Differential survival and dispersal of avian feather mites with contrasting host specificities

Host specificity is a fundamental life history trait of symbionts and exists on a broad continuum from symbionts that are specific to one or a few hosts (host specialists), to those associated with multiple different host species (host generalists). However, the biological mechanisms underlying the complexity and wide variation in symbiont host specificity are poorly understood from both the symbiont and host perspectives across many symbiotic systems. Feather mites are common avian symbionts that vary in their host specificity from extreme host generalists to host specialists, even among species within the same genus. Here, we measured and compared survival probability and rate of dispersal to determine how these traits differ between two species of feather mites in the same genus: one host generalist associated with 17 host species (Amerodectes ischyros) and one host specialist with only one known host (A. protonotaria). We initially predicted that the host generalist would live longer and disperse more rapidly but discovered that while the host generalist mite survived longer, the host specialist mite dispersed more quickly. The differing environmental and ecological conditions in which the hosts of these mites are associated may explain the survival and dispersal patterns we uncovered, as differential microclimates may have led to different selective pressures on each species of mite. We also noted mite behavioural observations and suggest experiments to extend our understanding of feather mite ecology and evolution.