Does ant dispersal of seeds in Sclerolaena diacantha (Chenopodiaceae) generate local spatial genetic structure?

Sclerolaena diacantha is unusual in that it can exhibit contrasting diaspore dispersal at adjacent sites. At most sites, the diaspores merely, fall to the ground where secondary dispersal occurs. However, at some sites ants actively collect the diaspore that contains a food body and subsequently thousands of seeds accumulate on the long-lived ant mounds. The study evaluated the patterns of local spatial genetic structure within and among replicated sites with and without ant dispersal. Spatial autocorrelation, relatedness coefficients and gene correlation statistics based on four polymorphic allozyme loci showed that local spatial structure was minimal at two sites without ant dispersal. In contrast, moderate local spatial structure was apparent at one of the ant-dispersed sites whereas weak spatial structure was detected at the other. Restricted diaspore dispersal centred on long-lived ant mounds may explain the observed spatial structure at the first site whereas other forces appear to have contributed to the erosion of spatial structure at the second site. This multisite spatial study highlights the complexity of the interacting forces that may create or erode genetic structure in natural plant nonulations.