Extension of the primary dispersal distance through peduncle laying and elongation promotes myrmecochory in Japanese sedges.

Postfloral peduncle laying is regarded as an element of myrmecochorous syndrome, which is presumed to facilitate seed discovery by ants by presenting seeds on the ground. However, this presumption does not explain why the peduncles should lay down rather than dropping diaspores on the ground. In this study, an alternative hypothesis is proposed, the distance hypothesis, stating that peduncle laying extends the primary dispersal distance and thereby enhances myrmecochory or functions as an insurance against myrmecochory failure. To test the distance hypothesis, I focused on several myrmecochorous sedge species. First, the occurrence of postfloral peduncle elongation was examined, which contributes to the extension of primary dispersal distance and is not directly relevant to seed presentation on the ground. The primary dispersal distances relative to sedge canopy radius were quantified to infer the insurance function, that is, the extent to which peduncle laying and elongation alone isolate seedlings from the sedge canopy. The effect of primary dispersal distances on myrmecochory were examined in a field experiment. Postfloral peduncle elongation was observed in all species examined. The insurance function of peduncle laying and elongation was supported in a subset of sedge species, in which primary dispersal distances were approximately twice as long as the sedge canopy radius. The field experiment revealed that longer primary dispersal distances increased both the number of ant nests into which diaspores were transported and myrmecochorous dispersal distances. These results support the distance hypothesis and highlight the need to reconsider the function of peduncle laying in myrmecochores. [ABSTRACT FROM AUTHOR]