Cross-tolerance and transcriptional shifts underlying abiotic stress in the seabird tick, Ixodes uriae

The seabird tick, Ixodes uriae , is a significant ectoparasite of penguins in Antarctica and of other seabirds, mainly in coastal, polar regions of the Northern and Southern hemispheres, but the tick’s distribution extends into more temperate regions as well. The expansive range of this tick suggests that it is exposed to a wide range of abiotic stresses, including dehydration, heat, and cold. To better understand how I. uriae responds to stress exposure, we examined cross-tolerance between dehydration and thermal stress based on survival analyses and used RNA-seq to monitor transcriptional responses to cold, heat, and dehydration. Slight dehydration improved cold, but not heat tolerance, whereas severe dehydration reduced subsequent thermal tolerance. Dehydration exposure prompted transcript-level shifts underlying protein metabolism, recovery from stress, and processes allowing subsequent rehydration by water vapor uptake. Both cold and heat stress yielded expression changes involved in cuticle modification. One gene increased in expression (enzyme P450) and one decreased (transcription factor Hairy) in response to all three stresses. This study provides the groundwork for assessing stress tolerance in this bipolar ectoparasite.