The different fates of two Asian horseshoe crab species with different dispersal abilities

Impending anthropogenic climate change will severely impact coastal
organisms at unprecedented speed. Knowledge on organisms’ evolutionary
responses to past sea level fluctuations and estimation of their
evolutionary potential is therefore indispensable in efforts to mitigate
the effects of future climate change. We sampled tens of thousands of
genomic markers of ~300 individuals in two of the four extant horseshoe
crab species across the complex archipelagic Singapore Straits.
Carcinoscorpius rotundicauda Latreille, a less mobile mangrove species,
has finer population structure and lower genetic diversity compared to the
dispersive deep-sea Tachypleus gigas Müller. Even though the source
populations of both species during the Last Glacial Maximum exhibited
comparable effective population sizes, the less dispersive C. rotundicauda
seems to lose genetic diversity much more quickly because of population
fragmentation. Contra previous studies’ results, we predict that the more
commonly sighted C. rotundicauda faces a more uncertain conservation
plight, with a continuing loss in evolutionary potential and higher
vulnerability to future climate change. Our study provides important
genomic baseline data for the redirection of conservation measures in the
face of climate change, and can be used as a blueprint for assessment and
mitigation of the adverse effects of impending sea level rise in other
systems.