Data from: The kin-selected context of duelling in horned aphids: cooperation or conflict?

We investigated the influence of relatedness on the function of dyadic
butting contests over access to a food resource (plant phloem) in the
group-living horned aphid Astegopteryx bambusae on bamboo leaves.
Relatedness between duelling pairs did not differ significantly from that
of randomly selected aphid pairs. Microsatellite genotyping showed that
the average genetic relatedness between a duelling pair was 0.79 ± 0.12
(mean ± SD, N = 75), with 56% (42/75) of duels occurring between clonal
pairs. Butting contests observed in the field lasted longer when the
competing aphids were of similar age and when the attacker won, but they
involved low costs in terms of time or injury. Neither the duration nor
outcome of the contests was associated with the pairwise relatedness,
suggesting that there was no kin-discrimination in the butting pair of
aphids. 83% (50/60) of the contests between aphids of different ages were
won by the older and larger aphid. These results suggest that the aphids
discriminate between their opponents on the basis not of
relatedness but of size or age. We suggest that the duels in these
Astegopteryx aphids are not an aggressive fight for resources between
different genotypes, but a low-cost method by which the aphids assess each
other’s reproductive value, providing an indirect fitness benefit for
losing younger individuals that yield a feeding site to older kin. This
provides a selective context for the evolution of the young, rather than
old, altruistic soldiers that are observed in the open colonies of many
cerataphidine species.