Wake up of transposable elements following Drosophila simulans worldwide colonization

Abstract

Transposable elements (TEs) make up around 10%-15% of the Drosophila melanogaster genome, but its sibling species Drosophila simulans carries only one third as many such repeat sequences. We do not, however, have an overall view of copy numbers of the various classes of TEs (long terminal repeat [LTR] retrotransposons, non-LTR retrotransposons, and transposons) in genomes of natural populations of both species. We analyzed 34 elements in individuals from various natural populations of these species. We show that D. melanogaster has higher average chromosomal insertion site numbers per genome than D. simulans for all TEs except five. The LTR retrotransposons gypsy, ZAM, and 1731 and the transposon bari-1 present similar low copy numbers in both species. The transposon hobo has a large number of insertion sites, with significantly more sites in D. simulans. High variation between populations in number of insertion sites of some elements of D. simulans suggests that these elements can invade the genome of the entire species starting from a local population. We propose that TEs in the D. simulans genome are being awakened and amplified as they had been a long time ago in D. melanogaster.

The mariner transposable element in natural populations of Drosophila simulans

“…The PMM may also be affected by several parameters, including the effective population sizes (Ne; Lynch and Conery, 2003), and for instance via the active copy number, the genetic status and/or the stressful conditions of the invasive populations facing new environments (Biémont et al, 1997;Vieira et al, 1999). The effect of these parameters remains difficult to assess because generally we do not know (1) whether a population is a recent invasive or a long-established one; (2) the adaptation latency for a natural population; (3) the effective population size and (4) to what extent selection affects and decreases the activity level of a population.…”

Genome size evolution: Within-species variation in genome size

“…A recent study of genome size in various Drosophila species (Bosco et al, 2007) concludes that there is a significant statistical difference in genome size between species, and some significant differences between strains in some species. Vieira et al (1999Vieira et al ( , 2002 have also identified genome-size differences between populations of both Drosophila melanogaster and D. simulans, but no differences between replicates of batches of flies reared in the same vial. In the Bosco et al (2007) paper, the variation in genome size was related to variation in heterochromatin composition, mostly of satellite DNA, whereas TEs were mostly involved in the Vieira et al (1999Vieira et al ( , 2002 study.…”

“…Vieira et al (1999Vieira et al ( , 2002 have also identified genome-size differences between populations of both Drosophila melanogaster and D. simulans, but no differences between replicates of batches of flies reared in the same vial. In the Bosco et al (2007) paper, the variation in genome size was related to variation in heterochromatin composition, mostly of satellite DNA, whereas TEs were mostly involved in the Vieira et al (1999Vieira et al ( , 2002 study. Such data give credibility to between-individual variations in the amount of heterochromatic TEs that have been estimated using dot blots and in situ hybridization in Drosophila (Charlesworth et al, 1994).…”

Variation of the genome size estimate with environmental conditions in Drosophila melanogaster

“…(12,13) have suggested that natural selection could be involved in regulating genome size, although a change in size is primarily due to the genome's tolerance for repeated sequences (5) and its ability to mobilize them (14). Intra-species variation in genome size has also been shown to be associated with environmental conditions in plants, and seems to involve mobilization of some transposable elements in plants (15), Drosophila (14,16), and pocket gophers (17). Any stressful conditions known to mobilize transposable elements, such as UV light, temperature, breeding conditions, etc.…”