scholarly journals Genomic evidence for two phylogenetic species and long-term population bottlenecks in red pandas

2020 ◽  
Vol 6 (9) ◽  
pp. eaax5751 ◽  
Author(s):  
Yibo Hu ◽  
Arjun Thapa ◽  
Huizhong Fan ◽  
Tianxiao Ma ◽  
Qi Wu ◽  
...  
Keyword(s):  
Large Population ◽  
Genetic Load ◽  
Population Expansion ◽  
High Linkage Disequilibrium ◽  
Genetic Evidence ◽  
Morphological Evidence ◽  
Population Bottlenecks ◽  
Phylogenetic Species ◽  
Low Genetic Diversity ◽  
Red Panda

The red panda (Ailurus fulgens), an endangered Himalaya-endemic mammal, has been classified as two subspecies or even two species – the Himalayan red panda (A. fulgens) and the Chinese red panda (Ailurus styani) – based on differences in morphology and biogeography. However, this classification has remained controversial largely due to lack of genetic evidence, directly impairing scientific conservation management. Data from 65 whole genomes, 49 Y-chromosomes, and 49 mitochondrial genomes provide the first comprehensive genetic evidence for species divergence in red pandas, demonstrating substantial inter-species genetic divergence for all three markers and correcting species-distribution boundaries. Combined with morphological evidence, these data thus clearly define two phylogenetic species in red pandas. We also demonstrate different demographic trajectories in the two species: A. styani has experienced two population bottlenecks and one large population expansion over time, whereas A. fulgens has experienced three bottlenecks and one very small expansion, resulting in very low genetic diversity, high linkage disequilibrium, and high genetic load.

scholarly journals Estimates of genetic load in small populations suggest extensive purging of deleterious alleles

2019 ◽  
Author(s):  
Tom van der Valk ◽  
Marc de Manuel ◽  
Tomas Marques-Bonet ◽  
Katerina Guschanski
Keyword(s):  
Large Population ◽  
Genetic Load ◽  
Small Population ◽  
Small Populations ◽  
Population Declines ◽  
Current Conservation ◽  
Low Genetic Diversity ◽  
Deleterious Alleles ◽  
Declining Populations ◽  
Genetic Purging

AbstractDeclining populations are expected to experience negative genetic consequences of inbreeding, which over time can drive them to extinction. Yet, many species have survived in small populations for thousands of generations without apparent fitness effects, possibly due to genetic purging of partially deleterious recessive alleles in inbred populations. We estimate the abundance of deleterious alleles in a range of mammals and find that conversely to current conservation thinking species with historically small population size and low genetic diversity generally have lower genetic load compared to species with large population sizes. Rapid population declines will thus disproportionally affect species with high diversity, as they carry many deleterious alleles that can reach fixation before being removed by genetic purging.

scholarly journals POPULATION BOTTLENECKS AND NONEQUILIBRIUM MODELS IN POPULATION GENETICS. II. NUMBER OF ALLELES IN A SMALL POPULATION THAT WAS FORMED BY A RECENT BOTTLENECK

Genetics ◽  
1985 ◽  
Vol 111 (3) ◽  
pp. 675-689
Author(s):  
Takeo Maruyama ◽  
Paul A Fuerst
Keyword(s):  
Gene Diversity ◽  
Large Population ◽  
Population Expansion ◽  
Small Population ◽  
Allelic Loss ◽  
Population Bottlenecks ◽  
Sufficient Statistic ◽  
Allele Number ◽  
Excess Number ◽  
Recent Bottleneck

ABSTRACT A model is presented in which a large population in mutation/drift equilibrium undergoes a severe restriction in size and subsequently remains at the small size. The rate of loss of genetic variability has been studied. Allelic loss occurs more rapidly than loss of genic heterozygosity. Rare alleles are lost especially rapidly. The result is a transient deficiency in the total number of alleles observed in samples taken from the reduced population when compared with the number expected in a sample from a steady-state population having the same observed heterozygosity. Alternatively, the population can be considered to posses excess gene diversity if the number of alleles is used as the statistical estimator of mutation rate. The deficit in allele number arises principally from a lack of those alleles that are expected to appear only once or twice in the sample. The magnitude of the allelic deficiency is less, however, than the excess that an earlier study predicted to follow a rapid population expansion. This suggests that populations that have undergone a single bottleneck event, followed by rapid population growth, should have an apparent excess number of alleles, given the observed level of genic heterozygosity and provided that the bottleneck has not occurred very recently. Conversely, such populations will be deficient for observed heterozygosity if allele number is used as the sufficient statistic for the estimation of 4Nev. Populations that have undergone very recent restrictions in size should show the opposite tendencies.

scholarly journals Inbreeding depression due to mildly deleterious mutations in finite populations: size does matter

2000 ◽  
Vol 75 (1) ◽  
pp. 75-81 ◽  
Author(s):  
THOMAS BATAILLON ◽  
MARK KIRKPATRICK
Keyword(s):  
Population Size ◽  
Inbreeding Depression ◽  
Deleterious Mutation ◽  
Large Population ◽  
Genetic Load ◽  
Breeding Systems ◽  
Deleterious Mutations ◽  
Single Locus Analysis ◽  
Population Sizes ◽  
Inbreeding Rate

We studied the effects of population size on the inbreeding depression and genetic load caused by deleterious mutations at a single locus. Analysis shows how the inbreeding depression decreases as population size becomes smaller and/or the rate of inbreeding increases. This pattern contrasts with that for the load, which increases as population size becomes smaller but decreases as inbreeding rate goes up. The depression and load both approach asymptotic limits when the population size becomes very large or very small. Numerical results show that the transition between the small and the large population regimes is quite rapid, and occurs largely over a range of population sizes that vary by a factor of 10. The effects of drift on inbreeding depression may bias some estimates of the genomic rate of deleterious mutation. These effects could also be important in the evolution of breeding systems in hermaphroditic organisms and in the conservation of endangered populations.

Weak genetic structuring suggests historically high genetic connectivity among recently fragmented urban populations of the scincid lizard, Ctenotus fallens

2015 ◽  
Vol 63 (4) ◽  
pp. 279 ◽  
Author(s):  
Josef Krawiec ◽  
Siegfried L. Krauss ◽  
Robert A. Davis ◽  
Peter B. S. Spencer
Keyword(s):  
Genetic Diversity ◽  
Gene Flow ◽  
Large Population ◽  
Geographic Distance ◽  
Genetic Erosion ◽  
Genetic Connectivity ◽  
Genetic Structuring ◽  
Low Genetic Diversity ◽  
Population Sizes

Populations in fragmented urban remnants may be at risk of genetic erosion as a result of reduced gene flow and elevated levels of inbreeding. This may have serious genetic implications for the long-term viability of remnant populations, in addition to the more immediate pressures caused by urbanisation. The population genetic structure of the generalist skink Ctenotus fallens was examined using nine microsatellite markers within and among natural vegetation remnants within a highly fragmented urban matrix in the Perth metropolitan area in Western Australia. These data were compared with samples from a large unfragmented site on the edge of the urban area. Overall, estimates of genetic diversity and inbreeding within all populations were similar and low. Weak genetic differentiation, and a significant association between geographic and genetic distance, suggests historically strong genetic connectivity that decreases with geographic distance. Due to recent fragmentation, and genetic inertia associated with low genetic diversity and large population sizes, it is not possible from these data to infer current genetic connectivity levels. However, the historically high levels of gene flow that our data suggest indicate that a reduction in contemporary connectivity due to fragmentation in C. fallens is likely to result in negative genetic consequences in the longer term.

Comparative genetic diversity of Cryptosporidium species causing human infections

Parasitology ◽  
2020 ◽  
Vol 147 (13) ◽  
pp. 1532-1537 ◽  
Author(s):  
Juan C. Garcia-R ◽  
Murray P. Cox ◽  
David T. S. Hayman
Keyword(s):  
Genetic Diversity ◽  
Population Expansion ◽  
Recent Population Expansion ◽  
Cryptosporidium Hominis ◽  
High Genetic Diversity ◽  
Genetic Changes ◽  
Low Genetic Diversity ◽  
Human Infections ◽  
Host Parasite ◽  
Founder Events

AbstractParasites sometimes expand their host range and cause new disease aetiologies. Genetic changes can then occur due to host-specific adaptive alterations, particularly when parasites cross between evolutionarily distant hosts. Characterizing genetic variation in Cryptosporidium from humans and other animals may have important implications for understanding disease dynamics and transmission. We analyse sequences from four loci (gp60, HSP-70, COWP and actin) representing multiple Cryptosporidium species reported in humans. We predicted low genetic diversity in species that present unusual human infections due to founder events and bottlenecks. High genetic diversity was observed in isolates from humans of Cryptosporidium meleagridis, Cryptosporidium cuniculus, Cryptosporidium hominis and Cryptosporidium parvum. A deviation of expected values of neutrality using Tajima's D was observed in C. cuniculus and C. meleagridis. The high genetic diversity in C. meleagridis and C. cuniculus did not match our expectations but deviations from neutrality indicate a recent decrease in genetic variability through a population bottleneck after an expansion event. Cryptosporidium hominis was also found with a significant Tajima's D positive value likely caused by recent population expansion of unusual genotypes in humans. These insights indicate that changes in genetic diversity can help us to understand host-parasite adaptation and evolution.

Genetic stock structure of blue-eye trevalla (Hyperoglyphe antarctica) and warehous (Seriolella brama and Seriolella punctata) in south-eastern Australian waters

2008 ◽  
Vol 59 (6) ◽  
pp. 502 ◽  
Author(s):  
Nick Robinson ◽  
Alexandra Skinner ◽  
Lakshmi Sethuraman ◽  
Helen McPartlan ◽  
Neil Murray ◽  
...  
Keyword(s):  
Haplotype Diversity ◽  
Population Expansion ◽  
Stock Structure ◽  
Population Bottlenecks ◽  
Sources Of Information ◽  
Multiple Sources ◽  
Genetic Structuring ◽  
Genetic Stock ◽  
Important Species ◽  
History Of

Blue-eye trevalla (Hyperoglyphe antarctica), blue warehou (Seriolella brama) and silver warehou (Seriolella punctata) from the family Centrolophidae are three commercially important species in the Australian fishery. These species are currently managed as single stocks. We tested the hypothesis that patterns of phenotypic structuring in these species reflect underlying genetic stock structure using an analysis of mitochondrial DNA control region sequences. The analysis revealed high levels of haplotype diversity within populations. The most common haplotypes for the species occurred in all geographical locations sampled. For S. brama, although structuring was not significant after Bonferroni correction, differences between two sites were sufficient to warrant caution in the management of fishery zones for this species. There were also some indications of structuring when sites were grouped into common regions. Demographic analysis suggested that S. brama might have had a history of population bottlenecks followed by sudden population expansion, potentially contributing to genetic structuring in the fishery. No structuring was detected for H. antarctica and S. punctata. The present study highlights the need for, and the utility of, multiple sources of information, that is, genetic, phenotypic, behavioural and ecological, when managing marine fisheries and the need to take a cautionary approach to the interpretation of genetic data for fisheries management.

Genetic evidence for population expansion in Hydrotaea irritans (Fallen) (Diptera: Muscidae)

2004 ◽  
Vol 42 (3) ◽  
pp. 257-261
Author(s):  
V. Loeschcke ◽  
B. O. Nielsen ◽  
A. Aa. Pedersen ◽  
J. G. Sorensen ◽  
H. R. Siegismund
Keyword(s):  
Population Expansion ◽  
Genetic Evidence

Nuclear and cytoplasmic genetic diversity reveals long-term population decline in Abies semenovii, an endemic fir of central Asia

2012 ◽  
Vol 42 (12) ◽  
pp. 2142-2152 ◽  
Author(s):  
Svetlana A. Semerikova ◽  
Martin Lascoux ◽  
Vladimir L. Semerikov
Keyword(s):  
Genetic Diversity ◽  
Central Asia ◽  
Population Decline ◽  
Population Expansion ◽  
Nuclear Marker ◽  
Effective Population ◽  
Species Status ◽  
Siberian Fir ◽  
Low Genetic Diversity

The genus Abies is one of the largest conifer genera and many of the marginal species remain poorly characterized. Abies semenovii B. Fedtsch. is a rare mountain fir species from central Asia, and its species status is still disputed. We used both nuclear (allozymes and AFLP) and chloroplastic (cpSSR) markers to show that A. semenovii deserves to be considered as a species and that its low genetic diversity justifies more a proactive conservation policy. First, A. semenovii was significantly differentiated from the Siberian fir Abies sibirica Ledeb. and we did not detect gene flow between the two species. Second, A. semenovii has a very low nuclear genetic diversity, suggesting a prolonged restricted effective population size. Abies semenovii had low cpSSR diversity too but the identification of seven closely related haplotypes suggests that these mutations accumulated recently during a phase of population expansion. This agrees well with the palynological record and is in contrast with the situation observed in another rare Eurasian fir endemic to Kamchatka, Abies gracilis Kom., which was devoid of variation in cpSSRs but that also had a more substantial nuclear marker diversity than A. semenovii, thereby suggesting a more recent but less severe population bottleneck.

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