ORCID Profile
0000-0002-0233-9708
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Publisher: Oxford University Press (OUP)
Date: 10-05-2019
DOI: 10.1093/AOB/MCZ059
Abstract: Many plants exhibit a mixed mating system. Published models suggest that this might be an evolutionarily stable rather than a transitional state despite the presence of inbreeding depression, but there is little empirical evidence. Through field experimentation, we studied the role of inbreeding depression in eliminating inbred progeny from the reproductive cohort of the forest tree Eucalyptus regnans, and demonstrate a stable mixed primary mating system over two successive generations. Two field experiments were conducted using seed from natural populations. We sowed open-pollinated seeds to simulate a natural regeneration event and determined isozyme genotypes of dominant and suppressed in iduals over 10 years. We also planted a mixture of open-pollinated, outcross and selfed families with common maternal parentage monitored survival of cross types over 29 years and determined the percentage of outcrosses in open-pollinated seed from a s le of reproductively mature trees using microsatellite analysis. Both experiments demonstrated progressive competitive elimination of inbred plants. By 29 years, the reproductive cohort in the planted experiment consisted only of outcrosses which produced seed which averaged 66 % outcrosses, similar to the estimate for the parental natural population (74 %). Selective elimination of inbred genotypes during the intense intra-specific competition characteristic of the pre-reproductive phase of the life cycle of E. regnans results in a fully outcrossed reproductive population, in which self-fertility is comparable with that of its parental generation. The mixed mating system may be viewed as an unavoidable consequence of the species’ reproductive ecology, which includes the demonstrated effects of inbreeding depression, rather than a strategy which is actively favoured by natural selection.
Publisher: CSIRO Publishing
Date: 2003
DOI: 10.1071/SB01044
Abstract: Acacia tumida F.Muell ex. Benth. is a morphologically variable species from north-western Australia. Variants range from low, multi-stemmed shrubs to single-stemmed trees. Acacia tumida is cultivated for firewood, windbreaks and sand stabilisation. To examine patterns of genetic variation that could be utilised in domestication programs, 22 populations representing its natural distribution were surveyed by using allozymes. Estimates of genetic ersity (HE = 0.149) were within the range of other tropical, widespread woody plants, but varied widely among populations (HE = 0.064–0.203). There were strong clinal trends in ersity estimates A, P, HO, HE were correlated with longitude and declined from west to east. HE decreased as mean monthly maximum temperatures increased and allelic richness (A) increased with mean minimum monthly temperatures. There were also significant correlations between allele frequencies at certain loci and geographic and climatic parameters. Significant isolation-by-distance and relatively high levels of differentiation (θ = 0.176) were detected among populations. Populations of the narrow-phylloded form (Pilbara region) were the most genetically ergent, despite their geographic proximity to other populations. The low-shrub and tall-tree forms could not be distinguished by allozyme profiles. Slight genetic differences were detected between the non-pruinose and pruinose forms from within one population. Phylogenetic analysis supported morphological evidence of hybridisation between A. tumida and A. difficilis Maiden in their zone of overlap. The results are discussed in relation to the taxonomy and domestication of A. tumida.
Publisher: Oxford University Press (OUP)
Date: 1989
DOI: 10.2307/2409180
Publisher: Canadian Science Publishing
Date: 05-1988
DOI: 10.1139/X88-074
Abstract: Pinusradiata is restricted to three mainland coastal populations in California and two island populations off Baja California, Mexico. In this study each population was ided into two geographic stands based on natural disjunctions within populations. In addition to the ision mentioned above, each mainland population was also ided into a number of ecological stands based on ecological and environmental criteria. Genetic variation was measured by analysing 31 allozyme loci electrophoretically using germinated seed from 272 families across all stands and populations. Moderate levels of allozyme variation were found as shown by population averages for mean number of alleles per locus (1.79), percent polymorphic loci (46.4%, 0.99 criterion), and expected heterozygosity (0.098). In fact, the overall genetic ersity in P. radiata (H T = 0.117) is low compared with that of other conifers. In comparison with populations, the levels of allozyme variation in both ecological and geographic stands were slightly lower (means across ecological stands: A = 1.56, P = 39.3%, and H e = 0.095). Of the total genetic ersity in P. radiata, 16.2% could be apportioned between populations, a high proportion for a conifer. In contrast, only 2.0 and 1.3% of the genetic ersity on average within mainland populations was between ecological and geographic stands, respectively. These results indicate a low level of genetic differentiation within populations, at least based on the ecological or geographic criteria used in this study. The implications and usefulness of these findings for the development of insitu conservation strategies are discussed.
Publisher: Springer Science and Business Media LLC
Date: 1990
DOI: 10.1007/BF00937801
Publisher: Springer Science and Business Media LLC
Date: 05-1996
DOI: 10.1007/BF00226088
Publisher: CSIRO Publishing
Date: 1989
DOI: 10.1071/BT9890169
Abstract: Twenty populations of Casuarina cunninghamiana Miq. covering its large geographic range were used in a study of genetic ersity. Genetic variation was measured by analysing 19 allozyme loci using 50 seedlings from each of the populations. The overall genetic ersity (HT = 0.287) in C. cunninghamiana is high compared to many other plant species. A significant fraction (26.4%) of the total genetic ersity could be apportioned among populations. This genetic differentiation between populations was not random. Populations in the eastern part of the range had high correlation (r = 0.91) of genetic ersity with latitude and this involved changes in allelic frequencies at several loci. At the population level, there was a significant positive correlation between genetic ersity and 1 year height growth. The western population from King River in the Northern Territory was very distinct genetically from all the other populations and this supported previous suggestions that the northwest part of the range is occupied by a different race of the species.
Publisher: Springer Science and Business Media LLC
Date: 30-07-2009
Publisher: CSIRO Publishing
Date: 1993
DOI: 10.1071/BT9930355
Abstract: A study of allozyme variation in Acacia melanoxylon R. Br. in 27 populations from across the geographic range of the species indicated high genetic ersity compared to other Australian trees and plants generally. Clines of increasing genetic variability with increasing latitude were found for four measures of genetic ersity. Most of the genetic ersity is found within populations but there was an unusually high level of the variation between populations (37.7%). A distinct genetic separation between the northern and southern populations was located approximately at the Hunter River region, where there is also a disjunction in the distribution of the species. The Nei (1978) genetic distance between these populations within this species is larger than observed between some plant species. Clearly the species has evolved separately in the two regions for a considerable time.
Publisher: CSIRO Publishing
Date: 2003
DOI: 10.1071/BT02106
Abstract: Eucalyptus cladocalyx F.Muell. is a widely cultivated tree in dryland southern Australia. It is grown for firewood, timber production and as a windbreak and ornamental species. Natural populations of E. cladocalyx are endemic to South Australia where they occur in three disjunct regions. This study assessed the mating system and patterns of genetic ersity in natural populations of E. cladocalyx by using allozymes. Populations had relatively low levels of genetic ersity (HE = 0.148) and high levels of genetic ergence (θ = 0.26) among populations, similar to other regionally distributed eucalypts. Populations clustered into three distinct groups, which corresponded to its disjunct natural distribution. Genetic differentiation among populations and between regions was highly significant. Relatively high levels of inbreeding (tm = 0.57) were detected in natural populations of E.�cladocalyx. Outcrossing rates were highly variable among families, ranging from 0 to 100%. One-third of families from four populations had outcrossing rates that were not significantly different from zero. The origins of three commercially significant, cultivated stands of E. cladocalyx were also assessed. Allozyme profiles of cultivated stands from Wail and Lismore in western Victoria suggested origins in the Wirrabara region of the southern Flinders Ranges, while a cultivated stand of E. cladocalyx var. nana Hort. ex Yates had an allozyme profile consistent with origins in the Eyre Peninsula region. The results are discussed in relation to the species' morphological variation, biogeography and the implications for its domestication and conservation.
Publisher: Springer Science and Business Media LLC
Date: 10-11-2010
Publisher: CSIRO Publishing
Date: 1996
DOI: 10.1071/BT9960157
Abstract: Isozyme variation in two closely related red mahoganies (Eucalyptus pellita F. Muell. and E. scias L.A.S.Johnson and K.D.Hill) was examined in 17 populations of E. pellita from Australia, Papua New Guinea and Indonesia and 8 of E. scias (including all 3 subspecies) from south-eastern coastal Australia. Measures of genetic ersity and relationships between species and subspecies were based on 15 variable loci. Both E. pellita and E. scias had moderately high levels of genetic ersity, comparable to other similarly distributed species. Most genetic ersity within each species was found within populations (80% in E. pellita and 83% in E. scias). There were substantial allelic differences between the species at several loci the populations clustered into groups corresponding to the two species. Yet genetic differentiation between the two species was relatively low, and the three subspecies of E. scias were not well separated. Outcrossing rates in E. pellita are variable, with low rates ( %) measured in populations from Irian Jaya and Cape York Peninsula, and 73% in a population from northeast Queensland.
Publisher: CSIRO Publishing
Date: 2000
DOI: 10.1071/BT98043
Abstract: Twenty-three isozyme loci were used to examine genetic ersity within and between 19 natural populations of Acacia mearnsii De Wild. selected to represent its entire geographic range. Acacia mearnsii was found to have moderate genetic ersity (species level gene ersity HT = 0.201) with the majority (89.2%) of variation occurring within populations. All measures of population ersity were higher in the northern (New South Wales) than the southern (Victoria, South Australia, Tasmania) populations. There was some evidence of differentiation between populations but no strong clustering at a regional level.
Publisher: Springer Science and Business Media LLC
Date: 22-05-2010
Publisher: CSIRO Publishing
Date: 1988
DOI: 10.1071/BT9880355
Abstract: Isozyme characteristics of 280 isolates from populations of Phytophthora cinnamomi in native veg- etation in six locations in south-eastern Australia were examined at 19 enzyme loci. No new enzyme genotypic arrays were identified as compared with earlier s lings. This work indicates that the low variability for P. cinnamomi in Australia obtained in earlier work, from separate isolates in a wide range of locations, is paralleled in detailed population s les in south-eastern Australia. At one location, A1 and A2 mating types coexisted in soil s les. The lack of recombinants in these population s les suggests an absence of sexual reproduction in the field.
Publisher: CSIRO Publishing
Date: 2000
DOI: 10.1071/SB00005
Abstract: The distribution of genetic variation within and among species inCorymbia section‘Politaria’ was examined using allozymes.This section consists of four species,Corymbia citriodora (Hook.) K.D.Hill & L.A.S.Johnson, C. maculata (Hook.) K.D.Hill & L.A.S.Johnson, C. henryi (Blake) K.D.Hill & L.A.S.Johnson and C. variegata (F.Muell.) K.D.Hill & L.A.S.Johnson, which are of commercial interest for plantation and farmforestry. Thirty populations representing the species’ range-widedistributions were studied, extending from upland tropical regions of northQueensland, south to eastern Victoria. Despite relatively low allozyme ergence between species, there was a relationship between geographicdistribution patterns of populations and allozyme variation. The section wasshown to comprise very closely related species with only 15% of thetotal genetic ersity attributed to differences between species. Twodistinct genetic alliances were evident:C. maculata–C. henryi andC. citriodora–C. variegata.Corymbia citriodora andC. variegata, however, could not be distinguished bytheir allozyme profiles. The lack of genetic differentiation between thesetaxa suggests that they represent one species composed of two chemical races.Corymbia maculata and C. henryiwere shown to be closely allied but genetically distinct.Corymbia henryi had the highest genetic ersity in thegroup and lowest differentiation among populations, whileC. maculata had the lowest ersity but the highestgenetic differentiation among populations. There was evidence ofisolation-by-distance among populations ofC. citriodora, C. maculata andC. variegata but not in C. henryi,which has a smaller geographic range. The inclusion in the study ofC. torelliana (F.Muell.) K.D.Hill & L.A.S.Johnson asan outgroup accentuated the small genetic differences between species in thegroup. The patterns of genetic ersity are discussed in relation to thespecies’ taxonomic relationships, breeding systems and utilisation.
Publisher: Canadian Science Publishing
Date: 10-2002
DOI: 10.1139/G02-064
Abstract: Fifty microsatellite markers were developed and characterized in Pinus radiata, and from among these, a subset of 10 easily scored and highly polymorphic markers was selected for use in fingerprinting, quality control, and breeding applications. The markers were characterized based on reliable and reproducible lification, observed and expected heterozygosities, number of alleles, a low frequency of null alleles, and a lack of close linkage with other selected markers. Allele numbers and frequencies were estimated using 24 first-generation breeding clones from Australia and New Zealand. Observed heterozygosities for the selected markers were all greater than 0.67, and there was an average of 10.5 alleles/locus. The occurrence of null alleles was checked with megagametophytes from mother trees for loci that appeared to be homozygous. The 10 markers are not closely linked (r 0.20 and LOD 3) to each other. The selected microsatellites fall into three discrete size classes, and with appropriate selection of fluorescent dyes for 5' end labeling, can be multiplexed with up to 6 markers/s le on an ABI PRISM 310 or similar instrument.Key words: pine microsatellites, multiplexing, null alleles.
Publisher: Wiley
Date: 23-09-2006
DOI: 10.1111/J.1420-9101.2005.00982.X
Abstract: Most conifer species occur in large continuous populations, but radiata pine, Pinus radiata, occurs only in five disjunctive natural populations in California and Mexico. The Mexican island populations were presumably colonized from the mainland millions of years ago. According to Axelrod (1981), the mainland populations are relicts of an earlier much wider distribution, reduced some 8,000 years ago, whereas according to Millar (1997, 2000), the patchy metapopulation-like structure is typical of the long-term population demography of the species. We used 19 highly polymorphic microsatellite loci to describe population structure and to search for signs of the dynamics of population demography over space and time. Frequencies of null alleles at microsatellite loci were estimated using an approach based on the probability of identity by descent. Microsatellite genetic ersities were high in all populations [expected heterozygosity (H(e)) = 0.68-0.77], but the island populations had significantly lower estimates. Variation between loci in genetic differentiation (F(ST)) was high, but no locus deviated statistically significantly from the rest at an experiment wide level of 0.05. Thus, all loci were included in subsequent analysis. The average differentiation was measured as F(ST) = 0.14 (SD 0.012), comparable with earlier allozyme results. The island populations were more erged from the other populations and from an inferred common ancestral gene pool than the mainland ones. All populations showed a deficiency of expected heterozygosity given the number of alleles, the mainland populations more so than the island ones. The results thus do not support a recent important contraction in the mainland range of radiata pine.
Publisher: Springer Science and Business Media LLC
Date: 1992
DOI: 10.1007/BF00940804
Publisher: Springer Science and Business Media LLC
Date: 02-1987
DOI: 10.1007/BF00289203
Publisher: Springer Science and Business Media LLC
Date: 29-12-2012
Publisher: CSIRO Publishing
Date: 1992
DOI: 10.1071/BT9920365
Abstract: Melaleuca alternifolia (Maiden & Betche) Cheel is harvested from natural stands and plantations for production of Australian tea-tree oil. Genetic variation was examined and outcrossing rates estimated to provide baseline information for breeding and selection programs. The overall genetic ersity (HT = 0.186) is comparable to other regionally distributed Australian tree species. There was a general trend for more isolated populations to have less genetic variation than populations from the centre of the species distribution. The level of differentiation among populations was low (12%), associated with a high outcrossing rate (93%) and high levels of gene flow. Geographic separation of Queensland and New South Wales populations corresponds with genetic distance measures.
Publisher: JSTOR
Date: 09-1989
DOI: 10.2307/2388652
Publisher: CSIRO Publishing
Date: 1990
DOI: 10.1071/BT9900079
Abstract: Eucalyptus paliformis is restricted to a small, isolated plateau on the eastern escarpment of south-eastern Australia. Eucalyptus parvifolia populations are scattered discontinuously in a narrow band of nearby grazing land that has been substantially cleared over the last 100 years. Allozyme ersity was examined in six of the seven known populations of E. paliformis and in all the eight known populations of E. parvifolia to help assess the potential for the survival of these species under current conditions of management. Levels of genetic ersity in E. paliformis are comparable to levels in other eucalypts of restricted distribution and, in conjunction with its large population sizes, are likely to be adequate for its survival. The greatest threat to E. paliformis is its localised distribution, which renders it susceptible to extinction by disturbance. By contrast, the levels and distribution of ersity in E. parvifolia, and estimates of migration between populations, suggest that the high variability measured in this species may be a consequence of a once more continuous distribution. The recent dissection of its range through clearing is likely to lead to a decline in levels of genetic ersity in E. parvifolia, which, when combined with destruction of the habitat where it can best outcompete other eucalypts, suggests its survival is threatened.
Publisher: CSIRO Publishing
Date: 1997
DOI: 10.1071/BT96073
Abstract: Genetic variation in 23 natural populations of Grevillea robusta A.Cunn. from across the natural range of the species was examined using 20 isozyme loci assayed in young seedlings. Mean expected heterozygosity per population, He , varied from 0.080 to 0.131 with an average of 0.105. The genetic ersity of in idual populations did not appear to be related to their ecological characteristics (araucarian vine forest or riverine habitat types) or their geographic locations. A genetic distance analysis indicated a significant separation of the populations into two regional groups, eight from the northern part of the natural range and the remaining 15 from central and southern areas. Between-population differences accounted for 17.9% of the total genetic variation, one-third of which was attributable to the difference between the two regional groups. Most alleles at the 20 loci occurred across most or all of the geographic range. This, and the low level of genetic differentiation between populations, suggest that genetic exchange between populations has been maintained, despite the pattern of natural distribution of the species in small, separated populations.
Publisher: CSIRO Publishing
Date: 2003
DOI: 10.1071/SB00005_CO
Abstract: The distribution of genetic variation within and among species inCorymbia section‘Politaria’ was examined using allozymes.This section consists of four species,Corymbia citriodora (Hook.) K.D.Hill & L.A.S.Johnson, C. maculata (Hook.) K.D.Hill & L.A.S.Johnson, C. henryi (Blake) K.D.Hill & L.A.S.Johnson and C. variegata (F.Muell.) K.D.Hill & L.A.S.Johnson, which are of commercial interest for plantation and farmforestry. Thirty populations representing the species’ range-widedistributions were studied, extending from upland tropical regions of northQueensland, south to eastern Victoria. Despite relatively low allozyme ergence between species, there was a relationship between geographicdistribution patterns of populations and allozyme variation. The section wasshown to comprise very closely related species with only 15% of thetotal genetic ersity attributed to differences between species. Twodistinct genetic alliances were evident:C. maculata–C. henryi andC. citriodora–C. variegata.Corymbia citriodora andC. variegata, however, could not be distinguished bytheir allozyme profiles. The lack of genetic differentiation between thesetaxa suggests that they represent one species composed of two chemical races.Corymbia maculata and C. henryiwere shown to be closely allied but genetically distinct.Corymbia henryi had the highest genetic ersity in thegroup and lowest differentiation among populations, whileC. maculata had the lowest ersity but the highestgenetic differentiation among populations. There was evidence ofisolation-by-distance among populations ofC. citriodora, C. maculata andC. variegata but not in C. henryi,which has a smaller geographic range. The inclusion in the study ofC. torelliana (F.Muell.) K.D.Hill & L.A.S.Johnson asan outgroup accentuated the small genetic differences between species in thegroup. The patterns of genetic ersity are discussed in relation to thespecies’ taxonomic relationships, breeding systems and utilisation.
No related grants have been discovered for John Bell.