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

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 distinct pop- ulations. DNA barcodes are short, conserved genomic fragments and commonly used to reconstruct the biogeography of species. With my Clunio populations as example I wanted to point out what issues can arise from blindly using those highly conserved DNA frag- ments. The second aim was to get the basic mitochondrial biogeography of all distinct population as a foundation to the investigations into the evolution of lunar-arrhythmic ecotypes. My second chapter is separated into two parts. At first I take a look at the evolution of lunar-arrhythmicity in the studied populations. Population structure and admixture analyses in addition to the mitochondrial biogeography were combined to identify the his- torical scenario which lead to the evolution of lunar-arrhythmic populations. Secondly, I used direct genomic comparisons to find differentiated regions and adaptive loci between rhythmic populations from the Atlantic coast and the arrhythmic populations from the Baltic Sea specifically. Established laboratory cultures of two sympatric populations were crossed for further insight into the nature of the maintenance of both populations under gene flow. In my article I identify genetic variants differentiated between lunar-rhythmic and lunar-arrhythmic populations. Genetic clusters affected by those genetic variants com- prise genes for the control of circadian rhythms, neuronal development, mating behavior, responses to hypoxia and sodium ion transport. In my third chapter I performed a crossing experiment to identify putative genotypes linked to lunar-rhythmic phenotypes. By crossing two sympatric populations with differ- ing ecotypes, I was able to raise an F2 generation with a mix of rhythmic and arrhythmic phenotypes. With the use of PCR-primers designed specifically for differentiated regions between the grandparent genomes I obtained genotypes for six distinct loci per chro- mosome of 237 individuals. The QTL analysis revealed multiple significant loci on all chromosomes with nine investigated phenotypes linked to lunar-rhythmicity. My thesis takes a large step towards the understanding of the circalunar rhythms in C. marinus by comparing rhythmic to naturally occurring arrhythmic populations. I generated a comprehensive genomic resource for geographically and ecologically distant populations of the same species. Genomic screens for ecotype-adaptive loci identified a putative involvement of circadian clock genes in circalunar rhythms of C. marinus. A crossing experiment between rhythmic and arrhythmic ecotypes of the sympatric Bergen populations hinted towards the involvement of multiple loci across the genome in lunar- rhythmicity. The addition of further genetic markers could identify a link of the circadian clock to circalunar rhythms as well as unravel the maintenance of sympatric ecotypes

Metallicities of M Dwarf Planet Hosts from Spectral Synthesis

We present the first spectroscopic metallicities of three M dwarfs with known or candidate planetary mass companions. We have analyzed high resolution, high signal-to-noise spectra of these stars which we obtained at McDonald Observatory. Our analysis technique is based on spectral synthesis of atomic and molecular features using recently revised cool-star model atmospheres and spectrum synthesis code. The technique has been shown to yield results consistent with the analyses of solar-type stars and allows measurements of M dwarf [M/H] values to 0.12 dex precision. From our analysis, we find [M/H] = -0.12, -0.32, and -0.33 for GJ 876, GJ 436, and GJ 581 respectively. These three M dwarf planet hosts have sub-solar metallicities, a surprising departure from the trend observed in FGK-type stars. This study is the first part of our ongoing work to determine the metallicities of the M dwarfs included in the McDonald Observatory planet search program.Comment: 13 pages, 2 figures, accepted for publication in ApJ

From Solar Proton Burning to Pionic Deuterium through the Nambu-Jona-Lasinio model of light nuclei

Within the Nambu-Jona-Lasinio model of light nuclei (the NNJL model), describing strong low-energy nuclear interactions, we compute the width of the energy level of the ground state of pionic deuterium. The theoretical value fits well the experimental data. Using the cross sections for the reactions nu_e + d -> p + p + e^- and nu_e + d -> p + n + nu_e, computed in the NNJL model, and the experimental values of the events of these reactions, detected by the SNO Collaboration, we compute the boron neutrino fluxes. The theoretical values agree well with the experimental data and the theoretical predictions within the Standard Solar Model by Bahcall. We argue the applicability of the constraints on the astrophysical factor for the solar proton burning, imposed by helioseismology, to the width of the energy level of the ground state of pionic deuterium. We show that the experimental data on the width satisfy these constraints. This testifies an indirect measurement of the recommended value of the astrophysical factor for the solar proton burning in terrestrial laboratories in terms of the width of the energy level of the ground state of pionic deuterium.Comment: 10 pages, no figures, Late

Detailed analysis of Balmer lines in cool dwarf stars

An analysis of H alpha and H beta spectra in a sample of 30 cool dwarf and subgiant stars is presented using MARCS model atmospheres based on the most recent calculations of the line opacities. A detailed quantitative comparison of the solar flux spectra with model spectra shows that Balmer line profile shapes, and therefore the temperature structure in the line formation region, are best represented under the mixing length theory by any combination of a low mixing-length parameter alpha and a low convective structure parameter y. A slightly lower effective temperature is obtained for the sun than the accepted value, which we attribute to errors in models and line opacities. The programme stars span temperatures from 4800 to 7100 K and include a small number of population II stars. Effective temperatures have been derived using a quantitative fitting method with a detailed error analysis. Our temperatures find good agreement with those from the Infrared Flux Method (IRFM) near solar metallicity but show differences at low metallicity where the two available IRFM determinations themselves are in disagreement. Comparison with recent temperature determinations using Balmer lines by Fuhrmann (1998, 2000), who employed a different description of the wing absorption due to self-broadening, does not show the large differences predicted by Barklem et al. (2000). In fact, perhaps fortuitously, reasonable agreement is found near solar metallicity, while we find significantly cooler temperatures for low metallicity stars of around solar temperature.Comment: 17 pages, 9 figures, to appear in A&