Dynamics between ectoparasitic mites and their hosts in relation to environmental conditions, resistance, and trade-offs

 
Parasites are influential agents of natural selection. Traits to prevent parasitism show genetic variation, where there are fitness costs underlying resistance. In addition, specific environmental conditions impact both resistance in the host and rate of attack by the parasites. Here, we examined how periods of drought impact parasitism and specific factors underlying resistance in naturally occurring parasitic mites, Gamasodes queeslandicus, in the host, Drosophila melanogaster. During periods of dehydration, mite parasitism, both rate and duration, increased. This was related to the hydration status of the mite, where dehydration, not only exposure to dehydrating conditions, increases parasitism. This suggests that drying fruit may be a trigger for increased mite parasitism, potentially as a mechanism to move to new locations. In flies selected for resistance, RNA-seq analyses and nutrient reserve processing assessments, revealed that resistant flies utilize nutrient reserves more quickly, leading to decreased starvation resistance. This increase is predominantly due to increased nighttime activity and oxygen consumption when flies are usually least active. These studies enhance our understanding of how environmental conditions impact fly-mite interactions and the mechanistic links between resistance and pleiotropic costs. Dynamics between the environment and resistance will shape the rate the ectoparasitic mite successfully attack their fly host.