Fig. 1
A Major morphological features of the Trithemis forewing (top) and hindwing (bottom). C = costa; N = nodus, Cs = subcosta; R + M = radius and media; R1 = first radius; R2 = second radius; R3—third radius; R4 = fourth radius; MA = media anterior; IR3 = intercalary vein behind R3, Cu = cubitus; CuP = cubitus posterior, Ps = pterostigma. Note that, unlike other dragonfly genera, the major structures features of the Trithemis forewing and hindwing are quite similar (see also Additional file 1: Plates 1 and 2), facilitating detailed direct comparisons between individual wings and across species within this genus. B Positions of the 38 landmarks (white) and semilandmarks (black) used to quantify Trithemis forewing (top) and hindwing (bottom) form. Landmarks are located at the origins, intersections or peripheral termini of major wing veins (see Additional files 2: Landmark-Semilandmark Definitions). Peripheral landmarks 1, 6, 13, 20, 25 and 31 were used to subdivide the wing outlines into five zones with the number of evenly spaced semilandmarks interpolated within these zones being sufficient to represent their zone-based peripheral outline geometries to a minimum accuracy of > 95% across all specimens in the sample. This form-sampling system ensures accurate and even representation of the wing outline characterization and improves inter-semilandmark correspondence across specimens