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Results for “Inbreeding Depression”

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At least 433 records · Page 24Linked to original sources

PubMed1976

Two-way selection for growth rate in the common carp (Cyprinus carpio L.)

The domesticated European carp was subjected to a two-way selection for growth rate. Five generations of mall selection for faster growth rate did not yield any response, but subsequent selection between groups (families) resulted in considerable progress while maintaining a large genetic variance. Selection for slow growth rate yielded relatively strong response for the first three generations. Random-bred control lines suffered from strong inbreeding depression and when two lines were crossed, the F1 showed a high degree of heterosis. Selection was performed on pond-raised fish, but growth rate was also tested in cages. A strong pond-cage genetic interaction was found. A theoretical explanation was suggested involving overdominance for fast growth rate and amplification through competition of intra-group but not inter-group variation.

Animals↗

PubMedDate not supplied

Reproductive and mate choice strategies in the hermaphroditic flatworm Echinostoma caproni.

Due to the important role that mating systems play in the evolution of species, we investigate the selfing rate and mate choice in the simultaneous hermaphroditic parasite Echinostoma caproni (Trematoda). The echinostomes were maintained in two situations in mice: (1) double infections where the two individuals do or do not belong to the same geographic area isolate, and (2) triple infections where two of the three individuals originate from the same isolate and the third one originates from a different isolate. This experimental design permits analysis of intra- and interisolate selfing rates and of mate preference. We predict, in the first experiment, no difference between intra- and interisolate selfing rates. In the second experiment we expect a preferential outcrossing between individuals originating from the same isolate in order to avoid hybrid breakdown. The results obtained corroborate our predictions and emphasize the important and synergistic roles of selfing, inbreeding depression, and hybrid breakdown in the evolution of echinostome reproductive strategies.

Animals↗

PubMedDate not supplied

Molecular genetic and morphological analyses of the African wild dog (Lycaon pictus).

African wild dog populations have declined precipitously during the last 100 years in eastern Africa. The possible causes of this decline include a reduction in prey abundance and habitat; disease; and loss of genetic variability accompanied by inbreeding depression. We examined the levels of genetic variability and distinctiveness among populations of African wild dogs using mitochondrial DNA (mtDNA) restriction site and sequence analyses and multivariate analysis of cranial and dental measurements. Our results indicate that the genetic variability of eastern African wild dog populations is comparable to that of southern Africa and similar to levels of variability found in other large canids. Southern and eastern populations of wild dogs show about 1% divergence in mtDNA sequence and form two monophyletic assemblages containing three mtDNA genotypes each. No genotypes are shared between the two regions. With one exception, all wild dogs examined from zoos had southern African genotypes. Morphological analysis supports the distinction of eastern and southern African wild dog populations, and we suggest they should be considered separate subspecies. An eastern African wild dog breeding program should be initiated to ensure preservation of the eastern African form and to slow the loss of genetic variability that, while not yet apparent, will inevitably occur if wild populations continue to decline. Finally, we examined the phylogenetic relationships of wild dogs to other wolf-like canids through analysis of 736 base pairs (bp) of cytochrome b sequence and showed wild dogs to belong to a phylogenetically distinct lineage of the wolf-like canids.

Africa, Eastern↗

PubMed2002

Low nucleotide diversity at the pal1 locus in the widely distributed Pinus sylvestris.

Nucleotide polymorphism in Scots pine (Pinus sylvestris) was studied in the gene encoding phenylalanine ammonia-lyase (Pal, EC 4.3.1.5). Scots pine, like many other pine species, has a large current population size. The observed levels of inbreeding depression suggest that Scots pine may have a high mutation rate to deleterious alleles. Many Scots pine markers such as isozymes, RFLPs, and microsatellites are highly variable. These observations suggest that the levels of nucleotide variation should be higher than those in other plant species. A 2,045-bp fragment of the pal1 locus was sequenced from five megagametophytes each from a different individual from each of four populations, from northern and southern Finland, central Russia, and northern Spain. There were 12 segregating sites in the locus. The synonymous site overall nucleotide diversity was only 0.0049. In order to compare pal1 with other pine genes, sequence was obtained from two alleles of 11 other loci (total length 4,606 bp). For these, the synonymous nucleotide diversity was 0.0056. These estimates are lower than those from other plants. This is most likely because of a low mutation rate, as estimated from between-pine species synonymous site divergence. In other respects, Scots pine has the characteristics of a species with a large effective population. There was no linkage disequilibrium even between closely linked sites. This resulted in high haplotype diversity (14 different haplotypes among 20 sequences). This could also give rise to high per locus diversity at the protein level. Divergence between populations in the main range was low, whereas an isolated Spanish population had slightly lower diversity and higher divergence than the remaining populations.

ATP-Binding Cassette Transporters↗

PubMed2000

Effective population size may limit the power of laboratory experiments to demonstrate sympatric and parapatric speciation.

Laboratory experiments designed to elucidate the mechanisms of sympatric and parapatric speciation may have been handicapped by too small population sizes, although this possibility has seldom been discussed. In this paper we review the published records of sympatric and parapatric speciation experiments to test the relative importance of selection intensity applied, duration of experiment and effective population size. Our results show that among these factors only effective population size has had a general effect on the generation of assortative mating. Reduced interbreeding is less likely to develop in small populations where the selection process often seems to have been opposed by inbreeding depression or loss of genetic variation. This study demonstrates that the experimental evidence frequently used as an argument against sympatric and parapatric speciation models is not as strong as previously believed.

Animals↗

PubMed2001

Outbreeding increases offspring survival in wild greater horseshoe bats (Rhinolophus ferrumequinum).

The factors influencing the survival of greater horseshoe bat (Rhinolophus ferrumequinum) offspring born over seven years at a maternity colony in south-west Britain were studied. The effects of a range of phenotypic and maternal variables were analysed using a historical data set. In addition, the influence of two genetic measures on mortality, individual heterozygosity and a new measure of outbreeding, termed mean d(2), was assessed. Logistic regressions were undertaken with survival modelled as a binary response variable. Survival to two life stages was studied for each variable and all models were developed for both sexes separately and together. Only one variable, mean d(2), was significantly associated with survival. Male offspring with high mean d(2) scores were more likely to survive to their first and second summers. The influence of mean d(2) was not due to a single locus under selection but a wider multilocus effect and probably represents heterosis as opposed to solely inbreeding depression. Therefore, the extent to which an individual is outbred may determine survival more than widely used phenotypic characteristics such as size and mass. Mean d(2) may reflect immunocompetence, which influences mortality. Protection of mating sites in order to facilitate gene flow and, therefore, outbreeding may help to promote population stability and growth.

Animals↗

PubMed1994

Selection by parasites for clonal diversity and mixed mating.

On theoretical grounds, coevolutionary interactions with parasites can select for cross-fertilization, even when there is a twofold advantage gained by reproducing through uniparental means. The suspected advantage of cross-fertilization stems from the production of genetically rare offspring, which are expected to be more likely to escape infection by coevolving enemies. In the present study, we consider the effects that parasites have on parthenogenetic mutants in obligately sexual, dioecious populations. Computer simulations show that repeated mutation to parthenogenesis can lead to the accumulation of clones with different resistance genotypes, and that a moderately diverse set of clones could competitively exclude the ancestral sexual subpopulation. The simulations also show that, when there are reasonable rates of deleterious mutation, Muller's ratchet combined with coevolutionary interactions with parasites can lead to the evolutionary stability of cross-fertilization. In addition, we consider the effects that parasites can have on the evolution of uniparental reproduction in cosexual populations. Strategy models show that parasites and inbreeding depression could interact to select for evolutionarily stable reproductive strategies that involve mixtures of selfed and outcrossed progeny.

Animals↗

PubMed1996

The genetical history of an isolated population of the endangered grey wolf Canis lupus: a study of nuclear and mitochondrial polymorphisms.

The grey wolf was thought to have been exterminated in the Scandinavian peninsula when the sudden appearance of a few animals in southern Sweden was reported in 1980. These wolves founded a new Swedish population which currently numbers at least 25 individuals, one of the world's smallest populations of the species. The sudden occurrence of the founder animals caused speculation that these had not appeared by 'natural' means but rather were Swedish zoo animals deliberately released by man. To analyse if this was the case and to elucidate the genetic status of this small and isolated population, we assessed nuclear and mitochondrial (mt) genetic variability in wild and captive grey wolves, using microsatellite typing and sequence analysis of the mtDNA D-loop. The new population was found to be monomorphic for a mtDNA haplotype which also was present in the Swedish zoo population. A total of four different mtDNA haplotypes were found among all captive and wild wolves (including two animals from an occasional establishment of a few wolves in northern Sweden in the late 1970s), with a maximum sequence divergence of 3.1%. Despite the mtDNA congruence, animals from the zoo population could most likely be excluded as founders for the wild population since the latter group of animals displayed several unique microsatellite alleles (i.e. alleles not found in the zoo population). Moreover, a phylogenetic analysis of individual wolves, using microsatellite allele sharing as distance measure, placed all wild animals on a branch separated from that of the captive animals. The average degree of nuclear variability as well as allelic diversity was similar in the wild and the captive populations, respectively, but was lower than that reported for North-American populations of grey wolves. Polymorphism has declined in wild wolves born in recent years suggesting that this small population is currently suffering from a loss of genetic variability due to inbreeding. Inbreeding depression is documented in captive wolves and the long-term survival of the wild Swedish population may therefore depend on immigration of animals from Russia. This study illustrates the usefulness of microsatellites for dissecting close genetic relationships and for addressing the genetic status of individuals.

Animals↗

PubMed2003

Breakdown in correlations during laboratory evolution. II. Selection on stress resistance in Drosophila populations.

We trace the evolutionary correlation between stress resistance and longevity in populations of Drosophila melanogaster selected for stress resistance over many generations. Females selected for desiccation resistance and both females and males selected for increasing starvation resistance initially show concurrent increases in longevity, but then begin to decrease in longevity, even as stress resistance continues to increase. We demonstrate that the correlation between two fitness traits can change and that this change is due to sustained selection rather than a genotype-by-environment interaction or inbreeding depression. The breakdown in evolutionary correlation we report underscores the difficulty of extrapolating the results from short-term selection experiments to predictions of long-term evolution.

Animals↗

PubMed1989

Selection of Anopheles stephensi for refractoriness and susceptibility to Plasmodium falciparum.

Variation in susceptibility of the vector Anopheles stephensi Liston to the human malaria parasite Plasmodium falciparum (Welch) was demonstrated using twelve strains of mosquitoes and one strain of parasites cultured in vitro. The Beech strain of An. stephensi exhibited greatest natural refractoriness, but with high intrapopulation variability. By selection for the required characteristic, two refractory lines of the Punjab strain and one highly susceptible line of the Sind strain were obtained. The median number of oocysts in the two refractory lines was less than 4% of that in the unselected line, whilst the highly susceptible line yielded about twice as many oocysts as the unselected line. Selection progressed more by keeping the descendants of individual females separate and selecting between them (individual selection) rather than pooling the progeny of all selected mosquitoes (mass selection). Using the former procedure many lines were lost due to inbreeding depression, but the outcome was more successful.

Animals↗

PubMed2004

Effects of variation at the flower-colour A locus on mating system parameters in Ipomoea purpurea.

Although alleles at both the W and A loci in the common morning glory, Ipomoea purpurea, produce similar white-flowered phenotypes, these alleles differ by over an order of magnitude in average frequency. In this initial attempt to determine the causes of this difference, we employed artificial arrays of plants to estimate mating system characteristics (total siring success, selfing rates and contribution to the outcross pollen pool) for the homozygous pigmented and white-flowered genotypes at the A locus. This experiment demonstrates that: (1) at both low and high frequencies, white-flowered plants were visited by pollinators at the same rate as plants with pigmented flowers; (2) at both frequencies, the a allele exhibited a greater total siring success (self and outcross pollen) than the A allele; (3) individuals of both genotypes contributed equally to the outcross pollen pool; and (4) aa plants may have a higher selfing rate than AA plants. Coupled with minimal inbreeding depression in I. purpurea, these observations indicate that the allele producing white flowers enjoys a transmission advantage that would tend to cause this allele to increase in frequency. This transmission advantage is very similar to that shown previously to be operating on the white-flowered allele at the W locus, although the specific causes of the advantage appear to differ between loci. The frequency difference between the two alleles is thus not likely to be due to differences in the effect of flower-colour variation on transmission. Rather, substantially greater deleterious pleiotropic effects associated with the white-flower a allele is likely to be the primary cause of the frequency difference.

Anthocyanins↗

PubMed2004

Population genetics after fragmentation: the case of the endangered Spanish imperial eagle (Aquila adalberti).

The highly endangered Spanish imperial eagle, Aquila adalberti, has suffered from both population decline and fragmentation during the last century. Here we describe the current genetic status of the population using an extensive sampling of its current distribution range and both mitochondrial control region sequences and nuclear microsatellite markers. Results were evaluated in comparison to those obtained for the Eastern imperial eagle, Aquila heliaca, its nearest extant relative. Mitochondrial haplotype diversity was lower in the Spanish than in the Eastern species whereas microsatellite allelic richness and expected heterozygosity did not differ. Both allelic richness and expected heterozygosity were lower in the small Parque Nacional de Doñana breeding nucleus compared to the remaining nuclei. A signal for a recent genetic bottleneck was not detected in the current Spanish imperial eagle population. We obtained low but significant pairwise FST values that were congruent with a model of isolation by distance. FST and exact tests showed differentiation among the peripheral and small Parque Nacional de Doñana population and the remaining breeding subgroups. The centrally located Montes de Toledo population did not differ from the surrounding Centro, Extremadura and Sierra Morena populations whereas the latter were significantly differentiated. On the other hand, a Bayesian approach identified two groups, Parque Nacional de Doñana and the rest of breeding nuclei. Recent migration rates into and from Parque Nacional de Doñana and the rest of breeding nuclei were detected by assignment methods and estimated as 2.4 and 5.7 individuals per generation, respectively, by a Bayesian approach. We discuss how management strategies should aim at the maintenance of current genetic variability levels and the avoidance of inbreeding depression through the connection of the different nuclei.

Animals↗

PubMed2004

Sex-specific correlation between heterozygosity and clone size in the trematode Schistosoma mansoni.

The mode of reproduction (sexual and/or asexual) and the mating system determine the patterns of gene transmission and genotype formation across generations. Schistosoma mansoni is a dioecious trematode that necessarily alternates sexual and asexual reproduction during its life cycle. In a previous study of the distribution of S. mansoni genetic variability within and between definitive host individuals, we noticed that deleting multilocus genotypes from each infrapopulation so as to keep only one copy of each multilocus genotype, seemed to have a substantial effect on FIS values. More precisely, female FIS increased when repeated genotypes were removed whereas no effect was observed on male FIS. This suggested that multilocus genotypes at high frequency tended to be more heterozygous. The aim of the present study is specifically to test and analyse this phenomenon. We demonstrate that the number of repetitions per clone correlates with individual heterozygosity. This effect is however, sex-specific: only female clone size correlates with heterozygosity. We discuss this phenomenon in relation to the heterozygosity-fitness relationship and the sex-specific response to inbreeding depression.

Animals↗

PubMed2005

Environmental and population dependency of genetic variability-fitness correlations in Rana temporaria.

Abstract Considerable effort has been invested in studying the relationship between fitness and genetic variability. While evidence exists both for and against positive genetic variability-fitness correlations (GFC), the possible environment and population-dependency of GFCs has seldom been tested. We investigated GFCs in common frog (Rana temporaria) tadpoles reared under different temperatures and feeding regimes in four replicate populations. Genetic variability in eight microsatellite loci in 238 parents was used to estimate heterozygosity (H) and mean expected d2 in 158-sibships (4515 offspring). Generalized linear mixed model analyses of offspring fitness traits (survival to metamorphosis, developmental and growth rate) revealed that offspring survival probability was positively correlated with H, and that relationships were similar in all four populations tested. However, significant interaction between other genetic variability measures (d2, relatedness) and treatment conditions indicated that GFCs were detectable in some, but not in all environments. Interestingly, GFCs between survival and both heterozygosity and relatedness were most pronounced in stressful environments (i.e. limited food). Developmental and growth rates were significantly associated with d2 but less with H and relatedness. Furthermore, many of these GFCs were population-specific. These results suggest--in line with the contention that expression of inbreeding depression can be environment dependent--that GFCs can also be highly sensitive to the environmental conditions under which they are measured. The results further suggest that the observed positive correlation between H and survival probability is likely to be explainable by the 'general', rather than by the 'local' or 'direct' effect hypotheses.

Animals↗

PubMed2005

Molecular evidence for multiple introductions of garlic mustard (Alliaria petiolata, Brassicaceae) to North America.

Invasive species offer excellent model systems for studying rapid evolutionary change. In this context, molecular markers play an important role because they provide information about pathways of introduction, the amount of genetic variation introduced, and the extent to which founder effects and inbreeding after population bottlenecks may have contributed to evolutionary change. Here, we studied microsatellite variation in eight polymorphic loci among and within 27 native and 26 introduced populations of garlic mustard (Alliaria petiolata), a European herb which is a current serious invader in North American deciduous forests. Overall, introduced populations were genetically less diverse. However, considerable variability was present and when compared to the probable source regions, no bottleneck was evident. Observed heterozygosity was very low and resulted in high inbreeding coefficients, which did not differ significantly between native and introduced populations. Thus, selfing seems to be equally dominant in both ranges. Consequently, there was strong population differentiation in the native (F(ST) = 0.704) and the introduced (F(ST) = 0.789) ranges. The high allelic diversity in the introduced range strongly suggests multiple introductions of Alliaria petiolata to North America. Out of six European regions, the British Isles, northern Europe, and central Europe had significantly higher proportions of alleles, which are common to the introduced range, and are therefore the most probable source regions. The genetic diversity established by multiple introductions, and the lack of inbreeding depression in this highly selfing species, may have contributed to the invasion success of Alliaria petiolata.

Analysis of Variance↗

PubMed2006

Seasonal changes in pollinator activity influence pollen dispersal and seed production of the alpine shrub Rhododendron aureum (Ericaceae).

In alpine ecosystems, microscale variation in snowmelt timing often causes different flowering phenology of the same plant species and seasonal changes in pollinator activity. We compared the variations in insect visitation, pollen dispersal, mating patterns, and sexual reproduction of Rhododendron aureum early and late in the flowering season using five microsatellites. Insects visiting the flowers were rare early in the flowering season (mid-June), when major pollinators were bumblebee queens and flies. In contrast, frequent visitations by bumblebee workers were observed late in the season (late July). Two-generation analysis of pollen pool structure demonstrated that quality of pollen-mediated gene flow was more diverse late in the season in parallel with the high pollinator activity. The effective number of pollen donors per fruit (N(ep)) increased late in the season (N(ep) = 2.2-2.7 early, 3.4-4.4 late). However, both the outcrossing rate (t(m)) and seed-set ratio per fruit were smaller late in the season (t(m) = 0.89 and 0.71, seed-set ratio = 0.52 and 0.18, early and late in the season, respectively). In addition, biparental inbreeding occurred only late in the season. We conclude that R. aureum shows contrasting patterns of pollen movement and seed production between early and late season: in early season, seed production can be high but genetically less diverse and, during late season, be reduced, possibly due to higher inbreeding and inbreeding depression, but have greater genetic diversity. Thus, more pollinator activity does not always mean more pollen movement.

Animals↗

PubMed2006

Population structure in a critically endangered arctic fox population: does genetics matter?

The arctic fox (Alopex lagopus) in Scandinavia is classified as critically endangered after having gone through a severe decline in population size in the beginning of the 20th century, from which it has failed to recover despite more than 65 years of protection. Arctic foxes have a high dispersal rate and often disperse over long distances, suggesting that there was probably little population differentiation within Scandinavia prior to the bottleneck. It is, however, possible that the recent decline in population size has led to a decrease in dispersal and an increase in population fragmentation. To examine this, we used 10 microsatellite loci to analyse genetic variation in 150 arctic foxes from Scandinavia and Russia. The results showed that the arctic fox in Scandinavia presently is subdivided into four populations, and that the Kola Peninsula and northwest Russia together form a large fifth population. Current dispersal between the populations seemed to be very low, but genetic variation within them was relatively high. This and the relative F(ST) values among the populations are consistent with a model of recent fragmentation within Scandinavia. Since the amount of genetic variation is high within the populations, but the populations are small and isolated, demographic stochasticity seems to pose a higher threat to the populations' persistence than inbreeding depression and low genetic variation.

Alleles↗

PubMed2006

Increased ecological amplitude through heterosis following wide outcrossing in Banksia ilicifolia R.Br. (Proteaceae).

To assess whether wide outcrossing (over 30 km) in the naturally fragmented Banksia ilicifolia R.Br. increases the ecological amplitude of offspring, we performed a comparative greenhouse growth study involving seedlings of three hand-pollinated progeny classes (self, local outcross, wide outcross) and a range of substrates and stress conditions. Outcrossed seedlings outperformed selfed seedlings, with the magnitude of inbreeding depression as high as 62% for seed germination and 37% for leaf area. Wide outcrossed seedlings outperformed local outcrossed seedlings, especially in non-native soils, facilitated in part by an improved capacity to overcome soil constraints through greater root carboxylate exudation. Soil type significantly affected seedling growth, and waterlogging and water deficit decreased growth, production of cluster roots, root exudation and total plant P uptake. Our results suggest that the interaction of narrow ecological amplitude and the genetic consequences of small fragmented populations may in part explain the narrow range of local endemics, but that wide outcrossing may provide opportunities for increased genetic variation, increased ecological amplitude and range expansion.

Ecology↗