Seed handling behaviours of native and invasive seed-dispersing ants differentially influence seedling emergence in an introduced plant

1. Myrmecochory, or ant-mediated seed dispersal, is an important ecological interaction in which ants benefit by gaining nutrition from lipid-rich elaiosomes attached to seeds and plants benefit from having their seeds dispersed away from parent plants. Most research on the benefits of myrmecochory focuses on primary dispersal, in which ants move seeds to nests, or secondary dispersal, in which ants deposit intact seeds in middens after consuming elaiosomes. Less is known about how ants handle seeds inside nests and if handling influences plant fitness. The seed handling behaviours of a native keystone disperser', Aphaenogaster rudis s.l., and an invasive seed-disperser, Myrmica rubra L., on an introduced herb, Chelidonium majus L., were compared. We conducted a greenhouse experiment to test if handling by ants, manual removal of elaiosomes, or no handling (controls) influenced seedling emergence. Colony-level differences in handling behaviours and plant responses were also examined.Aphaenogaster rudis retained seeds inside nests longer than M. rubra, but there was no difference in the amount of elaiosome removed by the two species. There was no difference in the proportion of seedlings that emerged among treatments, but seedlings emerged earlier when handled by A. rudis. Additionally, more seedlings emerged and seedlings emerged earlier the longer seeds were retained inside ant nests. This study suggests that handling by ants may be a benefit of myrmecochory. This is probably not due to elaiosome removal; rather favourable nest conditions may enhance emergence. Also, functional differences in ant species may result in different outcomes for plant partners.