Elytra reduction may affect the evolution of beetle hind wings

Abstract

Beetles are one of the largest and most diverse groups of animals in the world. Conversion of forewings into hardened shields is perceived as a key adaptation that has greatly supported the evolutionary success of this taxa. Beetle elytra play an essential role: they minimize the influence of unfavorable external factors and protect insects against predators. Therefore, it is particularly interesting why some beetles have reduced their shields. This rare phenomenon is called brachelytry and its evolution and implications remain largely unexplored. In this paper, we focused on rare group of brachelytrous beetles with exposed hind wings. We have investigated whether the elytra loss in different beetle taxa is accompanied with the hind wing shape modification, and whether these changes are similar among unrelated beetle taxa. We found that hind wings shape differ markedly between related brachelytrous and macroelytrous beetles. Moreover, we revealed that modifications of hind wings have followed similar patterns and resulted in homoplasy in this trait among some unrelated groups of wing-exposed brachelytrous beetles. Our results suggest that elytra reduction may affect the evolution of beetle hind wings.

Fossil evidence of elytra reduction in ship-timber beetles

“…Nonetheless, this phenomenon is found repeatedly across the order, indicating multiple independent origins. Because the condition and degree of development of the elytra varies greatly among beetles, a previous study classified the reduced elytra into three morpho-types 7 : 1) elytra reduced along with a reduction in the hindwings, e . g .…”

“…The third form is the rarest and most interesting elytral type because it apparently does not have a protective function and other merits. Despite these disadvantages, this elytral form is found in unrelated beetle lineages 7 . The origin and role of this type of brachelytry have still not been adequately explored.…”

“…The origin and role of this type of brachelytry have still not been adequately explored. However, it was suggested that elytra reduction affects the evolution of beetle hindwings by optimising the aerodynamic efficiency or changes in flight mechanics induced by elytra loss 7 . In atractocerine species, extreme cases of reduced elytra are known.…”

“…are exceptional because they lack trace of elytra 9 . Excluding Platerodrilus , the degree of elytral reduction ranges from moderate to almost completely reduced, as seen in the ship-timber beetle subfamily Atractocerinae (Lymexylidae) 7 ; the latter have exposed their abdomens and functional hindwings (Fig. 1i,j and Supplementary Fig.…”

“…They protect the hindwings and dorsal abdomen from predators or harsh environmental conditions. Elytra also support desiccation tolerance, minimise the effect of rapid temperature shifts, and even play roles in mimicry or camouflage 4 – 7 . The strong sclerotisation enabled early beetles to penetrate and adapt to life under bark, like the adults of extant archostematan beetles (Cupedidae and Ommatidae) 8 .…”