Transcriptomic responses of gecarcinid land crabs to acute and prolonged desiccation stress

Decapod crabs have repeatedly and convergently colonized land. Because of their aquatic ancestry, desiccation is their greatest physiological challenge, yet the genetic basis of their responses to desiccation are unknown. For this study, we sought to identify osmoregulatory genes that were differentially expressed in their antennal glands and posterior gills in response to desiccation stress. We dehydrated and tracked gene expression across three confamilial species displaying increasing degrees of terrestrial adaptation: Tuerkayana celeste, T. magna, and Gecarcoidea natalis. We observed acute dramatic upregulation in the posterior gills of T. celeste and G. natalis and a more muted response in T. magna; however some genes with known osmoregulatory functions were downregulated throughout the trial. We also found that some modules of orthologous genes with correlated expression were associated with greater degrees of terrestriality whereas others reflected shared ancestry, suggesting that different parts of the transcriptome are under varying degrees of terrestrial selective pressure. Finally, while differentially expressed genes were likely to be conserved across the three species, genes from expanded gene families and species-specific genes may also play a role in how land crabs adapt to the unique selective challenges that accompany a terrestrial life.