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Husband BC, Barrett SCH. EFFECTIVE POPULATION SIZE AND GENETIC DRIFT IN TRISTYLOUSEICHHORNIA PANICULATA(PONTEDERIACEAE). Evolution 2017; 46:1875-1890. [DOI: 10.1111/j.1558-5646.1992.tb01175.x] [Citation(s) in RCA: 58] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/1991] [Accepted: 02/22/1992] [Indexed: 10/19/2022]
Affiliation(s)
- Brian C. Husband
- Department of Botany; University of Toronto; Toronto Ontario M5S 3B2 Canada
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Kohn JR, Barrett SCH. POLLEN DISCOUNTING AND THE SPREAD OF A SELFING VARIANT IN TRISTYLOUS EICHHORNIA PANICULATA: EVIDENCE FROM EXPERIMENTAL POPULATIONS. Evolution 2017; 48:1576-1594. [PMID: 28568426 DOI: 10.1111/j.1558-5646.1994.tb02197.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/1993] [Accepted: 12/07/1993] [Indexed: 11/28/2022]
Abstract
Floral traits that increase self-fertilization are expected to spread unless countered by the effects of inbreeding depression, pollen discounting (reduced outcross pollen success by individuals with increased rates of self-fertilization), or both. Few studies have attempted to measure pollen discounting because to do so requires estimating the male outcrossing success of plants that differ in selfing rate. In natural populations of tristylous Eichhornia paniculata, selfing variants of the mid-styled morph are usually absent from populations containing all three style morphs but often predominate in nontrimorphic populations. We used experimental garden populations of genetically marked plants to investigate whether the effects of population morph structure on relative gamete transmission by unmodified (M) and selfing variants (M') of the mid-styled morph could explain their observed distribution. Transmission through ovules and self and outcross pollen by plants of the M and M' morphs were compared under trimorphic, dimorphic (S morph absent), and monomorphic (L and S morphs absent) population structures. Neither population structure nor floral morphology affected female reproductive success, but both had strong effects on the relative transmission of male gametes. The frequency of self-fertilization in the M' morph was consistently higher than that of the M morph under all morph structures, and the frequency of self-fertilization by both morphs increased as morph diversity of experimental populations declined. In trimorphic populations, total transmission by the M and M' morphs did not differ. The small, nonsignificant increase in selfing by the M' relative to the M morph was balanced by decreased outcross siring success, particularly on the S morph. In populations lacking the S morph, male gamete transmission by the M' morph was approximately 1.5 times greater than that by the M morph because of both increased selfing and increased success through outcross pollen donation. Therefore, gamete transmission strongly favored the M' morph only in the absence of the S morph, a result consistent with the distribution of the M' morph in nature. This study indicates that floral traits that alter the selfing rate can have large and context-dependent influences on outcross pollen donation.
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Affiliation(s)
- Joshua R Kohn
- University of California at San Diego, Department of Biology 0116, La Jolla, California, 92093
| | - Spencer C H Barrett
- Department of Botany, University of Toronto, Toronto, Ontario, M5S 3B2, Canada
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Kohn JR, Barrett SCH. EXPERIMENTAL STUDIES ON THE FUNCTIONAL SIGNIFICANCE OF HETEROSTYLY. Evolution 2017; 46:43-55. [PMID: 28564966 DOI: 10.1111/j.1558-5646.1992.tb01983.x] [Citation(s) in RCA: 77] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/1990] [Accepted: 06/27/1991] [Indexed: 11/27/2022]
Abstract
Heterostyly has been viewed as both an antiselfing device and a mechanism that increases the proficiency of pollen transfer between plants. We used experimental manipulation of the morph structure of garden populations of self-compatible, tristylous Eichhornia paniculata to investigate the function of floral polymorphism. Outcrossing rates (t), levels of intermorph mating (d), and morph-specific male and female reproductive success were compared in replicate trimorphic and monomorphic populations. In trimorphic populations, t and d averaged 0.81 (2 SE = 0.03) and 0.77 (2 SE = 0.03) respectively, with no difference in either parameter among morphs. Ninety-five percent of outcrossed seeds were therefore the result of intermorph fertilizations. Male reproductive success of the long-styled morph was low, especially in comparison with plants of the short-styled morph. Outcrossing rates for each morph were higher in trimorphic than monomorphic populations where t averaged 0.71 (2 SE = 0.01), 0.30 (2 SE = 0.04) and 0.43 (2 SE = 0.1) for the long-, mid-, and short-styled morphs, respectively. Seed set was lower in monomorphic populations, particularly those composed of the L morph, reflecting reduced pollen deposition. Floral polymorphism therefore increased both outcrossing rate and fecundity but the magnitude of the differences varied among morphs. If the ancestral condition in heterostylous groups resembled the L morph, as has been suggested, data from this study suggests that the selective basis for the establishment of floral polymorphism could have been increased pollen transfer rather than higher levels of outcrossing.
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Affiliation(s)
- Joshua R Kohn
- Department of Botany, University of Toronto, Toronto, ON, M5S 3B2, CANADA
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Barrett SCH, Morgan MT, Husband BC. THE DISSOLUTION OF A COMPLEX GENETIC POLYMORPHISM: THE EVOLUTION OF SELF-FERTILIZATION IN TRISTYLOUS EICHHORNIA PANICULATA
(PONTEDERIACEAE). Evolution 2017; 43:1398-1416. [DOI: 10.1111/j.1558-5646.1989.tb02591.x] [Citation(s) in RCA: 117] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/1988] [Accepted: 05/31/1989] [Indexed: 10/19/2022]
Affiliation(s)
| | - Martin T. Morgan
- Department of Botany; University of Toronto; Toronto ON M5S 3B2 CANADA
| | - Brian C. Husband
- Department of Botany; University of Toronto; Toronto ON M5S 3B2 CANADA
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Cruzan MB, Barrett SCH. CONTRIBUTION OF CRYPTIC INCOMPATIBILITY TO THE MATING SYSTEM OFEICHHORNIA PANICULA TA(PONTEDERIACEAE). Evolution 2017; 47:925-934. [DOI: 10.1111/j.1558-5646.1993.tb01245.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/1991] [Accepted: 11/02/1992] [Indexed: 11/30/2022]
Affiliation(s)
- Mitchell B. Cruzan
- Department of Botany; University of Toronto; Toronto Ontario M5S 3B2 Canada
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The evolution of selfing is accompanied by reduced efficacy of selection and purging of deleterious mutations. Genetics 2014; 199:817-29. [PMID: 25552275 DOI: 10.1534/genetics.114.172809] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The transition from outcrossing to selfing is predicted to reduce the genome-wide efficacy of selection because of the lower effective population size (Ne) that accompanies this change in mating system. However, strongly recessive deleterious mutations exposed in the homozygous backgrounds of selfers should be under strong purifying selection. Here, we examine estimates of the distribution of fitness effects (DFE) and changes in the magnitude of effective selection coefficients (Nes) acting on mutations during the transition from outcrossing to selfing. Using forward simulations, we investigated the ability of a DFE inference approach to detect the joint influence of mating system and the dominance of deleterious mutations on selection efficacy. We investigated predictions from our simulations in the annual plant Eichhornia paniculata, in which selfing has evolved from outcrossing on multiple occasions. We used range-wide sampling to generate population genomic datasets and identified nonsynonymous and synonymous polymorphisms segregating in outcrossing and selfing populations. We found that the transition to selfing was accompanied by a change in the DFE, with a larger fraction of effectively neutral sites (Nes < 1), a result consistent with the effects of reduced Ne in selfers. Moreover, an increased proportion of sites in selfers were under strong purifying selection (Nes > 100), and simulations suggest that this is due to the exposure of recessive deleterious mutations. We conclude that the transition to selfing has been accompanied by the genome-wide influences of reduced Ne and strong purifying selection against deleterious recessive mutations, an example of purging at the molecular level.
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Caetano S, Currat M, Pennington RT, Prado D, Excoffier L, Naciri Y. Recent colonization of the Galápagos by the tree Geoffroea spinosa Jacq. (Leguminosae). Mol Ecol 2012; 21:2743-60. [PMID: 22509817 DOI: 10.1111/j.1365-294x.2012.05562.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
This study puts together genetic data and an approximate bayesian computation (ABC) approach to infer the time at which the tree Geoffroea spinosa colonized the Galápagos Islands. The genetic diversity and differentiation between Peru and Galápagos population samples, estimated using three chloroplast spacers and six microsatellite loci, reveal significant differences between two mainland regions separated by the Andes mountains (Inter Andean vs. Pacific Coast) as well as a significant genetic differentiation of island populations. Microsatellites identify two distinct geographical clusters, the Galápagos and the mainland, and chloroplast markers show a private haplotype in the Galápagos. The nuclear distinctiveness of the Inter Andean populations suggests current restricted pollen flow, but chloroplast points to cross-Andean dispersals via seeds, indicating that the Andes might not be an effective biogeographical barrier. The ABC analyses clearly point to the colonization of the Galápagos within the last 160,000 years and possibly as recently as 4750 years ago (475 generations). Founder events associated with colonization of the two islands where the species occurs are detected, with Española having been colonized after Floreana. We discuss two nonmutually exclusive possibilities for the colonization of the Galápagos, recent natural dispersal vs. human introduction.
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Affiliation(s)
- S Caetano
- Plant Systematics and Biodiversity Laboratory, Molecular Phylogeny and Genetics Unit, Conservatoire et Jardin botaniques, 1 Chemin de l'Impératrice, CP 60, CH-1292 Chambésy, Genève, Switzerland
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Namoff S, Veloz A, Jiménez F, Rodríguez-Peña RA, Peguero B, Lewis C, Moynihan J, Abdo M, Maunder M, Von Wettberg E, Meerow AW, Griffith MP, Francisco-Ortega J. Sweet drinks are made of this: conservation genetics of an endemic palm species from the Dominican Republic. J Hered 2011; 102:1-10. [PMID: 21172825 DOI: 10.1093/jhered/esq118] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Pseudophoenix ekmanii is a threatened palm species endemic to the Dominican Republic. Sap from trees is extracted to make a local drink; once they are tapped the individual usually dies. Plants are also illegally harvested for the nursery trade and destroyed by poachers hunting the endemic and threatened Hispaniolan parrot. We used 7 DNA microsatellite markers to assist land managers in developing conservation strategies for this palm. We sampled 4 populations along the known distribution range of this species (3 populations from the mainland and 1 from the small island of Isla Beata), for a total sample of n = 104. We found strong evidence for genetic drift, inbreeding, and moderate gene flow (i.e., all populations had at least 4 loci that were not in Hardy-Weinberg equilibrium, at least 9 loci pairs were in linkage disequilibrium, the pairwise F(ST) values ranged from 0.069 to 0.266, and had positive F(IS) values). Data supported an isolation-by-distance model, and cluster analyses based on genetic distances resolved 2 groups that match a north-south split. The population from Isla Beata had the lowest levels of genetic diversity and was the only one in which we found pairs of individuals with identical shared multilocus genotypes.
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Affiliation(s)
- Sandra Namoff
- Center for Tropical Plant Conservation, Fairchild Tropical Botanic Garden, Coral Gables, Miami, FL 33156, USA
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Mating-system variation, demographic history and patterns of nucleotide diversity in the Tristylous plant Eichhornia paniculata. Genetics 2009; 184:381-92. [PMID: 19917767 DOI: 10.1534/genetics.109.110130] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Inbreeding in highly selfing populations reduces effective size and, combined with demographic conditions associated with selfing, this can erode genetic diversity and increase population differentiation. Here we investigate the role that variation in mating patterns and demographic history play in shaping the distribution of nucleotide variation within and among populations of the annual neotropical colonizing plant Eichhornia paniculata, a species with wide variation in selfing rates. We sequenced 10 EST-derived nuclear loci in 225 individuals from 25 populations sampled from much of the geographic range and used coalescent simulations to investigate demographic history. Highly selfing populations exhibited moderate reductions in diversity but there was no significant difference in variation between outcrossing and mixed mating populations. Population size interacted strongly with mating system and explained more of the variation in diversity within populations. Bayesian structure analysis revealed strong regional clustering and selfing populations were highly differentiated on the basis of an analysis of F(st). There was no evidence for a significant loss of within-locus linkage disequilibrium within populations, but regional samples revealed greater breakdown in Brazil than in selfing populations from the Caribbean. Coalescent simulations indicate a moderate bottleneck associated with colonization of the Caribbean from Brazil approximately 125,000 years before the present. Our results suggest that the recent multiple origins of selfing in E. paniculata from diverse outcrossing populations result in higher diversity than expected under long-term equilibrium.
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10
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Affre L, Thompson JD. Population genetic structure and levels of inbreeding depression in the Mediterranean island endemic Cyclamen creticum (Primulaceae). Biol J Linn Soc Lond 2008. [DOI: 10.1111/j.1095-8312.1997.tb01511.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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11
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Piñeiro R, Fuertes Aguilar J, Munt DD, Nieto Feliner G. Ecology matters: Atlantic-Mediterranean disjunction in the sand-dune shrub Armeria pungens (Plumbaginaceae). Mol Ecol 2008; 16:2155-71. [PMID: 17498238 DOI: 10.1111/j.1365-294x.2007.03280.x] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Inferring the evolutionary history of Mediterranean plant lineages from current genetic, distributional and taxonomic patterns is complex because of a number of palaeoclimatic and geological interconnected factors together with landscape heterogeneity and human influence. Therefore, choosing spatially simplified systems as study groups is a suitable approach. An amplified fragment length polymorphism (AFLP) study using two restriction enzyme combinations (EcoRI/MseI and KpnI/MseI) was carried out to estimate the structure of genetic variation throughout the range of Armeria pungens. This species has a West Iberian-Corso/Sardinian disjunct distribution on coastal sand-dune ecosystems. Bayesian, amova and genetic distance analyses of the AFLP data revealed the same distinguishable genetic groups, which do not match the main geographical disjunction. Corso-Sardinian populations were found to be genetically closer to southwest Portuguese than to those from the Gulf of Cadiz (the closest geographically). Eastwards long-distance dispersal is therefore invoked to explain this geographical disjunction. A GIS analysis based on bioclimatic envelope modelling aiming to characterize the current locations of A. pungens found strong similarities between the Portugal and Corsica-Sardinia sites and less so between these areas and the Gulf of Cadiz. This coincident pattern between AFLP and climatic data suggests that the geographical disjunction is better explained by climatic factors than by the likeliness of a stochastic dispersal event. Such a combined phylogeographical-GIS modelling approach proves to be enlightening in reconstructing the evolutionary history of plant species.
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Affiliation(s)
- Rosalía Piñeiro
- Real Jardín Botánico de Madrid, CSIC, Plaza de Murillo 2, 28014 Madrid, Spain.
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12
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SAKAI SHOKO, WRIGHT SJOSEPH. Reproductive ecology of 21 coexisting Psychotria species (Rubiaceae): when is heterostyly lost? Biol J Linn Soc Lond 2007. [DOI: 10.1111/j.1095-8312.2007.00890.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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13
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Valliant MT, Mack RN, Novak SJ. Introduction history and population genetics of the invasive grass Bromus tectorum (Poaceae) in Canada. AMERICAN JOURNAL OF BOTANY 2007; 94:1156-1169. [PMID: 21636483 DOI: 10.3732/ajb.94.7.1156] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The invasive annual Bromus tectorum (cheatgrass) is distributed in Canada primarily south of 52° N latitude in two diffuse ranges separated by the extensive coniferous forest in western Ontario. The grass was likely introduced independently to eastern and western Canada post-1880. We detected regional variation in the grass's genetic diversity using starch gel electrophoresis to analyze genetic diversity at 25 allozyme loci in 60 populations collected across Canada. The Pgm-1a & Pgm-2a multilocus genotype, which occurs in the grass's native range in Eastern Europe, is prevalent in eastern Canada but occurs at low frequency in western Canada. In contrast, the Got-4c multilocus genotype, found in the native range in Central Europe, is widespread in populations from western Canada. Overall genetic diversity of B. tectorum is much higher in eastern Canada than in the eastern U.S., while the genetic diversity in populations in western North America is similar between Canada and the U.S. The distribution of genetic diversity across Canada strongly suggests multiple introduction events. Heterozygous individuals, which are exceedingly rare in B. tectorum, were detected in three Canadian populations. Formation of novel genotypes through occasional outcrossing events could spark adaptive evolution and further range expansion across Canada of this exceedingly damaging grass.
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Affiliation(s)
- Morgan T Valliant
- School of Biological Sciences, Washington State University, Pullman, Washington 99164 USA
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14
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SUEHS CAREYM, AFFRE LAURENCE, MEDAIL FREDERIC. Unexpected insularity effects in invasive plant mating systems: the case of Carpobrotus (Aizoaceae) taxa in the Mediterranean Basin. Biol J Linn Soc Lond 2005. [DOI: 10.1111/j.1095-8312.2005.00473.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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15
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Richardson JE, Fay MF, Cronk QCB, Chase MW. Species delimitation and the origin of populations in island representatives of Phylica (Rhamnaceae). Evolution 2003; 57:816-27. [PMID: 12778551 DOI: 10.1111/j.0014-3820.2003.tb00293.x] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Relationships between the closely related island species of Phylica (Rhamnaceae) and a mainland species, P. paniculata, were elucidated using amplified fragment length polymorphisms (AFLPs). Parsimony, neighbor joining, and principal coordinate (PCO) analyses indicated that each of the species studied is distinct. AFLPs were also useful in elucidating the genetic relationships and possible infraspecific origins of different island populations in the Atlantic and Indian Oceans. Phylica nitida on Réunion is likely to have been derived from P. nitida on Mauritius. Although the sampling on New Amsterdam is not extensive, the data are also consistent with the hypothesis that P. arborea on New Amsterdam was derived from a single colonization of P. arborea from Gough Island. Similarly, the Gough Island population appears to have been derived from a single colonization event, but it is so distinct from those on Tristan da Cunha, that there may have been two separate dispersals to Gough and Tristan/Nightingale from different lines of the mainland progenitor. There is also evidence of a recolonization from Gough to Tristan da Cunha. Thus, Phylica arborea is capable of repeated long distance dispersal, up to 8000 km, even though the fruits and seeds are not of a type normally associated with this phenomenon.
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Affiliation(s)
- James E Richardson
- Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3DS, United Kingdom.
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16
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Richardson JE, Fay MF, Cronk QCB, Chase MW. SPECIES DELIMITATION AND THE ORIGIN OF POPULATIONS IN ISLAND REPRESENTATIVES OF PHYLICA (RHAMNACEAE). Evolution 2003. [DOI: 10.1554/0014-3820(2003)057[0816:sdatoo]2.0.co;2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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17
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Rivera-Ocasio E, Aide TM, McMillan WO. Patterns of genetic diversity and biogeographical history of the tropical wetland tree, Pterocarpus officinalis (Jacq.), in the Caribbean basin. Mol Ecol 2002; 11:675-83. [PMID: 11972756 DOI: 10.1046/j.1365-294x.2002.01476.x] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Studies examining intraspecific variation in plant species with widespread distributions and disjunct populations have mainly concentrated on temperate species. Here, we determined the genetic structure of a broadly distributed wetland tropical tree, Pterocarpus officinalis (Jacq.), from eight Neotropical populations using amplified length fragment polymorphisms (AFLP). AFLPs proved highly variable with almost half (48%) of the genetic variation at these loci occurring among individuals within populations. Nonetheless, there was a strong geographical pattern in the distribution of AFLP variation within P. officinalis. Caribbean and continental populations fell into two well-defined genetic clusters supported by the presence of a number of unique AFLP bands. Within these two regions, there were also strong genetic differences among populations, caused mainly by frequency differences in AFLP bands, making it difficult to determine the evolutionary relationships among populations. In addition, our analysis of P. officinalis revealed striking differences in the levels of AFLP variation among the eight populations sampled. In general, Caribbean populations had lower genetic diversity than continental populations. Moreover, there was a clear loss in AFLP diversity with distance from the continent among Caribbean populations. The overall genetic pattern within P. officinalis suggests that past colonization history, coupled with genetic drift within local populations, rather than contemporary gene flow are the major forces shaping variation within this species.
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Affiliation(s)
- E Rivera-Ocasio
- PO Box 23360, Department of Biology, University of Puerto Rico-Rio Piedras, San Juan, Puerto Rico 00931-3360, USA.
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18
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Daehler CC. Variation in self-fertility and the reproductive advantage of self-fertility for an invading plant (Spartina alterniflora). Evol Ecol 1998. [DOI: 10.1023/a:1006556709662] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Frankham R. Do island populations have less genetic variation than mainland populations? Heredity (Edinb) 1997; 78 ( Pt 3):311-27. [PMID: 9119706 DOI: 10.1038/hdy.1997.46] [Citation(s) in RCA: 455] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Island populations are much more prone to extinction than mainland populations. The reasons for this remain controversial. If inbreeding and loss of genetic variation are involved, then genetic variation must be lower on average in island than mainland populations. Published data on levels of genetic variation for allozymes, nuclear DNA markers, mitochondrial DNA, inversions and quantitative characters in island and mainland populations were analysed. A large and highly significant majority of island populations have less allozyme genetic variation than their mainland counterparts (165 of 202 comparisons), the average reduction being 29 per cent. The magnitude of differences was related to dispersal ability. There were related differences for all the other measures. Island endemic species showed lower genetic variation than related mainland species in 34 of 38 cases. The proportionate reduction in genetic variation was significantly greater in island endemic than in nonendemic island populations in mammals and birds, but not in insects. Genetic factors cannot be discounted as a cause of higher extinction rates of island than mainland populations.
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Affiliation(s)
- R Frankham
- Key Centre for Biodiversity and Bioresources, Macquarie University, Sydney, NSW, Australia.
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20
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Abstract
Island and mainland populations of plants often differ in their reproductive biology and genetics. The differences become more pronounced the further islands are from mainland sources. Altered pollination conditions have influenced the floral biology and mating systems of island plants in distinct ways. Insufficient pollination has favoured selection of floral traits promoting selfing. In contrast, inferior pollinator service resulting in selfing and inbreeding depression appears to be a factor involved in the evolution of sexual dimorphisms. Stochastic forces play a major role in governing patterns of genetic variation. Island populations are usually more differentiated and contain less diversity than comparable mainland samples. Many general issues in evolutionary biology can be addressed by studies of reproduction and genetics in island plants.
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21
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The successful founder: genetics of introduced Carduelis chloris (greenfinch) populations in New Zealand. Heredity (Edinb) 1996. [DOI: 10.1038/hdy.1996.161] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
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22
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Ohara M, Takeda H, Ohno Y, Shimamoto Y. Variations in the breeding system and the population genetic structure of Trillium kamtschaticum (Liliaceae). Heredity (Edinb) 1996. [DOI: 10.1038/hdy.1996.70] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
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23
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Rabarivola C, Meier B, Langer C, Scheffrahn W, Rumpler Y. Population genetics ofEulemur macaco macaco (Primates: Lemuridae) on the islands of Nosy-Be and Nosy-Komba and the Peninsula of Ambato (Madagascar). Primates 1996. [DOI: 10.1007/bf02381409] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Molina-Freaner F, Jain SK. Breeding systems of hermaphroditic and gynodioecious populations of the colonizing species Trifolium hirtum All. in California. TAG. THEORETICAL AND APPLIED GENETICS. THEORETISCHE UND ANGEWANDTE GENETIK 1992; 84:155-160. [PMID: 24203042 DOI: 10.1007/bf00223995] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/20/1991] [Accepted: 10/01/1991] [Indexed: 06/02/2023]
Abstract
A multilocus procedure was used to estimate outcrossing rates in ten roadside populations of Trifolium hirtum in California. Three groups of populations were studied: cultivars, hermaphroditic, and gynodioecious (sexually dimorphic) populations. The multilocus outcrossing rate (tm) varied from 0.05 to 0.43 among populations. Population level tm estimates were significantly correlated with the observed heterozygosity in gynodioecious populations but not in hermaphroditic populations. The outcrossing rate of hermaphrodites and females was estimated in three gynodioecious populations; the estimates of tm varied from 0.09 to 0.23 for hermaphrodites and from 0.73 to 0.80 for females. The distribution of outcrossing rates in gynodioecious populations is bimodal. Our results indicate that for the levels of selfing observed among hermaphrodites, inbreeding depression is likely to be a major factor in the maintenance of females in gynodioecious populations.
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Affiliation(s)
- F Molina-Freaner
- Department of Agronomy and Range Science, University of California, 95616, Davis, CA, USA
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Barrett SC, Charlesworth D. Effects of a change in the level of inbreeding on the genetic load. Nature 1991; 352:522-4. [PMID: 1865906 DOI: 10.1038/352522a0] [Citation(s) in RCA: 261] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
"The effects of inbreeding may not be as noticeable in the first generation as the invigoration immediately apparent after crossing". This statement, published in 1919, has received little attention, and has apparently never been tested empirically, although the reduction of the genetic load of populations by inbreeding is well known in theoretical terms. Because inbreeding increases homozygosity, and hence the effectiveness of selection against recessive or partially recessive detrimental alleles, changes in levels of inbreeding can lead to a reduction in the frequencies of such mutant alleles. This results in equilibration at higher population mean fitness and is referred to as 'purging' populations of their genetic load. Severe inbreeding can also reduce genetic load due to overdominant alleles, provided selection coefficients are not symmetrical at all loci, because alleles giving lower fitness will be reduced in frequency at equilibrium. With either fitness model, however, reduction in genetic load takes time, and the initial effect of an increase in inbreeding is reduced fitness due to homozygosity. There are few data relating to the extent to which fitness is reduced during inbreeding in a set of lines and to how long the reduction lasts before increasing again to the initial level, or higher. Inbreeding experiments involving sib mating in mice and Drosophila subobscura, and successive bottlenecks in house flies have yielded some evidence consistent with the purging hypothesis. Here, we report results of an experiment demonstrating a prolonged time-course of recovery of mean fitness under self-fertilization of a naturally outcrossing plant, and also compare our results with expectations derived by computer calculations. Our results show that the genetic load present in an outcrossing population can be explained only with a high mutation rate to partially recessive deleterious alleles, and that inbreeding purges the population of mutant alleles.
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Affiliation(s)
- S C Barrett
- Department of Botany, University of Toronto, Ontario, Canada
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Tetrasomic inheritance and isozyme variation in Turnera ulmifolia vars. elegans Urb. and intermedia Urb. (Turneraceae). Heredity (Edinb) 1991. [DOI: 10.1038/hdy.1991.39] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
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Husband BC, Barrett SCH. Colonization history and population genetic structure of Eichhornia paniculata in Jamaica. Heredity (Edinb) 1991. [DOI: 10.1038/hdy.1991.36] [Citation(s) in RCA: 77] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
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Morgan MT, Barrett SCH. Outcrossing rates and correlated mating within a population of Eichhornia paniculata (Pontederiaceae). Heredity (Edinb) 1990. [DOI: 10.1038/hdy.1990.33] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
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Wendel JF, Percy RG. Allozyme diversity and introgression in the Galapagos Islands endemic Gossypium darwinii and its relationship to continental G. barbadense. BIOCHEM SYST ECOL 1990. [DOI: 10.1016/0305-1978(90)90123-w] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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31
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Holtsford TP, Ellstrand NC. Variation in outcrossing rate and population genetic structure of Clarkia tembloriensis (Onagraceae). TAG. THEORETICAL AND APPLIED GENETICS. THEORETISCHE UND ANGEWANDTE GENETIK 1989; 78:480-488. [PMID: 24225674 DOI: 10.1007/bf00290831] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/22/1989] [Accepted: 04/12/1989] [Indexed: 06/02/2023]
Abstract
Outcrossing rate estimates for eight accessions of Clarkia tembloriensis indicate that this annual plant species has a wide interpopulational range of outcrossing rate ([Formula: see text]). Populations' t estimates were significantly correlated with observed heterozygosity and mean number of alleles per locus. Estimated fixation indices, [Formula: see text], for most populations were very close to their expected values, Feq, for a given [Formula: see text] Nei's gene diversity statistics showed that the group of outcrossing populations have more total genetic variation and less differentiation among populations than does the group of selfing populations. These results indicate that the breeding system of C. tembloriensis has had a strong influence on the amount and distribution of genetic variation within and among its populations.
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Affiliation(s)
- T P Holtsford
- Department of Botany and Plant Sciences, University of California, 92521-0124, Riverside, CA, USA
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Parker JS, Wilby AS. Extreme chromosomal heterogeneity in a small-island population of Rumex acetosa. Heredity (Edinb) 1989; 62 ( Pt 1):133-40. [PMID: 2732084 DOI: 10.1038/hdy.1989.18] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Chromosome analyses of 227 mature plants of the dioecious species Rumex acetosa collected on the small island of Skomer have revealed an extremely high level of unique and polymorphic variation. The three common polymorphisms in this species--supernumerary segments on chromosomes 1 and 6, and B-chromosomes--are widespread on the island and the frequency of supernumerary segment 1 is higher than in all 37 mainland populations previously studied. Novel variants, unknown elsewhere, occur in each polymorphism. Fourteen different chromosome rearrangements are unique to the island, and eleven of these were detected in 67 plants from a small area which had undergone a population crash in 1977. It is argued that the genome of R. acetosa is undergoing rapid reorganisation on this small island which may be associated with an enforced shift towards inbreeding in this dioecious species.
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Affiliation(s)
- J S Parker
- School of Biological Sciences, Queen Mary College, London
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Population structure and pattern of geographic variation in Muscari comosum along its range of distribution. Genetica 1986. [DOI: 10.1007/bf00058673] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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