In the Light of Evolution Volume V: Cooperation and Conflict (2011) / Chapter Skim
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10 Selfish Genetic Elements, Genetic Conflict, and Evolutionary Innovation--JOHN H. WERREN
10 Selfish Genetic Elements, Genetic Conflict, and Evolutionary Innovation--JOHN H. WERREN
Pages 213-234
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From page 213... ...
There is growing evidence that SGEs, and the resulting genetic conflict, are an important motor for evolutionary change and innovation. In this review, the kinds of SGEs and their evolutionary consequences are described, includ ing how these elements shape basic biological features, such as genome struc ture and gene regulation, evolution of new genes, origin of new species, and mechanisms of sex determination and development.
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From page 214... ...
Examples include transposable elements (TEs) , meiotic drivers, supernumerary B chromosomes, postsegregation killers, and heritable microbes and organelles that distort sex determination.
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From page 215... ...
Genetic conflict within the genome will then result, because enhanced transmission of an SGE decreases transmission of other genetic elements. An evolutionary "arms race" can then occur among different components of the genome over basic biological processes.
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From page 216... ...
A meiotic drive allele reduces the nondriving allele among the gametes of hetero zygous individuals; therefore, these alternative alleles (and tightly linked loci) experience antagonistic selective pressures over the phenotype (one is selected to drive and the other to suppress the drive)
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From page 217... ...
. Intraindividual conflicts occur among genetic elements with different inheritance patterns (e.g., cytoplasmic genes; nuclear genes; X, Y, and autosomally located genes; mobile elements)
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From page 218... ...
SGEs can be placed into the following broad categories (Werren et al., 1988; Hurst and Werren, 2001; Burt and Trivers, 2006) : TEs, biased gene converters, meiotic drivers, postsegregation drivers, and cytoplasmic drivers.
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From page 219... ...
The rationale is that evolutionary suppression of TEs by the host will lead to their eventual mutational degradation and loss, except for TEs that move laterally to "infect" and invade new hosts. Although many active TEs have relatively short evolutionary asso ciations with particular hosts, some can be maintained for long evolu
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From page 220... ...
In Drosophila melanogaster, the flamenco locus is a large genomic region containing TE insertions that is used by the piwi-interacting RNA (piRNA) pathway t o suppress active TEs dispersed elsewhere in the genome.
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From page 221... ...
reports that at least seven key DNA binding proteins probably evolved from TEs in taxa ranging from plants and fungi to metazoans. Retrogenes occur when host mRNA is reverse-transcribed and inserted into the genome.
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From page 222... ...
. In larger populations, clonal selection will lead to loss of active TEs, assuming their effects are mostly deleterious (Dolgin and Charlesworth, 2006)
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From page 223... ...
. Meiotic Drivers Meiosis results in a reduction of the diploid germ cells to haploid gam etes.
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pole in meiosis. This process could have played an important role in the evolution of chromosome structure and will result in meiotic drive.
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. The change in landscape is attributable to the discovery that meiotic drive is often cryptic and much more common than previously thought and to detailed molecular and genetic studies of hybrid incompatibility genes that have revealed or implicated meiotic drive.
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From page 226... ...
. In general, daughter cell killing only imparts an indirect and weak advantage to the progenitor cell lineage unless daughter cells compete with each other for resources, in which case the benefits are more direct.
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From page 227... ...
. An usual example of B chromosome-induced PSD occurs in Nasonia and Trichogramma wasps, which have haplodiploid sex determination; haploid males develop from unfertilized eggs and females from fertilized eggs (Werren and Stouthamer, 2003)
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From page 228... ...
. The difference in inheritance patterns between heritable cytoplasmic elements and nuclear genes causes genetic conflict (Eberhard, 1 980; Cosmides and Tooby, 1981; Werren and Beukeboom, 1998)
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From page 229... ...
Nevertheless, supporting data continue to grow, including theoretical studies indicating that CI differences can be stable, maintain divergence, and select for premating isolation; empirical studies showing CI as contributing to reproductive isolation and reinforcement of mate discrimination between species (Jaenike et al., 2006) ; and the finding that Wolbachia infections are much more common than previously recognized (in ~70% of species rather than original estimates of 20%)
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From page 230... ...
Are TEs main tained over long evolutionary timescales because they induce beneficial mutations and innovations, thus allowing species to adapt (the evolv ability hypothesis) or because they are self-replicating elements that are maintained by replicating at faster rates than they are lost (the parasite hypothesis)
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From page 231... ...
There is ample evidence that TEs can accumulate in genomes as a result of transposition and induce harmful mutations, that organisms have evolved many mechanisms to suppress TEs, that genomes are littered with fossil suppressed and degraded elements, and that TEs move laterally between species, often across large evolutionary distances. These observations are consistent with the parasitic hypothesis, and no additional conditions are needed to explain the persistence of TEs over evolutionary time or their widespread occurrence.
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From page 232... ...
sexual species, however. The parasitic hypothesis predicts that active TEs will decline in asexual species because of the deleterious effects of transposition, whereas
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From page 233... ...
Asexual Bdelloid rotifers have significantly reduced TE numbers compared with sexual relatives, including loss of retroele ments (Arkhipova and Meselson, 2000) , and asexual Daphnia species show reduced numbers of active TEs compared with sexual Daphnia species (Schaack et al., 2010b)
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From page 234... ...
Growing evidence supports a significant role of SGEs in eukaryotic development and speciation, and possibly also in extinc tion of species. Genome domestication of SGEs leads to evolutionary innovations, including acquisition of new genes and gene regulation f rom TEs, heritable microbes (e.g., Wolbachia)
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