Fig. 4

Intron position and expression of one cluster of nAChR genes. a Phylogenetic relationship, the corresponding gene structure and intron position of one group of nAChRs, containing both of intron-rich (> 2 introns) and intron-poor nAChRs (≤2 introns). The intron positions shaded blue are conserved. Genes shaded in green have only one intron. Numbers (0, 1, 2) above the intron position indicate intron insertion phases: 0, between two consecutive codons; 1, between the first and second codon position, and 2, between the second and third codon position. b Heat maps of expression at different developmental stages and in different organs in C. gigas (left) and P. f. martensii (right). Genes above the black line are intron-rich, and genes below the black line are intron-poor nAChRs. Scale bars refer to relative expression. E, egg; TC, two cells; FC, four cells; EM, early morula; M, morula; B, blastula; RM, rotary movement; FS, free swimming; EG, early gastrula stage; G, gastrula; T1, trochophore 1; T2, trochophore 2; T3, trochophore 3; T4, trochophore 4; T5, trochophore 5; ED1, early D-larva 1; ED2, early D-larva 2; D1, D-larva 1; D2, D-larva 2; D3, D-larva 3; D4, D-larva 4; D5, D-larva 5; D6, D-larva 6; D7, D-larva 7; EU1, early umbo larva 1; EU2, early umbo larva 2; U1, umbo larva 1; U2, umbo larva 2; U3, umbo larva 3; U4, umbo larva 4; U5, umbo larva 5; U6, umbo larva 6; LU1, late umbo larva 1; LU2, late umbo larva 2; P1, pediveliger 1; P2, pediveliger 2; S, spat; J, juvenile; Fe, fertilization; B, blastula; G, gastrula; ET, early trochophore; DF, D-larvae before feeding; EU, early umbo larvae; PV, post-veliger; CT, 2–8 cell stage; M, mantle; Di, digestive gland; A, adductor muscle; F, foot; Go, gonad; Fg, female gonad; Mg, male gonad; PS, pearl sac at 180 d; MP, mantle pallium; MC, mantle central; He, hemocyte; Lp, labial palp