Linking early history of Pterygota to habitat structure: The role of dendritic ecological networks in insect natural history
Species living in dendritic ecological networks such as branching plant structures and stream and river networks benefit from strategies for dispersal both within and outside of their branching, hierarchical geometries. Out of network dispersal strategies are known to promote population stability, persistence, and establishment. The combination of flight and an additional dispersal mechanism, such as walking, in insects allows the ability for a species to specialize to life within a dendritic habitat while still gaining the advantages of out of network movement strategies. Because the earliest known flying insects are thought to have been arboreal, and because the most basal extant flying insects are aquatic, did the relationship between insect flight and dendritic networks play a role in the natural history of Pterygota (winged insects and those that have secondarily lost flight)?
A review of the literature on Devonian and Carboniferous natural history, when flying insects are thought to have originated and diversified, suggests that the pterygote insects known from that time, members of the superorder Paleodictyopteridea, the sister taxon to extant pterygote insects, were mainly arboreal and specialized to forests habitats, which were restricted to swamps and riparian corridors with unpredicatable flow regimes. Studies on insect flight loss and retention suggest that riparian corridors and lotic habitats with unpredictable flow are positively correlated with retention of flight, and this literature review suggests that this describes the conditions such arboreal insects would have been subject to. This review had led to the generation of two hypotheses: 1) flight was an adaptation to the dendritic structure of arboreal and riparian habitats, and 2) the aquatic insect ancestors to Ephemeroptera (and possibly the Odonata & Neoptera clade), evolved from arboreal species that utilized the advantage of flight in branching lotic systems with unpredictable flow regimes. The next step is to investigate the phylogenetics of insects using comparative methods to determine if these evolutionary changes are correlated with dendritic habitats.