Changes of inversion polymorphism in laboratory populations of Drosophila melanogaster

Abstract

Thirty eight laboratory populations (20 mass cultures and 18 isofemale lines) of Drosophila melanogaster were established from population samples of 20 geographic localities (12 north and 8 south) in India. Each population was kept for 20 generations in the laboratory by transferring 50 flies to fresh culture bottles in every generation after which chromosomal analysis of 100 or more larvae was made. In mass cultures, a decline in the frequency of all the polymorphic inversions detected in natural populations, associated with decreasing heterozygosity, was observed irrespective of their geographic origin or initial frequency. Some inversions were also found to be lost completely in some mass cultures. In order to quantify the degree of genetic divergence between initial and final populations, genetic distance was estimated which was found to be higher in south Indian populations than in those from north which is likely to be due to high frequency of inversions in initial populations from south. However, in isofemale lines, 17inver-sions were found to persist and were maintained at a considerable frequency. Significant deviation from Hardy-Weinberg expectation occurred for 4 inversions and eight Inversion pairs (linked as well as unlinked) showed strong non-random association. These results have been discussed in the term of "drift" and "founder principle" causing changes of inversion polymorphism in laboratory populations of D. melanogaster.

Clinal variation as a tool to understand climate change

“…D. melanogaster populations from Northern and Southern Japan were found to differ with respect to the In(3R)P inversions , in that southern populations possess higher number of inversions than the northern ones (see Figure 2). Similar trend of In(3R)P inversions was found along latitudinal gradients along the eastern coast of Australia, North America (Knibb 1982) as well as in Asian populations (Singh and Das 1992) of D. melanogaster. Chromosomal inversion studies hint that inversions also play a central role in evolutionary processes (through local adaptation) (Kirkpatrick and Barton 2006).…”

The latitudinal cline in the In(3R)Payne inversion polymorphism has shifted in the last 20 years in Australian Drosophila melanogaster populations

“…A potential confounding effect in this comparison is that the inversion was sampled in 1979 in isofemale lines that had been maintained in the laboratory for up to nine generations, whereas in the current study field‐caught females were genotyped. Laboratory culture might result in a decrease in inversion frequency in mass‐bred populations but this is likely to be small (Singh & Das 1992) and we have not found any systematic shift in the frequency of In(3R)Payne arrangements in any of our laboratory populations.…”

Climatic selection on genes and traits after a 100 year-old invasion: a critical look at the temperate-tropical clines in Drosophila melanogaster from eastern Australia

“…Four inversions of D. melanogaster that are cosmopolitan, In(2L)t, In(2R)NS, In(3L)Payne and In(3R)Payne, show clines in North America where inverted sequences become more common in warmer lower latitudes (Mettler et al 1977). They also show clines in eastern Australia as established by Knibb et al (1981) and on other continents Singh and Das 1992). Knibb et al (1981) scored inversion frequencies cytologically in isofemale lines sampled from 19 Australasian populations (5-76 lines per population) in a region extending from New Guinea to Tasmania.…”