Asellus aquaticus is a freshwater isopod that has key ecological and methodological features that facilitate truly integrative studies. First, A. aquaticus is a keystone species in aquatic ecosystems, which occurs in temperate zones across Europe and parts of Asia and that, unlike most other established eco-evo models, is an invertebrate detritivore. This is important because it has a major role in nutrient cycling and contributes to the recycling of nutrients and biomass (Carpenter & Lodge, 1986; Graça, Maltby, & Calow, 1994b; Bjelke & Herrmann, 2005). Second, in addition to its role in nutrient cycling, A. asellus is involved in a range of species interactions; notably it serves as prey for mesopredators (Hart & Gill, 1992; Hargeby, Johansson, & Ahnesjö, 2004)), and acts as a host to parasites, endosymbionts and epibionts (Cook et al. 1998; Zimmer and Bartholme 2003; Dezfuli 2000). Third, A. aquaticus occurs in a broad range of aquatic habitats, is able to cope with stressful environmental conditions, including high levels of organic pollution (Van Ginneken, Blust, & Bervoets, 2019, Hargeby, 1990b), (Aston & Milner, 1980) and is phenotypically variable across environments (Aston & Milner, 1980). This indicates a high potential for phenotypic alterations (via plasticity or genetic change) in response to environmental heterogeneity.