Transcription in space – environmental vs. genetic effects on differential immune gene expression

Understanding how organisms adapt to their local environment is one of the key goals in molecular ecology. Adaptation can be achieved through qualitative changes in the coding sequence and/or quantitative changes in gene expression, where the optimal dosage of a gene's product in a given environment is being selected for. Differences in gene expression among populations inhabiting distinct environments can be suggestive of locally adapted gene regulation and have thus been studied in different species (Whitehead & Crawford 2006 ; Hodgins‐Davis & Townsend 2009 ). However, in contrast to a gene's coding sequence, its expression level at a given point in time may depend on various factors, including the current environment. Although critical for understanding the extent of local adaptation, it is usually difficult to disentangle the heritable differences in gene regulation from environmental effects. In this issue of Molecular Ecology, Stutz et al. ( 2015 ) describe an experiment in which they reciprocally transplanted three‐spined sticklebacks (Gasterosteus aculeatus) between independent pairs of small and large lakes. Their experimental design allows them to attribute differences in gene expression among sticklebacks either to lake of origin or destination lake. Interestingly, they find that translocated sticklebacks show a pattern of gene expression more similar to individuals from the destination lake than to individuals from the lake of origin, suggesting that expression of the targeted genes is more strongly regulated by environmental effects than by genetics. The environmental effect by itself is not entirely surprising; however, the relative extent of it is. Especially when put in the context of local adaptation and population differentiation, as done here, these findings cast a new light onto the heritability of differential gene expression and specifically its relative importance during population divergence and ultimately ecological speciation.