The vertebrate photoperiodic neuroendocrine system uses photoperiod as a proxy to time annual rhythms in reproduction. To investigate seasonal adaptation in mammals, the hinge region and the first part of the transmembrane domain of the Tshr gene were sequenced for 278 common vole (Microtus arvalis) specimens from 15 localities in Western Europe, and 28 localities in Eastern Europe. Forty-nine single nucleotide polymorphisms (SNPs; 22 intronic, 27 exonic) were found, with weak or zero correlation with pairwise geographical distance, latitude, longitude and altitude. By applying a temperature threshold to the local photoperiod-temperature ellipsoid, we obtained a predicted critical photoperiod (pCPP) as a proxy for spring onset of local primary food production (grass). The pCPP obtained explains the distribution of genetic variation in Tshr in Western Europe through highly significant correlations. Thus, Tshr, which plays a pivotal role in the sensitivity of the mammalian photoperiodic neuroendocrine system, was targeted by natural selection, resulting in optimized timing of seasonal reproduction.

The population numbers of taiga bean goose (Anser fabalis fabalis) have halved during recent decades. Since this subspecies is hunted throughout most of its range, the decline is of management concern. Knowledge of the genetic population structure and diversity is important for guiding management and conservation efforts. Genetically unique subpopulations might be hunted to extinction if not managed separately, and any inbreeding depression or lack of genetic diversity may affect the ability to adapt to changing environments and increase the extinction risk. We used microsatellite and mitochondrial DNA markers to study the genetic population structure and diversity among taiga bean geese breeding within the Central flyway management unit using non-invasively collected feathers. We found some genetic structuring with the maternally inherited mitochondrial DNA between four geographic regions (ɸST = 0.11-0.20) but none with the nuclear microsatellite markers (all pairwise FST-values 0.002- 0.005). These results could be explained by female natal philopatry and male-biased dispersal, which completely homogenizes the nuclear genome. Therefore, the population could be managed as a single unit. Genetic diversity was still at a moderate level (average HE = 0.69) and there were no signs of past population size reductions, although significantly positive inbreeding coefficients in all sampling sites (FIS = 0.05-0.10) and high relatedness values (r = 0.60-0.86) between some individuals could indicate inbreeding. In addition, there was evidence of either incomplete lineage sorting or introgression from the pink-footed goose (A. brachyrhynchus). The current population is not under threat by genetic impoverishment but monitoring in the future is desirable.