A comparative analysis of morphological and ecological characters of European aphids and lycaenids in relation to ant attendance.

Ants are a major environmental factor for many insect species. For example, aphids and lycaenids have evolved an array of associations with ants ranging from obligate myrmecophily to the avoidance of contact. Here we (1) analyze the predictive power of different ecological and morphological traits for explaining the strength of the association between ants and aphids/lycaenids and (2) contrast different taxonomic levels with respect to the variance explained by ant attendance. Data come from a literature survey including 112 species of aphids and 103 species of lycaenids from Europe. For aphids, feeding on woody plant parts is positively associated with ant attendance, while a high degree of mobility, feeding in isolation, and the possession of wings in the adult stage are negatively associated with ant attendance. In lycaenids, feeding on inflorescences and feeding on Fabaceae host plants is closely associated with ant attendance, while living in forests bears a smaller likelihood to establish mutualistic relationships. Body size always appeared to be a poor predictor for the degree of ant attendance. Overall, in both insect groups less than 10% of the variation in the ecological traits recorded is explained by the different modes of ant association. When decomposing the variance in traits explained by ant attendance at different taxonomic levels, aphids and lycaenids show contrasting results. In aphids, most variance in the degree of ant attendance is explained at the subfamily level and least at the species level. The opposite is true for lycaenids, where most variance is explained at the lowest taxonomic level. Possible mechanisms explaining these different patterns of associations with ants are suggested.