Extremely low genetic diversity across mangrove taxa reflects past sea level changes and hints at poor future responses

Abstract

The projected increases in sea levels are expected to affect coastal ecosystems. Tropical communities, anchored by mangrove trees and having experienced frequent past sea level changes, appear to be vibrant at present. However, any optimism about the resilience of these ecosystems is premature because the impact of past climate events may not be reflected in the current abundance. To assess the impact of historical sea level changes, we conducted an extensive genetic diversity survey on the Indo-Malayan coast, a hotspot with a large global mangrove distribution. A survey of 26 populations in six species reveals extremely low genome-wide nucleotide diversity and hence very small effective population sizes (N ) in all populations. Whole-genome sequencing of three mangrove species further shows the decline in N to be strongly associated with the speed of past changes in sea level. We also used a recent series of flooding events in Yalong Bay, southern China, to test the robustness of mangroves to sea level changes in relation to their genetic diversity. The events resulted in the death of half of the mangrove trees in this area. Significantly, less genetically diverse mangrove species suffered much greater destruction. The dieback was accompanied by a drastic reduction in local invertebrate biodiversity. We thus predict that tropical coastal communities will be seriously endangered as the global sea level rises. Well-planned coastal development near mangrove forests will be essential to avert this crisis.

Constant conflict between Gypsy LTR retrotransposons and CHH methylation within a stress‐adapted mangrove genome

“…The increase in genetic diversity caused by stress‐induced transposon activation may increase the capacity of species to evolve stress resistance traits (Kidwell & Lisch, ; Horvath & Slotte, ). This scenario is particularly intriguing in mangroves because these species harbor extremely low standing genetic variation (Guo et al ., ), but live in stressful habitats that require constant adaptation. Additional transposition events can thus increase the evolutionary potential of these species.…”

Constant conflict betweenGypsyLTR retrotransposons and CHH methylation within a stress-adapted mangrove genome

“…The increase in genetic diversity due to stress-induced transposon activation may increase the capacity of species to evolve stress resistance traits (Kidwell & Lisch, 1997; Horvath & Slotte, 2017). This scenario is particularly intriguing in mangroves because these species harbor extremely low standing genetic variation (Guo et al , 2017) but live in stressful habitats that require constant adaptation. Additional transposition events can thus increase the evolutionary potential of these species.…”

Molecular adaptation to salinity fluctuation in tropical intertidal environments of a mangrove tree Sonneratia alba

“…Thus, they are good model systems for investigating adaptive evolution. Indeed, adaptation in this group has been studied at the phenotypic, ecological, physiological, and genomic levels [5][6][7][8][9][10]. However, little attention has been paid to transcriptional regulation even though it has been strongly selected for rapid adaptation to changes in environmental conditions and may play a critical role at ecological and evolutionary timescales [11].…”