Dispersal modes affect Rhamnaceae diversification rates in a differentiated manner

Abstract

The evolution of dispersal modes has been proposed to promote the diversification of angiosperms. However, little is known about the relative impact of different dispersal modes on plant diversification. We test the association between dispersal modes and diversification rates using Rhamnaceae, the cosmopolitan buckthorn family, as a model. We found that species with diplochory have the highest diversification rates followed by those with myrmecochory and ballistic dispersal, while lineages dispersed by vertebrates and wind have relatively low diversification rates. The difference in diversification rates may be closely linked to the difference in dispersal distance and ecological interactions implied by each dispersal mode. Species which disperse over larger geographical distances may have much higher speciation rates due to the increased chance of establishing isolated populations due to geological barriers or habitat fragmentation. However, long-distance dispersal may also increase the chance of extinction. By contrast, species with short-distance dispersal modes may have low speciation rates. Complex interactions with the surrounding environment may, however, impact diversification rates positively by increasing plant survival and reproductive success.

Keywords: Rhamnaceae; dispersal mode; diversification rate; extinction; speciation.

Figure 1.

Ancestral state reconstruction of Rhamnaceae dispersal modes based on the ER model. Pies at the nodes represent the probability of each state.

Figure 2.

Dispersal modes and speciation rates, extinction rates and diversification rates for Rhamnaceae inferred from MuSEE analyses: (a–b) speciation rate, (c–d) extinction rate, (e–f) diversification rate. The box plots indicate the median, 1st and 3rd quartiles, and limits of the 95% Bayesian credibility intervals, outliers outside the 95% credibility intervals are shown as dots. The density plots show the marginal distributions.