Differences in Genome Size Between Closely Related Species: The Drosophila melanogaster Species Subgroup

Abstract

Genome size varies considerably among organisms due to differences in the amplification, deletion, and divergence of various kinds of repetitive sequences, including the transposable elements, which constitute a large fraction of the genome. However, while the changes in genome size observed at a wide taxonomic level have been thoroughly investigated, we still know little about the process involved in closely related species. We estimated genome sizes and the reverse transcriptase-related sequence (RTRS) content in the nine species of the Drosophila melanogaster species subgroup. We showed that the species differ with regard to their genome size and that the RTRS content is correlated with genome size for all species except Drosophila orena. The genome of D. orena, which is 1.6-fold as big as that of D. melanogaster, has in fact not undergone any major increase in its RTRS content.

DNA Transposons and the Evolution of Eukaryotic Genomes

“…It is now well established that these variations largely account for the wide differences in genome size observed among eukaryotes, and even between closely related species (64,100). Retrotransposons seem to be major players in promoting rapid increase, and perhaps also decrease, in the genome size of multicellular eukaryotes (7,10,124,128,150,171,185). This is best exemplified by studies of maize and of the rice Oryza australiensis, showing that massive bursts of LTR retrotransposon amplification caused a concomitant doubling of the genome independently in the lineages of these two species (152,169).…”

The genome size evolution of medaka (Oryzias latipes) and fugu (Takifugu rubripes)

“…Then, we examined the involvement of their compositions in the genome size evolution as seen in other species (Boulesteix et al, 2006). The classification of repetitive elements in medaka is not comprehensive, but the composition clearly differs between medaka and Takifugu.…”

“…The genome size of the organism is highly diverse among species (Gregory, 2005), and the genome size diversity is found even between very closely related species (Wendel and Cronn, 2003;Hickey and Clements, 2005;Boulesteix et al, 2006). This phenomenon is classically referred to as "C-value paradox" (Thomas, 1971), which represents the discrepancy between the amount of genome DNA and developmental complexity of the organism.…”

“…Recently, amplification of the repetitive elements has received more attention as another driving force (Kidwell, 2002;Neafsey and Palumbi, 2003;Boulesteix et al, 2006) because repetitive elements occupy a significant portion of the eukaryote genome, as evidenced for human (International Human Genome Sequencing Consortium, 2001) and other organisms (SanMiguel et al, 1996). As an exception, pufferfishes contain minute amounts of repetitive elements, having the smallest genome (~400 Mb) among vertebrates (Crollius et al, 2000;Aparicio et al, 2002).…”

Genome size evolution: Within-species variation in genome size

“…These results show that both TEs and satellite DNA can influence genome size, and lead to within-species variation. Satellite DNA is indeed a major constituent of the genomes of many organisms (see Palomeque and Lorite, 2008 for a review), and it explains why the genome of the species D. orena (0.28 pg) is so much larger than that of D. melanogaster (0.18 pg) (Boulesteix et al, 2006). Marked differences in genome size between closely related lines of flax (Linum usitatissimum) have been shown to occur over a very short period, and to involve a change in rDNA amount (Cullis, 2005;Davison et al, 2007), as well as specific LIS-1 insertion events, although possible changes in the amount of other repetitive sequences were not determined.…”