Stuart Barker - Academia.edu (original) (raw)
Papers by Stuart Barker
A major goal of evolutionary genetics is to provide explanations for the maintenance of genetic v... more A major goal of evolutionary genetics is to provide explanations for the maintenance of genetic variation within populations. Among numerous possibilities that have been considered, substantial attention has been devoted to effects of heterogeneous environments (Hedrick, 1986), the basic premise being that selection pressures will then be variable in space and/or in time, and that such variable selection may play a significant role in maintaining polymorphism. Nevo (1988, and references therein) argues that there is sufficient evidence from natural populations to implicate environmental heterogeneity as a significant factor in maintaining polymorphisms. Nevertheless, he does point out that it is not at all clear what proportion of polymorphic loci are maintained by environmental heterogeneity or by other mechanisms, and emphasises the need for critical experimentation to substantiate causal ecological-genetic relationships.
PLOS ONE, 2017
Genetic variation for resistance to heat stress has been found for a number of life-history compo... more Genetic variation for resistance to heat stress has been found for a number of life-history components in Drosophila species. For male and female fertility (or sterility), stress resistance of the parents is confounded with stress resistance of the haploid gametes. Many genes are known to influence male fertility in Drosophila melanogaster. Some may carry temperature sensitive alleles that reduce fertility through effects on mature sperm when exposed to heat stress. In this study, sperm from each of 320 males were either not heat shocked (control) or exposed to a heat shock (36.9˚C for 2 hours) either in the male testes or in the female reproductive tract. We did not detect any temperature sensitive sterility alleles. These results are relevant in relation to haploid gene expression and the findings of considerable amounts of mRNA in mature sperm, potentially important for sperm function and fertilization.
Molecular Biology and Evolution, 1993
Ecological and Evolutionary Genetics of Drosophila, 1990
Variation in proteins and nucleic acid sequences can be used in a variety of ways to study evolut... more Variation in proteins and nucleic acid sequences can be used in a variety of ways to study evolutionary patterns and processes. In recent years, DNA sequences have largely superseded allozyme frequencies as the raw data for Drosophila molecular evolutionary biologists. DNA sequencing has been applied to three areas of investigation: the estimation of population genetic parameters, phylogenetic reconstructions, including estimates of rates of change in specific gene products, and the molecular basis of structural and regulatory gene mutations.
Ecological and Evolutionary Genetics of Drosophila, 1990
International journal of systematic bacteriology, 1998
Five new yeast species, Wickerhamiella australiensis, Wickerhamiella cacticola, Wickerhamiella oc... more Five new yeast species, Wickerhamiella australiensis, Wickerhamiella cacticola, Wickerhamiella occidentalis, Candida drosophilae and Candida lipophila, are described to accommodate isolates recovered from flowers and floricolous insects of Australian Hibiscus trees, cosmopolitan morning glories (Ipomoea spp.) and Brazilian cereoid cacti. The new Wickerhamiella species are heterothallic, occur in the haploid condition and are clearly separated reproductively from one another. Although they exhibit little physiological variation, they are easily delineated from Wickerhamiella domercqiae, the only species known previously, by their resistance to cycloheximide and the production of strong extracellular lipases. C. drosophilae and C. lipophila share the latter property, but unlike the Wickerhamiella species, they fail to utilize nitrate as sole nitrogen source. PFGE indicates that these yeasts have an unusually low number of chromosomes. The large-subunit rDNA (D1/D2) sequences demonstra...
Animal Production, 1966
1. An analysis has been made of the relationship between first lactation progeny test for milk yi... more 1. An analysis has been made of the relationship between first lactation progeny test for milk yield and the survival of a bull's daughters to different ages using data for British Friesian, Ayrshire and Holstein-Friesian cows. It was found that the relative effect on survival of differences between bulls in milk yield increased by about 10% per 100 gallons for each lactation survived, e.g. for two bulls differing in heifer progeny test by 100 gallons, that with the higher figure will have 10% more daughters surviving to have a second lactation, 20% more having a third and so on. The probable effect on total length of life is 1·2 lactations per 100 gallons.2. No evidence was found that selection on first lactation progeny test would reduce productive life in the dairy herd or even that it would increase the proportion culled for reasons other than yield in later lactations.3. The genetic effects of culling in the first lactation on yield were in agreement with those expected fro...
The American Naturalist, 1987
The spatial structure of 12 allele frequencies was examined for 57 populations of the cactophilic... more The spatial structure of 12 allele frequencies was examined for 57 populations of the cactophilic fly Drosophila buzzatii from eastern Australia. Techniques include spatial-autocorrelation analysis and the newly developed directional spatial autocorrelation. Although 11 allele frequencies differ among localities, only 6 show spatial structure along one dimension. Directional correlograms support clines or major geographic trends in different directions for 5 allele frequencies. Spatial correlograms were also computed for genetic distances. The overall results-genetic heterogeneity among localities, weak correlation between allele-frequency surfaces, moderate spatial structure, and moderate parallelism of correlograms-permit elimination of genetic drift, selection against a single environmental gradient, or the effects of a single migrational event, and they suggest that selection operates on different spatial scales ranging from a continental one to a strictly local one. These results are interpreted in terms of the known history and biology of these organisms in Australia and are compared with spatial analyses of allele frequencies in other organisms.
Records of the Australian Museum, 2001
Proceedings of the Royal Society B: Biological Sciences, 2008
The majority of experimental studies of the effects of population bottlenecks on fitness are perf... more The majority of experimental studies of the effects of population bottlenecks on fitness are performed under laboratory conditions, which do not account for the environmental complexity that populations face in nature. In this study, we test inbreeding depression in multiple replicates of inbred when compared with non-inbred lines ofDrosophila melanogasterunder different temperature conditions. Egg-to-adult viability, developmental time and sex ratio of emerging adults are studied under low, intermediate and high temperatures under laboratory as well as semi-natural conditions. The results show inbreeding depression for egg-to-adult viability. The level of inbreeding depression is highly dependent on test temperature and is observed only at low and high temperatures. Inbreeding did not affect the developmental time or the sex ratio of emerging adults. However, temperature affected the sex ratio with more females relative to males emerging at low temperatures, suggesting that selecti...
Oikos, 2007
ABSTRACT The effective population size (Ne), and the ratio between Ne and census population size ... more ABSTRACT The effective population size (Ne), and the ratio between Ne and census population size (N) are often used as measures of population viability. We show that using the harmonic mean of population sizes over time – a common proxy for Ne– has some important evolutionary consequences and implications for conservation management. This stems from the fact that there is no unambiguous relationship between the arithmetic and harmonic means for populations fluctuating in size. As long as the variance of population size increases moderately with increasing arithmetic mean population size, the harmonic mean also increases. However, if the variance of population size increases more rapidly, which existing data often suggest, then the harmonic mean may actually decrease with increasing arithmetic mean. Thus maximizing N may not maximize Ne, but could instead lower the adaptive potential and hence limit the evolutionary response to environmental change. Large census size has the clear advantage of lowering demographic stochasticity, and hence extinction risk, and under certain conditions large census size also minimizes the loss of genetic variation. Consequently, maximising census size has served as a useful dogma in ecology, genetics and conservation. Nonetheless, due to the intricate relationships among Ne, population viability and the properties of population fluctuations, we suggest that this dogma should be taken only as a rule of thumb.
Molecular Ecology, 2011
... (2002). Of the 10 loci, four are pure dinucleotide repeats and the other six are interrupted ... more ... (2002). Of the 10 loci, four are pure dinucleotide repeats and the other six are interrupted pure or compound. Based on the estimate of Schug et al. (1998) of a dinu-cleotide mutation rate of 9.3 · 10 )6 in D. melanogaster and the Zhu et al. ...
Journal of Evolutionary Biology, 2004
Prospects for estimation of parameters of models of sperm competition from field data have improv... more Prospects for estimation of parameters of models of sperm competition from field data have improved recently with the development of methods that employ multilocus genotype data from brood-structured samples. Sperm competition in Drosophila buzzatii is of special interest because it is possible to directly observe the breeding behaviour of this species in its natural habitat of rotting cactus. Previous laboratory experiments showed that this species exhibits an unusual pattern of frequent remating and sperm partitioning. This paper reports the first attempt to estimate the frequency of female remating and sperm competition in natural populations of D. buzzatii. For the Australian population studied, the mean remating frequency was lower (alpha = 2.12-2.20) than previously estimated in laboratory experiments with the same population, whereas mean sperm displacement (beta = 0.69-0.71) fell within the limits of previous laboratory results. The evolution of the D. buzzatii mating system is discussed.
Journal of Evolutionary Biology, 1993
Drosophila uldrichi and D. huzzatii are cactophilic species that colonised Australia about 55560 ... more Drosophila uldrichi and D. huzzatii are cactophilic species that colonised Australia about 55560 years ago. They are sympatric only in Australia. Thus they may be in the process of adapting to new environments and to each other, and diversifying among local, possibly isolated, populations. Larval competitive effects for three
Journal of Evolutionary Biology, 1995
ABSTRACT
A major goal of evolutionary genetics is to provide explanations for the maintenance of genetic v... more A major goal of evolutionary genetics is to provide explanations for the maintenance of genetic variation within populations. Among numerous possibilities that have been considered, substantial attention has been devoted to effects of heterogeneous environments (Hedrick, 1986), the basic premise being that selection pressures will then be variable in space and/or in time, and that such variable selection may play a significant role in maintaining polymorphism. Nevo (1988, and references therein) argues that there is sufficient evidence from natural populations to implicate environmental heterogeneity as a significant factor in maintaining polymorphisms. Nevertheless, he does point out that it is not at all clear what proportion of polymorphic loci are maintained by environmental heterogeneity or by other mechanisms, and emphasises the need for critical experimentation to substantiate causal ecological-genetic relationships.
PLOS ONE, 2017
Genetic variation for resistance to heat stress has been found for a number of life-history compo... more Genetic variation for resistance to heat stress has been found for a number of life-history components in Drosophila species. For male and female fertility (or sterility), stress resistance of the parents is confounded with stress resistance of the haploid gametes. Many genes are known to influence male fertility in Drosophila melanogaster. Some may carry temperature sensitive alleles that reduce fertility through effects on mature sperm when exposed to heat stress. In this study, sperm from each of 320 males were either not heat shocked (control) or exposed to a heat shock (36.9˚C for 2 hours) either in the male testes or in the female reproductive tract. We did not detect any temperature sensitive sterility alleles. These results are relevant in relation to haploid gene expression and the findings of considerable amounts of mRNA in mature sperm, potentially important for sperm function and fertilization.
Molecular Biology and Evolution, 1993
Ecological and Evolutionary Genetics of Drosophila, 1990
Variation in proteins and nucleic acid sequences can be used in a variety of ways to study evolut... more Variation in proteins and nucleic acid sequences can be used in a variety of ways to study evolutionary patterns and processes. In recent years, DNA sequences have largely superseded allozyme frequencies as the raw data for Drosophila molecular evolutionary biologists. DNA sequencing has been applied to three areas of investigation: the estimation of population genetic parameters, phylogenetic reconstructions, including estimates of rates of change in specific gene products, and the molecular basis of structural and regulatory gene mutations.
Ecological and Evolutionary Genetics of Drosophila, 1990
International journal of systematic bacteriology, 1998
Five new yeast species, Wickerhamiella australiensis, Wickerhamiella cacticola, Wickerhamiella oc... more Five new yeast species, Wickerhamiella australiensis, Wickerhamiella cacticola, Wickerhamiella occidentalis, Candida drosophilae and Candida lipophila, are described to accommodate isolates recovered from flowers and floricolous insects of Australian Hibiscus trees, cosmopolitan morning glories (Ipomoea spp.) and Brazilian cereoid cacti. The new Wickerhamiella species are heterothallic, occur in the haploid condition and are clearly separated reproductively from one another. Although they exhibit little physiological variation, they are easily delineated from Wickerhamiella domercqiae, the only species known previously, by their resistance to cycloheximide and the production of strong extracellular lipases. C. drosophilae and C. lipophila share the latter property, but unlike the Wickerhamiella species, they fail to utilize nitrate as sole nitrogen source. PFGE indicates that these yeasts have an unusually low number of chromosomes. The large-subunit rDNA (D1/D2) sequences demonstra...
Animal Production, 1966
1. An analysis has been made of the relationship between first lactation progeny test for milk yi... more 1. An analysis has been made of the relationship between first lactation progeny test for milk yield and the survival of a bull's daughters to different ages using data for British Friesian, Ayrshire and Holstein-Friesian cows. It was found that the relative effect on survival of differences between bulls in milk yield increased by about 10% per 100 gallons for each lactation survived, e.g. for two bulls differing in heifer progeny test by 100 gallons, that with the higher figure will have 10% more daughters surviving to have a second lactation, 20% more having a third and so on. The probable effect on total length of life is 1·2 lactations per 100 gallons.2. No evidence was found that selection on first lactation progeny test would reduce productive life in the dairy herd or even that it would increase the proportion culled for reasons other than yield in later lactations.3. The genetic effects of culling in the first lactation on yield were in agreement with those expected fro...
The American Naturalist, 1987
The spatial structure of 12 allele frequencies was examined for 57 populations of the cactophilic... more The spatial structure of 12 allele frequencies was examined for 57 populations of the cactophilic fly Drosophila buzzatii from eastern Australia. Techniques include spatial-autocorrelation analysis and the newly developed directional spatial autocorrelation. Although 11 allele frequencies differ among localities, only 6 show spatial structure along one dimension. Directional correlograms support clines or major geographic trends in different directions for 5 allele frequencies. Spatial correlograms were also computed for genetic distances. The overall results-genetic heterogeneity among localities, weak correlation between allele-frequency surfaces, moderate spatial structure, and moderate parallelism of correlograms-permit elimination of genetic drift, selection against a single environmental gradient, or the effects of a single migrational event, and they suggest that selection operates on different spatial scales ranging from a continental one to a strictly local one. These results are interpreted in terms of the known history and biology of these organisms in Australia and are compared with spatial analyses of allele frequencies in other organisms.
Records of the Australian Museum, 2001
Proceedings of the Royal Society B: Biological Sciences, 2008
The majority of experimental studies of the effects of population bottlenecks on fitness are perf... more The majority of experimental studies of the effects of population bottlenecks on fitness are performed under laboratory conditions, which do not account for the environmental complexity that populations face in nature. In this study, we test inbreeding depression in multiple replicates of inbred when compared with non-inbred lines ofDrosophila melanogasterunder different temperature conditions. Egg-to-adult viability, developmental time and sex ratio of emerging adults are studied under low, intermediate and high temperatures under laboratory as well as semi-natural conditions. The results show inbreeding depression for egg-to-adult viability. The level of inbreeding depression is highly dependent on test temperature and is observed only at low and high temperatures. Inbreeding did not affect the developmental time or the sex ratio of emerging adults. However, temperature affected the sex ratio with more females relative to males emerging at low temperatures, suggesting that selecti...
Oikos, 2007
ABSTRACT The effective population size (Ne), and the ratio between Ne and census population size ... more ABSTRACT The effective population size (Ne), and the ratio between Ne and census population size (N) are often used as measures of population viability. We show that using the harmonic mean of population sizes over time – a common proxy for Ne– has some important evolutionary consequences and implications for conservation management. This stems from the fact that there is no unambiguous relationship between the arithmetic and harmonic means for populations fluctuating in size. As long as the variance of population size increases moderately with increasing arithmetic mean population size, the harmonic mean also increases. However, if the variance of population size increases more rapidly, which existing data often suggest, then the harmonic mean may actually decrease with increasing arithmetic mean. Thus maximizing N may not maximize Ne, but could instead lower the adaptive potential and hence limit the evolutionary response to environmental change. Large census size has the clear advantage of lowering demographic stochasticity, and hence extinction risk, and under certain conditions large census size also minimizes the loss of genetic variation. Consequently, maximising census size has served as a useful dogma in ecology, genetics and conservation. Nonetheless, due to the intricate relationships among Ne, population viability and the properties of population fluctuations, we suggest that this dogma should be taken only as a rule of thumb.
Molecular Ecology, 2011
... (2002). Of the 10 loci, four are pure dinucleotide repeats and the other six are interrupted ... more ... (2002). Of the 10 loci, four are pure dinucleotide repeats and the other six are interrupted pure or compound. Based on the estimate of Schug et al. (1998) of a dinu-cleotide mutation rate of 9.3 · 10 )6 in D. melanogaster and the Zhu et al. ...
Journal of Evolutionary Biology, 2004
Prospects for estimation of parameters of models of sperm competition from field data have improv... more Prospects for estimation of parameters of models of sperm competition from field data have improved recently with the development of methods that employ multilocus genotype data from brood-structured samples. Sperm competition in Drosophila buzzatii is of special interest because it is possible to directly observe the breeding behaviour of this species in its natural habitat of rotting cactus. Previous laboratory experiments showed that this species exhibits an unusual pattern of frequent remating and sperm partitioning. This paper reports the first attempt to estimate the frequency of female remating and sperm competition in natural populations of D. buzzatii. For the Australian population studied, the mean remating frequency was lower (alpha = 2.12-2.20) than previously estimated in laboratory experiments with the same population, whereas mean sperm displacement (beta = 0.69-0.71) fell within the limits of previous laboratory results. The evolution of the D. buzzatii mating system is discussed.
Journal of Evolutionary Biology, 1993
Drosophila uldrichi and D. huzzatii are cactophilic species that colonised Australia about 55560 ... more Drosophila uldrichi and D. huzzatii are cactophilic species that colonised Australia about 55560 years ago. They are sympatric only in Australia. Thus they may be in the process of adapting to new environments and to each other, and diversifying among local, possibly isolated, populations. Larval competitive effects for three
Journal of Evolutionary Biology, 1995
ABSTRACT