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Severe Bottleneck (severe + bottleneck)

Distribution by Scientific Domains

Life Sciences	100%

Selected Abstracts

Historic and contemporary levels of genetic variation in two New Zealand passerines with different histories of decline

JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 5 2007
S. S. TAYLOR
Abstract We compared historic and contemporary genetic variation in two threatened New Zealand birds (saddlebacks and robins) with disparate bottleneck histories. Saddlebacks showed massive loss of genetic variation when extirpated from the mainland, but no significant loss of variation following a severe bottleneck in the 1960s when the last population was reduced from ,1000 to 36 birds. Low genetic variation was probably characteristic of this isolated island population: considerably more genetic variation would exist in saddlebacks today if a mainland population had survived. In contrast to saddlebacks, contemporary robin populations showed only a small decrease in genetic variation compared with historical populations. Genetic variation in robins was probably maintained because of their superior ability to disperse and coexist with introduced predators. These results demonstrate that contemporary genetic variation may depend more greatly on the nature of the source population and its genetic past than it does on recent bottlenecks. [source]

Genetic variation in Holocene bowhead whales from Svalbard

MOLECULAR ECOLOGY, Issue 11 2007
T. BORGE
Abstract Bowhead whales (Balaena mysticetus) are distributed in the Arctic in five putative stocks. All stocks have been heavily depleted due to centuries of exploitation. In the present study, nucleotide sequence variation of the mitochondrial control region was determined from bone remains of 99 bowhead whales. The bones, 14C dated from recent to more than 50 000 bp, were collected on Svalbard (Spitsbergen) and are expected to relate to ancestors of the today nearly extinct Spitsbergen stock. Fifty-eight haplotypes were found, a few being frequent but many only found in one individual. The most abundant haplotypes of the Spitsbergen stock are the same as those most abundant in the extant Bering-Chukchi-Beaufort (BCB) Seas stock of bowhead whales. Although FST indicates a slight but statistically significant genetic differentiation between the Spitsbergen and the BCB stocks this was not considered informative due to the very high levels of genetic diversity of mitochondrial DNA haplotypes in both bowhead whale stocks. Other measures such as KST also indicated very low genetic differentiation between the two populations. Nucleotide diversity and haplotype diversity showed only minor differences between the Spitsbergen and BCB stocks. The data suggest that the historic Spitsbergen stock , before the severe bottleneck caused by whaling , did not have substantially more genetic variation than the extant BCB stock. The similar haplotypes of the Holocene Svalbard samples and the current BCB stock indicate significant migration between these two stocks and question the current designation of five distinct stocks of bowhead whales in the Arctic. [source]

Brief communication: Restricted geographic distribution for Y-Q* paragroup in South America

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 3 2009
Graciela Bailliet
Abstract We analyzed 21 paragroup Q* Y chromosomes from South American aboriginal and urban populations. Our aims were to evaluate the phylogenetic status, geographic distribution, and genetic diversity in these groups of chromosomes and compare the degree of genetic variation in relation to Q1a3a haplotypes. All Q* chromosomes from our series and five samples from North American Q* presented the derivate state for M346, that is present upstream to M3, and determined Q1a3* paragroup. We found a restrictive geographic distribution and low frequency of Q1a3* in South America. We assumed that this low frequency could be reflecting extreme drift effects. However, several estimates of gene diversity do not support the existence of a severe bottleneck. The mean haplotype diversity expected was similar to that for South American Q1a3* and Q1a3a (0.478 and 0.501, respectively). The analysis of previous reports from other research groups and this study shows the highest frequencies of Q* for the West Corner and the Grand Chaco regions of South America. At present, there is no information on whether the phylogenetic status of Q* paragoup described in previous reports is similar to that of Q1a3* paragroup though our results support this possibility. Am J Phys Anthropol, 2009. © 2009 Wiley-Liss, Inc. [source]

Brief communication: The Thule migration: Rejecting population histories using computer simulation

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 2 2007
E.E. Marchani
Abstract Locked within our genetic code are the histories of our genes and the genes of our ancestors. Deciphering a population's history from genetic data often involves lengthy investigations of many loci for many individuals. We test hypothetical population histories of the Thule expansion using a new coalescent simulation method that uses little more than mitochondrial haplogroup data. This new methodology rejects a severe bottleneck at expansion and reveals the range of probable population histories on which to focus future research. Am J Phys Anthropol, 2007. © 2007 Wiley-Liss, Inc. [source]

Decreased immunocompetence in a severely bottlenecked population of an endemic New Zealand bird

ANIMAL CONSERVATION, Issue 1 2007
K. A. Hale
Abstract Inbreeding resulting from severe population bottlenecks may impair an individual's immune system and render it more susceptible to disease. Although a reduced immune response could threaten the survival of highly endangered species, few studies have assessed the effect of population bottlenecks on immunocompetence. We compared the counts of leucocytes and external, blood and gastrointestinal parasite loads in two populations of the endemic New Zealand robin Petroica australis to assess the immunocompetence of birds in a severely bottlenecked population relative to its more genetically diverse source population. Despite similar parasite loads in both populations, robins in the severely bottlenecked population showed lower counts of both total leucocyte and total lymphocyte numbers. When the immune system was experimentally challenged using the phytohaemagglutinin skin test, robins in the severely bottlenecked population exhibited a significantly lower immune response than the source population, suggesting that birds passing through a severe bottleneck have a compromised immunocompetence. Our results confirm that severe bottlenecks reduce the immune response of birds and highlight the need to avoid severe bottlenecks in the recovery programmes of endangered species. [source]

A Comparison of the Variability Spectra of Two Genomic Loci in a European Group of Individuals Reveals Fundamental Differences Pointing to Selection or a Population Bottleneck

ANNALS OF HUMAN GENETICS, Issue 3 2007
C. Schmegner
Summary Knowledge about the variability spectra of neutrally evolving sequences in a population is a prerequisite for the identification of genes, which may have been under positive selection during recent human evolution. Here, we report the results of a re-sequencing project of a presumably neutrally evolving chromosome 22 locus with a severely reduced recombination frequency in a group of 24 individuals of German origin. The comparison of these data with the results of a similar analysis of a chromosome 17 locus revealed striking differences, although the same group of individuals was used. For the chromosome 17 locus two well-separated groups of sequences, a positive value of Tajima's D and a TMRCA of 700 000 years were observed. In contrast, the sequences from the chromosome 22 locus were found to be relatively homogeneous, with no deep splits between subgroups; the obtained value for Tajima's D was negative and the TMRCA was only 260 000 years. These discrepancies may be explained by selection or demographic processes. Regarding demography, the most plausible explanation is the assumption of a severe bottleneck in the history of the European population: in the case of the chromosome 17 locus two ancient lineages passed this bottleneck; for the chromosome 22 locus it was only one ancient lineage. [source]

Contrasting genetic structures of two parasitic nematodes, determined on the basis of neutral microsatellite markers and selected anthelmintic resistance markers

MOLECULAR ECOLOGY, Issue 24 2009
A. SILVESTRE
Abstract For the first time, the neutral genetic relatedness of natural populations of Trichostrongylid nematodes was investigated in relation to polymorphism of the ,-tubulin gene, which is selected for anthelminthic treatments. The aim of the study was to assess the contribution of several evolutionary processes: migration and genetic drift by neutral genetic markers and selection by anthelminthic treatments on the presence of resistance alleles at ,-tubulin. We studied two nematode species (Teladorsagia circumcincta and Haemonchus contortus) common in temperate climatic zones; these species are characterized by contrasting life history traits. We studied 10 isolated populations of goat nematode parasites: no infected adult goat had been exchanged after the herds were established. Beta-tubulin polymorphism was similar in these two species. One and two ,-tubulin alleles from T. circumcincta and H. contortus respectively were shared by several populations. Most of the ,-tubulin alleles were ,private' alleles. No recombination between alleles was detected in BZ-resistant alleles from T. circumcincta and H. contortus. The T. circumcincta populations have not diverged much since their isolation (FST <0.08), whereas H. contortus displayed marked local genetic differentiation (FST ranging from 0.08 to 0.18). These findings suggest that there are severe bottlenecks in the H. contortus populations, possibly because of their reduced abundance during unfavourable periods and their high reproductive rate, which allows the species to persist even after severe population reduction. Overall, the data reported contradict the hypothesis of the origin of ,-tubulin resistance alleles in these populations from a single mutational event, but two other hypotheses (recurrent mutation generating new alleles in isolated populations and the introduction of existing alleles) emerge as equally likely. [source]

Heterozygosity,fitness correlations and their relevance to studies on inbreeding depression in threatened species

MOLECULAR ECOLOGY, Issue 18 2008
CATHERINE E GRUEBER
Abstract The majority of reported multilocus heterozygosity,fitness correlations (HFCs) are from large, outbred populations, and their relevance to studies on inbreeding depression in threatened populations is often stressed. The results of such HFC studies conducted on outbred populations may be of limited application to threatened population management, however, as bottlenecked populations exhibit increased incidence of inbreeding, increased linkage disequilibrium, reduced genetic diversity and possible effects of historical inbreeding such as purging. These differences may affect both our ability to detect inbreeding depression in threatened species, and our interpretation of the underlying mechanisms for observed heterozygosity,fitness relationships. The study of HFCs in outbred populations is of interest in itself, but the results may not translate directly to threatened populations that have undergone severe bottlenecks. [source]