Covariation of Defensive Traits in Tiger Beetles (Genus Cicindela): A Phylogenetic Approach Using mtDNA

Inferences about the evolution of defensive strategies in tiger beetles (genus Cicindela) have been contentious, largely due to the lack of a phylogenetic hypothesis for the group. We used a dataset that includes measures of chemical defense, habitat association, and body coloration for a representative sample of North American Cicindela (Pearson et al. 1988) to reassess, within a phylogenetic context, the problem of covariation in defensive strategies. We reconstructed a phylogenetic hypothesis from mtDNA for a total of 44 Cicindela and seven outgroup taxa using 1896 base pairs from three segments of the mitochondrial genome. Characters involved in predator deterrence and escape were optimized onto this phylogeny. Although most taxa producing large amounts of benzaldehyde fall into two monophyletic clades, numerous changes in the level of benzaldehyde secretion across the genus suggest that this parameter is poorly conserved phylogenetically. In contrast to previous studies, we also found little support for correlated character changes in benzaldehyde secretion and habitat type, a presumed indicator of the selective regime. Aposematic coloration of the abdomen was restricted to a single monophyletic group of taxa producing large amounts of benzaldehyde. Bright iridescent coloration, implicated in predator evasion during flight, was only loosely correlated with the phylogenetic affinities of taxa and appears to be part of a defensive strategy not usually acting in combination with chemical defenses. Our study of character covariation clarifies earlier analyses of the adaptive significance of benzaldehyde defense, which were inconclusive without a phylogenetic hypothesis.