“…While it is challenging to conclusively link an isolated behaviour to fitness, activity level is commonly positively correlated with metabolism (Careau et al, 2008), growth rate (Stamps, 2007), general health (Cavigelli, 2005), and survival (Smith & Blumestein, 2010) across taxa. Additionally, both male (Bierbach et al, 2021) and female (Houde & Torio, 1992;López, 1998) guppies prefer more active mates which, as well as suggesting activity level is linked to fitness, indicates that it is likely a transmission-relevant host behaviour for this directly, socially-transmitted ectoparasitic monogenean platyhelminth. Importantly for our questions, we (Stephenson & Adelman, 2022) and others (Burns, 2008;Harris et al, 2010) find that guppy activity level is significantly repeatable in the absence of infection, i.e.…”