Wing interference patterns are consistent and sexually dimorphic in the four families of crane flies (Diptera, Tipuloidea)

Abstract

Wing interference patterns (WIP) are stable structural colors in insect wings caused by thin-film interference. This study seeks to establish WIP as a stable, sexually dimorphic, species-level character across the four families of Tipuloidea and investigate generic level WIP. Thirteen species of Tipuloidea were selected from museum specimens in the Academy of Natural Sciences of Drexel University collection. One wing from a male and female of each representative species was excised and mounted to a slide with coverslip, placed against a black background, and imaged using an integrated microscope camera. Images were minimally retouched but otherwise unchanged. Descriptions of the WIP for each sex of each species are provided. Twelve of thirteen species imaged had WIP, which were stable and species specific while eight of those twelve had sexually dimorphic WIP. Comparisons of three species of Nephrotoma were inconclusive regarding a generic level WIP. Gnophomyiatristissima had higher intraspecific variation than other species examined. This study confirms stable, species specific WIP in all four families of crane flies for the first time. More research must be done regarding generic-level stability of WIP in crane flies as well as the role sexual and natural selection play in the evolution of wing interference patterns in insects.

Keywords: Cryptic; Cylindrotomidae; Limoniidae; Pediciidae; Tipulidae; WIP; dimorphism; morphology.

Figure 1.

Comparison of the variation in WIP of three female and three male specimens of Gnophomyiatristissima. Females examined in this study were found to have a range of WIP from A dark blue/ purple B blue with mottled yellow C green/yellow with hints of blue which appeared most like the male WIP. Males examined also had a range of WIP from D green with mottled blue which appeared most like the female WIPE solidly green F green with mottled magenta. Patterns B and E were the most encountered patterns for females and males, respectively. Scale bars: 1.0 mm.

Figure 2.

Excised wing of a male specimen of Dolichopezaobscura against a white background with notations of wing veins and cells used in this study. Veins are noted in blue with uppercase letters while cells are noted in red with lowercase letters; naming and notations follow those of Saigusa (2006). Abbreviations: A/a: anal vein/cell, bm: basal medial cell, br: basal radial cell, C/c: costal vein/cell, CuA/cua: anterior cubitus vein/cell, CuP/cup: posterior cubitus vein/cell, d: discal cell, M/m: Medial vein/cell, R/r: radial vein/cell, Rs: radial sector vein, Sc/sc: subcostal vein/cell. Image not to scale.

Figure 3.

Wing Interference Pattern on excised wings of male/ female pair of two species of Tipuloidea. Excised wings of a male/ female pair of two species of crane flies. Wings were excised, flattened between a glass slide and cover slip, and photographed under a microscope using transmitted light ACylindrotomadistinctissima female BCylindrotomadistinctissima male CGnophomyiatristissima female DGnophomyiatristissima male. Scale bars: 1.0 mm.

Figure 4.

Wing Interference Pattern on excised wings of male/ female pair of two species of TipuloideaADactylolabiscubitalis female BDactylolabiscubitalis male CDicranomyialiberta female DDicranomyialiberta male. Scale bars: 1.0 mm.

Figure 5.

Wing Interference Pattern on excised wings of male/ female pair of two species of TipuloideaATricyphonainconstansinconstans female BTricyphonainconstansinconstans male CDolichopezaobscura female DDolichopezaobscura male. Scale bars: 1.0 mm.

Figure 6.

Wing Interference Pattern on excised wings of male/ female pair of two species of TipuloideaABrachypremnadispellens female BBrachypremnadispellens male CHolorusiahespera female DHolorusiahespera male. Scale bars: 1.0 mm (A, B), 1.0 cm (C, D).

Figure 7.

Wing Interference Pattern on excised wings of male/ female pair of two species of TipuloideaANephrotomaferruguina female BNephrotomaferruguina male CNephrotomamacrocera female DNephrotomamacrocera male ENephrotomavirscens female FNephrotomavirscens male. Scale bars: 1.0 mm.

Figure 8.

Wing Interference Pattern on excised wings of male/ female pair of two species of TipuloideaATipula (Beringotipula) borealis female BTipula (Beringotipula) borealis male CTipula (Yamatotipula) sayi female DTipula (Yamatotipula) sayi male. Scale bars: 1.0 mm.

Figure 9.

Images showing WIP on several species of crane fly in nature A male Tipula (Yamatotipula) aprilina Alexander, 1918 displaying WIP in nature B female Tipula (Yamatotipula) aprilina displaying WIP in nature C pair of Gnophomyiatristissima perched on a leaf in copula. Both flies are displaying their sexually dimorphic WIP. The female (bottom) has a blue WIP while the male (top) displays a green WIPD an individual of Ellipteraclausa Osten Sacken, 1877 displaying a WIP with wings folded. Sex unknown. Copyright (A, B) 2021, photograph JK Gelhaus; (C) 2020, photograph Katja Schulz, used with permission by the artist and under a creative commons license (https://creativecommons.org/licenses/by/4.0/) with alterations limited to cropping and resizing of this image; (D) 2016, photograph JK Gelhaus. Images are not to scale.