SEARCH · PubMed Health

Results for “Inbreeding Depression”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 397 records · Page 22Linked to original sources

PubMed2000

Microsatellite analysis of the regeneration process of Magnolia obovata Thunb.

We analysed the regeneration process of Magnolia obovata using polymorphic microsatellite markers. Eighty-three adult trees standing in a watershed covering an area of 69 ha, and saplings collected from a smaller research plot (6 ha) located at the centre of the watershed were genotyped using microsatellite markers. Among 91 saplings analysed, 24 (26%) had both parents, 31 (34%) had one parent and 36 (40%) had no parent within the watershed. The proportion of genes in saplings inherited from the adults within the watershed was 43%, and therefore 57% were from outside the site, indicating active gene exchange across the watershed area. Average distance between parents and saplings (264.6 +/- 135.3 (SD) m) was significantly smaller than that of pairs randomly chosen between adults and saplings (436.7 +/- 203.0 (SD) m). The distance of pollen movement inferred from the distance between the two parents of each sapling ranged from 3.2 m to 540 m with an average of 131.1 m +/- 121.1 m (SD). Because 34% ( = 31/91) of saplings had only one parent within the watershed, the estimate of average pollen movement must be smaller than the actual one. Long-distance seed dispersal by birds, inbreeding depression and limitation in acceptance of pollen because of the difference of phenology in each individual flower were considered to be the probable causes of large gene exchange across the watershed.

Alleles↗

PubMed2000

Local drift load and the heterosis of interconnected populations.

We use Wright's distribution of equilibrium allele frequency to demonstrate that hybrids between populations interconnected by low to moderate levels of migration can have large positive heterosis, especially if the populations are small in size. Beneficial alleles neither fix in all populations nor equilibrate at the same frequency. Instead, populations reach a mutation-selection-drift-migration balance with sufficient among-population variance that some partially recessive, deleterious mutations can be masked upon crossbreeding. This heterosis is greatest with intermediate mutation rates, intermediate selection coefficients, low migration rates and recessive alleles. Hybrid vigour should not be taken as evidence for the complete isolation of populations. Moreover, we show that heterosis in crosses between populations has a different genetic basis than inbreeding depression within populations and is much more likely to result from alleles of intermediate effect.

Alleles↗

PubMed2001

Additive and non-additive genetic architecture of two different-sized populations of Scabiosa canescens.

Future adaptation to changes in the environment depends on the existence of additive genetic variances within populations. Recently, considerable attention has also been given to the non-additive component, which plays an important role in inbreeding depression and bottleneck situations. In this study, I used data from a North Carolina II crossing experiment, analysed with restricted maximum-likelihood methods, to estimate the additive and dominance genetic (co)variances for eight quantitative characters in two different-sized populations of Scabiosa canescens, a rare and threatened plant in Sweden. There was no evidence for genetic erosion in the small Hällestad population ( approximately 25 individuals) relative to the large Ahus population ( approximately 5000 individuals). In fact, slightly higher heritabilities were found in the Hällestad population. The additive genetic variance was statistically significant for all traits in both populations, but only a few additive covariances reached significance. The Hällestad population also had higher mean levels and more traits with significant dominance variance than the Ahus population. The variance attributable to maternal effects was too low to be considered significant. There was only a weak correspondence between heritabilities for each trait in the present study and previous estimates based on open-pollinated families of the same populations, but the mean heritability (over characters) was consistent between the studies.

Analysis of Variance↗

PubMed2001

Field and allozyme studies investigating optimal mating success in two sympatric spring-ephemeral plants, Trillium erectum and T. grandiflorum.

A combination of field experiments and allozyme studies was used to test whether two spring-ephemeral plants growing in eastern North America, Trillium erectum and T. grandiflorum (Liliaceae), exhibited an optimal outcrossing distance for fruit and seed production. Furthermore, the spatial genetic structure of the Trillium populations was examined in light of the outcrossing results. In field experiments, recipient plants were pollinated with either self pollen or with pollen from donors growing 1 m, 10 m, 100 m, and 1500 m away. These distances represented crosses between individuals growing within the same population (1 m, 10 m, and 100 m crosses) and between individuals growing in different populations (1500 m crosses). Self-pollinated T. erectum and T. grandiflorum produced 71% and 89% fewer seeds, respectively, than all other outcrossing treatments. However, there were no significant differences among outcrossing treatments for fruit or seed production. As neither T. erectum nor T. grandiflorum exhibited an optimal outcrossing distance for fruit or seed production, it was predicted that populations of the two would not demonstrate strong spatial genetic structure or isolation by distance. The allozyme results only partially supported the patterns revealed in the outcrossing treatments. Populations of T. erectum and T. grandiflorum showed moderate spatial genetic differentiation based on F-statistics, and only T. grandiflorum exhibited significant isolation by distance based on spatial autocorrelation analyses. The lack of optimal outcrossing distances and the patterns of allozyme variation in T. erectum and T. grandiflorum populations may be attributed to a number of factors, including active seed dispersal by ants, rare long-distance gene-flow events, post-pollination and post-fertilization selection, and/or the severity of inbreeding depression.

Isoenzymes↗

PubMed2001

A comparison of microsatellite-based pairwise relatedness estimators.

Studies of inbreeding depression or kin selection require knowledge of relatedness between individuals. If pedigree information is lacking, one has to rely on genotypic information to infer relatedness. In this study we investigated the performance (absolute and relative) of 10 marker-based relatedness estimators using allele frequencies at microsatellite loci obtained from natural populations of two bird species and one mammal species. Using Monte Carlo simulations we show that many factors affect the performance of estimators and that different sets of loci promote the use of different estimators: in general, there is no single best-performing estimator. The use of locus-specific weights turns out to greatly improve the performance of estimators when marker loci are used that differ strongly in allele frequency distribution. Microsatellite-based estimates are expected to explain between 25 and 79% of variation in true relatedness depending on the microsatellite dataset and on the population composition (i.e. the frequency distribution of relationship in the population). We recommend performing Monte Carlo simulations to decide which estimator to use in studies of pairwise relatedness.

Animals↗

PubMed2002

Insights into recently fragmented vole populations from combined genetic and demographic data.

We combined demographic and genetic data to evaluate the effects of habitat fragmentation on the population structure of the California red-backed vole (Clethrionomys californicus). We analysed variation in the mitochondrial DNA (mtDNA) control region and five nuclear microsatellite loci in small samples collected from two forest fragments and an unfragmented control site in 1990-91. We intensively sampled the same forest fragments and two different control sites in 1998 and 1999. Vole abundances fluctuated greatly at sizes below 50 individuals per fragment. Fragment populations had significantly lower mtDNA allelic diversity than controls, but not nuclear heterozygosity or numbers of alleles. The use of only trapping and/or mtDNA marker data would imply that fragment populations are at least partially isolated and vulnerable to inbreeding depression. In contrast, the abundance estimates combined with microsatellite data show that small fragment populations must be linked to nearby forests by high rates of migration. These results provide evidence for the usefulness of combining genetic and demographic data to understand nonequilibrium population structure in recently fragmented habitats.

Animals↗

PubMed2002

Loss of genetic diversity in sea otters (Enhydra lutris) associated with the fur trade of the 18th and 19th centuries.

Sea otter (Enhydra lutris) populations experienced widespread reduction and extirpation due to the fur trade of the 18th and 19th centuries. We examined genetic variation within four microsatellite markers and the mitochondrial DNA (mtDNA) d-loop in one prefur trade population and compared it to five modern populations to determine potential losses in genetic variation. While mtDNA sequence variability was low within both modern and extinct populations, analysis of microsatellite allelic data revealed that the prefur trade population had significantly more variation than all the extant sea otter populations. Reduced genetic variation may lead to inbreeding depression and we believe sea otter populations should be closely monitored for potential associated negative effects.

Animals↗

PubMed2003

Fluctuating asymmetry in a secondary sexual trait: no associations with individual fitness, environmental stress or inbreeding, and no heritability.

It has been suggested that fluctuating asymmetry (FA) in secondary sexual traits may be a useful indicator of either individual quality or environmental stress. We tested this concept using a series of analyses of FA in male antler size in a wild red deer (Cervus elaphus) population, using four measures of size repeated across successive years on the same individuals. We found no consistent evidence of correlations between traits in levels of FA, nor of any associations between known environmental or developmental conditions. None of the four measures of FA showed a significant heritability (average h2 = 0.041), nor was there any evidence of inbreeding depression. For three of the four traits, fluctuating asymmetry did not predict either annual or lifetime breeding success. However there were significant associations between breeding success and FA in antler length. Given the series of null results in our other tests, it seems likely that this was a direct mechanistic effect rather than because measures of FA were indicative of individual quality or condition.

Animals↗

PubMedDate not supplied

Sexual dimorphism in gender plasticity and its consequences for breeding system evolution.

Flowering plants are able to develop gametes throughout their lives. As a consequence, environmental conditions can impact this development and alter a plant's functional gender or the degree to which it achieves fitness through male or female function. Two dimorphic breeding systems are widespread among angiosperm families: gynodioecy (hermaphrodites and females) and dioecy (males and females). Gynodioecy can evolve into dioecy, via loss of female function on the hermaphrodites, or it can remain stable. Here I discuss how developmental plasticity of gender can impact the sex ratio of populations and thereby influence the transition of one breeding system into another. I review studies showing that greater plasticity of fruit production by hermaphrodites as compared with females causes sex ratios among populations to vary in response to environmental conditions, with higher female frequency expected in harsh or low-quality sites. I also review how dioecy may evolve in dry sites to avoid inbreeding and any consequent inbreeding depression. Taken together, these studies show the importance of understanding how ecological development affects functional gender and consequently the evolutionary stability or malleability of dimorphic breeding systems.

Asteraceae↗

PubMedDate not supplied

Reproductive biotechnologies for endangered mammalian species.

Assisted reproductive techniques (gamete cryopreservation, artificial insemination, embryo transfer, and in vitro fertilization) allow to propagate small fragmented populations of wild endangered species or domestic breeds. There are the best way for producing several offspring from selected genitors in order to avoid inbreeding depression. However, few mammalian species have been well studied for their reproductive biology whereas huge differences have been observed between these species. Furthermore, materials, methods and experimental designs have to be adapted for each case and each limiting factor (wildness, poor quantity of biological material, disparate locations). Genome resource banking is currently arising and the most applied reproductive biotechnology remains artificial insemination. Assisted reproductive techniques currently developed in domestic species (intracytoplasmic sperm injection, nuclear transfer) may offer new opportunities for the propagation of endangered species.

Animals↗

PubMed2004

Reduced fecundity in small populations of the rare plant Gentianopsis ciliate (Gentianaceae).

Habitat destruction is the main cause for the biodiversity crisis. Surviving populations are often fragmented, i.e., small and isolated from each other. Reproduction of plants in small populations is often reduced, and this has been attributed to inbreeding depression, reduced attractiveness for pollinators, and reduced habitat quality in small populations. Here we present data on the effects of fragmentation on the rare, self-compatible perennial herb Gentianopsis ciliata (Gentianaceae), a species with very small and presumably well-dispersed seeds. We studied the relationship between population size, plant size, and the number of flowers produced in 63 populations from 1996-1998. In one of the years, leaf and flower size and the number of seeds produced per fruit was studied in a subset of 25 populations. Plant size, flower size, and the number of seeds per fruit and per plant increased with population size, whereas leaf length and the number of flowers per plant did not. The effects of population size on reproduction and on flower size remained significant if the effects were adjusted for differences in plant size, indicating that they could not be explained by differences in habitat quality. The strongly reduced reproduction in small populations may be due to pollination limitation, while the reduced flower size could indicate genetic effects.

Biodiversity↗

PubMed2006

Fine-scale spatial genetic structure of the distylous Primula veris in fragmented habitats.

In Flanders (northern Belgium), the distylous self-incompatible perennial herb Primula veris is common, but mainly occurs in fragmented habitats. Distyly, which favours disassortative mating, is characterized in P. veris by two genetically determined floral morph types (pin or thrum). Using 18 polymorphic loci, we investigated fine-scale spatial genetic structure (SGS) and spatial distribution of the morphs within four populations from two regions that differ in degree of habitat fragmentation. We studied the contributions made by sexual reproduction and clonal propagation and compared the SGS patterns between pin and thrum morph types. Clonal growth was very restricted to a few individuals and to short distances. One population showed a non-random spatial distribution of the morphs. Pin and thrum individuals differed in SGS patterns at a small scale, suggesting intrapin biparental inbreeding, also related to high plant densities. This may be explained by partial self-compatibility of the pin morph combined with restricted seed dispersal and pollinator behaviour. There is an indication of more pronounced SGS when populations occur in highly fragmented habitats. From our findings, we may hypothesize disruption of the gene flow processes if these large populations evolve into patchworks of small remnants, but also a possible risk for long-term population survival if higher intrapin biparental inbreeding leads to inbreeding depression. Our study emphasizes the need for investigating the interactions between the heterostylous breeding system, population demographic and genetic structure for understanding population dynamics in fragmented habitats and for developing sustainable conservation strategies.

Breeding↗

PubMed2005

Reproductive physiology and artificial insemination studies in wild and captive gerenuk ( Litocranius walleri walleri ).

Gerenuk antelope in North American zoos are descended from 28 founders imported from Kenya approximately 20 years ago. Intensive management is required to prevent inbreeding depression. Artificial insemination has potential for augmenting genetic management, but successful application requires a thorough understanding of species' reproductive norms. Semen collected from captive (n = 10) and wild (n = 6) gerenuk contained low numbers of morphologically normal spermatozoa (approximately 40%). Age, but not season, influenced (P < 0.05) the proportion of morphologically normal spermatozoa (mean +/- s.e.m., 12-17 months of age, 10.3 +/- 1.9%; 18-26 months of age, 34.4 +/- 6.2%; 3-6 years of age, 40.0 +/- 4.7%). Seasonality was investigated by analysing faecal testosterone and progesterone in males and females, respectively, by radioimmunoassays. Females cycled all year (ovarian cycle length, 18.7 +/- 0.9 days). Testosterone in males did not vary (P > 0.05) with time of year. Three females (3/9, 33%) became pregnant by insemination with 9.75-54.0 x 0(6) motile fresh or frozen sperm after oestrus synchronisation with two prostaglandin F(2alpha) injections, 12 days apart. One female inseminated with frozen-thawed sperm delivered a full-term stillborn calf after 213 days gestation. These results characterise gerenuk reproductive norms and indicate that artificial insemination may be a useful tool in the genetic management of gerenuk.

Age Factors↗

PubMed2004

Most species are not driven to extinction before genetic factors impact them.

There is controversy concerning the role of genetic factors in species extinctions. Many authors have asserted that species are usually driven to extinction before genetic factors have time to impact them, but few studies have seriously addressed this issue. If this assertion is true, there will be little difference in genetic diversity between threatened and taxonomically related nonthreatened species. We compared average heterozygosities in 170 threatened taxa with those in taxonomically related nonthreatened taxa in a comprehensive metaanalysis. Heterozygosity was lower in threatened taxa in 77% of comparisons, a highly significant departure from the predictions of the no genetic impact hypothesis. Heterozygosity was on average 35% lower (median 40%) in threatened taxa than in related nonthreatened ones. These differences in heterozygosity indicate lowered evolutionary potential, compromised reproductive fitness, and elevated extinction risk in the wild. Independent evidence from stochastic computer projections has demonstrated that inbreeding depression elevates extinction risk for threatened species in natural habitats when all other threatening processes are included in the models. Thus, most taxa are not driven to extinction before genetic factors affect them adversely.

Animals↗

PubMed2005

Complementary sex determination substantially increases extinction proneness of haplodiploid populations.

The role of genetic factors in extinction is firmly established for diploid organisms, but haplodiploids have been considered immune to genetic load impacts because deleterious alleles are readily purged in haploid males. However, we show that single-locus complementary sex determination ancestral to the haplodiploid Hymenoptera (ants, bees, and wasps) imposes a substantial genetic load through homozygosity at the sex locus that results in the production of inviable or sterile diploid males. Using stochastic modeling, we have discovered that diploid male production (DMP) can initiate a rapid and previously uncharacterized extinction vortex. The extinction rate in haplodiploid populations with DMP is an order of magnitude greater than in its absence under realistic but conservative demographic parameter values. Furthermore, DMP alone can elevate the base extinction risk in haplodiploids by over an order of magnitude higher than that caused by inbreeding depression in threatened diploids. Thus, contrary to previous expectations, haplodiploids are more, rather than less, prone to extinction for genetic reasons. Our findings necessitate a fundamental shift in approaches to the conservation and population biology of these ecologically and economically crucial insects.

Animals↗

PubMed1992

Application of DNA fingerprinting to the recovery program of the endangered Puerto Rican parrot.

The Puerto Rican parrot was reduced to approximately 13 animals in 1975 and as a conservation measure, a captive population was established from a few founders taken from the wild between 1973 and 1983. The number of successful breeding pairs in captivity has been low, and the captive breeding program has not been as productive as that of the closely related Hispaniolan parrot. Therefore, a genetic study was initiated to examine the relative levels of relatedness of the captive founders using levels of bandsharing in DNA fingerprints. Unrelated captive founder Puerto Rican parrots had the same average level of bandsharing (0.41) as second-degree relatives of the Hispaniolan parrot (0.38, P > 0.05), with an inbreeding coefficient of 0.04. High levels of bandsharing (> 40%) between pairs of males and females correlated with reproductive failure, suggesting that inbreeding depression is partly responsible for the low number of breeding pairs. Consequently, DNA profiling can be used to guide the captive breeding program for the Puerto Rican parrot, and other endangered species, by identifying pairs of males and females with low levels of bandsharing.

Animals↗

PubMed1996

Island colonization and evolution of the insular woody habit in Echium L. (Boraginaceae).

Numerous island-inhabiting species of predominantly herbaceous angiosperm genera are woody shrubs or trees. Such "insular woodiness" is strongly manifested in the genus Echium, in which the continental species of circummediterranean distribution are herbaceous, whereas endemic species of islands along the Atlantic coast of north Africa are woody perennial shrubs. The history of 37 Echium species was traced with 70 kb of noncoding DNA determined from both chloroplast and nuclear genomes. In all, 239 polymorphic positions with 137 informative sites, in addition to 27 informative indels, were found. Island-dwelling Echium species are shown to descend from herbaceous continental ancestors via a single island colonization event that occurred < 20 million years ago. Founding colonization appears to have taken place on the Canary Islands, from which the Madeira and Cape Verde archipelagos were invaded. Colonization of island habitats correlates with a recent origin of perennial woodiness from herbaceous habit and was furthermore accompanied by intense speciation, which brought forth remarkable diversity of forms among contemporary island endemics. We argue that the origin of insular woodiness involved response to counter-selection of inbreeding depression in founding island colonies.

Adaptation, Physiological↗

PubMed1997

A gene-culture coevolutionary model for brother-sister mating.

We present a gene-culture coevolutionary model for brother-sister mating in the human. It is shown that cultural--as opposed to innate--determination of mate preference may evolve, provided the inbreeding depression is sufficiently high. At this coevolutionary equilibrium, sib mating is avoided because of cultural pressures.

Biological Evolution↗