Trade‐off or coordination? Correlations between ballochorous and myrmecochorous phases of diplochory

Abstract

The combination of two dispersal syndromes (diplochory) brings additional benefits to seeds, yet the relative costs and benefits of the two phases are poorly understood. Our goal is to provide the first quantification to test the long‐standing assumption that there are trade‐offs between the two phases in ballistic–ant diplochory. Dispersal investment data were empirically measured for 91 Euphorbiaceae species across different regions of the world. Dispersal distance data of ballochory (seed dispersal by explosion), myrmecochory (seed dispersal by ants) and diplochory was collated from the literature for 210 records (148 species from 44 families). The data were analysed using Model II regression, Kolmogorov–Smirnov test and t test, complemented by phylogenetic comparative approaches. Across diaspores of diplochorous species, the relative investment in myrmecochory increased more than that in ballochory. Fruit coat mass and elaiosome mass covaried in an allometric manner, regardless of seed mass. Diplochorous diaspores were significantly heavier than diaspores dispersed solely by ballochory. Dispersal distances of the two diplochorous phases were independent and comparable to that of sole ballochory or sole myrmecochory. Our results do not support a trade‐off, but a coordinated dispersal strategy between the two diplochorous phases. Large diaspores may evolve diplochory to overcome dispersal difficulties in term of dispersal distance. As the most comprehensive study of ballistic–ant diplochory, our findings advance the understanding of the relative importance of the two phases in diplochory. A plain language summary is available for this article.

Trade‐off between seed dispersal in space and time

“…Large seeds are maladaptive for longdistance dispersal under the same condition with the dispersal of small seeds (Thomson et al 2011). However, the dispersal difficulties for species with large seeds are often counterbalanced by their advantages on seed release height, resource allocation and dispersal mode (Thomson et al 2011;Chen et al 2019a). This leads to the discrepancy of the lasting assumption that large seeds face difficulties of dispersal potential and the fact that large seeds actually reach further dispersal distances than small seeds (Thomson et al 2011), as shown in our SEM models.…”

Seed traits and phylogeny explain plant distribution at large geographic scale

“…It is worth noting that the regression slopes of seed mass variability were statistically different among dispersal modes in our study. This could be explained by different seed mass allocation strategies among dispersal modes (Chen et al, 2018;Chen et al, 2019a).…”

“…However, we know little about the effects of dispersal modes on species distribution. Furthermore, because dispersal modes are often related to seed mass variation (Moles et al, 2007;Chen et al, 2019a), discerning the relative importance of seed mass and dispersal on the geographic distribution of seed plants is important but elusive.…”

An Ant-Plant Mesocosm Experiment Reveals Dispersal Patterns of Myrmecochorous Plants

“…Nevertheless, there was an increase in dispersal distance due to the presence of Myrmica ants. Thus, V. riviniana can be clearly referred to as a diplochorous species producing seeds that are primarily dispersed ballochorously (seed dispersal by explosion) and that might occasionally be picked up and carried by ants afterwards [35]. The genus Viola comprises a set of myrmecochorous species with large elaiosomes, comparable to Scilla or Corydalis in our study, and a set of ballistic diplochorous species with rather small elaiosomes, like the Northern American Common Violet (Viola papilionacea Pursh [36]), or our Central European Viola riviniana.…”