The critical role of ants in the extensive dispersal of Acacia seeds revealed by genetic parentage assignment
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Ants are prominent seed dispersal agents in many ecosystems, and dispersal distances are small in comparison with vertebrate dispersal agents. However, the distance and distribution of ant-mediated dispersal in arid/semi-arid environments remains poorly explored. We used microsatellite markers and parentage assignment to quantify the distance and distribution of dispersed seeds of Acacia karina, retrieved from the middens of Iridomyrmex agilis and Melophorus turneri perthensis. From parentage assignment, we could not distinguish the maternal from each parent pair assigned to each seed, so we applied two approaches to estimate dispersal distances, one conservative (CONS), where the parent closest to the ant midden was considered to be maternal, and the second where both parents were deemed equally likely (EL) to be maternal, and used both distances. Parentage was assigned to 124 seeds from eight middens. Maximum seed dispersal distances detected were 417 m (CONS) and 423 m (EL), more than double the estimated global maximum. Mean seed dispersal distances of 40 m (±5.8 SE) (CONS) and 79 m (±6.4 SE) (EL) exceeded the published global average of 2.24 m (±7.19 SD) by at least one order of magnitude. For both approaches and both ant species, seed dispersal was predominantly (44–84 % of all seeds) within 50 m from the maternal source, with fewer dispersal events at longer distances. Ants in this semi-arid environment have demonstrated a greater capacity to disperse seeds than estimated elsewhere, which highlights their important role in this system, and suggests significant novel ecological and evolutionary consequences for myrmecochorous species in arid/semi-arid Australia.
KeywordsSeed dispersal Myrmecochory Semi-arid zone Plant density Parentage assignment
We thank Karara Mining Ltd for funding, Brian Heterick (Curtin University) for his assistance in identification of ant species collected from the field and comments on their biology and Melanie Britton for laboratory assistance. Phyllode and seed material was collected under permit number 63-1314 issued to SK under the Western Australian Wildlife Conservation Act 1950. The authors declare that they have no conflict of interest.
Author contribution statement
PGN originally formulated the idea. PGN, CMP, CPE, JDM, JA and SLK designed the study. PGN, CMP, CPE and JA collected the samples and/or data. CMP, CPE and SLK analysed the data. CMP, PGN CPE, JDM and SLK wrote the manuscript.
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