Circannual rhythms, Photoperiodism, Neuroendocrinology, Developmental programming, Comparative physiology.

Accurate timing and anticipation of seasonal changes is required to initiate physiological adaptations over the course of the year such as hibernation, changes in metabolism, fattening and reproductive activity. To achieve this, organisms have evolved complex seasonal timekeeping systems that rely on day length sensing (photoperiodism), coupled to innate long-term timers ("circannual clock"). The fundamental biological processes giving rise circannual rhythms are not known for any organism. This is a highly integrative topic of wide relevance, integrating multiple levels of understanding from genome to ecosystem. Within this area, my specific interests are:

• The cellular and molecular mechanisms involved in seasonal timekeeping processes
• The adjustment of homeostatic set points in physiology (rheostasis)
• The function of a specialised cell type in the hypothalamus, the tanycyte, in the above processes
• The use of hibernation and maternal photoperiodic programming to investigate the above processes

Current projects:

• Arctic seasonal timekeeping initiative (ASTI), role:  Deputy director

ASTI is a capacity-building project to establish UiT as a centre of excellence for research into seasonal timekeeping mechanisms. This fills a strategic gap in chronobiology research worldwide, and is an excellent fit to UiT as the world’s northernmost research university. See the website for themes and specific research projects: https://uit.no/research/asti

• Tromsø Forskningsstiftelse (TFS) starter grant: Epigenetic light, role: project leader

Website. The project aim was establish my lab in seasonal timekeeping and hibernation at the university of Tromsø. Specific areas of research were the epigenetic basis of seasonal timing, the role of circadian clocks in seasonal timekeeping, and maternal photoperiodic programming effects.

• Sentinel North Transdisciplinary Research Program Université
  Laval and UiT, The role of circadian clocks in seasonal synchrony in the Arctic, role: Co-PI

This is a comparative circadian/seasonal clockwork project with an emphasis on birds, fish and diatoms.

• Clocks and hypoxia: Linking oxygen to time, role: Co-PI

This is a project investigating the role of circadian clocks and hypoxia in a
diving mammal (hooded seal) . It uses high-resolution respirometry of mitochondria, astrocyte/neuronal culture techniques, and lentiviral
reporters to unpick responses to hypoxia in a highly hypoxia-tolerant
animal.

Physiological adaptations of birds and mammals, with main focus on temperature regulation, energetics, physiology and protetcion mechanisms towards hypoxia in diving species.

I am interested in the evolution of clocks and calendars in wild organisms and how the timing of daily and seasonal events is affected by global environmental change. My research strategy involves a combination of field and laboratory experiments and analyses of long-term datasets, mostly using songbirds.

Wild clocks:
Most organisms organize their activities through circadian (i.e. day/night) clocks, which in turn are entrained to environmental information such as light. Circadian clocks allow organisms to anticipate daily events and are ubiquitous in nature. They “tick” at different rates in different individuals, thus showing variation in their properties, such as period length, which is highly heritable. But the evolution of clocks is only possible if this variation is also associated with fitness differences. Currently, however, the selection of clocks under natural conditions remain poorly understood, for this, we need to study ‘wild clocks’ and connect the clock properties measured in the lab with fitness measures in the wild.

Urban clocks:
The light/dark cycle is the most important synchronizer of the biological clocks. Cities remarkably change the environment and one of the obvious impacts is the amount of artificial light at night present in the urban environment. I study the process of urbanization as a natural experiment to test the prediction that by dramatically changing the environment, cities expose organisms to profoundly distinct selective pressures compared to their natural environment and select different clock properties. Using the great tit (Parus major) as a model species, I measure the clock of individuals in cities and forests and carry out a large-scale common-garden study to separate genetic and environmental effects. I am particularly interested in possible differences in the clock's sensitivity to light.

Latitudinal clocks:
Following up on the urban clock project, I am interested in exploring the latitudinal adaptation of circadian clocks. When they move to the arctic, organisms are exposed to more extreme conditions of light, what would be the effects of artificial light at night on the clock in such environments? I am also using the great tits in this project and I hope to expand the common garden protocol to include birds from distinct latitudes.

Calendars in a changing world:
Animals need to time their daily and seasonal activities so they match favourable conditions in the environment. To do so, they use predictive environmental cues, with the photoperiodic and temperature variation being the most important ones for seasonal rhythms. Climate change is a major challenge that organisms face because by disrupting those important cues, they interfere with the animals' abilities to make predictions and may impact survival and reproductive success. I studied the effects of climate change on the timing of annual-cycle stages of a migratory bird: the pied flycatcher (Ficedula hypoleuca). Long-distance migrants, such as flycatchers, have complex annual cycles comprising several events, like breeding and migration, that need to be fitted into one year. Climate change advances annual-cycle stages, but, because not all stages respond to changes in temperatures, the shifts may vary depending on the stage (e.g. reproduction advances faster than migration). This could lead to a mismatch across the entire annual cycle because it modifies the time available for each stage.

External collaborators: Marcel E. Visser, Kees van Oers (NIOO, Netherlands Institute of Ecology)

The most interesting animals transform their physiology to cope/exploit seasonal changes in their environment; nowhere is this more apparent than in the Arctic. By combining classical experimental designs with cutting edge tools, my research aims to identify the pathways that control seasonal transformation and explores how biological timekeeping is influenced by the Arctic environment.

Current projects:

• Seasonal regulation of pituitary prolactin
• Seasonal control of reproduction in birds
• Arctic circadian clocks
• Seasonal control of smoltification in Atlantic salmon

Publications

Evidence for circadian-based photoperiodic timekeeping in Svalbard ptarmigan, the northernmost resident bird. Daniel Appenroth, Gabriela C. Wagner, David G. Hazlerigg, and Alexander C. West. Current Biology (2021). DOI: 10.1016/j.cub.2021.04.009
Body temperature and activity rhythms under different photoperiods in high Arctic Svalbard ptarmigan (Lagopus muta hyperborea). Daniel Appenroth, Andreas Nord, David Gray Hazlerigg, and Gabriela Christina Wagner. Frontiers in physiology 12 (2021): 256. DOI: 10.3389/fphys.2021.633866
Photoperiodic induction without light-mediated circadian entrainment in a high arctic resident bird. Daniel Appenroth, Vebjørn J. Melum, Alexander C. West, Hugues Dardente, David G. Hazlerigg, and Gabriela C. Wagner. Journal of Experimental Biology 223, no. 16 (2020). DOI: 10.1242/jeb.220699
Mechanisms of temperature modulation in mammalian seasonal timing. Laura van Rosmalen, Jayme van Dalum, Daniel Appenroth, Renzo TM Roodenrijs, Lauren de Wit, David G. Hazlerigg, and Roelof A. Hut. The FASEB Journal 35, no. 5 (2021): e21605. DOI: 10.1096/fj.202100162R
 

Other academic works

Circadian-based processes in the High Arctic: activity, thermoregulation and photoperiodism in the Svalbard ptarmigan (Lagopus muta hyperborea). Daniel Appenroth. Dissertation, UiT Norges arktiske universitet (Norway), 2021. DOI: 10037/20675
Core body temperature cycles in captive Svalbard rock ptarmigan (Lagopus muta hyperborea). Daniel Appenroth. Master's thesis, UiT Norges arktiske universitet (Norway), 2016. DOI: 10037/10005
Analysis of functional and morphological changes in the anterior cingulate cortex of Sharp-1 and Sharp-2 double knockout mice. Daniel Appenroth. Bachelor’s thesis, University of Göttingen (Germany), 2013.

Hibernation, core body temperature and energy metabolism

Comparative evolution, seasonality, seasonal timekeeping, comparative genetics, evolutionary genetics, seasonal physiology, high latitude adaptations, animal welfare and conservation.

Keywords: Chronobiology, Physiology, neurobiology, neuroendocrinology, thermoregulation, hibernation, maternal photoperiodic programming, development

PhD candidate with focus on tanycyte function utilizing maternal photoperiodic programming and hibernation as research paradigms. 

Techniques:

• Hibernation animal handling
• Rodent surgery
• LASER capture microdissection of tanycytes in brain sections
• RNA/DNA extraction protocols 
• In situ hybridization

Analysis techniques:

• RNAseq
• LC-MS/MS untargeted metabolomics from plasma samples
• Core body temperature recordings

My PhD project has the hooded seal (Cystophora cristata) as model organisms and it focuses on two main objectives:

1. Describe biological rhythms in diving species and how the molecular clock and hypoxia tolerance mechanisms are influencing each other;
2. Define the main mitochondrial adaptations that give extreme hypoxia tolerance to the pinnipeds neural tissue.