The loss of circalunar rhythms in arctic and tide-free habitats: genomic investigations into lunar-arrhythmic populations of Clunio marinus

• Main Author: Fuhrmann, N.
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Christian-Albrechts-Universität 2022
• Subjects: Arctic
• Online Access: http://hdl.handle.net/21.11116/0000-000A-0252-7; http://hdl.handle.net/21.11116/0000-000A-0254-5

Biological rhythms are adaptations to periodically changing environmental conditions. The non-biting midge Clunio marinus (Diptera: Chironomidae) is known for the link between its reproduction and the tidal regime. The short-lived adults emerge when most of the intertidal habitat is exposed. The spring low tides occur at location specific times on days around the full moon and new moon. C. marinus populations at the European Atlantic coast are locally adapted to the day time and lunar phase of the spring low tides. This timing is achieved through the combination of an circadian and circalunar rhythm. While the circadian rhythm is controlled by a transcriptional-translational feedback loop, the molecular workings of the circalunar rhythm are not understood yet. As tides are almost neglectable in the Baltic Sea, the local Clunio populations have adapted to lay the egg clutches in the open sea instead of an exposed intertidal substrate. This simultaneously removed the selective pressure to time the reproduction to the lunar phase and allowed for lunar-arrhythmic emergence throughout the entire mating season. In arctic habitats of the Atlantic coast tides are still present. During the mating season the sun illuminates the habitat around the clock, preventing the perception of moon light. C. marinus changed from circadian-circalunar-controlled emergence to circatidal rhythms in polar day conditions. The adults emerge every day at every low tide throughout the mating season. In my thesis, I investigated these cases of lunar-arrhythmicity in Northern European Clunio populations. By exploring the genetic features linked to the evolution of the here described ecotypes of C. marinus, we step further towards understanding the enigmatic circalunar rhythms. My investigations resulted in one published article, one published preprint and an additional chapter. The first article had two aims: First, I investigated the ability of short mitochondrial fragments to recover the whole mitochondrial biogeography of geographically ...