PMC

Scatterplots of fecundity (a) and egg hatchability (b) in the control (C), parental (P) and F₁ crosses, and backcrosses (B₁) between Samia cynthia pryeri (SCP) and Samia cynthia walkeri (SCW). Grey bars represent median. Open circles show the number of eggs laid (a) and hatchability of eggs (b) for each mating.

Scatterplots of the egg hatchability in crosses between F₂ hybrids of Samia cynthia ssp. (a) Hatchability of eggs in 21 pairs of F₂ hybrids from crosses between S. c. pryeri females and S. c. walkeri males. W+ and W− indicate F₂ hybrids with and without the W chromosome, respectively. (b) Hatchability of eggs in 12 pairs of F₂ hybrids from crosses between S. c. walkeri females and S. c. pryeri males. neo-W+ and neo-W− indicate F₂ hybrids with and without the neo-W chromosome, respectively. Grey bars represent median. Open circles show hatchability of eggs for each mating.

Schematic illustrations of sex chromosome constitutions in both sexes of Samia cynthia pryeri and Samia cynthia walkeri. S. c. pryeri has a WZ/ZZ sex chromosome system with 2n=28♀/28♂ and S. c. walkeri a neo-Wneo-Z/neo-Zneo-Z system with 2n=26♀/26♂. The neo-Z chromosome of S. c. walkeri arose by fusion of an ancestral Z chromosome (grey) and an autosome corresponding to chromosome 13 (Chr13) of S. c. pryeri. The W chromosome in S. c. pryeri consists of a highly heterochromatic part (black) and euchromatin-like part (striped grey), the latter corresponding to a part of the neo-W chromosome in S. c. walkeri.

Upper panel: FISH with sex chromosome-derived probes in mitotic metaphase complements of parents (a, b) and F₁ (c, d) and F₂ (e-l) offspring of crosses between Samia cynthia walkeri females and Samia cynthia pryeri males. Chromosomes were stained with DAPI (grey). Cy3-labelled probe of the 32B23 fosmid clone (red signals) mapped to chromosome 13 or the corresponding autosomal part of the neo-Z and neo-W chromosomes, and Green-labelled probe of the 45A6 fosmid clone (green signals) to the Z chromosome or the ancestral part of the neo-Z chromosome. Cy3-labelled W-painting probe (yellow signals) highlighted the ancestral part of the neo-W chromosome of S. c. walkeri. Bar=5.0 μm. Arrows, arrowheads, and asterisks indicate the neo-Z chromosome, Z chromosome and chromosome 13, respectively. (a) S. c. walkeri female, (b) S. c. pryeri male, (c) F₁ female, (d) F₁ male, (e, f, i, j) F₂ females and (g, h, k, l) F₂ males. Mitotic metaphase complements of F₂ hybrids were examined in eight males and eight females (). Lower panel: schematic illustrations of sex chromosome constitutions in parents and F₁ and F₂ hybrids from matings between S. c. walkeri females and S. c. pryeri males, based on the FISH results.

Upper panel: FISH with sex chromosome derived probes in mitotic metaphase complements of parents (a, b) and F₁ (c, d) and F₂ (e–l) offspring of crosses between Samia cynthia pryeri females and Samia cynthia walkeri males. Chromosomes were stained with DAPI (grey). Cy3-labelled probe of the 32B23 fosmid clone (red signals) mapped to chromosome 13 or the corresponding autosomal part of the neo-Z chromosome and Green-labelled probe of the 45A6 fosmid clone (green signals) to the Z chromosome or the ancestral part of the neo-Z chromosome. Cy3-labelled W-painting probe (magenta signals) highlighted the S. c. pryeri W chromosome. Bar=5.0 μm. Arrows, arrowheads and asterisks indicate the neo-Z chromosome, Z chromosome, and chromosome 13, respectively. (a) S. c. pryeri female, (b) S. c. walkeri male, (c) F₁ female, (d) F₁ male, (e, f, i, j) F₂ females and (g, h, k, l) F₂ males. Mitotic metaphase complements of F₂ hybrids were examined in eight males and eight females (). Lower panel: schematic illustrations of sex chromosome constitutions in parents and F₁ and F₂ hybrids from matings between S. c. pryeri females and S. c. walkeri males, based on the FISH results.