Abstracts (first author)
Fragility and robustness – the evolution of tropical intertidal communities as sea level rises and falls
Sea level changes may strongly impact intertidal communities. In the tropics, their dominant primary producers are the woody plants of mangroves, which are particularly susceptible to such changes. In this study, we surveyed the genetic diversity of 6 mangrove species in the Indo-western Pacific (IWP) region. In all species, the genetic diversity is organized into two regional clades that are separated by the Strait of Malacca. Under repeated freezes (F) and thaws (T) with past glaciations, or the TFT cycle, the two regions experienced phases of isolation and admixture as the Strait opens and closes. The genetic diversity is built up in isolation and shuffled in the admixture phase. Computer simulations of the TFT model show that the historical effective population size in each region is very small, between 200 and 1200. The results support the conjecture of fragile habitats in tropical intertidal zones under rapid sea level changes. Nevertheless, the geographical distributions of haplotypes suggest adaptive complexes being separately built up in the isolation phase, resulting in robust adaptation in the admixture phase and speciation. Hence, the TFT cycle is a double-edged sword that endowed both fragility and robustness on the intertidal communities of IWP. The confluence of several historical factors in the last 5000 years has tilted the balance toward robustness. However, this balance may quickly swing the other way under multiple influences of local human perturbations and global sea level rises.