A PHYLOGENETIC ANALYSIS OF SOLDIER EVOLUTION IN THE APHID FAMILY HORMAPHIDIDAE

Aphid soldiers, altruistic larvae that protect the colony from predato rs, are an example of highly social behaviour in an insect group with a natural history different from the eusocial Hymenoptera and Isoptera . Aphids therefore allow independent tests of theory developed to expl ain the evolution of eusociality. Although soldiers have been discover ed in five tribes from two families, the number and pattern of origins and losses of soldiers is unknown due to a lack of phylogenetic data. Here I present a mtDNA based phylogeny for the Hormaphididae, and tes t the hypothesis that soldiers in the tribe Cerataphidini produced dur ing two points in the life cycle represent independent origins. The re sults support this hypothesis. In addition, a minimum of five evolutio nary events, either four origins and one loss or five origins, are req uired to explain the distribution of soldiers in the family. The posit ions of the origins and losses are well resolved, and this phylogeny p rovides an historical framework for studies on the causes of soldier a phid evolution.