Seasonal changes in chromosomal inversion polymorphism in a Drosophila subobscura natural population from a southeastern European continental refugium of the last glaciation period

Abstract

Chromosomal inversion polymorphism was studied in a natural population of Drosophila subobscura from the Djerdap gorge of the Danube River, which is one of southeastern European continental refugia during the last glaciation period. The existence of changes in chromosomal inversion polymorphism during different periods of time was tested. The observed high abundance of chromosomal arrangements and lower IFR value allowed this population to be classified with central European populations. It was characterized by the O-7 and O3 + 4 + 5 arrangements, not found in other populations from the region analyzed. Within the region studied, the E1 + 2 + 9 + 12 chromosomal arrangement was found, apart from this population from a warm habitat, only in one population from a Mediterranean refugium. Many similarities have been observed between the population from the Djerdap gorge and other populations from the region analyzed, which indicates that postglacial migration may have started from this southeastern European refugium. Seasonal changes in the frequencies of the E-st and O3 + 4 + 7 chromosomal arrangements, E-st and O3 + 4 + 7, being more frequent in spring and in summer, respectively, were found. The changes in the J chromosome (J(st)/J(st)), E chromosome (E-st/E1 + 2 + 9 and E-8/E1 + 2 + 9), and O chromosome (O-st/O3 + 4 + 22; O3 + 4/O3 + 4; and O3 + 4 + 1/O3 + 4 + 7), whose karyotypic combination frequencies were associated with seasonal changes, were also found. These changes are most probably associated with seasonal climatic changes in the population analyzed, which confirms that the chromosomal inversions in D. subobscura are adaptive.