Evidence for aposematism in a southern hemisphere stonefly family (Plecoptera: Austroperlidae)

Abstract

Aposematism is a phenomenon in which defended prey advertise their unprofitability to predators through conspicuous signals. Aposematic (warning) colouration is widespread across numerous insect orders but rarely occurs in insects that inhabit aquatic environments where conditions can impose constraints on visual signal transmission. In the semi-aquatic insect order Plecoptera (stoneflies), only the terrestrial adult stage of Austroperla cyrene (Austroperlidae) from New Zealand has been suggested to possess aposematic colouration, associated with the presence of hydrogen cyanide and documented unpalatability to predators. Here, we review evidence for the occurrence of aposematic colouration in Australian and South American Austroperlidae based on a synthesis of taxonomic literature and studies examining feeding preferences of predators in aquatic environments. Contrasting black, white and yellow colouration occurs commonly in adult Austroperlidae, and nymphs of several surveyed species were found to be aversive to predators, together suggesting that aposematism may be widespread in this family. The wider prevalence of aposematism in Austroperlidae should be examined further by directly testing the palatability of various species to predators and by analysing the chemical compositions of their defensive secretions. Austroperlid stoneflies offer new potential for understanding the evolution of aposematism in ecological and phylogenetic contexts that have not yet been explored.