Scanning electron microscopy (SEM) images of the head (A) and the compound eye (B) of a female Megaphragma viggianii (side view). Ifb – inter-facet bristle. The compound eye comprises 29 ommatidia named here as in Chua et al. (2023).

A three-dimensional (3D) reconstruction of the compound eye of M. viggianii.

(A) A front view from the cornea side; (B) a rear view from the retinal side; (C) a side view; (D) a rear view of the ommatidia DA; (E) a rear view of the ommatidia DA; (F) a semi-side view of pigment granules of all cells. Abbreviations: cc – crystalline cones; cl – corneal lense; DRAm – dorsal rim area ommatidia (morphological specialization); DRA+ – transitional zone ommatidia; ppc – primary pigment cells; ppcpg – pigment granules of PPC; prpg – retinal (photoreceptor) pigment granules; rpcpg – rim cells pigment granules; spc – secondary pigment cells; spcpg – secondary pigment cell pigment granules. Ommatidia are named as in Chua et al. (2023).

Linear measurements (µm) of M. viggianii eye components

. Diameter1,2 – diameter of rhabdom measured in orthogonal planes, according to its not round shape. Hereinafter mean ± s.d. DRA – dorsal rim ommatidia in general (DRAm and DRA+); DRAm – dorsal rim area ommatidia (morphological specialization); DRA+ – transitional zone ommatidia; non-DRA – regular (non-DRA) ommatidia. Raw data—Appendix 1 Table 1.

Cross-sections of M. viggianii ommatidia sampled from a vEM (FIB-SEM) dataset.

(A– F) DRA ommatidia (B5); (G–L) non-DRA ommatidia (C3). (A, G) a longitudinal section through one ommatidium; (B, H) a cross-section through the proximal part of a corneal lens; (C, I) a cross-section through the center of a cone; (D, J) a cross-section through a distal rhabdom, directly under the cone; (E, K) a cross-section through the center of a rhabdom; (F, L) a cross-section through a distal rhabdom. Abbreviations: cc – crystalline cone; ccn – nuclei of crystalline cone cells; cl – corneal lens; ppc – primary pigment cells; R1–R8 – retinal cells; spc – secondary pigment cells; asterisk (*) marks cone cell projections.

Mean volumes (µm3) for cellular and subcellular elements of ommatidia in M. viggianii.

The volumes were obtained from 3D models. DRA – dorsal rim ommatidia in general (DRAm and DRA+); DRAm – dorsal rim area ommatidia (morphological specialization); DRA+ – transitional zone ommatidia; non-DRA – regular (non-DRA) ommatidia; R1-R8 – retinal cells; PPC – primary pigment cells; SPC – secondary pigmen cells. Raw data—Appendix 2 Table 2.

3D reconstruction of nuclei in ommatidium cells of M. viggianii.

(A, B, E, F, I, J) DRA ommatitida (B6); (C, D, G, H, K, L) non-DRA ommatidia (C4). Abbreviations: cc1–4 – crystalline cone cells; cc1n–4n – nuclei of crystalline cone cells; cl – corneal lens; ppc1, 2 – primary pigment cells; ppc1n, ppc2n – nuclei of PPC; R1–R8 – retinal cells; R1n–8n – nuclei of retinal cells; spc – secondary pigment cells; spcn – nuclei of secondary pigment cells. Colors of nuclei same as colors of their cells.

3D reconstruction of pigment granules in the ommatidium cells of M. viggianii.

(A, B, E, F, I, J) DRA ommatidia (B6); (C, D, G, H, K, L) non-DRA ommatidia (C4). Abbreviations: ppc1, 2 – primary pigment cells; ppc1pg, ppc2pg – pigment granules of PPC; R1–R8 – retinal cells; R1pg– R8pg – pigment granules of retinal cells; spc – secondary pigment cells; spcpg – pigment granules of secondary pigment cells. Colors of pigment granules are the same as the colors of their cells.

3D reconstruction of mitochondria in the ommatidium cells of M. viggianii.

(A, B, E, F, I, J) DRA ommatidia (B6); (C, D, G, H, K, L) non-DRA ommatidia (C4). Abbreviations: ppc1, 2 – primary pigment cells; ppc1mt, ppc 2mt – mitochondria of PPC; R1–R8 – retinal cells; R1mt–R8mt – mitochondria of retinal cells; spc – secondary pigment cells; spcpg – mitochondria of secondary pigment cells. Colors of mitochondria are the same as colors of their cells.

Volumes (µm3) of pigment granules and mitochondria in ommatidia of M. viggianii and Trichogramma evanescens.

The data for T. evanescens are from Fischer et al. (2019). R1–R8 – retinal cells; mt – mitochondria; pg – pigment granules; PPC – primary pigment cells; SPC – secondary pigment cells. B6, C4, A3, A0 – ommatidia on which cells pigment granules and mitochondria were reconstructed. Raw data—see Appendix 2 Table 5.

‘Ectopic’ photoreceptors and rind photoreceptor shield in the compound eye of M. viggianii.

(A) A 3D reconstruction of the eye: posterior view from the retinal area with labeled ePRs; (B) a 3D reconstruction of ePRs; (C, D) an EM section through dorsal border of the eye; (F) an EM section through the eye showing rim pigment cells (RPC). Abbreviations: cc – crystalline cones; cl – corneal lens; ePR1-3 – ‘ectopic’ photoreceptors; mt – mitochondria; nuc – nuclei; pg – pigment granules; ppc – primary pigment cells; rbd – rhabdom; rbm – rhabdomeres of ‘ectopic’ photoreceptors; spc – secondary pigment cells. B6, D7, E7 – DRA ommatidia abutting ‘ectopic’ photoreceptors.

Volumes (µm3) and number for ‘ectopic’ photoreceptors in M. viggianii. EPR1–3 – ‘ectopic’ photoreceptors.

Features of DRA and non-DRA ommatidia obtained by reconstruction of compound eyes of M. viggianii.

DRA – dorsal rim ommatidia in general (DRAm and DRA+); DA – dioptric apparatus; non-DRA – regular (non-DRA) ommatidia; PC – pigment cells; PPC – primary pigment cells; R1–R8 – retinal cells. t-test * 0.001 ≤ p < 0.01, ** 0.0001 ≤ p < 0.001, *** p < 0.0001.

Regional specialization of the compound eye in M. viggianii.

Bubble size indicates the value of each parameter. (A) Rhabdom volume; (B) volume of rhabdomere R7’; (C) volume of rhabdomere R8; (D) inner curvature of the lens; (E) focal length; (F) cone volume; (G) f-number; (H) acceptance angle of the rhabdom; (I) sensitivity of the ommatidium. DRAm – dorsal rim area ommatidia (morphological specialization); DRA+ – transitional zone ommatidia. Ommatidia are named as in Chua et al. (2023).

Comparison of volumes (µm3) of ommatidial components for Trichogramma evanescens and M. viggianii.

Data on T. evanescens are from Fischer et al. (2019). CC – crystalline cones R1–R8 – retinal cells; PPC – primary pigment cells; SPC – secondary pigmen cells.