Small-scale habitat heterogeneity and genotype modulate in situ gene expression of the Antarctic bivalve Aequiyoldia eightsii in front of a melting glacier.

Regulation of gene expression is a pivotal adaptive mechanism of organisms facing environmental variation. We studied the in situ gene expression of the shallow-water bivalve Aequiyoldia eightsii in Potter Cove (King George Island, Antarctica) occupying different habitats in front of a melting glacier on a local scale (1 km). The expression of nuclear genes was determined by (1) variation of the nuclear genome itself (nuclear SNPs) and equally strongly by (2) different environmental conditions characterizing the three locations and (3) the composition of the mitochondrial genotype (mitochondrial SNPs). Mitochondrial SNPs divided Antarctic animals into two groups, each composed of organisms featuring mitochondrial homoplasmy and heteroplasmy. We validated our results by contrasting the observed magnitudes of differentially expressed genes (DEGs) with magnitudes expected by stochasticity in randomized group comparisons. Habitat comparison revealed further differences in DEGs at local scale suggesting a high evolutionary adaptive potential to the specific microenvironments. Interestingly, differential expression analysis between mitotypes resulted in a higher number of DEGs than the obtained in the comparison by stations, distinguishing heteroplasmic from homoplasmic organisms. Our results suggest that the mitochondrial genome and possibly heteroplasmy may play a role in the regulation of nuclear gene expression with adaptive implications.