Non-invasive assessment of heat stress in UK lakes: the effects of global change on Arctic charr populations.

Lakes and reservoirs are warming rapidly globally reflecting increased air temperatures: 97% of Scottish systems experienced warming between 2015 and 2019. These ecosystems support many species of economic and conservation concern, including many cold-adapted, so-called glacial relict taxa such as the Arctic charr. This species has a circumpolar distribution, with the UK and Ireland forming the southern limit of its range. As cold-water adapted fishes, Arctic charr are vulnerable to warming temperatures and their UK populations are assessed as threatened due to climate change. Ultimately warming may result in range shifts and possible extinction of this species from the UK. Prior to this, it is likely that charr will be affected by increased levels of physiological stress due to warming, changes in population demography through lack of recruitment, negative interspecific interactions and increased levels of infectious diseases. Early warning of the presence and intensity of these chronic, non-lethal stresses will be key to the adaptive conservation management of salmonids.

This project will extend the eDNA concept by exploiting recent developments in environmental RNA for biomonitoring purposes to characterize the expression levels of genes linked to heat stress.  Gene expression analysis is a popular technique to study organism development or responses to environmental changes, but it is difficult to monitor these changes dynamically. Typically, an animal must be lethally sampled or have tissue subsampled for this to take place, which is invasive and requires licenses to work with vertebrate animals. We will develop non-invasive sampling methodology which can be deployed to understand the responses of natural populations, which will include eDNA and eRNA analyses (RT-qPCR and transcriptomics). The student will subsequently explore the distribution and impacts of stressors by deploying the assays during fieldwork in the UK, to characterize habitats and populations which are most severely affected. We will additionally assess the effect of heat stress on the wider elements of the freshwater assemblage, in order to examine the role of both direct and indirect effects of warming on charr. This project will provide a pathway to non-invasively study the effects of warming on a variety of freshwater taxa and detect early warning signals before mass die-offs.