The Experts below are selected from a list of 276 Experts worldwide ranked by ideXlab platform
Josephine M Pemberton - One of the best experts on this subject based on the ideXlab platform.
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no evidence for warming climate theory of coat colour change in Soay sheep a comment on maloney et al
Biology Letters, 2010Co-Authors: Jacob Gratten, Josephine M Pemberton, Dario Beraldi, Allan F Mcrae, Peter M Visscher, Alastair J Wilson, Jon SlateAbstract:[Maloney et al . (2009)][1] propose that the decline in frequency of dark Soay sheep on St Kilda, first reported by [Gratten et al . (2008)][2], is due to climate change. As supporting evidence, they report that the proportion of dark sheep is negatively correlated with average minimum winter
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metazoan protozoan parasite co infections and host body weight in st kilda Soay sheep
Parasitology, 2008Co-Authors: B H Craig, L J Tempest, Jill G Pilkington, Josephine M PembertonAbstract:: For hundreds of years, the unmanaged Soay sheep population on St Kilda has survived despite enduring presumably deleterious co-infections of helminth, protozoan and arthropod parasites and intermittent periods of starvation. Important parasite taxa in young Soay sheep are strongyles (Trichostrongylus axei, Trichostrongylus vitrinus and Teladorsagia circumcincta), coccidia (11 Eimeria species) and keds (Melophagus ovinus) and in older animals, Teladorsagia circumcincta. In this research, associations between the intensity of different parasite taxa were investigated. Secondly, the intensities of different parasite taxa were tested for associations with variation in host weight, which is itself a determinant of over-winter survival in the host population. In lambs, the intensity of strongyle eggs was positively correlated with that of Nematodirus spp. eggs, while in yearlings and adults strongyle eggs and coccidia oocysts were positively correlated. In lambs and yearlings, of the parasite taxa tested, only strongyle eggs were significantly and negatively associated with host weight. However, in adult hosts, strongyles and coccidia were independently and negatively associated with host weight. These results are consistent with the idea that strongyles and coccidia are exerting independent selection on Soay sheep.
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quantitative trait loci qtl mapping of resistance to strongyles and coccidia in the free living Soay sheep ovis aries
International Journal for Parasitology, 2007Co-Authors: Dario Beraldi, Jill G Pilkington, Allan F Mcrae, Jacob Gratten, Jon Slate, Peter M Visscher, Josephine M PembertonAbstract:A genome-wide scan was performed to detect quantitative trait loci (QTL) for resistance to gastrointestinal parasites and ectoparasitic keds segregating in the free-living Soay sheep population on St. Kilda (UK). The mapping panel consisted of a single pedigree of 882 individuals of which 588 were genotyped. The Soay linkage map used for the scans comprised 251 markers covering the whole genome at average spacing of 15 cM. The traits here investigated were the strongyle faecal egg count (FEC), the coccidia faecal oocyst count (FOC) and a count of keds (Melophagus ovinus). QTL mapping was performed by means of variance component analysis so that the genetic parameters of the study traits were also estimated and compared with previous studies in Soay and domestic sheep. Strongyle FEC and coccidia FOC showed moderate heritability (h 2 = 0.26 and 0.22, respectively) in lambs but low heritability in adults (h 2 < 0.10). Ked count appeared to have very low h 2 in both lambs and adults. Genome scans were performed for the traits with moderate heritability and two genomic regions reached the level of suggestive linkage for coccidia FOC in lambs (logarithm of the odds = 2.68 and 2.21 on chromosomes 3 and X, respectively). We believe this is the first study to report a QTL search for parasite resistance in a freeliving animal population and therefore may represent a useful reference for similar studies aimed at understanding the genetics of hostparasite co-evolution in the wild.
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gastrointestinal nematode species burdens and host mortality in a feral sheep population
Parasitology, 2006Co-Authors: B H Craig, Jill G Pilkington, Josephine M PembertonAbstract:SUMMARY Every few years a large proportion of the feral sheep on Hirta, St Kilda die due to food shortage. The effects of malnutrition are exacerbated by gastrointestinal nematodes. As found in sheep flocks in mainland Britain, Teladorsagia circumcincta has long been considered the predominant and most pathogenic nematode species in all age classes of Soay sheep. Previous research indicated that intensity of this species showed a negative association with host age and comprised 75% of the entire gastrointestinal burden. Here we present new data that show Trichostrongylus axei and Trichostrongylus vitrinus to be the predominant worm pathogens in young Soay sheep. In the present study, Trichostrongylus spp. burdens declined with host age whereas T. circumcincta actually increased in burden over the first few age classes. Also, male hosts had significantly higher burdens of Trichostrongylus spp. than females, with this genus making up a higher proportion of the strongyle egg producing community in male hosts than female hosts. These new findings raise questions concerning our previous interpretation of the main nematode species contributing to strongyle egg count in the population, and the contrasting infection patterns of these nematode species in unmanaged St Kilda Soay sheep compared with domestic sheep in mainland Britain.
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modeling linkage disequilibrium in natural populations the example of the Soay sheep population of st kilda scotland
Genetics, 2005Co-Authors: Allan F Mcrae, Josephine M Pemberton, Peter M VisscherAbstract:The use of linkage disequilibrium to localize the genes underlying quantitative traits has received considerable attention in the livestock genetics community over the past few years. This has resulted in the investigation of linkage disequilibrium structures of several domestic livestock populations to assess their potential use in fine-mapping efforts. However, the linkage disequilibrium structure of free-living populations has been less well investigated. As the direct evaluation of linkage disequilibrium can be both time consuming and expensive the use of simulations that include as many aspects of population history as possible is advocated as an alternative. A simulation of the linkage disequilibrium structure of the Soay sheep population of St. Kilda, Scotland, is provided as an example. The simulated population showed significant decline of linkage disequilibrium with genetic distance and low levels of background linkage disequilibrium, indicating that the Soay sheep population is a viable resource for linkage disequilibrium fine mapping of quantitative trait loci.
Peter M Visscher - One of the best experts on this subject based on the ideXlab platform.
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no evidence for warming climate theory of coat colour change in Soay sheep a comment on maloney et al
Biology Letters, 2010Co-Authors: Jacob Gratten, Josephine M Pemberton, Dario Beraldi, Allan F Mcrae, Peter M Visscher, Alastair J Wilson, Jon SlateAbstract:[Maloney et al . (2009)][1] propose that the decline in frequency of dark Soay sheep on St Kilda, first reported by [Gratten et al . (2008)][2], is due to climate change. As supporting evidence, they report that the proportion of dark sheep is negatively correlated with average minimum winter
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quantitative trait loci qtl mapping of resistance to strongyles and coccidia in the free living Soay sheep ovis aries
International Journal for Parasitology, 2007Co-Authors: Dario Beraldi, Jill G Pilkington, Allan F Mcrae, Jacob Gratten, Jon Slate, Peter M Visscher, Josephine M PembertonAbstract:A genome-wide scan was performed to detect quantitative trait loci (QTL) for resistance to gastrointestinal parasites and ectoparasitic keds segregating in the free-living Soay sheep population on St. Kilda (UK). The mapping panel consisted of a single pedigree of 882 individuals of which 588 were genotyped. The Soay linkage map used for the scans comprised 251 markers covering the whole genome at average spacing of 15 cM. The traits here investigated were the strongyle faecal egg count (FEC), the coccidia faecal oocyst count (FOC) and a count of keds (Melophagus ovinus). QTL mapping was performed by means of variance component analysis so that the genetic parameters of the study traits were also estimated and compared with previous studies in Soay and domestic sheep. Strongyle FEC and coccidia FOC showed moderate heritability (h 2 = 0.26 and 0.22, respectively) in lambs but low heritability in adults (h 2 < 0.10). Ked count appeared to have very low h 2 in both lambs and adults. Genome scans were performed for the traits with moderate heritability and two genomic regions reached the level of suggestive linkage for coccidia FOC in lambs (logarithm of the odds = 2.68 and 2.21 on chromosomes 3 and X, respectively). We believe this is the first study to report a QTL search for parasite resistance in a freeliving animal population and therefore may represent a useful reference for similar studies aimed at understanding the genetics of hostparasite co-evolution in the wild.
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modeling linkage disequilibrium in natural populations the example of the Soay sheep population of st kilda scotland
Genetics, 2005Co-Authors: Allan F Mcrae, Josephine M Pemberton, Peter M VisscherAbstract:The use of linkage disequilibrium to localize the genes underlying quantitative traits has received considerable attention in the livestock genetics community over the past few years. This has resulted in the investigation of linkage disequilibrium structures of several domestic livestock populations to assess their potential use in fine-mapping efforts. However, the linkage disequilibrium structure of free-living populations has been less well investigated. As the direct evaluation of linkage disequilibrium can be both time consuming and expensive the use of simulations that include as many aspects of population history as possible is advocated as an alternative. A simulation of the linkage disequilibrium structure of the Soay sheep population of St. Kilda, Scotland, is provided as an example. The simulated population showed significant decline of linkage disequilibrium with genetic distance and low levels of background linkage disequilibrium, indicating that the Soay sheep population is a viable resource for linkage disequilibrium fine mapping of quantitative trait loci.
T H Cluttonbrock - One of the best experts on this subject based on the ideXlab platform.
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the maintenance of genetic polymorphism in small island populations large mammals in the hebrides
Philosophical Transactions of the Royal Society B, 1996Co-Authors: Josephine M Pemberton, Jon Slate, J A Smith, Tim Coulson, T C Marshall, Steve Paterson, S D Albon, T H CluttonbrockAbstract:Conventionally, small populations living on islands are expected to lose genetic variation by drift. Fluctuations in population size, combined with polygynous mating systems, are expected to contribute to the process by increasing sampling effects on genetic variation. However, in individually monitored populations of Red deer on Rum and Soay sheep on St. Kilda, which experience fluctuations in population size, two processes have been identified which mitigate loss of genetic variation. First, in a number of examples, population reductions are associated with selection. Selection may be in favour of heterozygotes, or, as we have documented in several cases, it may fluctuate in direction temporally. Second, in Soay sheep, in which mortality over population crashes is male-biased, ostensibly leading to low effective numbers of males, molecular studies show that there are systematic changes in the reproductive success of young males, and in variance in male success, that broaden genetic representation compared with expectation.
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state dependent life history evolution in Soay sheep dynamic modelling of reproductive scheduling
Philosophical Transactions of the Royal Society B, 1996Co-Authors: Paul Marrow, John M Mcnamara, Alasdair I Houston, Ian R Stevenson, T H CluttonbrockAbstract:Adaptive decisions concerning the scheduling of reproduction in an animal's lifetime, including age at maturity and clutch or litter size, should depend on an animal's body condition or state. In this state-dependent case, we are concerned with the optimization of sequences of actions and so dynamic optimization techniques are appropriate. Here we show how stochastic dynamic programming can be used to study the reproductive strategies and population dynamics of natural populations, assuming optimal decisions. As examples we describe models based upon field data from an island population of Soay sheep on St. Kilda. This population shows persistent instability, with cycles culminating in high mortality every three or four years. We explore different assumptions about the extent to which Soay ewes use information about the population cycle in making adaptive decisions. We compare the observed distributions of strategies and population dynamics with model predictions; the results indicate that Soay ewes make optimal reproductive decisions given that they have no information about the population cycle. This study represents the first use of a dynamic optimization life history model of realistic complexity in the study of a field population. The techniques we use are potentially applicable to many other populations, and we discuss their extension to other species and other life history questions.
Allan F Mcrae - One of the best experts on this subject based on the ideXlab platform.
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no evidence for warming climate theory of coat colour change in Soay sheep a comment on maloney et al
Biology Letters, 2010Co-Authors: Jacob Gratten, Josephine M Pemberton, Dario Beraldi, Allan F Mcrae, Peter M Visscher, Alastair J Wilson, Jon SlateAbstract:[Maloney et al . (2009)][1] propose that the decline in frequency of dark Soay sheep on St Kilda, first reported by [Gratten et al . (2008)][2], is due to climate change. As supporting evidence, they report that the proportion of dark sheep is negatively correlated with average minimum winter
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quantitative trait loci qtl mapping of resistance to strongyles and coccidia in the free living Soay sheep ovis aries
International Journal for Parasitology, 2007Co-Authors: Dario Beraldi, Jill G Pilkington, Allan F Mcrae, Jacob Gratten, Jon Slate, Peter M Visscher, Josephine M PembertonAbstract:A genome-wide scan was performed to detect quantitative trait loci (QTL) for resistance to gastrointestinal parasites and ectoparasitic keds segregating in the free-living Soay sheep population on St. Kilda (UK). The mapping panel consisted of a single pedigree of 882 individuals of which 588 were genotyped. The Soay linkage map used for the scans comprised 251 markers covering the whole genome at average spacing of 15 cM. The traits here investigated were the strongyle faecal egg count (FEC), the coccidia faecal oocyst count (FOC) and a count of keds (Melophagus ovinus). QTL mapping was performed by means of variance component analysis so that the genetic parameters of the study traits were also estimated and compared with previous studies in Soay and domestic sheep. Strongyle FEC and coccidia FOC showed moderate heritability (h 2 = 0.26 and 0.22, respectively) in lambs but low heritability in adults (h 2 < 0.10). Ked count appeared to have very low h 2 in both lambs and adults. Genome scans were performed for the traits with moderate heritability and two genomic regions reached the level of suggestive linkage for coccidia FOC in lambs (logarithm of the odds = 2.68 and 2.21 on chromosomes 3 and X, respectively). We believe this is the first study to report a QTL search for parasite resistance in a freeliving animal population and therefore may represent a useful reference for similar studies aimed at understanding the genetics of hostparasite co-evolution in the wild.
-
modeling linkage disequilibrium in natural populations the example of the Soay sheep population of st kilda scotland
Genetics, 2005Co-Authors: Allan F Mcrae, Josephine M Pemberton, Peter M VisscherAbstract:The use of linkage disequilibrium to localize the genes underlying quantitative traits has received considerable attention in the livestock genetics community over the past few years. This has resulted in the investigation of linkage disequilibrium structures of several domestic livestock populations to assess their potential use in fine-mapping efforts. However, the linkage disequilibrium structure of free-living populations has been less well investigated. As the direct evaluation of linkage disequilibrium can be both time consuming and expensive the use of simulations that include as many aspects of population history as possible is advocated as an alternative. A simulation of the linkage disequilibrium structure of the Soay sheep population of St. Kilda, Scotland, is provided as an example. The simulated population showed significant decline of linkage disequilibrium with genetic distance and low levels of background linkage disequilibrium, indicating that the Soay sheep population is a viable resource for linkage disequilibrium fine mapping of quantitative trait loci.
Jill G Pilkington - One of the best experts on this subject based on the ideXlab platform.
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metazoan protozoan parasite co infections and host body weight in st kilda Soay sheep
Parasitology, 2008Co-Authors: B H Craig, L J Tempest, Jill G Pilkington, Josephine M PembertonAbstract:: For hundreds of years, the unmanaged Soay sheep population on St Kilda has survived despite enduring presumably deleterious co-infections of helminth, protozoan and arthropod parasites and intermittent periods of starvation. Important parasite taxa in young Soay sheep are strongyles (Trichostrongylus axei, Trichostrongylus vitrinus and Teladorsagia circumcincta), coccidia (11 Eimeria species) and keds (Melophagus ovinus) and in older animals, Teladorsagia circumcincta. In this research, associations between the intensity of different parasite taxa were investigated. Secondly, the intensities of different parasite taxa were tested for associations with variation in host weight, which is itself a determinant of over-winter survival in the host population. In lambs, the intensity of strongyle eggs was positively correlated with that of Nematodirus spp. eggs, while in yearlings and adults strongyle eggs and coccidia oocysts were positively correlated. In lambs and yearlings, of the parasite taxa tested, only strongyle eggs were significantly and negatively associated with host weight. However, in adult hosts, strongyles and coccidia were independently and negatively associated with host weight. These results are consistent with the idea that strongyles and coccidia are exerting independent selection on Soay sheep.
-
quantitative trait loci qtl mapping of resistance to strongyles and coccidia in the free living Soay sheep ovis aries
International Journal for Parasitology, 2007Co-Authors: Dario Beraldi, Jill G Pilkington, Allan F Mcrae, Jacob Gratten, Jon Slate, Peter M Visscher, Josephine M PembertonAbstract:A genome-wide scan was performed to detect quantitative trait loci (QTL) for resistance to gastrointestinal parasites and ectoparasitic keds segregating in the free-living Soay sheep population on St. Kilda (UK). The mapping panel consisted of a single pedigree of 882 individuals of which 588 were genotyped. The Soay linkage map used for the scans comprised 251 markers covering the whole genome at average spacing of 15 cM. The traits here investigated were the strongyle faecal egg count (FEC), the coccidia faecal oocyst count (FOC) and a count of keds (Melophagus ovinus). QTL mapping was performed by means of variance component analysis so that the genetic parameters of the study traits were also estimated and compared with previous studies in Soay and domestic sheep. Strongyle FEC and coccidia FOC showed moderate heritability (h 2 = 0.26 and 0.22, respectively) in lambs but low heritability in adults (h 2 < 0.10). Ked count appeared to have very low h 2 in both lambs and adults. Genome scans were performed for the traits with moderate heritability and two genomic regions reached the level of suggestive linkage for coccidia FOC in lambs (logarithm of the odds = 2.68 and 2.21 on chromosomes 3 and X, respectively). We believe this is the first study to report a QTL search for parasite resistance in a freeliving animal population and therefore may represent a useful reference for similar studies aimed at understanding the genetics of hostparasite co-evolution in the wild.
-
gastrointestinal nematode species burdens and host mortality in a feral sheep population
Parasitology, 2006Co-Authors: B H Craig, Jill G Pilkington, Josephine M PembertonAbstract:SUMMARY Every few years a large proportion of the feral sheep on Hirta, St Kilda die due to food shortage. The effects of malnutrition are exacerbated by gastrointestinal nematodes. As found in sheep flocks in mainland Britain, Teladorsagia circumcincta has long been considered the predominant and most pathogenic nematode species in all age classes of Soay sheep. Previous research indicated that intensity of this species showed a negative association with host age and comprised 75% of the entire gastrointestinal burden. Here we present new data that show Trichostrongylus axei and Trichostrongylus vitrinus to be the predominant worm pathogens in young Soay sheep. In the present study, Trichostrongylus spp. burdens declined with host age whereas T. circumcincta actually increased in burden over the first few age classes. Also, male hosts had significantly higher burdens of Trichostrongylus spp. than females, with this genus making up a higher proportion of the strongyle egg producing community in male hosts than female hosts. These new findings raise questions concerning our previous interpretation of the main nematode species contributing to strongyle egg count in the population, and the contrasting infection patterns of these nematode species in unmanaged St Kilda Soay sheep compared with domestic sheep in mainland Britain.
