Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Introduction to evolution wikipedia , lookup
Sexual selection wikipedia , lookup
Symbiogenesis wikipedia , lookup
Genetics and the Origin of Species wikipedia , lookup
Population genetics wikipedia , lookup
Reproductive isolation wikipedia , lookup
Plant evolutionary developmental biology wikipedia , lookup
Evolutionary landscape wikipedia , lookup
Mimulus as a model for speciation • • • • • • Long history of ecological genetic studies Small genome (comparable to rice) Short generation time (~2 months) Easy to cultivate Highly speciose genus Diversity in mating system, floral form and habitat Frontiers in Biological Research: Integrated Ecological and Genomic Analysis of Speciation in Mimulus Michigan State Univ. Univ. of Washington Toby Bradshaw Doug Schemske Duke Univ. John Willis Andrea Sweigart Univ. of Montana Andrea Case CUGI Fred Dietrich Jeffery Tomkins Lila Fishman UNC Chapel Hill Todd Vision Selfing has evolved several times in the Mimulus guttatus complex Mimulus guttatus Mimulus platycalyx Mimulus laciniatus Mimulus nasutus Reproductive isolation between M. guttatus and M. nasutus • Largely allopatric • Sympatry in some ephemeral habitats • Natural hybrids are observed in the field M. guttatus M. nasutus M. guttatus M. guttatus + M. nasutus Isolating mechanisms • Premating barriers – Microhabitat – Flowering time – Cleistogamy – Pollen tube competition • Postmating barriers – Partial male and female sterility of F1 and F2 hybrids Quantitative trait loci (QTL) P1 (+) P2 (-) F1 (0) F2 + + 0 LOD M. guttatus x nasutus map • • • • 600 F2 plants 174 markers over 1780 cM ~85% coverage 14 linkage groups Fishman, Kelly and Willis (2002) Evolution 56, 2138-2155. QTL for species differentiation • Prezygotic isolation – Many minor QTL underly floral morphological differences • Postzygotic isolation – Hybrid sterility due to two interacting nuclear loci – Cytonuclear incompatibility – Meiotic drive Dobzhansky-Muller loci and hybrid sterility/inviability AABB aaBB AAbb X AaBb DM factors in M. guttatus x nasutus? N + G G Male sterile: N F1 Bg F2 Bn 0 3/16 1/4 Model: sterility requires aaB- genotype Genotype AABB AABb AAbb AaBB AaBb Aabb aaBB aaBb aabb F1 0 0 0 1 0 0 0 0 0 Total Steriles F2 1/16 2/16 1/16 2/16 4/16 2/16 1/16 2/16 1/16 Bg 1/4 1/4 0 1/4 1/4 0 0 0 0 Bn 0 0 0 1/4 1/4 0 0 1/4 1/4 ABn* 0 0 0 0 0 0 0 1/2 1/2 Male_sterile no no no no no no yes yes no 0 3/16 0 1/4 1/2 * Using male steriles as dams Fine mapping the A locus • Analysis of linkage to A in aaBB x AaBB • ~1000 plants screened with markers from all over the genome • Mapped to a ~15 cM interval MgSTS45 MgSTS11 A MgSTS104 Fine mapping the B locus • Analysis of linkage to B in aaBb x aabb • 2900 plants screened with markers from all over genome • Only 4 recombinants with MgSTS28 – If region is typical, this implies ~30 kb distance 0.14 cM B MgSTS28 0.7 cM MgSTS606 What happens in the opposite cross? N G + F1 F2 Male sterile: 1/4 Cytoplasmic male sterility • Common in hermaphroditic plants and animals • The mechanism is typically a mitochondrial fusion protein • Evolutionary dynamics – Maternally transmitted organelles that increase female fitness at the expense of male fitness spread rapidly – Nuclear restorers arise that suppress CMS – CMS can be uncovered when wide crosses separate CMS cytoplasm from its restorer Evolutionary dynamics of CMS + CMS + + CMS R + + CMS F2 + Isolating CMS factors • Model: M. guttatus has male sterilizing cytoplasm and a dominant restorer (R) • Restorer being mapped in Rr x rr – On linkage group 4, 20 cM from MgSTS34 • Mitochondrial factor being isolated by looking for fusion proteins Segregation distortion • In F2, 50% of alleles should be from each parent • Eleven regions of severe segregation distortion in guttatus x nasutus cross – Nine in favor of guttatus • Occurs during gamete formation in females Female gametogenesis in angiosperms • Only one of the four meiotic products leads to an egg • Potential for conflict between alleles Evolutionary dynamics of meiotic drive • Distorter locus spreads due to its transmission advantage – Linked suppressor locus can arise to prevent drive against itself • Once both are fixed, the system is quiescent until revealed by a wide cross • May contribute to pericentromeric heterochromatin tracts in mammals, plants • Question: do distorters map to centromeres in guttatus? Are speciation genes fixed by genetic drift or natural selection? x Neutrality Population bottleneck Selection B y Some closing thoughts • Genomic conflicts should be stronger in outcrossers than selfers – CMS in guttatus – Meiotic drive in guttatus • Genetic incompatibilities may be accelerated by a shift in mating system • Not something that can be studied in Drosophila, the predominant model for the genetics of speciation