Abstract
BackgroundThe full catalog of satellite DNA (satDNA) within a same genome constitutes the satellitome. The Library Hypothesis predicts that satDNA in relative species reflects that in their common ancestor, but the evolutionary mechanisms and pathways of satDNA evolution have never been analyzed for full satellitomes. We compare here the satellitomes of two Oedipodine grasshoppers (Locusta migratoria and Oedaleus decorus) which shared their most recent common ancestor about 22.8 Ma ago.ResultsWe found that about one third of their satDNA families (near 60 in every species) showed sequence homology and were grouped into 12 orthologous superfamilies. The turnover rate of consensus sequences was extremely variable among the 20 orthologous family pairs analyzed in both species. The satDNAs shared by both species showed poor association with sequence signatures and motives frequently argued as functional, except for short inverted repeats allowing short dyad symmetries and non-B DNA conformations. Orthologous satDNAs frequently showed different FISH patterns at both intra- and interspecific levels. We defined indices of homogenization and degeneration and quantified the level of incomplete library sorting between species.ConclusionsOur analyses revealed that satDNA degenerates through point mutation and homogenizes through partial turnovers caused by massive tandem duplications (the so-called satDNA amplification). Remarkably, satDNA amplification increases homogenization, at intragenomic level, and diversification between species, thus constituting the basis for concerted evolution. We suggest a model of satDNA evolution by means of recursive cycles of amplification and degeneration, leading to mostly contingent evolutionary pathways where concerted evolution emerges promptly after lineages split.
Highlights
The full catalog of satellite DNA within a same genome constitutes the satellitome
One third of satellite DNA (satDNA) families showed sequence homology between species The range of variation for repeat unit length (RUL) was 8–400 bp for the 60 satDNA families found in L. migratoria and 12–469 bp for the 58 families found in O. decorus
After comparing the consensus sequences of all satDNA families present in both species, we found that 21 families in O. decorus showed homology with 20 in L. migratoria (Additional file 1: Table S2)
Summary
The full catalog of satellite DNA (satDNA) within a same genome constitutes the satellitome. The Library Hypothesis predicts that satDNA in relative species reflects that in their common ancestor, but the evolutionary mechanisms and pathways of satDNA evolution have never been analyzed for full satellitomes. The first model for satDNA evolution was devised by Smith [3], who demonstrated that DNA sequences that are not maintained by natural selection evolve a tandem repeat structure due to unequal crossing-over. Changes in satDNA amount are mainly due to unequal crossing-over, other mechanisms have been proposed to explain both amplification and spread of satDNA repeats (for review, see Garrido-Ramos [12]). Replication slippage might be an amplification process [10, 13], mainly involved in lengthening satellite monomers from basic shorter ones [20]
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