellow lines designate gene pairs of P. fucata and C. gigas supported by high bootstrap values (≥80 %), indicating that the genes probably existed in the common ancestor of the two bivalves. Nine outer red arcs, except the largest one on the left, show groups composed of four or more protostome genes. Nodes of the tree supported with high bootstrap values (≥80 %) are marked with black dots with the number, while larger black dots without a number indicate 100 % bootstrap support. The scale bar represents expected substitutions per site in the aligned regions. The first three letters of the protein ID indicate the species name; pfu: P. fucata, Cgi: C. gigas, Lgi: Lottia gigantea, Hro: Helobdella robusta, Cte: Capitella teleta, and Dme: Drosophila melanogaster. HSP70 domain sequences with lengths of 200 amino acids or more were used for analysis with the WAG + GAMMA + F model