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PubMed2002

Inbreeding alters resistance to insect herbivory and host plant quality in Mimulus guttatus (Scrophulariaceae).

Previous studies have demonstrated genetic variation for resistance to insect herbivores and host plant quality. The effect of plant mating system, an important determinant of the distribution of genetic variation, on host plant characteristics has received almost no attention. This study used a controlled greenhouse experiment to examine the effect of self- and cross-pollination in Mimulus guttatus (Scrophulariaceae) on resistance to and host plant quality for the xylem-feeding spittlebug Philaenus spumarius (Homoptera: Cercopidae). Spittlebugs were found to have a negative effect on two important fitness components in M. guttatus, flower production and above ground biomass. One of two M. guttatus populations examined showed a significant interaction between the pollination and herbivore treatments. In this case, the detrimental effects of herbivores on biomass and flower production were much more pronounced in inbred (self) plants. The presence of spittlebug nymphs increased inbreeding depression by as much as three times. Pollination treatments also had significant effects on important components of herbivore fitness, but these effects were in opposite directions in our two host plant populations. Spittlebug nymphs maturing on self plants emerged as significantly larger adults in one of our host plant populations, indicating that inbreeding increased host plant quality. In our second host plant population, spittlebug nymphs took significantly longer to develop to adulthood on self plants, indicating that inbreeding decreased host plant quality. Taken together these results suggest that the degree of inbreeding in host plant populations can have important and perhaps complex effects on the dynamics of plant-herbivore interactions and on mating-system evolution in the host.

Animals↗
PubMed2002

Inbreeding depression: tests of the overdominance and partial dominance hypotheses.

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.

Analysis of Variance↗
PubMed2003

Inbreeding and interbreeding in Darwin's finches.

Studies of inbreeding and interspecific hybridization are generally pursued separately with different metrics. There is a need to integrate them because they have the common goal of seeking an understanding of the genetic and ecological basis of fitness variation in populations. We use mean expected heterozygosity as an axis of variation on which to compare the fitness of inbreeding and hybridizing Darwin's finches (Geospiza scandens and G. fortis) relative to the fitness of matched outbred controls. We find that relative fitness of inbred finches is less than one in the 1991 cohorts of both species. Inbreeding depression is stronger in the species (G. scandens) with the lower genetically effective population size. Relative fitness of hybrids (backcrosses) in the same cohort of G. scandens is greater than one. Evidence of heterosis in G. fortis is mixed. Thus the two interbreeding species displayed somewhat different fitness patterns under the same set of environmental conditions. Hybridization may enhance fitness to different degrees by counteracting the effects of inbreeding depression, by other additive and nonadditive genetic effects, and by producing phenotypes well suited to exploit particular ecological conditions.

Animals↗
PubMed2003

Inbreeding in the greater white-toothed shrew, Crocidura russula.

We combined mark-and-recapture studies with genetic techniques of parentage assignment to evaluate the interactions between mating, dispersal, and inbreeding, in a free-ranging population of Crocidura russula. We found a pattern of limited and female-biased dispersal, followed by random mating within individual neighborhoods. This results in significant inbreeding at the population level: mating among relatives occurs more often than random, and F(IT) analyses reveal significant deficits in heterozygotes. However, related mating partners were not less fecund, and inbred offspring had no lower lifetime reproductive output. Power analyses show these negative results to be quite robust. Absence of phenotypic evidence of inbreeding depression might result from a history of purging: local populations are small and undergo disequilibrium gene dynamics. Dispersal is likely caused by local saturation and (re)colonization of empty breeding sites, rather than inbreeding avoidance.

Animals↗
PubMed2004

Inbreeding and population structure in two pairs of cryptic fig wasp species.

We used recently developed microsatellites to directly estimate inbreeding levels in two pairs of coexisting cryptic fig wasp species ('Pegoscapus hoffmeyeri sp. A and sp. B', 'P. gemellus sp. A and sp. B'). Previous tests of Hamilton's local mate competition (LMC) theory in fig wasps have used the number of dead foundresses in a fig fruit to indirectly estimate the relative contribution of each to the common brood and thereby the level of local mate competition. Further, the population level of inbreeding has been indirectly estimated using the distribution of foundress numbers across broods. Our direct genetic estimates confirmed previous assumptions that the species characterized by lower foundress numbers showed higher relative levels of inbreeding. However, there were quantitative differences between the observed level of inbreeding and the expectation based on the distribution of foundress numbers in both pollinator species associated with Ficus obtusifolia. Here, genotype compositions of broods revealed that only 23% of fruits with multiple foundresses actually contained brood from more than one foundress, thus explaining at least part of the underestimate of actual sibmating. Within the four wasp species there was no evidence for genetic differentiation among the wasp populations sampled from different trees across 20 km and from different points in time. Further, no genotypic disequilibrium was detected within any of the species. Although F1 hybrids were observed between the two species pollinating F. obtusifolia, there was no evidence of genetic introgression. Finally, we found that 11% of the sons of allospecifically mated mothers were diploid hybrids suggesting a break down of the sex determination system in hybrids.

Animals↗
PubMed2005

Gene flow and inbreeding depression inferred from fine-scale genetic structure in an endangered heterostylous perennial, Primula sieboldii.

We estimated the gene dispersal distance and the magnitude of inbreeding depression from the fine-scale genetic structure in the endangered heterostylous perennial Primula sieboldii. We indirectly estimated the neighbourhood size (Nb) and the standard deviation of gene dispersal distance (sigma(g)) from the detected genetic structure by using 10 microsatellite markers. We also estimated the fitness reduction in mating among neighbouring individuals caused by biparental inbreeding according to the genetic structure. We found clear fine-scale genetic structure (a significantly positive kinship coefficient within 42.3 m), and the indirect estimates of sigma(g) and Nb were 15.7 m and 50.9, respectively. These indirect estimates were similar to the direct estimates (18.4 m and 44.0). The slightly larger indirect estimate of Nb may reflect that inbreeding depression and genetic structure or rare long-distance dispersal that were overlooked in the direct estimate have elongated the long-term average of gene dispersal distance. P. sieboldii is also likely to suffer about 19% fitness reduction in progenies from mating among individuals 5 m apart. Our results suggest that biparental inbreeding and genetic structure can affect the range of gene dispersal and seed reproductive success in P. sieboldii.

DNA, Plant↗
PubMed2006

Inbreeding, outbreeding and environmental effects on genetic diversity in 46 walleye (Sander vitreus) populations.

Genetic diversity is recognized as an important population attribute for both conservation and evolutionary purposes; however, the functional relationships between the environment, genetic diversity, and fitness-related traits are poorly understood. We examined relationships between selected lake parameters and population genetic diversity measures in 46 walleye (Sander vitreus) populations across the province of Ontario, Canada, and then tested for relationships between six life history traits (in three categories: growth, reproductive investment, and mortality) that are closely related to fitness, and genetic diversity measures (heterozygosity, d2, and Wright's inbreeding coefficient). Positive relationships were observed between lake surface area, growing degree days, number of species, and hatchery supplementation versus genetic diversity. Walleye early growth rate was the only life history trait significantly correlated with population heterozygosity in both males and females. The relationship between FIS and male early growth rate was negative and significant (P < 0.01) and marginally nonsignificant for females (P = 0.06), consistent with inbreeding depression effects. Only one significant relationship was observed for d2: female early growth rate (P < 0.05). Stepwise regression models showed that surface area and heterozygosity had a significant effect on female early growth rate, while hatchery supplementation, surface area and heterozygosity had a significant effect on male early growth rate. The strong relationship between lake parameters, such as surface area, and hatchery supplementation, versus genetic diversity suggests inbreeding and outbreeding in some of the populations; however, the weak relationships between genetic diversity and life history traits indicate that inbreeding and outbreeding depression are not yet seriously impacting Ontario walleye populations.

Animals↗
PubMed2006

Genetic structure at range edge: low diversity and high inbreeding in Southeast Asian mangrove (Avicennia marina) populations.

Understanding the genetic composition and mating systems of edge populations provides important insights into the environmental and demographic factors shaping species' distribution ranges. We analysed samples of the mangrove Avicennia marina from Vietnam, northern Philippines and Australia, with microsatellite markers. We compared genetic diversity and structure in edge (Southeast Asia, and Southern Australia) and core (North and Eastern Australia) populations, and also compared our results with previously published data from core and southern edge populations. Comparisons highlighted significantly reduced gene diversity and higher genetic structure in both margins compared to core populations, which can be attributed to very low effective population size, pollinator scarcity and high environmental pressure at distribution margins. The estimated level of inbreeding was significantly higher in northeastern populations compared to core and southern populations. This suggests that despite the high genetic load usually associated with inbreeding, inbreeding or even selfing may be advantageous in margin habitats due to the possible advantages of reproductive assurance, or local adaptation. The very high level of genetic structure and inbreeding show that populations of A. marina are functioning as independent evolutionary units more than as components of a metapopulation system connected by gene flow. The combinations of those characteristics make these peripheral populations likely to develop local adaptations and therefore to be of particular interest for conservation strategies as well as for adaptation to possible future environmental changes.

Australia↗
PubMed2004

Mutation-selection balance accounting for genetic variation for viability in Drosophila melanogaster as deduced from an inbreeding and artificial selection experiment.

We carried out an experiment of inbreeding and upward artificial selection for egg-to-adult viability in a recently captured population of Drosophila melanogaster, as well as computer simulations of the experimental design, in order to obtain information on the nature of genetic variation for this important fitness component. The inbreeding depression was linear with a rate of 0.70 +/- 0.11% of the initial mean per 1% increase in inbreeding coefficient, and the realized heritability was 0.06 +/- 0.07. We compared the empirical observations of inbreeding depression and selection response with computer simulations assuming a balance between the occurrence of partially recessive deleterious mutations and their elimination by selection. Our results suggest that a model assuming mutation-selection balance with realistic mutational parameters can explain the genetic variation for viability in the natural population studied. Several mutational models are incompatible with some observations and can be discarded. Mutational models assuming a low rate of mutations of large average effect and highly recessive gene action, and others assuming a high rate of mutations of small average effect and close to additive gene action, are compatible with all the observations.

Animals↗
PubMed2004

Levels of inbreeding depression over seven generations of selfing in the androdioecious clam shrimp, Eulimnadia texana.

Androdioecy (mixtures of males and hermaphrodites) is a rare mating system in both plants and animals. Theory suggests that high levels of inbreeding depression can maintain males in androdioecious populations if hermaphrodites commonly self-fertilize. However, if inbreeding depression (delta) can be 'purged' from selfing populations, maintaining males is more difficult. In the androdioecious clam shrimp, Eulimnadia texana, delta is estimated to be as high as 0.7. Previous work suggests that this high level is maintained in the face of high levels of inbreeding due to an associative overdominance of fitness-related loci with the sex-determining locus. Such associative overdominance would make purging of inbreeding depression difficult to impossible. The current experiment was designed to determine if delta can be purged in these shrimp by tracking fitness across seven generations in selfing and outcrossing treatments. Evidence of purging was found in one of four populations, but the remaining populations demonstrated a consistent pattern of delta across generations. Although the experimental design allowed ample opportunity for purging, the majority of populations were unable to purge their genetic load. Therefore, delta in this species is likely due to associative overdominance caused by deleterious recessive alleles linked to the sex determining locus.

Analysis of Variance↗
PubMed2005

Inbreeding depression and heterosis in populations of Schiedea viscosa, a highly selfing species.

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.

Age Factors↗
PubMed2007

Host inbreeding increases susceptibility to ectoparasitism.

Inbreeding, which increases homozygosity throughout the genome by increasing the proportion of alleles that are identical by descent, is expected to compromise resistance against parasitism. Here, we demonstrate that host inbreeding increases susceptibility to ectoparasitism in a natural fruit fly (Drosophila nigrospiracula) - mite (Macrocheles subbadius) association, and that this effect depends on host genetic background. Moreover, flies generated from reciprocal crosses between susceptible inbred lines exhibited elevated levels of resistance similar to that in the mass-bred base population, confirming in reverse direction the causative link between expected heterozygosity and resistance. We also show that inbreeding reduces the host's ability to sustain energetically expensive behaviours, and that host exhaustion dramatically increases susceptibility. These findings suggest that inbreeding depression for resistance results from an inability to sustain defensive behaviours because of compromised physiological competence.

Analysis of Variance↗
PubMed2005

Modes and rates of selfing and associated inbreeding depression in the self-incompatible plant Senecio squalidus (Asteraceae): a successful colonizing species in the British Isles.

The strength of the self-incompatibility (SI) response in Senecio squalidus was measured across its British range. Geographic variation in SI was investigated and the extent and inheritance of pseudo-self-compatibility (PSC) and inbreeding depression were determined. Mean self-fruit-set per capitulum was calculated for individuals and sample populations. The heritability of PSC and the magnitude of inbreeding depression were assessed by comparing selfing rates and fitness trait values between SI and PSC parent-progeny lines. SI was found to be strongly expressed in S. squalidus throughout its British range, with only 3.1% of the individuals sampled showing PSC. This PSC had relatively low heritability with stronger expression of SI in selfed progeny relative to PSC parents. Inbreeding depression was shown to be great in S. squalidus, with mean life history stage values ranging from 0.18 to 0.25. The strength of SI in S. squalidus appears not to have weakened in response to its rapid colonization of Britain. The avoidance of inbreeding depression is likely to be the primary factor maintaining strong SI in this successful colonizing species.

Ecosystem↗
PubMed2006

Relative contribution of inbreeding depression and eroded adaptive diversity to extinction risk in small populations of shore campion.

To study the relative importance of inbreeding depression and the loss of adaptive diversity in determining the extinction risk of small populations, we carried out an experiment in which we crossed and self-fertilized founder plants from a single, large population of shore campion (Silene littorea Brot.). We used the seeds these plants produced to colonize 18 new locations within the distribution area of the species. The reintroduced populations were of three kinds: inbred and genetically homogeneous, each made up of selfed seed from a single plant; inbred and mixed, made up of a mixture of selfed seeds from all founder plants; and outbred and mixed, made up of a mixture of seeds obtained in outcrosses between the founders. We compared the inbred homogeneous populations with the inbred mixed to measure the effect of genetic diversity among individuals and the inbred mixed with the outbred mixed to measure the effect of inbreeding. Reintroduction success was seriously limited by inbreeding, whereas it was not affected by genetic diversity. This observation and the nonsignificant interaction between family and reintroduction location for individual plant characters suggest that the fixation of overall deleterious genes causing inbreeding depression posed a more serious threat to the short-term survival of the populations than the loss of genes involved in genotype and environment interactions. Thus, reintroduction success was related to adaptive diversity. Preventing such fixation might be the most important consideration in the genetic management and conservation of shore campion populations.

Adaptation, Physiological↗
PubMed2025

Conservation Arks: Genomic Erosion and Inbreeding in an Abundant Island Population of Koalas.

The persistence of many threatened species depends on isolated habitat patches such as conservation parks, fenced reserves, and islands. While these 'conservation arks' provide refuge from many contemporary threats, they can also pose risks of genetic diversity loss and inbreeding depression, further exacerbating extinction risk. A pertinent example is the Kangaroo Island koala population in South Australia that originated from a few translocated founding individuals in the 1920s but now sustains a large population with a low prevalence of infectious disease. We investigated the extent and consequences of founder effects on genomic diversity, inbreeding, and adaptive potential in Kangaroo Island koalas by comparing them with mainland Australian&#xa0;populations using high-coverage whole genomes. Our findings support sharp, recent declines in effective population sizes (Ne) in both mainland and Kangaroo Island populations. However, Kangaroo Island koalas had much lower individual and population-level diversity. Together with longer and more numerous runs of homozygosity and an increased proportion of homozygous genetic load, these results support the hypothesis that a severe bottleneck has contributed to inbreeding and maladaptation in Kangaroo Island koalas. While Kangaroo Island has the potential to conserve a viable population of koalas, we recommend genetic rescue to restore diversity and mitigate inbreeding depression in this isolated population. Our results emphasise the need for longitudinal genomic monitoring and genetic management to maintain long-term viability and resilience in potential conservation arks. Understanding the demographic history of such populations will help inform future conservation aimed at preventing genetic erosion and preserving biodiversity.

Animals↗
PubMed1994

An experimental study of inbreeding depression in a natural habitat.

Inbreeding is known to lead to decreased survival and reproduction in captive populations of animals. It is also important to know whether inbreeding has deleterious effects in natural habitats. An estimate was made of the effects of inbreeding in white-footed mice, Peromyscus leucopus noveboracensis, derived from a wild population. This study demonstrates that inbreeding had a significant detrimental effect on the survivorship of mice reintroduced into a natural habitat. This effect was more severe than the effect observed in laboratory studies of the population.

Analysis of Variance↗
PubMed2007

Optimisation of contribution of candidate parents to maximise genetic gain and restricting inbreeding using semidefinite programming.

An approach for optimising genetic contributions of candidates to control inbreeding in the offspring generation using semidefinite programming (SDP) was proposed. Formulations were done for maximising genetic gain while restricting inbreeding to a preset value and for minimising inbreeding without regard of gain. Adaptations to account for candidates with fixed contributions were also shown. Using small but traceable numerical examples, the SDP method was compared with an alternative based upon Lagrangian multipliers (RSRO). The SDP method always found the optimum solution that maximises genetic gain at any level of restriction imposed on inbreeding, unlike RSRO which failed to do so in several situations. For these situations, the expected gains from the solution obtained with RSRO were between 1.5-9% lower than those expected from the optimum solution found with SDP with assigned contributions varying widely. In conclusion SDP is a reliable and flexible method for solving contribution problems.

Animals↗
PubMed1991

A performance programmed method for computing inbreeding coefficients from large data sets for use in mixed-model analyses.

Coefficients of inbreeding are commonly used in mixed-model methods for forming inverses of Wright's numerator relationship matrix and transformation matrices used in variance component estimation and national cattle evaluation. Computation of exact coefficients of inbreeding from very large data sets has been believed to be too expensive or too difficult a task to perform. Approximate methods have been used instead. The effects of using approximation methods for inbred data that appear in national cattle data sets are demonstrated. An algorithm is given for the computation of inbreeding coefficients for large data sets. The algorithm feasibly computes inbreeding coefficients for large data sets even on small computing architectures.

Algorithms↗