Eusocial evolution without a nest: kin structure of social aphids forming open colonies on bamboo

Living in nests is an almost universal feature of eusocial animals. In some aphids, however, sterile soldier castes have evolved in open colonies without a nest. To clarify the factors promoting the evolution of eusociality in these colonies, we used newly developed microsatellite markers to compare the kin structure of the open colonies of two aphid species on bamboo: the non-eusocial colonies of Astegopteryx bambucifoliae and the eusocial colonies of Pseudoregma alexanderion Dendrocalamus latiflorus. Our samples, from over 1,000 hectares, contained 99 clones of A. bambucifoliae and 19 of P. alexanderi. Clonal mixing occurred in both species: average pairwise relatedness within a colony was 0.54 in A. bambucifoliae and 0.71 in P. alexanderi. Each clone of A. bambucifoliae occurred in a unique location, whereas those of P. alexanderi occurred in multiple locations and more than 90% of individuals came from just four clones. There was significant genetic variation among different colonie..., ,