Evolution of flightlessness in Scarabaeoidea (Insecta, Coleoptera)

Abstract

Flight clearly confers exceptional mobility on an insect, and conversely the lack of flight greatly restricts the area over which an insect can search for mates, oviposition sites and food. Therefore it is reasonable to expect that selection will favour the retention of flight in a highly variable environment and that non‐migratory life histories will most likely evolve in very persistent habitats. Environments with a higher than expected incidence of flightlessness amongst a wide variety of scarabaeoids are temperate highland forests in the tropics, mountains, deserts, islands, termite nests and cold regions. The flightlessness may be in either sexes or only the female and may be as a result of wing reduction or it may be behaviourally or physiologically induced. In some taxa flightlessness appears to be a random occurrence with a few species out of many in the taxon flightless whereas in others there is clearly a phylogenetic propensity for flightlessness with all or many species flightless. Flightlessness in some taxa is inexplicable in terms of current distribution and historical explanations must be advanced. The habitat with a predicted high incidence of flightlessness but which, in fact, has low incidence amongst scarabaeoids, is that in tropical forests. In addition, intimate phoretic associations with other animals, although relatively common and highly specialised, yield none of the expected evidence of flightlessness. It is proposed that biologically simple communities, in addition to stable habitats, contribute toward flightlessness. Flightlessness may evolve in one of two ways amongst scarabaeoids; where only females are flightless, the selective pressure to trade‐off flight against reproduction is paramount; where it occurs in both sexes, small microhabitats or high population density which increase the chances of sexual encounters, are overriding.

Dung feeding in hydrophilid, geotrupid and scarabaeid beetles: Examples of parallel evolution

“…The Geotrupidae are in one of these lineages, the Scarabaeidae (including Aphodiinae and Scarabaeinae) in the other -and the common ancestor is believed not to have fed on dung (Scholtz & Chown, 1995;Browne & Scholtz, 1999;Krell, 2000;Scholtz, 2000, Philips et al, 2004. If these assumptions are correct, dung feeding based on selective ingestion of very small particles, accompanied by identical morphological specialisations of the mouthparts, must have evolved independently within each lineage, providing a remarkable example of parallel evolution within the Scarabaeoidea.…”

The role of the subelytral spiracles in respiration in the flightless dung beetle Circellium bacchus

“…bacchus is a monotypic, canthonine dung beetle, which is rare and restricted to fragmented patches of dense, arid bush in South Africa (Scholtz, 2000). It is assumed that competition from large, flighted dung beetles has confined it to these areas, where its apterous state and large size are assumed to be advantageous in minimising water loss (Chown et al, 1995).…”

“…While these findings only correlate with our assumptions about the role of the subelytral cavity in reducing water loss, we can assume that, if our hypothesis is correct, this mechanism will be widespread among related species. Thirty percent of the Canthonini are flightless, and most are found in tropical or subtropical stable habitats (Scholtz, 2000). Secondary loss of flight is widespread in the Scarabaeidae and is polyphyletic within the Scarabaeini (Harrison, 1999).…”

Phylogeny of the African ball-rolling dung beetle genus Epirinus Reiche (Coleoptera:Scarabaeidae:Scarabaeinae)

“…Flightlessness is generally accepted as a derived condition from a flying ancestor. It has evolved independently many times in different Scarabaeoidea groups (Scholtz 2000). In the Scarabaeinae, examples include aptery evolving independently at least three times within Scarabaeini (Harrison and Philips 2003,) and twice in Epactoides (Canthonini) (Wirta and Montreuil 2008).…”

“…Its evolution was likely driven by environmental pressures. According to Scholtz (2000) increased environmental homogeneity is one of the conditions that favour secondary loss of wings. All the flightless species are found in forest habitats which provide stable and persistent microhabitats that promote flightlessness.…”