The Experts below are selected from a list of 291 Experts worldwide ranked by ideXlab platform
John H Willis - One of the best experts on this subject based on the ideXlab platform.
-
major qtl controls adaptation to serpentine soils in Mimulus guttatus
Molecular Ecology, 2018Co-Authors: Jessica P Selby, John H WillisAbstract:: Spatially varying selection is a critical driver of adaptive differentiation. Yet, there are few examples where the fitness effects of naturally segregating variants that contribute to local adaptation have been measured in the field. Plant adaptation to harsh soil habitats provides an ideal study system for investigating the genetic basis of local adaptation. The work presented here identifies a major locus underlying adaptation to serpentine soils in Mimulus guttatus and estimates the strength of selection on this locus in native field sites. Reciprocal transplant and common-garden studies show that serpentine and nonserpentine populations of M. guttatus differ in their ability to survive on serpentine soils. We directly mapped these field survival differences by performing a bulk segregant analysis with F2 survivors from a field transplant study and identify a single QTL where individuals that are homozygous for the nonserpentine allele do not survive on serpentine soils. Genotyping the survivors from an independent mapping population reveals that this same QTL controls serpentine tolerance in a second, geographically distant population. Finally, we show that this QTL controls tolerance to soil properties, as opposed to some other aspect of the field sites that may differ, by performing a laboratory-based common-garden experiment in native serpentine soils that replicates the survival differences observed in the field. These results indicate that despite the myriad chemical and physical challenges plants face in serpentine habitats, adaptation to these soils in M. guttatus has a simple genetic basis.
-
major qtl controls adaptation to serpentine soils in Mimulus guttatus
bioRxiv, 2018Co-Authors: Jessica P Selby, John H WillisAbstract:Spatially varying selection is a critical driver of adaptive differentiation. Yet, there are few examples where the fitness effects of naturally segregating variants that contribute to local adaptation have been measured in the field. This project investigates the genetic basis of adaption to serpentine soils in Mimulus guttatus. Reciprocal transplant studies show that serpentine and non-serpentine populations of M. guttatus are genetically differentiated in their ability to survive on serpentine soils. We mapped serpentine tolerance by performing a bulk segregant analysis on F2 survivors from a field transplant study and identify a single QTL where individuals that are homozygous for the non-serpentine allele do not survive on serpentine soils. This same QTL controls serpentine tolerance in a second, geographically distant population. A common garden study where the two serpentine populations were grown on each other's soil finds that one of the populations has significantly lower survival on this "foreign" serpentine soil compared to its home soil. So, while these two populations share a major QTL they either differ at other loci involved in serpentine adaptation or have different causal alleles at this QTL. This raises the possibility that serpentine populations may not be broadly tolerant to serpentine soils but may instead be locally adapted to their particular patch. Nevertheless, despite the myriad chemical and physical challenges that plants face in serpentine habitats, adaptation to these soils in M. guttatus has a simple genetic basis.
-
A Segregating Inversion Generates Fitness Variation in Yellow Monkeyflower (Mimulus guttatus).
Genetics, 2016Co-Authors: Young Lee, John Kelly, Lila Fishman, John H WillisAbstract:Polymorphic chromosomal rearrangements can bind hundreds of genes into single genetic loci with diverse effects. Rearrangements are often associated with local adaptation and speciation and may also be an important component of genetic variation within populations. We genetically and phenotypically characterize a segregating inversion (inv6) in the Iron Mountain (IM) population of Mimulus guttatus (yellow monkeyflower). We initially mapped inv6 as a region of recombination suppression in three F2 populations resulting from crosses among IM plants. In each case, the F1 parent was heterozygous for a derived haplotype, homogenous across markers spanning over 5 Mb of chromsome 6. In the three F2 populations, inv6 reduced male and female fitness components. In addition, inv6 carriers suffered an ∼30% loss of pollen viability in the field. Despite these costs, inv6 exists at moderate frequency (∼8%) in the natural population, suggesting counterbalancing fitness benefits that maintain the polymorphism. Across 4 years of monitoring in the field, inv6 had an overall significant positive effect on seed production (lifetime female fitness) of carriers. This benefit was particularly strong in harsh years and may be mediated (in part) by strong positive effects on flower production. These data suggest that opposing fitness effects maintain an intermediate frequency, and as a consequence, inv6 generates inbreeding depression and high genetic variance. We discuss these findings in relation to the theory of inbreeding depression and the maintenance of fitness variation.
-
major qtls for critical photoperiod and vernalization underlie extensive variation in flowering in the Mimulus guttatus species complex
New Phytologist, 2013Co-Authors: Jannice Friedman, John H WillisAbstract:Summary Species with extensive ranges experience highly variable environments with respect to temperature, light and soil moisture. Synchronizing the transition from vegetative to floral growth is important to employ favorable conditions for reproduction. Optimal timing of this transition might be different for semelparous annual plants and iteroparous perennial plants. We studied variation in the critical photoperiod necessary for floral induction and the requirement for a period of cold-chilling (vernalization) in 46 populations of annuals and perennials in the Mimulus guttatus species complex. We then examined critical photoperiod and vernalization QTLs in growth chambers using F2 progeny from annual and perennial parents that differed in their requirements for flowering. We identify extensive variation in critical photoperiod, with most annual populations requiring substantially shorter day lengths to initiate flowering than perennial populations. We discover a novel type of vernalization requirement in perennial populations that is contingent on plants experiencing short days first. QTL analyses identify two large-effect QTLs which influence critical photoperiod. In two separate vernalization experiments we discover each set of crosses contain different large-effect QTLs for vernalization. Mimulus guttatus harbors extensive variation in critical photoperiod and vernalization that may be a consequence of local adaptation.
-
spatially and temporally varying selection on intrapopulation quantitative trait loci for a life history trade off in Mimulus guttatus
Molecular Ecology, 2012Co-Authors: Julius P. Mojica, John H Willis, Young Lee, John KellyAbstract:Why do populations remain genetically variable despite strong continuous natural selection? Mutation reconstitutes variation eliminated by selection and genetic drift, but theoretical and experimental studies each suggest that mutation-selection balance insufficient to explain extant genetic variation in most complex traits. The alternative hypothesis of balancing selection, wherein selection maintains genetic variation, is an aggregate of multiple mechanisms (spatial and temporal heterogeneity in selection, frequency-dependent selection, antagonistic pleiotropy, etc.). Most of these mechanisms have been demonstrated for Mendelian traits, but there is little comparable data for loci affecting quantitative characters. Here, we report a 3-year field study of selection on intrapopulation quantitative trait loci (QTL) of flower size, a highly polygenic trait in Mimulus guttatus. The QTL exhibit antagonistic pleiotropy: alleles that increase flower size, reduce viability, but increase fecundity. The magnitude and direction of selection fluctuates yearly and on a spatial scale of metres. This study provides direct evidence of balancing selection mechanisms on QTL of an ecologically relevant trait.
Mark R. Macnair - One of the best experts on this subject based on the ideXlab platform.
-
The potential for adaptive evolution of pollen grain size in Mimulus guttatus
The New phytologist, 2005Co-Authors: Ellen Lamborn, James E. Cresswell, Mark R. MacnairAbstract:Summary • We tested whether pollen grain size (PGS) shows heritable variation in three independent populations of Mimulus guttatus by imposing artificial selection for this character. In addition, we looked for correlated responses to selection in a range of 15 other floral characters. • Heritable variation in PGS was found in all three populations, with heritabilities of between 19 and 40% (average 30%). After three generations, upward and downward lines differed on average by 30% in pollen volume. • No consistent patterns of correlated response were found in other characters, indicating that PGS can respond to selective forces acting on PGS alone. • Possible selection mechanisms on PGS in this species could include intermale selection, if large pollen grains produce more competitive gametophytes; or optimization of patterns of resource allocation, if local mate competition varies.
-
Bumble bee selection of Mimulus guttatus flowers : The effects of pollen quality and reward depletion
Ecology, 1999Co-Authors: Alastair W. Robertson, Claire Mountjoy, Brian E. Faulkner, Matthew V. Roberts, Mark R. MacnairAbstract:The ability of flower visitors to monitor returns when collecting pollen from flowers has been seldom studied despite the importance of pollen as a food resource, particularly for bees. Californian populations of Mimulus guttatus are polymorphic for pollen quality: many plants produce a high proportion of cytoplasmless pollen grains that render the grains incapable of fertilizing ovules or of supporting bees nutritionally. We found that different genotypes maintained a consistent proportion of inviable pollen within a genotype and over time. The number of pollen grains per flower was also consistent within a plant at each date but declined over time. We studied the ability of British bumble bees (Bombus spp.) to discriminate among plants of Mimulus guttatus on the basis of pollen quality and quantity at three scales: indoors with choices of two genotypes, in outdoor plots of several genotypes that varied in pollen quality, and outdoors at a whole-patch scale where two patches of plants differed in quality. We found that bees could discriminate among plants on the basis of pollen quality provided that flowers still retained most of the pollen. In the two-genotype trials, bees chose genotypes primarily on the quantity of viable pollen, and nectar was much less important. Similarly, where patches of low- and high-pollen quality plants were established, bees responded by visiting the high-quality patch more often and by visiting more flowers within the patch. However, the results from the outdoor plots that contained genotypes of varying phenotypes were inconsistent. A meta-analysis of a large number of separate plots showed that the overall correlation between visitation rate and pollen quality was significant, but variation among plots was also significant. A possible explanation for this inconsistency was suggested in a greenhouse trial in which we showed that, when foraging density was high, depletion of the standing crop of pollen happened quickly, and this reduced the ability of the foragers to choose the higher-quality genotypes. The results have implications for the evolution of pollen production in Mimulus guttatus and reward production in other plants.
-
can an increased copper requirement in copper tolerant Mimulus guttatus explain the cost of tolerance ii reproductive phase
New Phytologist, 1998Co-Authors: Frances A. Harper, Suzanne E. Smith, Mark R. MacnairAbstract:Circumstantial evidence suggests that plants that have evolved metal tolerance are at a disadvantage on normal soil, i.e. there is a cost of tolerance. One hypothesis for the cause of this cost is that individuals have a greater requirement for copper, and so suffer micronutrient deficiency on normal soils, as a result of a reduced uptake, distribution and/or utilization of copper. We provided highly and less copper-tolerant plants of Mimulus guttatus Fischer ex DC. (the common monkey flower) with sub-optimal copper, and demonstrated the importance of copper as an essential micronutrient during the reproductive phase, both in the production of viable pollen and in seed set. We also looked at the effect of sub-optimal copper supply on the growth of the microgametophyte, and the efficiency with which seed was set. No evidence was found that highly tolerant plants have an increased copper requirement during the reproductive phase. This is in agreement with earlier work on Mimulus guttatus, which investigated the copper requirement of highly tolerant plants during vegetative growth and found that any differences in copper requirement were small. The ‘metal requirement hypothesis’ is, therefore, not the sole explanation for the cost of copper tolerance in M. guttatus.
-
Can an increased copper requirement in copper‐tolerant Mimulus guttatus explain the cost of tolerance? II. Reproductive phase
New Phytologist, 1998Co-Authors: Frances A. Harper, Suzanne E. Smith, Mark R. MacnairAbstract:Circumstantial evidence suggests that plants that have evolved metal tolerance are at a disadvantage on normal soil, i.e. there is a cost of tolerance. One hypothesis for the cause of this cost is that individuals have a greater requirement for copper, and so suffer micronutrient deficiency on normal soils, as a result of a reduced uptake, distribution and/or utilization of copper. We provided highly and less copper-tolerant plants of Mimulus guttatus Fischer ex DC. (the common monkey flower) with sub-optimal copper, and demonstrated the importance of copper as an essential micronutrient during the reproductive phase, both in the production of viable pollen and in seed set. We also looked at the effect of sub-optimal copper supply on the growth of the microgametophyte, and the efficiency with which seed was set. No evidence was found that highly tolerant plants have an increased copper requirement during the reproductive phase. This is in agreement with earlier work on Mimulus guttatus, which investigated the copper requirement of highly tolerant plants during vegetative growth and found that any differences in copper requirement were small. The ‘metal requirement hypothesis’ is, therefore, not the sole explanation for the cost of copper tolerance in M. guttatus.
-
Hypostatic modifiers cause variation in degree of copper tolerance in Mimulus guttatus
Heredity, 1998Co-Authors: Suzanne E. Smith, Mark R. MacnairAbstract:Previous research into copper tolerance in the monkey flower Mimulus guttatus has found that: (i) it is primarily determined by a single dominant gene; and (ii) there is variation between tolerant plants that has been ascribed to ‘modifiers’. Modifiers can be either nonspecific, which act additively on both tolerant (T) and nontolerant (NT) genotypes, or specific, which act only on the tolerant genotype, and are thus hypostatic to the tolerance locus. We show here that there are hypostatic modifiers of tolerance in this species. Two selection lines that differ in degree of tolerance (and thus in the presence of putative modifiers) were crossed to a single NT plant. The F1s were selfed to produce F2s that segregated 3:1 T:NT. NT F2 individuals were crossed to a single homozygous T plant of low tolerance. The families differed in tolerance, showing that the NT F2 individuals differed in genes that only have an effect on tolerance phenotype in the presence of the tolerance gene. F3 individuals from F2s of contrasting phenotype were crossed to a second tester tolerant plant, and these F3s also varied, confirming the presence of the specific modifiers. There was no evidence of the segregation that would suggest a single modifier gene, but there is evidence from the F2s of at least one additive, nonspecific modifier in addition to the specific modifiers.
John Kelly - One of the best experts on this subject based on the ideXlab platform.
-
Severe inbreeding depression is predicted by the "rare allele load" in Mimulus guttatus.
Evolution; international journal of organic evolution, 2019Co-Authors: Keely E. Brown, John KellyAbstract:Most flowering plants are hermaphroditic and experience strong pressures to evolve self-pollination (automatic selection and reproductive assurance). Inbreeding depression (ID) can oppose selection for selfing, but it remains unclear if ID is typically strong enough to maintain outcrossing. To measure the full cost of sustained inbreeding on fitness, and its genomic basis, we planted highly homozygous, fully genome-sequenced inbred lines of yellow monkeyflower (Mimulus guttatus) in the field next to outbred plants from crosses between the same lines. The cost of full homozygosity is severe: 65% for survival and 86% for lifetime seed production. Accounting for the unmeasured effect of lethal and sterile mutations, we estimate that the average fitness of fully inbred genotypes is only 3-4% that of outbred competitors. The genome sequence data provide no indication of simple overdominance, but the number of rare alleles carried by a line, especially within rare allele clusters nonrandomly distributed across the genome, is a significant negative predictor of fitness measurements. These findings are consistent with a deleterious allele model for ID. High variance in rare allele load among lines and the genomic distribution of rare alleles both suggest that migration might be an important source of deleterious alleles to local populations.
-
The Genomic Architecture of Flowering Time Varies Across Space and Time in Mimulus guttatus.
Genetics, 2017Co-Authors: Patrick J. Monnahan, John KellyAbstract:The degree to which genomic architecture varies across space and time is central to the evolution of genomes in response to natural selection. Bulked-segregant mapping combined with pooled sequencing provides an efficient means to estimate the effect of genetic variants on quantitative traits. We develop a novel likelihood framework to identify segregating variation within multiple populations and generations while accommodating estimation error on a sample- and SNP-specific basis. We use this method to map loci for flowering time within natural populations of Mimulus guttatus, collecting the early- and late-flowering plants from each of three neighboring populations and two consecutive generations. Structural variants, such as inversions, and genes from multiple flowering-time pathways exhibit the strongest associations with flowering time. We find appreciable variation in genetic effects on flowering time across both time and space; the greatest differences evident between populations, where numerous factors (environmental variation, genomic background, and private polymorphisms) likely contribute to heterogeneity. However, the changes across years within populations clearly identify genotype-by-environment interactions as an important influence on flowering time variation.
-
The genomic architecture of flowering time varies across space and time in Mimulus guttatus
2017Co-Authors: Patrick J. Monnahan, John KellyAbstract:The degree to which genomic architecture varies across space and time is central to the evolution of genomes in response to natural selection. Bulked-segregant mapping combined with pooled sequencing provides an efficient method to estimate the effect of genetic variants on quantitative traits. We develop a novel likelihood framework to identify segregating variation within multiple populations and generations while accommodating estimation error on a sample-and SNP-specific basis. We use this method to map loci for flowering time within natural populations of Mimulus guttatus, collecting the early and late flowering plants from each of three neighboring populations and two consecutive generations. We find appreciable variation in genetic effects on flowering time across both time and space; the greatest differences evident between populations. Structural variants, such as inversions, and genes from multiple flowering time pathways exhibit the strongest associations with flowering time. It is also clear that genotype-by-environment interactions are an important influence on flowering time variation.
-
Transgenerational plasticity is sex-dependent and persistent in yellow monkeyflower (Mimulus guttatus).
Environmental epigenetics, 2016Co-Authors: Kayla C. Akkerman, John Kelly, Arash Sattarin, Alison G. ScovilleAbstract:Transgenerational phenotypic plasticity, whereby environmental cues experienced by parents alter the phenotype of their progeny, has now been documented in diverse organisms. Transmission of environmentally determined responses is known to occur through both maternal and paternal gametes, but the underlying mechanisms have rarely been compared. In addition, the persistence of induction over multiple generations appears to vary widely, but has been characterized for relatively few systems. Yellow monkeyflower (Mimulus guttatus) is known to exhibit transgenerational induction of increased glandular trichome production in response to simulated insect damage. Here, we test for differences between maternal and paternal transmission of this response and examine its persistence over five generations following damage. Maternal and paternal damage resulted in similar and apparently additive increases in progeny trichome production. Treatment of germinating seeds with the genome-wide demethylating agent 5-azacytidine erased the effect of maternal but not paternal damage. The number of glandular trichomes remained elevated for three generations following damage. These results indicate that transgenerational transmission occurs through both maternal and paternal germ lines, but that they differ in the proximate mechanism of epigenetic inheritance. Our results also indicate that a wounding response can persist for multiple generations in the absence of subsequent damage.
-
A Segregating Inversion Generates Fitness Variation in Yellow Monkeyflower (Mimulus guttatus).
Genetics, 2016Co-Authors: Young Lee, John Kelly, Lila Fishman, John H WillisAbstract:Polymorphic chromosomal rearrangements can bind hundreds of genes into single genetic loci with diverse effects. Rearrangements are often associated with local adaptation and speciation and may also be an important component of genetic variation within populations. We genetically and phenotypically characterize a segregating inversion (inv6) in the Iron Mountain (IM) population of Mimulus guttatus (yellow monkeyflower). We initially mapped inv6 as a region of recombination suppression in three F2 populations resulting from crosses among IM plants. In each case, the F1 parent was heterozygous for a derived haplotype, homogenous across markers spanning over 5 Mb of chromsome 6. In the three F2 populations, inv6 reduced male and female fitness components. In addition, inv6 carriers suffered an ∼30% loss of pollen viability in the field. Despite these costs, inv6 exists at moderate frequency (∼8%) in the natural population, suggesting counterbalancing fitness benefits that maintain the polymorphism. Across 4 years of monitoring in the field, inv6 had an overall significant positive effect on seed production (lifetime female fitness) of carriers. This benefit was particularly strong in harsh years and may be mediated (in part) by strong positive effects on flower production. These data suggest that opposing fitness effects maintain an intermediate frequency, and as a consequence, inv6 generates inbreeding depression and high genetic variance. We discuss these findings in relation to the theory of inbreeding depression and the maintenance of fitness variation.
Lila Fishman - One of the best experts on this subject based on the ideXlab platform.
-
the genetics of extreme microgeographic adaptation an integrated approach identifies a major gene underlying leaf trichome divergence in yellowstone Mimulus guttatus
Molecular Ecology, 2016Co-Authors: Margaret F Hendrick, Findley R Finseth, Minna E Mathiasson, Kristen A Palmer, Emma M Broder, Peter Breigenzer, Lila FishmanAbstract:Microgeographic adaptation provides a particularly interesting context for understanding the genetic basis of phenotypic divergence and may also present unique empirical challenges. In particular, plant adaptation to extreme soil mosaics may generate barriers to gene flow or shifts in mating system that confound simple genomic scans for adaptive loci. Here, we combine three approaches - quantitative trait locus (QTL) mapping of candidate intervals in controlled crosses, population resequencing (PoolSeq) and analyses of wild recombinant individuals - to investigate one trait associated with Mimulus guttatus (yellow monkeyflower) adaptation to geothermal soils in Yellowstone National Park. We mapped a major QTL causing dense leaf trichomes in thermally adapted plants to a <50-kb region of linkage Group 14 (Tr14) previously implicated in trichome divergence between independent M. guttatus populations. A PoolSeq scan of Tr14 region revealed a cluster of six genes, coincident with the inferred QTL peak, with high allele frequency differences sufficient to explain observed phenotypic differentiation. One of these, the R2R3 MYB transcription factor Migut.N02661, is a plausible functional candidate and was also strongly associated (r2 = 0.27) with trichome phenotype in analyses of wild-collected admixed individuals. Although functional analyses will be necessary to definitively link molecular variants in Tr14 with trichome divergence, our analyses are a major step in that direction. They point to a simple, and parallel, genetic basis for one axis of Mimulus guttatus adaptation to an extreme habitat, suggest a broadly conserved genetic basis for trichome variation across flowering plants and pave the way for further investigations of this challenging case of microgeographic incipient speciation.
-
The genetics of extreme microgeographic adaptation: an integrated approach identifies a major gene underlying leaf trichome divergence in Yellowstone Mimulus guttatus.
Molecular ecology, 2016Co-Authors: Margaret F Hendrick, Findley R Finseth, Minna E Mathiasson, Kristen A Palmer, Emma M Broder, Peter Breigenzer, Lila FishmanAbstract:Microgeographic adaptation provides a particularly interesting context for understanding the genetic basis of phenotypic divergence and may also present unique empirical challenges. In particular, plant adaptation to extreme soil mosaics may generate barriers to gene flow or shifts in mating system that confound simple genomic scans for adaptive loci. Here, we combine three approaches - quantitative trait locus (QTL) mapping of candidate intervals in controlled crosses, population resequencing (PoolSeq) and analyses of wild recombinant individuals - to investigate one trait associated with Mimulus guttatus (yellow monkeyflower) adaptation to geothermal soils in Yellowstone National Park. We mapped a major QTL causing dense leaf trichomes in thermally adapted plants to a
-
A Segregating Inversion Generates Fitness Variation in Yellow Monkeyflower (Mimulus guttatus).
Genetics, 2016Co-Authors: Young Lee, John Kelly, Lila Fishman, John H WillisAbstract:Polymorphic chromosomal rearrangements can bind hundreds of genes into single genetic loci with diverse effects. Rearrangements are often associated with local adaptation and speciation and may also be an important component of genetic variation within populations. We genetically and phenotypically characterize a segregating inversion (inv6) in the Iron Mountain (IM) population of Mimulus guttatus (yellow monkeyflower). We initially mapped inv6 as a region of recombination suppression in three F2 populations resulting from crosses among IM plants. In each case, the F1 parent was heterozygous for a derived haplotype, homogenous across markers spanning over 5 Mb of chromsome 6. In the three F2 populations, inv6 reduced male and female fitness components. In addition, inv6 carriers suffered an ∼30% loss of pollen viability in the field. Despite these costs, inv6 exists at moderate frequency (∼8%) in the natural population, suggesting counterbalancing fitness benefits that maintain the polymorphism. Across 4 years of monitoring in the field, inv6 had an overall significant positive effect on seed production (lifetime female fitness) of carriers. This benefit was particularly strong in harsh years and may be mediated (in part) by strong positive effects on flower production. These data suggest that opposing fitness effects maintain an intermediate frequency, and as a consequence, inv6 generates inbreeding depression and high genetic variance. We discuss these findings in relation to the theory of inbreeding depression and the maintenance of fitness variation.
-
Pollen limitation and natural selection on floral characters in the yellow monkeyflower, Mimulus guttatus.
The New phytologist, 2007Co-Authors: Lila Fishman, John H WillisAbstract:In flowering plants, pollen limitation has been proposed to intensify selection on floral characters important in pollinator attraction, but may also select for traits that increase seed set through autonomous selfing. Here, a factorial design (+/- pollen addition, +/- pollinator removal) was used to investigate how the pollination environment affects selection on floral morphology via female fitness in a mixed-mating population of the yellow monkeyflower, Mimulus guttatus (Phrymaceae). Female fitness was strongly pollen-limited, with supplementally pollinated plants setting 37% more seeds than open-pollinated individuals. Strong positive selection was found on flower length, weak positive selection on flower width : length ratio and no selection on stigma-anther distance in both open-pollinated and supplementally pollinated treatments. By contrast, flowers with relatively narrow corollas and low stigma-anther distances were favored in the pollinator exclusion treatment. These results provide mixed support for the idea that pollen limitation intensifies selection on floral characters. Despite strong phenotypic selection, natural pollen limitation did not mediate selection on characters associated with either pollinator attraction or self-fertilization. However, the novel pattern of selection on severely pollen-limited plants suggests that reproductive assurance against pollinator loss may have been directly involved in the floral evolution of closely related selfing taxa.
-
Evidence for Dobzhansky-Muller incompatibilites contributing to the sterility of hybrids between Mimulus guttatus and M. nasutus.
Evolution; international journal of organic evolution, 2001Co-Authors: Lila Fishman, John H WillisAbstract:Abstract Both chromosomal rearrangements and negative interactions among loci (Dobzhansky-Muller incompatibilities) have been advanced as the genetic mechanism underlying the sterility of interspecific hybrids. These alternatives invoke very different evolutionary histories during speciation and also predict different patterns of sterility in artificial hybrids. Chromosomal rearrangements require drift, inbreeding, or other special conditions for initial fixation and, because heterozygosity per se generates any problems with gamete formation, F1 hybrids will be most infertile. In contrast, Dobzhansky-Muller incompatibilities may arise as byproducts of adaptive evolution and often affect the segregating F2 generation most severely. To distinguish the effects of these two mechanisms early in divergence, we investigated the quantitative genetics of hybrid sterility in a line cross between two members of the Mimulus guttatus species complex (M. guttatus and M. nasutus). Hybrids showed partial male and female ...
Suzanne E. Smith - One of the best experts on this subject based on the ideXlab platform.
-
can an increased copper requirement in copper tolerant Mimulus guttatus explain the cost of tolerance ii reproductive phase
New Phytologist, 1998Co-Authors: Frances A. Harper, Suzanne E. Smith, Mark R. MacnairAbstract:Circumstantial evidence suggests that plants that have evolved metal tolerance are at a disadvantage on normal soil, i.e. there is a cost of tolerance. One hypothesis for the cause of this cost is that individuals have a greater requirement for copper, and so suffer micronutrient deficiency on normal soils, as a result of a reduced uptake, distribution and/or utilization of copper. We provided highly and less copper-tolerant plants of Mimulus guttatus Fischer ex DC. (the common monkey flower) with sub-optimal copper, and demonstrated the importance of copper as an essential micronutrient during the reproductive phase, both in the production of viable pollen and in seed set. We also looked at the effect of sub-optimal copper supply on the growth of the microgametophyte, and the efficiency with which seed was set. No evidence was found that highly tolerant plants have an increased copper requirement during the reproductive phase. This is in agreement with earlier work on Mimulus guttatus, which investigated the copper requirement of highly tolerant plants during vegetative growth and found that any differences in copper requirement were small. The ‘metal requirement hypothesis’ is, therefore, not the sole explanation for the cost of copper tolerance in M. guttatus.
-
Can an increased copper requirement in copper‐tolerant Mimulus guttatus explain the cost of tolerance? II. Reproductive phase
New Phytologist, 1998Co-Authors: Frances A. Harper, Suzanne E. Smith, Mark R. MacnairAbstract:Circumstantial evidence suggests that plants that have evolved metal tolerance are at a disadvantage on normal soil, i.e. there is a cost of tolerance. One hypothesis for the cause of this cost is that individuals have a greater requirement for copper, and so suffer micronutrient deficiency on normal soils, as a result of a reduced uptake, distribution and/or utilization of copper. We provided highly and less copper-tolerant plants of Mimulus guttatus Fischer ex DC. (the common monkey flower) with sub-optimal copper, and demonstrated the importance of copper as an essential micronutrient during the reproductive phase, both in the production of viable pollen and in seed set. We also looked at the effect of sub-optimal copper supply on the growth of the microgametophyte, and the efficiency with which seed was set. No evidence was found that highly tolerant plants have an increased copper requirement during the reproductive phase. This is in agreement with earlier work on Mimulus guttatus, which investigated the copper requirement of highly tolerant plants during vegetative growth and found that any differences in copper requirement were small. The ‘metal requirement hypothesis’ is, therefore, not the sole explanation for the cost of copper tolerance in M. guttatus.
-
Hypostatic modifiers cause variation in degree of copper tolerance in Mimulus guttatus
Heredity, 1998Co-Authors: Suzanne E. Smith, Mark R. MacnairAbstract:Previous research into copper tolerance in the monkey flower Mimulus guttatus has found that: (i) it is primarily determined by a single dominant gene; and (ii) there is variation between tolerant plants that has been ascribed to ‘modifiers’. Modifiers can be either nonspecific, which act additively on both tolerant (T) and nontolerant (NT) genotypes, or specific, which act only on the tolerant genotype, and are thus hypostatic to the tolerance locus. We show here that there are hypostatic modifiers of tolerance in this species. Two selection lines that differ in degree of tolerance (and thus in the presence of putative modifiers) were crossed to a single NT plant. The F1s were selfed to produce F2s that segregated 3:1 T:NT. NT F2 individuals were crossed to a single homozygous T plant of low tolerance. The families differed in tolerance, showing that the NT F2 individuals differed in genes that only have an effect on tolerance phenotype in the presence of the tolerance gene. F3 individuals from F2s of contrasting phenotype were crossed to a second tester tolerant plant, and these F3s also varied, confirming the presence of the specific modifiers. There was no evidence of the segregation that would suggest a single modifier gene, but there is evidence from the F2s of at least one additive, nonspecific modifier in addition to the specific modifiers.
-
Does copper tolerance give cadmium tolerance in Mimulus guttatus
Heredity, 1997Co-Authors: G H Tilstone, Mark R. Macnair, Suzanne E. SmithAbstract:Copper tolerance in Mimulus guttatus Fischer ex DC, is controlled by a single major gene, plus a number of minor genes (or modifiers) which elevate copper tolerance. Homozygous copper tolerant and nontolerant lines derived from Marin County, California, were screened in dose-response experiments against both copper and cadmium. Significant differences were found between these lines for copper, but not for cadmium, suggesting that cadmium tolerance is not conferred by the major copper tolerance gene. Ten selection lines, derived from three different copper mines, which all carry the major tolerance gene but vary in the degree of tolerance to copper were also screened against copper and cadmium. No significant correlation between copper and cadmium tolerances was found. Screening of modifier lines, in which modifiers for differing degrees of copper tolerance were inserted into a nontolerant background, showed that genotypes possessing fewer copper modifiers yield higher cadmium tolerance than those genotypes which have a greater number of modifiers. These results suggest that copper and cadmium tolerance are governed by independent genes in this species.
-
Can an increased copper requirement in copper-tolerant Mimulus guttatus explain the cost of tolerance?
New Phytologist, 1997Co-Authors: Frances A. Harper, Suzanne E. Smith, Mark R. MacnairAbstract:summary Circumstantial evidence suggests that plants that have evolved metal tolerance are at a disadvantage on normal soil, i.e. there is a cost of tolerance. One hypothesis for the cause of this cost is that individuals have a greater requirement for copper, and so suer micronutrient deficiency on normal soils, as a result of a reduced uptake, distribution and}or utilization of copper. We provided highly and less copper-tolerant plants of Mimulus guttatus Fischer ex DC. (the common monkey flower) with sub-optimal copper, and demonstrated the importance of copper as an essential micronutrient during the reproductive phase, both in the production of viable pollen and in seed set. We also looked at the eect of sub-optimal copper supply on the growth of the microgametophyte, and the eciency with which seed was set. No evidence was found that highly tolerant plants have an increased copper requirement during the reproductive phase. This is in agreement with earlier work on Mimulus guttatus, which investigated the copper requirement of highly tolerant plants during vegetative growth and found that any dierences in copper requirement were small. The ‘metal requirement hypothesis’ is, therefore, not the sole explanation for the cost of copper tolerance in M. guttatus.