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1.
Mating between relatives often results in negative fitness consequences or inbreeding depression. However, the expression of inbreeding in populations of wild cooperative mammals and the effects of environmental, maternal and social factors on inbreeding depression in these systems are currently not well understood. This study uses pedigree‐based inbreeding coefficients from a long‐term study of meerkats (Suricata suricatta) in South Africa to reveal that 44% of the population have detectably non‐zero (F > 0) inbreeding coefficients. 15% of these inbred individuals were the result of moderate inbreeding (F 0.125), although such inbreeding events almost solely occurred when mating individuals had no prior experience of each other. Inbreeding depression was evident for a range of traits: pup mass at emergence from the natal burrow, hind‐foot length, growth until independence and juvenile survival. However, we found no evidence of significant inbreeding depression for skull and forearm length or for pup survival. This research provides a rare investigation into inbreeding in a cooperative mammal, revealing high levels of inbreeding, considerable negative consequences and complex interactions with the social environment.  相似文献   

2.
The deleterious effects of inbreeding can be substantial in wild populations and mechanisms to avoid such matings have evolved in many organisms. In situations where social mate choice is restricted, extrapair paternity may be a strategy used by females to avoid inbreeding and increase offspring heterozygosity. In the cooperatively breeding Seychelles warbler, Acrocephalus sechellensis, neither social nor extrapair mate choice was used to avoid inbreeding facultatively, and close inbreeding occurred in approximately 5% of matings. However, a higher frequency of extra-group paternity may be selected for in female subordinates because this did reduce the frequency of mating between close relatives. Inbreeding resulted in reduced individual heterozygosity, which, against expectation, had an almost significant (P = 0.052), positive effect on survival. Conversely, low heterozygosity in the genetic mother was linked to reduced offspring survival, and the magnitude of this intergenerational inbreeding depression effect was environment-dependent. Because we controlled for genetic effects and most environmental effects (through the experimental cross-fostering of nestlings), we conclude that the reduced survival was a result of maternal effects. Our results show that inbreeding can have complicated effects even within a genetic bottlenecked population where the "purging" of recessive alleles is expected to reduce the effects of inbreeding depression.  相似文献   

3.
In a controlled crossing experiment on Lychnis flos-cuculi plants in the greenhouse, outbred and selfed maternal plants were each treated with pollen from unrelated plants, siblings and selves. The seeds thus obtained had expected inbreeding coefficients of 0, 0.25 and 0.5 for the outbred maternal plants, and 0, 0.5 and 0.75 for the selfed maternal plants. Seed abortion rate, seed weight and germination rate were estimated. Seedlings were transplanted to an outdoor garden, and monitored for survival, probability of flowering, number of capsules and area of capsules next spring. Inbred seeds germinated slower and in lower proportions than those less inbred, and seedlings had lower survival, flowering, fruit set and area of capsules if inbred. Combined fitness values were estimated from the survival and fecundity components, and severe inbreeding depression was detected for these estimates (0.51 and 0.56 for one generation of selfing). The fitness function decreased linearly with the increase in inbreeding coefficient, which is as expected if the inbreeding depression is additive among loci.  相似文献   

4.
Although inbreeding depression is a major genetic phenomena influencing individual fitness, it is difficult to measure in wild populations. An alternative approach is to correlate heterozygosity, measured using highly polymorphic markers, with a fitness-correlated trait. In clonal plants, genet size is predicted to be fitness correlated. Here we test the prediction that the genet size distribution of the marine clonal plant Zostera marina (eelgrass) is influenced by inbreeding depression. We used nine polymorphic microsatellite markers to access the fine scale clonal structure and to measure individual heterozygosity within 4 plots (each corresponds to 256 m2, sampled at 1-m intervals) in two populations along the German Baltic Coast. The same plots were also sampled for flowering and vegetative shoots to obtain estimates for sexual reproductive output at the level of the genetic individual. We found substantial differences in the genet size distribution between the two populations that may be explained by different disturbance frequency. In both populations, clone size was significantly positively correlated with the total number of flowering shoots, indicating that larger clones have a higher reproductive output. Individual heterozygosity was significantly positively associated with clone size. The effect was much stronger in Falkenstein (low disturbance) than in Maasholm (high disturbance). The results indicate that in a low disturbance population the relatively outbred clones occupy a higher proportion of the available space, possibly because they outcompete relatively inbred neighbours.  相似文献   

5.
The evolution of selfing taxa from outcrossing ancestors has occurred repeatedly and is the subject of many theoretical models, yet few empirical studies have examined the immediate consequences of inbreeding in a population with variable expression of self-incompatibility. Because self-incompatibility breaks down with floral age in Campanula rapunculoides, we were able to mate outbred and selfed maternal plants in a crossing design which produced progeny with inbreeding coefficients of 0, 0.25, 0.50 and 0.75. Cumulative inbreeding depression in plants that were selfed for one generation was very high in families derived from strongly self-incompatible plants (average δ = 0.98), and somewhat lower in families derived from plants with weaker expression of self-incompatibility (average δ = 0.90). Relative to outbred progeny, inbred progeny produced fewer seeds, had lower rates of germination, less vegetative growth and fewer flowers per plant. Inbred progeny also took longer to germinate, and longer to produce a first leaf and to flower. Interestingly, inbred plants also produced 40% fewer seeds than outcrossed plants (t-test P < 0.001) even when mated to the same, unrelated pollen donor, suggesting that inbreeding can produce profound maternal effects. Most importantly, our results demonstrate that progeny derived from plants with stronger expression of self-incompatibility exhibited greater levels of inbreeding depression than progeny from plants with weaker expression of self-incompatibility. Moreover, the decline in fitness (cumulative, ln-transformed) over the four inbreeding levels was steeper for the progeny of the strongly self-incompatible lineages. These empirical results suggest that inbreeding depression and mating system phenotype have the potential to coevolve.  相似文献   

6.
Inbreeding depression plays a major role in shaping mating systems: in particular, inbreeding avoidance is often proposed as a mechanism explaining extra‐pair reproduction in socially monogamous species. This suggestion relies on assumptions that are rarely comprehensively tested: that inbreeding depression is present, that higher kinship between social partners increases infidelity, and that infidelity reduces the frequency of inbreeding. Here, we test these assumptions using 26 years of data for a cooperatively breeding, socially monogamous bird with high female infidelity, the superb fairy‐wren (Malurus cyaneus). Although inbred individuals were rare (~6% of offspring), we found evidence of inbreeding depression in nestling mass (but not in fledgling survival). Mother–son social pairings resulted in 100% infidelity, but kinship between a social pair did not otherwise predict female infidelity. Nevertheless, extra‐pair offspring were less likely to be inbred than within‐pair offspring. Finally, the social environment (the number of helpers in a group) did not affect offspring inbreeding coefficients or inbreeding depression levels. In conclusion, despite some agreement with the assumptions that are necessary for inbreeding avoidance to drive infidelity, the apparent scarcity of inbreeding events and the observed levels of inbreeding depression seem insufficient to explain the ubiquitous infidelity in this system, beyond the mother–son mating avoidance.  相似文献   

7.
Inbreeding depression is the loss of fitness resulting from the mating of genetically related individuals. Traditionally, the study of inbreeding depression focused on genetic effects, although recent research has identified DNA methylation as also having a role in inbreeding effects. Since inbreeding depression and DNA methylation change with age and environmental stress, DNA methylation is a likely candidate for the regulation of genes associated with inbreeding depression. Here, we use a targeted, multigene approach to assess methylation at 22 growth‐, metabolic‐, immune‐ and stress‐related genes. We developed PCR‐based DNA methylation assays to test the effects of intense inbreeding on intragenic gene‐specific methylation in inbred and outbred Chinook salmon. Inbred fish had altered methylation at three genes, CK‐1, GTIIBS and hsp70, suggesting that methylation changes associated with inbreeding depression are targeted to specific genes and are not whole‐genome effects. While we did not find a significant inbreeding by age interaction, we found that DNA methylation generally increases with age, although methylation decreased with age in five genes, CK‐1, IFN‐?, HNRNPL, hsc71 and FSHb, potentially due to environmental context and sexual maturation. As expected, we found methylation patterns differed among tissue types, highlighting the need for careful selection of target tissue for methylation studies. This study provides insight into the role of epigenetic effects on ageing, environmental response and tissue function in Chinook salmon and shows that methylation is a targeted and regulated cellular process. We provide the first evidence of epigenetically based inbreeding depression in vertebrates.  相似文献   

8.
When replicate cultures ofT. confusum andT. castaneum are husbanded together under identical treatment conditions, sometimesT. confusum eliminatesT. castaneum, and other times,T. castaneum wins (i.e., competitive indeterminacy occurs). While several plausible explanations were advanced, the results of Mertz et al. (1976) implicated demographic stochasticity and not classical genetic founder effect as the predominant factor influencing the identity of the winning species. They also observed, however, that the size of the founding population had an influence on the competitive strength ofT. castaneum. The present study shows that the decline in competitive strength that accompanied decreasing founder size inT. castaneum can be amply explained by simple inbreeding depression. The eggs of inbred adults showed an approximate 15% reduction in hatchability when compared to outbred adults. No evidence was found that the decrease in competitive strength was due either to prior history differences or reduced genetic heterogeneity of the founding adults.  相似文献   

9.
An optimal crossing distance exists within plant populations if inbreeding and outbreeding depression operate simultaneously. In a population of tetraploid Digitalis purpurea, maternal plants were pollinated with donors at four distances: 0 (self-pollination), 1, 6 and 30 m. Lifetime fitness of F1 progeny was investigated in greenhouse experiments, and significant inbreeding and outbreeding depression were detected at five vs. three life history traits. Inbreeding depression increased at later life stages, whereas outbreeding depression was relatively constant. The existence of within-population outbreeding depression suggests substantial genetic structuring at moderate distances in D. purpurea, and corroborates recent findings of significant outbreeding depression in F1 progeny in polyploids. The moderate inbreeding depression found in this predominately outcrossing population supports the notion that effects of inbreeding are less severe in polyploids than in diploids.  相似文献   

10.
Summary Traditional methods of assessing population viability ignore both genetic—demographic interactions as well as community level dynamics. We address these deficiencies by presenting a model that investigates the effects of predation on a prey population experiencing inbreeding depression. Beginning with a simple Lotka—Volterra predator—prey system, we rewrite prey per capita mortality as a function of inbreeding. Inbreeding varies as a function of population size. Using computer simulation, we find that prey extinction times are inversely related to the level of inbreeding depression with and without predation. For all but very low levels of inbreeding depression, predation appreciably reduces persistence time. At moderate levels of inbreeding, predators go extinct before prey. When migration is introduced at low and moderate rates, persistence times only improve for those populations with low inbreeding depression measures. At a higher migration rate, persistence times are lengthened for low and moderately depressed prey populations. Increasing birth rates produce a visible, though noisy, trend towards increased times to extinction for low to moderate levels of inbreeding.  相似文献   

11.
The reproductive mechanism, that is whether an organism outcrosses, selfs or asexually reproduces, has a substantial impact on the amount and pattern of genetic variation. In this study, we estimate genetic variation and genetic load for a predominately asexual population of Mimulus guttatus, and then compare our results to other studies of predominately sexually reproducing (outcrossing and selfing) populations of M. guttatus. The asexual population had low levels of heterozygosity (He = 0.03) and low (but significantly non‐zero) inbreeding load, especially when compared with other M. guttatus populations. This differs greatly from the sexual populations of Mimulus that display substantial inbreeding depression. We discuss a variety of reasons why we see such low load in this study and suggest future research projects to further explore the questions.  相似文献   

12.
Inbreeding depression occurs when individuals who are closely related mate and produce offspring with reduced fitness. Although inbreeding depression is a genetic phenomenon, the magnitude of inbreeding depression can be influenced by environmental conditions and parental effects. In this study, we tested whether size-based parental effects influence the magnitude of inbreeding depression in an insect with elaborate and obligate parental care (the burying beetle, Nicrophorus orbicollis). We found that larger parents produced larger offspring. However, larval mass was also influenced by the interaction between parental body size and larval inbreeding status: when parents were small, inbred larvae were smaller than outbred larvae, but when parents were large this pattern was reversed. In contrast, survival from larval dispersal to adult emergence showed inbreeding depression that was unaffected by parental body size. Our results suggest that size-based parental effects can generate variation in the magnitude of inbreeding depression. Further work is needed to dissect the mechanisms through which this might occur and to better understand why parental size influences inbreeding depression in some traits but not others.  相似文献   

13.
Inbreeding and extinction: Effects of rate of inbreeding   总被引:5,自引:0,他引:5  
Deleterious alleles may be removed (purged) bynatural selection in populations undergoinginbreeding. However, there is controversyregarding the effectiveness of selection inreducing the risk of extinction due toinbreeding, especially in relation to the rateof inbreeding. We evaluated the effect of therate of inbreeding on reducing extinction risk,in populations of Drosophila melanogastermaintained using full-sib mating (160replicates), or at effective population sizes(N e) of 10 (80) or 20 (80).Extinction rates in the populations maintainedusing full-sib mating occurred at lower levelsof inbreeding than in the larger populations,whereas the two larger populations did notdiffer significantly from each other.Inbreeding coefficients at 50% extinction were0.62, 0.79 and 0.77 for the full-sib (N e = 2.6), N e = 10 and N e = 20 treatments, respectively. Populations of N e = 20 that remained extant after 60 generations, showed inbreeding depression, with the mean fitness of these populations being only 45% of the outbredcontrols. There was considerable variationamong the 31 inbred populations in fitness, butnone of the N e = 20 populations hadfitness that was higher than the outbredcontrol. We conclude that purging may slow therate of extinction slightly, but it cannot berelied on to eliminate the deleterious effectsof inbreeding.  相似文献   

14.
Despite strong empirical evidence of the harmful effects of inbreeding on fecundity, spontaneous recessive deleterious mutations are generally considered as acting on survival only in evolutionary models and population viability analyses. In this study, we modelled a species with separate sexes to assess the effect of selection on fecundity in small populations on the risk of extinction. We showed that the impact of inbreeding on short-term fitness changes and that population dynamics are strongly influenced by phenotypic interactions among males and females during reproduction. In particular, population persistence was found to be highly sensitive to the level at which selection acts (i.e. individual vs. pair) and to asymmetry among sexes (in terms of mutation rates and mutational effects).  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 86 , 467–476.  相似文献   

15.
There is ample evidence for inbreeding depression manifested as a reduction in fitness or fitness‐related traits in the focal individual. In many organisms, fitness is not only affected by genes carried by the individual, but also by genes carried by their parents, for example if receiving parental care. While maternal effects have been described in many systems, the extent to which inbreeding affects fitness directly through the focal individual, or indirectly through the inbreeding coefficients of its parents, has rarely been examined jointly. The Soay sheep study population is an excellent system in which to test for both effects, as lambs receive extended maternal care. Here, we tested for both maternal and individual inbreeding depression in three fitness‐related traits (birthweight and weight and hindleg length at 4 months of age) and three fitness components (first‐year survival, adult annual survival and annual breeding success), using either pedigree‐derived inbreeding or genomic estimators calculated using ~37 000 SNP markers. We found evidence for inbreeding depression in 4‐month hindleg and weight, first‐year survival in males, and annual survival and breeding success in adults. Maternal inbreeding was found to depress both birthweight and 4‐month weight. We detected more instances of significant inbreeding depression using genomic estimators than the pedigree, which is partly explained through the increased sample sizes available. In conclusion, our results highlight that cross‐generational inbreeding effects warrant further exploration in species with parental care and that modern genomic tools can be used successfully instead of, or alongside, pedigrees in natural populations.  相似文献   

16.
The nematode Caenorhabditis elegans reproduces primarily by self-fertilization of hermaphrodites, yet males are present at low frequencies in natural populations (androdioecy). The ancestral state of C. elegans was probably gonochorism (separate males and females), as in its relative C. remanei. Males may be maintained in C. elegans because outcrossed individuals escape inbreeding depression. The level of inbreeding depression is, however, expected to be low in such a highly selfing species, compared with an outcrosser like C. remanei. To investigate these issues, we measured life-history traits in the progeny of inbred versus outcrossed C. elegans and C. remanei individuals derived from recently isolated natural populations. In addition, we maintained inbred lines of C. remanei through 13 generations of full-sibling mating. Highly inbred C. remanei showed dramatic reductions in brood size and relative fitness compared to outcrossed individuals, with evidence of both direct genetic and maternal-effect inbreeding depression. This decline in fitness accumulated over time, causing extinction of nearly 90% of inbred lines, with no evidence of purging of deleterious mutations from the remaining lines. In contrast, pure strains of C. elegans performed better than crosses between strains, indicating outbreeding depression. The results are discussed in relation to the evolution of androdioecy and the effect of mating system on the level of inbreeding depression.  相似文献   

17.
In natural populations, the expression and severity of inbreeding depression can vary widely across taxa. Describing processes that influence the extent of inbreeding and inbreeding depression aid in our understanding of the evolutionary history of mating systems such as cooperative breeding and nonrandom mate selection. Such findings also help shape wildlife conservation theory because inbreeding depression reduces the viability of small populations. We evaluated the extent of inbreeding and inbreeding depression in a small, re‐introduced population of red wolves (Canis rufus) in North Carolina. Since red wolves were first re‐introduced in 1987, pedigree inbreeding coefficients (f) increased considerably and almost every wild born wolf was inbred (average = 0.154 and max = 0.383). The large inbreeding coefficients were due to both background relatedness associated with few founders and numerous close relative matings. Inbreeding depression was most evident for adult body size and generally absent for direct fitness measures such as reproductive success and survival; no lethal equivalents (LE = 0.00) were detected in juvenile survival. The lack of strong inbreeding depression in direct measures of fitness could be due to a founder effect or because there were no outbred individuals for comparison. Our results highlight the variable expression of inbreeding depression across traits and the need to measure a number of different traits when evaluating inbreeding depression in a wild population.  相似文献   

18.
Progeny from self-pollinations and intrapopulation crosses were examined in Schiedea viscosa to determine the extent of inbreeding depression in this highly selfing species. Progeny of interpopulation crosses were also investigated to determine whether deleterious alleles have been fixed in populations of S. viscosa. There was no inbreeding depression at early life history stages, including seeds per capsule, seed mass, or germination. Inbreeding depression was detected for the later life history stage of fruit biomass, although not for survival or life span. Heterosis for vegetative biomass and fruit biomass was detected in progeny from crosses between populations. Levels of inbreeding depression in S. viscosa are low relative to out-crossing species of Schiedea, especially when early life history stages are compared.  相似文献   

19.
The two principal theories of the causal mechanism for inbreeding depression are the partial dominance hypothesis and the overdominance hypothesis. According to the first hypothesis, inbreeding increases the frequency of homozygous combinations of deleterious recessive alleles thereby decreasing fitness, whereas the overdominance hypothesis posits that inbreeding increases homozygosity and thus reduces the frequency of the superior heterozygotes. These two hypotheses make different predictions on the effect of crossing inbred lines: the overdominance hypothesis predicts that trait means will be restored to the outbred means, whereas the partial dominance hypothesis predicts that trait means will exceed those of the outbred population. I tested these predictions using seven inbred lines of the sand cricket, Gryllus firmus. Fourteen generations of brother-sister mating resulted in an inbreeding depression of 20-34% in four traits: nymphal weights at ages 14 days, 21 days, 28 days, and early fecundity. An incomplete diallel cross of these lines showed genetic variation among lines and an increase in all trait means above the outbred means, with three being significantly higher. These results provide support for the partial dominance hypothesis and are inconsistent with the overdominance hypothesis.  相似文献   

20.
There have been relatively few studies designed to investigate the effects of inbreeding on behavioral traits. To study this phenomenon, five experimental lines ofDrosophila melanogaster made isogenic for chromosome 2 were evaluated for their male-mating ability and, subsequently, male courtship behavior. All lines showed significant reductions in overall mating ability, and males from all of these lines displayed impaired mating behavior, with two lines displaying particularly aberrant courtship patterns. Line 16 displayed an inability to successfully initiate copulation following successful courtship, while line 17 displayed significant reduction in locomotor activity, resulting in virtually no successful courtship or copulatory activity. The implications of these findings for competitive mating ability in wildDrosophila populations are presented. Further, the importance of mating success as a fitness component in the management of potentially highly inbred populations of endangered species is discussed.  相似文献   

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