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Lowe WH, Addis BR, Cochrane MM. Outbreeding reduces survival during metamorphosis in a headwater stream salamander. Mol Ecol 2024; 33:e17375. [PMID: 38699973 DOI: 10.1111/mec.17375] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2023] [Revised: 02/22/2024] [Accepted: 03/01/2024] [Indexed: 05/05/2024]
Abstract
Assessing direct fitness effects of individual genetic diversity is challenging due to the intensive and long-term data needed to quantify survival and reproduction in the wild. But resolving these effects is necessary to determine how inbreeding and outbreeding influence eco-evolutionary processes. We used 8 years of capture-recapture data and single nucleotide polymorphism genotypes for 1906 individuals to test for effects of individual heterozygosity on stage-specific survival probabilities in the salamander Gyrinophilus porphyriticus. The life cycle of G. porphyriticus includes an aquatic larval stage followed by metamorphosis into a semi-aquatic adult stage. In our study populations, the larval stage lasts 6-10 years, metamorphosis takes several months, and lifespan can reach 20 years. Previous studies showed that metamorphosis is a sensitive life stage, leading us to predict that fitness effects of individual heterozygosity would occur during metamorphosis. Consistent with this prediction, monthly probability of survival during metamorphosis declined with multi-locus heterozygosity (MLH), from 0.38 at the lowest MLH (0.10) to 0.06 at the highest MLH (0.38), a reduction of 84%. Body condition of larvae also declined significantly with increasing MLH. These relationships were consistent in the three study streams. With evidence of localised inbreeding within streams, these results suggest that outbreeding disrupts adaptations in pre-metamorphic and metamorphic individuals to environmental gradients along streams, adding to evidence that headwater streams are hotspots of microgeographic adaptation. Our results also underscore the importance of incorporating life history in analyses of the fitness effects of individual genetic diversity and suggest that metamorphosis and similar discrete life stage transitions may be critical periods of viability selection.
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Affiliation(s)
- Winsor H Lowe
- Division of Biological Sciences, University of Montana, Missoula, Montana, USA
| | - Brett R Addis
- Division of Biological Sciences, University of Montana, Missoula, Montana, USA
| | - Madaline M Cochrane
- Division of Biological Sciences, University of Montana, Missoula, Montana, USA
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2
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Coltman DW, Pilkington JG, Smith JA, Pemberton JM. PARASITE-MEDIATED SELECTION AGAINST INBRED SOAY SHEEP IN A FREE-LIVING ISLAND POPULATON. Evolution 2017; 53:1259-1267. [PMID: 28565537 DOI: 10.1111/j.1558-5646.1999.tb04538.x] [Citation(s) in RCA: 173] [Impact Index Per Article: 24.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/1998] [Accepted: 02/24/1999] [Indexed: 11/26/2022]
Abstract
Parasites are thought to provide a selective force capable of promoting genetic variation in natural populations. One rarely considered pathway for this action is via parasite-mediated selection against inbreeding. If parasites impose a fitness cost on their host and the offspring of close relatives have greater susceptibility to parasites due to the increased homozygosity that results from inbreeding, then parasite-mediated mortality may select against inbred individuals. This hypothesis has not yet been tested within a natural vertebrate population. Here we show that relatively inbred Soay sheep (Ovis aries), as assessed by microsatellite heterozygosity, are more susceptible to parasitism by gastrointestinal nematodes, with interactions indicating greatest susceptibility among adult sheep at high population density. During periods of high overwinter mortality on the island of Hirta, St. Kilda, Scotland, highly parasitised individuals were less likely to survive. More inbred individuals were also less likely to survive, which is due to their increased susceptibility to parasitism, because survival was random with respect to inbreeding among sheep that were experimentally cleared of their gastrointestinal parasite burden by anthelminthic treatment. As a consequence of this selection, average microsatellite heterozygosity increases with age in St. Kildan Soay sheep. We suggest that parasite-mediated selection acts to maintain genetic variation in this small island population by removing less heterozygous individuals.
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Affiliation(s)
- David W Coltman
- Institute of Cell, Animal and Population Biology, University of Edinburgh, Edinburgh, EH9 3JT, U.K
| | - Jill G Pilkington
- Institute of Cell, Animal and Population Biology, University of Edinburgh, Edinburgh, EH9 3JT, U.K
| | - Judith A Smith
- Institute of Cell, Animal and Population Biology, University of Edinburgh, Edinburgh, EH9 3JT, U.K
| | - Josephine M Pemberton
- Institute of Cell, Animal and Population Biology, University of Edinburgh, Edinburgh, EH9 3JT, U.K
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3
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Schmitt C, Garant D, Doyon K, Bousquet N, Gaudreau L, Bélisle M, Pelletier F. Patterns of Diversity and Spatial Variability of β-Defensin Innate Immune Genes in a Declining Wild Population of Tree Swallows. J Hered 2017; 108:262-269. [PMID: 28186244 DOI: 10.1093/jhered/esx005] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2016] [Accepted: 01/25/2017] [Indexed: 12/26/2022] Open
Abstract
Assessing the genetic variation and distribution of immune genes across heterogeneous environmental conditions in wild species is essential to further our understanding of the role of pathogen pressure and potential resistance or prevalence in hosts. Researchers have recently investigated β-defensin genes in the wild, because their variability suggests that they may play an important role in innate host defense. This study investigated the variation occurring at 6 innate immune genes of the β-defensin family in a declining population of tree swallows (Tachycineta bicolor) in southern Québec, Canada (N = 160). We found that all 6 genes showed synonymous and nonsynonymous single nucleotide polymorphisms (SNPs) within the exon coding for the mature peptide. These results indicated that this group of genes was diverse in tree swallows. Our results suggested a potential interaction of this group of genes with fluctuating pathogen diversity, however, we found no sign of positive or negative selection. We assessed whether or not the distribution of genetic diversity of β-defensin genes in our study population differed between 2 regions that strongly differ in their level of agricultural intensification. Adults are highly philopatric to their breeding sites and their immunological responses differ between these 2 regions. However, we found little evidence that the level and distribution of genetic variability differed between these heterogeneous environmental conditions. Further studies should aim to assess the link between genetic diversity of β-defensin genes and fitness-related traits in wild populations.
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Affiliation(s)
- Clarence Schmitt
- From the Département de biologie, Université de Sherbrooke, 2500 boulevard de l'Université, Sherbrooke, Québec, CanadaJ1K 2R1
| | - Dany Garant
- From the Département de biologie, Université de Sherbrooke, 2500 boulevard de l'Université, Sherbrooke, Québec, CanadaJ1K 2R1
| | - Kathy Doyon
- From the Département de biologie, Université de Sherbrooke, 2500 boulevard de l'Université, Sherbrooke, Québec, CanadaJ1K 2R1
| | - Nicolas Bousquet
- From the Département de biologie, Université de Sherbrooke, 2500 boulevard de l'Université, Sherbrooke, Québec, CanadaJ1K 2R1
| | - Luc Gaudreau
- From the Département de biologie, Université de Sherbrooke, 2500 boulevard de l'Université, Sherbrooke, Québec, CanadaJ1K 2R1
| | - Marc Bélisle
- From the Département de biologie, Université de Sherbrooke, 2500 boulevard de l'Université, Sherbrooke, Québec, CanadaJ1K 2R1
| | - Fanie Pelletier
- From the Département de biologie, Université de Sherbrooke, 2500 boulevard de l'Université, Sherbrooke, Québec, CanadaJ1K 2R1
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4
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Richter SC, Nunziata SO. Survival to metamorphosis is positively related to genetic variability in a critically endangered amphibian species. Anim Conserv 2013. [DOI: 10.1111/acv.12088] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Affiliation(s)
- S. C. Richter
- Department of Biological Sciences; Eastern Kentucky University; Richmond KY USA
| | - S. O. Nunziata
- Department of Biological Sciences; Eastern Kentucky University; Richmond KY USA
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Kekkonen J, Wikström M, Brommer JE. Heterozygosity in an isolated population of a large mammal founded by four individuals is predicted by an individual-based genetic model. PLoS One 2012; 7:e43482. [PMID: 23028456 PMCID: PMC3447869 DOI: 10.1371/journal.pone.0043482] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2012] [Accepted: 07/20/2012] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND Within-population genetic diversity is expected to be dramatically reduced if a population is founded by a low number of individuals. Three females and one male white-tailed deer Odocoileus virginianus, a North American species, were successfully introduced in Finland in 1934 and the population has since been growing rapidly, but remained in complete isolation from other populations. METHODOLOGY/PRINCIPAL FINDINGS Based on 14 microsatellite loci, the expected heterozygosity H was 0.692 with a mean allelic richness (AR) of 5.36, which was significantly lower than what was found in Oklahoma, U.S.A. (H = 0.742; AR = 9.07), demonstrating that a bottleneck occurred. Observed H was in line with predictions from an individual-based model where the genealogy of the males and females in the population were tracked and the population's demography was included. CONCLUSION Our findings provide a rare within-population empirical test of the founder effect and suggest that founding a population by a small number of individuals need not have a dramatic impact on heterozygosity in an iteroparous species.
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Affiliation(s)
- Jaana Kekkonen
- Department of Biosciences, University of Helsinki, Helsinki, Finland
| | | | - Jon E. Brommer
- Department of Biosciences, University of Helsinki, Helsinki, Finland
- ARONIA Coastal Zone Research Team, Novia University of Applied Sciences & Åbo Akademi University, Ekenäs, Finland
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Di Fonzo MMI, Pelletier F, Clutton-Brock TH, Pemberton JM, Coulson T. The population growth consequences of variation in individual heterozygosity. PLoS One 2011; 6:e19667. [PMID: 21611172 PMCID: PMC3097190 DOI: 10.1371/journal.pone.0019667] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2010] [Accepted: 04/03/2011] [Indexed: 11/19/2022] Open
Abstract
Heterozygosity has been associated with components of fitness in numerous studies across a wide range of taxa. Because heterozygosity is associated with individual performance it is also expected to be associated with population dynamics. However, investigations into the association between heterozygosity and population dynamics have been rare because of difficulties in linking evolutionary and ecological processes. The choice of heterozygosity measure is a further issue confounding such studies as it can be biased by individual differences in the frequencies of the alleles studied, the number of alleles at each locus as well as the total number of loci typed. In this study, we first examine the differences between the principal metrics used to calculate heterozygosity using long-term data from a marked population of Soay sheep (Ovis aries). Next, by means of statistical transformation of the homozygosity weighted by loci index, we determine how heterozygosity contributes to population growth in Soay sheep by modelling individual contributions to population growth (pt(i)) as a function of several covariates, including sex, weight and faecal egg count – a surrogate of parasitic nematode burden in the gut. We demonstrate that although heterozygosity is associated with some components of fitness, most notably adult male reproductive success, in general it is only weakly associated with population growth.
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Affiliation(s)
- Martina M I Di Fonzo
- Department of Life Sciences, Imperial College London, Ascot, Berkshire, United Kingdom.
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7
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Coltman D. Recipient of the 2010 Molecular Ecology Prize: Josephine Pemberton. Mol Ecol 2010. [DOI: 10.1111/j.1365-294x.2010.04956.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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8
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Evans SR, Sheldon BC. Interspecific patterns of genetic diversity in birds: correlations with extinction risk. CONSERVATION BIOLOGY : THE JOURNAL OF THE SOCIETY FOR CONSERVATION BIOLOGY 2008; 22:1016-1025. [PMID: 18616741 DOI: 10.1111/j.1523-1739.2008.00972.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Birds are frequently used as indicators of ecosystem health and are the most comprehensively studied class in the animal kingdom. Nevertheless, a comprehensive, interspecific assessment of the correlates of avian genetic diversity is lacking, even though indices of genetic diversity are of considerable interest in the conservation of threatened species. We used published data on variation at microsatellite loci from 194 bird species to examine correlates of diversity, particularly with respect to conservation status and population size. We found a significant decline in mean heterozygosity with increasing extinction risk, and showed, by excluding species whose heterozygosity values were calculated with heterospecific primers, that this relationship was not dependent on ascertainment bias. Results of subsequent regression analyses suggested that smaller population sizes of threatened species were largely responsible for this relationship. Thus, bird species at risk of extinction are relatively depauperate in terms of neutral genetic diversity, which is expected to make population recovery more difficult if it reflects adaptive genetic variation. Conservation policy will need to minimize further loss of diversity if the chances of saving threatened species are to be maximized.
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Affiliation(s)
- Simon R Evans
- Edward Grey Institute, Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, United Kingdom.
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Santucci F, Ibrahim KM, Bruzzone A, Hewit GM. Selection on MHC-linked microsatellite loci in sheep populations. Heredity (Edinb) 2007; 99:340-8. [PMID: 17519962 DOI: 10.1038/sj.hdy.6801006] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Microsatellites within the major histocompatibility complex (MHC) region have received increasing attention as proxy measures of the level of polymorphism at the Mhc genes themselves. We assessed the diversity of microsatellite loci within or in close proximity of the Mhc genes in several breeds of domestic sheep (Ovis aries) and the wild Mouflon (Ovis orientalis musimon). This was compared to variation at other microsatellite loci scattered throughout the sheep genome. Significantly higher number of alleles were observed at the MHC microsatellites. The sheep breeds studied fell into high- and low-diversity group. This grouping is not related to the agricultural use of the breeds, whether for milk, meat or wool. It is, however, correlated with the geographic origins of the breeds. Southern breeds are genetically more diverse than northern breeds. The observed heterozygosity was in most cases lower than Hardy-Weinberg expectations. The potential impact of selective breeding by man on this is discussed. Neutrality tests indicated that for most of the breeds, the distribution of alleles at the MHC-linked microsatellites are more even than would be expected if the genes were neutral and sampled from populations under drift-mutation equilibrium. Hitchhiking due to tight linkage with alleles at the MHC loci that are under balancing selection is proposed as a possible explanation for this pattern.
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Affiliation(s)
- F Santucci
- School of Biological Sciences, University of East Anglia, Norwich, UK.
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LINDSTRÖM JAN, RANTA ESA, KOKKO HANNA, LUNDBERG PER, KAITALA VEIJO. From arctic lemmings to adaptive dynamics: Charles Elton's legacy in population ecology. Biol Rev Camb Philos Soc 2007. [DOI: 10.1111/j.1469-185x.2000.tb00061.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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11
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Abstract
The fine-scale genetic structure of wild animal populations has rarely been analysed, yet is potentially important as a confounding factor in quantitative genetic and allelic association studies, as well as having implications for population dynamics, inbreeding and kin selection. In this study, we examined the extent to which the three spatial subunits, or hefts, of the Village Bay population of Soay sheep (Ovis aries) on St Kilda, Scotland, are genetically structured using data from 20 microsatellite and protein loci. Allele frequencies differed significantly among three hefts in all the study years we considered (1987-2000 inclusive). Small but significantly positive F(ST) and negative F(IS) values were observed in most years, indicating that the hefts are genetically differentiated, and that within each heft there is more observed heterozygosity than would be expected if each were an isolated breeding population. Males showed less fidelity to their natal heft, and as a consequence higher levels of relatedness within hefts were observed among females than among males. There was a significant negative relationship between geographical proximity and relatedness in pairwise comparisons involving females, and on average pairs of females located within 50 m of each other were related at the equivalent level of second cousins. Structure is therefore largely driven by incomplete postnatal dispersal by females. Mating appears to be random with respect to the spatial-genetic substructure of the hefts, and therefore genetic structure does not contribute to the overall rate of inbreeding in the population. However, genetic substructure can lead to allelic associations and generate environmental effects within lineages that have the potential to confound heritability analyses and allelic association studies.
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Affiliation(s)
- D W Coltman
- Department of Animal and Plant Sciences, University of Sheffield, Western Bank, UK.
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12
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Measuring genetic diversity in translocation programmes: principles and application to a chimpanzee release project. Anim Conserv 2002. [DOI: 10.1017/s1367943002002275] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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13
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Milner JM, Albon SD, Illius AW, Pemberton JM, Clutton‐Brock TH. Repeated selection of morphometric traits in the Soay sheep on St Kilda. J Anim Ecol 2001. [DOI: 10.1046/j.1365-2656.1999.00299.x] [Citation(s) in RCA: 126] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- J. M. Milner
- Institute of Terrestrial Ecology, Hill of Brathens, Banchory, Kincardineshire, AB31 4BY, UK
- Department of Biology, University College London, Gower Street, London WC1E 6BT, UK
| | - S. D. Albon
- Institute of Terrestrial Ecology, Hill of Brathens, Banchory, Kincardineshire, AB31 4BY, UK
| | - A. W. Illius
- Institute of Cell, Animal and Population Biology, University of Edinburgh, West Mains Road, Edinburgh, EH9 3JT, UK; and
| | - J. M. Pemberton
- Institute of Cell, Animal and Population Biology, University of Edinburgh, West Mains Road, Edinburgh, EH9 3JT, UK; and
| | - T. H. Clutton‐Brock
- Large Animal Research Group, Department of Zoology, University of Cambridge, Downing Street, Cambridge, CB2 3EJ, UK
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Abstract
Is this short review we explore the genetic threats facing declining populations, focusing in particular on empirical studies and the emerging questions they raise. At face value, the two primary threats are slow erosion of genetic variability by drift and short-term lowering of fitness owing to inbreeding depression, of which the latter appears the more potent force. However, the picture is not this simple. Populations that have passed through a severe bottleneck can show a markedly reduced ability to respond to change, particularly in the face of novel challenges. At the same time, several recent studies reveal subtle ways in which species are able to retain more useful genetic variability than they 'should', for example by enhanced reproductive success among the most outbred individuals in a population. Such findings call into question the validity of simple models based on random mating, and emphasize the need for more empirical data aimed at elucidating precisely what happens in natural populations.
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Affiliation(s)
- W Amos
- Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK.
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15
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Queney G, Ferrand N, Marchandeau S, Azevedo M, Mougel F, Branco M, Monnerot M. Absence of a genetic bottleneck in a wild rabbit (Oryctolagus cuniculus) population exposed to a severe viral epizootic. Mol Ecol 2000; 9:1253-64. [PMID: 10972766 DOI: 10.1046/j.1365-294x.2000.01003.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Infectious diseases and their demographic consequences are thought to influence the genetic diversity of populations. In Europe, during the last 50 years, the European rabbit (Oryctolagus cuniculus) has suffered two important viral epizootics: myxomatosis and rabbit viral haemorraghic disease (RVHD). Although mortality rates were very high, the impact of these diseases on genetic diversity has never been assessed directly. The subject of this paper is a wild rabbit population in France, which has been studied since the beginning of the 1980s. The first outbreak of RVHD occurred in 1995 and provoked a demographic crash. The population, sampled for the first time in 1982 and 1994, was sampled again at the end of 1996 to examine the impact of the epizootic on genetic diversity. In spite of the observed high mortality rate ( approximately 90%), analysis of 14 polymorphic loci (allozymes and microsatellites) showed no loss in genetic diversity after the epizootic. Determination of temporal changes in allele frequencies indicated that the population evolved under genetic drift. The temporal method of Waples demonstrated a significant decrease in the effective population size (Ne) correlated with the demographic crash due to the epizootic. However, the population had only been studied for two generations after the epizootic and the remnant population size probably stayed high enough ( approximately 50 individuals) to keep its genetic diversity at the precrash level. These results suggest that, contrary to what is usually thought and in spite of the subsequent high mortality rates, past epizootics (especially myxomatosis) may have had little effect on the genetic diversity of wild rabbit populations in Europe.
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Affiliation(s)
- G Queney
- Centre de Génétique Moléculaire (CGM), CNRS, 91198 Gif sur Yvette cedex, France.
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Milner JM, Elston DA, Albon SD. Estimating the contributions of population density and climatic fluctuations to interannual variation in survival of Soay sheep. J Anim Ecol 1999. [DOI: 10.1046/j.1365-2656.1999.00366.x] [Citation(s) in RCA: 156] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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17
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Coulson T, Albon S, Pilkington J, Clutton-Brock T. Small-scale spatial dynamics in a fluctuating ungulate population. J Anim Ecol 1999. [DOI: 10.1046/j.1365-2656.1999.00298.x] [Citation(s) in RCA: 95] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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18
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Coulson TN, Pemberton JM, Albon SD, Beaumont M, Marshall TC, Slate J, Guinness FE, Clutton-Brock TH. Microsatellites reveal heterosis in red deer. Proc Biol Sci 1998; 265:489-95. [PMID: 9569667 PMCID: PMC1688908 DOI: 10.1098/rspb.1998.0321] [Citation(s) in RCA: 312] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The fitness consequences of inbreeding and outbreeding are poorly understood in natural populations. We explore two microsatellite-based variables, individual heterozygosity (likely to correlate with recent inbreeding) and a new individual-specific internal distance measure, mean d2 (focusing on events deeper in the pedigree), in relation to two measures of fitness expressed early in life, birth weight and neonatal survival, in 670 red deer calves (Cervus elaphus) born on the Isle of Rum between 1982 and 1996. For comparison, we also analyse inbreeding coefficients derived from pedigrees in which paternity was inferred by molecular methods. Only 14 out of 231 calves (6.1%) had non-zero inbreeding coefficients, and neither inbreeding coefficient nor individual heterozygosity was consistently related to birth weight or neonatal survival. However, mean d2 was consistently related to both fitness measures. Low mean d2 was associated with low birth weight, especially following cold Aprils, in which foetal growth is reduced. Low mean d2 was also associated with low neonatal survival, but this effect was probably mediated by birth weight because fitting birth weight to the neonatal survival model displaced mean d2 as an explanatory variable. We conclude that in the deer population fitness measures expressed early in life do not show evidence of inbreeding depression, but they do show evidence of heterosis, possibly as a result of population mixing. We also demonstrate the practical problems of estimating inbreeding via pedigrees compared with a direct marker-based estimate of individual heterozygosity. We suggest that, together, individual heterozygosity and mean d2, estimated using microsatellites, are useful tools for exploring inbreeding and outbreeding in natural population.
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Affiliation(s)
- T N Coulson
- Institute of Zoology, Zoological Society of London, Regent's Park, London, UK.
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Pemberton JM, Smith JA, Coulson TN, Marshall TC, Slate J, Paterson S, Albon SD, Clutton-Brock TH. The maintenance of genetic polymorphism in small island populations: large mammals in the Hebrides. Philos Trans R Soc Lond B Biol Sci 1996; 351:745-52. [PMID: 8693018 DOI: 10.1098/rstb.1996.0069] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
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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Affiliation(s)
- J M Pemberton
- Institute of Cell, Animal and Population Biology, University of Edinburgh, U.K
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