“…For example, variation in environmental variables like temperature or humidity may cause changes in the host gut transcriptome and microbiome in concert, yet without a causal relationship between the transcriptome and gut microbiome. Host genotype also modulates both gene expression and microbiome composition (Tabrett & Horton, 2020), across a wide range of species (Chaston et al, 2016;Early et al, 2017;Fuess et al, 2021;Goodrich, Davenport, Beaumont, et al, 2016;Goodrich, Davenport, Waters, et al, 2016;Goodrich et al, 2014;Khan et al, 2019;Kurilshikov et al, 2021;Rajarajan et al, 2022;Small et al, 2019), and in humans can vary among populations and cultures (Syromyatnikov et al, 2022). Host genotype-by-environment effects may also modulate the microbiome (Hahn et al, 2022), though this possibility is under-researched.…”