The Adaptive Value of Chromosomal Inversions and Climatic Change—Studies on the Natural Populations of Drosophila subobscura from the Balkans

SIMPLE SUMMARY: Climatic change is a serious problem because it can irreversibly modify most ecosystems. Many species try to survive by adapting, through natural selection, to the new climatic conditions. In this scenario, the inversion chromosomal polymorphism of Drosophila subobscura is an excellent natural system through which to study the adaptations of organisms to climatic change. For analyzing the response of inversions to global warming, the chromosomes of annual samples (2019–2022) from a Petnica (Serbia) D. subobscura population were analyzed. These results were compared with those from other populations of this species, but belonging to different climatic regions (Avala, also in Serbia, and Font Groga, Spain). In all cases, significant differences were observed, indicating that the inversion composition conferring adaptive capacity to flies in these regions was different. In Petnica, not all inversions responded in the same way to climatic variables: those located in E and U chromosomes presented more changes. Moreover, by comparing data from 2019–2022 with those from a previous sample also from Petnica (1995), it was possible to relate the changes in meteorological variables to frequency variations of ‘cold’-, ‘warm’-, and ‘non-thermal’-adapted inversions for these years. These results allow for a better understanding of the genetic adaptations to new environmental conditions. ABSTRACT: The adaptive value of the Drosophila subobscura chromosomal inversion polymorphism with regard to environmental effects is well-known. However, the specific details of the inversion adaptations to the global warming scenario deserve to be analyzed. Toward this aim, polymorphism and karyotypes were studied in 574 individuals from Petnica (Serbia) in annual samples taken in June for the period 2019–2022. Comparing the results of Petnica (Cfa: humid subtropical climate) with those from Avala (Serbia: Cfb, temperate oceanic climate) and Font Groga (Barcelona, Spain; Csa: hot-summer Mediterranean climate), significant differences were observed for their chromosomal polymorphism. In Petnica, inversions from U and E chromosomes mainly reacted significantly with regard to temperature, humidity, and rainfall. Moreover, the inversion polymorphism from Petnica (2019–2022) was compared with that from 1995. In this period, a significant increase in mean and maximum temperature was observed. However, to properly explain the observed variations of inversions over time, it was necessary to carefully analyze annual seasonal changes and particular heat wave episodes. Interestingly, yearly fluctuations of U chromosome ‘warm’-adapted inversions corresponded with opposite changes in ‘non-thermal’ inversions. Perhaps these types of inversions were not correctly defined with regard to thermal adaptation, or these fluctuations were also due to adaptations to other physical and/or biological variables. Finally, a joint study of chromosomal inversion polymorphism from many Balkan populations of D. subobscura indicated that different climatic regions presented distinct composition, including thermal-adapted inversions.