Drosophila ananassae: a species characterized by spontaneous male recombination in appreciable frequency

Mutation and recombination are primarily responsible for generating the genetic variability in natural populations of microorganisms, plant and animal species including humans. Upon such genetic variations, elemental forces of evolution such as natural selection, random genetic drift and migration operate to bring about micro-evolutionary changes. Recombination or crossing-over produces new combinations of genes due to interchange of corresponding segments between nonsister chromatids of homologous chromosomes, thus, it is an important evolutionary factor. Since the time of T. H. Morgan, Drosophila has been subjected to extensive investigations on crossing over while employing a number of markers, which were used for gene mapping. Interestingly, recombination occurs in females of D. melanogaster but not in males. Later on, male crossing over was investigated in various species and its occurrence was reported in D. melanogaster, D. ananassae, D. simulans, D. willistoni, D. littoralis and D. bipectinata. Recombination occurs at very low rate in all these species except for D. ananassae, which shows spontaneous male crossing over in appreciable frequency, which is meiotic in origin. This unusual phenomenon in D. ananassae is influenced by various genetic factors as well as it shows strain variation as far as frequency of male recombination is concerned. Further, the presence of chiasmata during meiosis in males at a frequency capable of accounting for the observed recombination frequency extends evidence for meiotic origin of recombination in males of D. ananassae.

Effect of temperature on behavioural isolation : A study with Drosophila ananassae populations.

Experiments were conducted to study sexual isolation among two natural populations of Drosophila ananassae maintained at 18 °C and 24 °C for 12 generations in the laboratory to see the effect of this environmental variable on behavioural isolation. Multiple choice technique was used and matings were observed directly in Elens Wattiaux mating chamber. Results showed sexual isolation among strains that were maintained at different temperatures, indicating that temperature may have affected the mating behaviour of the flies which resulted in the induction of ethological isolation among the strains.

Drosophila ananassae: A good model species for genetical, behavioural and evolutionary studies.

Drosophila ananassae, a cosmopolitan and domestic species, was first described by Doleschall in 1858 from Indonesia. During 1930s, cytological and genetical investigations in D. ananassae were initiated in Japan and USA which showed that it is a genetically unique species. Since then a large number of studies have been carried out by researchers in Japan, USA, India, France and Germany in this genetically unique species. Present review briefly summarizes the work done on genetical, behavioural and evolutionary aspects in D. ananassae which demonstrates that it is a good model species for such studies. Further, it is also discussed how the work on D. ananassae has enriched our understanding of basic phenomena like evolution and behaviour compared to similar studies on other model Drosophilds like D. melanogaster, D. pseudoobscura or D.subobsura.