Historical Perspective and the Interpretation of Ecological Patterns: Defensive Compounds of Tiger Beetles (Coleoptera: Cicindelidae)

The defensive compounds produced by pygidial glands of adult tiger beetles were analyzed for 83 species from North America, India, and Peru. Benzal-dehyde, the most common defensive compound detected, was found in 39 species. The presence of this compound, which has evolved independently in only a few other arthropod groups, indicates a cyanogenic precursor. Each of these 83 tiger beetle species occurred primarily in one of seven distinct habitats, such as forest floor, sand dune, water edge, and saline flat. All 83 species were also grouped according to genitalic similarities into distinct systematic taxa that represent closely related species. We predicted two alternative patterns of benzaldehyde presence among these tiger beetle species. (1) Through historical influences of systematic relatedness, benzaldehyde should be either present or absent nonrandomly among closely related species regardless of habitat and associated ecological similarities and differences. (2) Through convergence of defense against similar predators within each habitat type, benzaldehyde should be present nonrandomly among species in some habitats and absent nonrandomly in others, regardless of geographical location and systematic relationship. Our results show that in systematic groups with four or more species analyzed, 34 of 39 pooled species were consistent within a group for the presence or absence of benzaldehyde, regardless of habitat type (P < 0.001). However, for only one of the seven habitats (sandy water edge) was benzaldehyde present nonrandomly regardless of geographical location and systematic relationship. We conclude that historical (phylogenetic) factors are likely to be generally important in interpreting ecological data, as either alternative or interactive processes.