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  • 1
    ISSN: 1573-6857
    Keywords: colonization ; Drosophila ; dynamic ; natural populations ; transposable elements
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Drosophila simulans presents a large variation in copy number among various transposable elements (TEs) and among natural populations for a given element. Some elements such as HMS beagle, blood, flea, tirant, coral, prygun jockey, F, nomade and mariner are absent in most populations, except in one or two which have copies on their chromosome arms. This suggests that some TEs are being awakened in D. simulans and are in the process of invading the species while it is colonizing the world. The elements 412 and roo/B104 present a wide insertion polymorphism among D. simulans populations, but only the 412 copy number follows a temperature cline. One population (Canberra from Australia) has a very high copy number for the 412 element and for many other TEs as well, indicating that some populations may have lost control of some of their TEs. While the 412 transposition rate is similar in all populations, its transcription level throughout developmental stages varies with populations, depending on copy number. Populations with 412 copy number higher than 10–12 exhibit co-suppression, while the expression in populations with lower numbers depends on the insertion location. All these results suggest genomic invasions by 412 and other TEs during the worldwide spread of the D. simulans species.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-6857
    Keywords: transposable elements ; populations ; Drosophila ; copy number regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract To investigate the main forces controlling the containment of transposable elements (TE) in natural populations, we analyzed the copia, mdg1, and 412 elements in various populations of Drosophila melanogaster and D. simulans. A lower proportion of insertion sites on the X chromosome in comparison with the autosomes suggests that selection against the detrimental effects of TE insertions is the major force containing TE copies in populations of Drosophila. This selection effect hypothesis is strengthened by the absence of the negative correlation between recombination rate and TE copy number along the chromosomes, which was expected under the alternative ectopic exchange model (selection against the deleterious rearrangements promoted by recombination between TE insertions). A cline in 412 copy number in relation to latitude was observed among the natural populations of D. simulans, with very high numbers existing in some local populations (around 60 copies in a sample from Canberra, Australia). An apparent absence of selection effects in this Canberra sample and a value of transposition rate equal to 1–2 × 10-3 whatever the population and its copy number agree with the idea of recent but temporarily drastic TE movements in local populations. The high values of transposition rate in D. simulans clearly disfavor the hypothesis that the low amount of transposable elements in this species could result from a low transposition rate.
    Type of Medium: Electronic Resource
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