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PubMed2005

Breeding soundness evaluations of Senepol bulls in the US Virgin Islands.

The breeding soundness evaluation (BSE) was used to evaluate Senepol (Bos taurus) bulls (n = 495) on St. Croix over a 7-year period. Young, unproven bulls (10-26 months of age) and breeding bulls (16 months to 8.5 years) were tested prior to sale or use in breeding. Inbreeding coefficients were determined for a subset of bulls (n = 290). The percentage of bulls passing the BSE increased (P < 0.0001) with age. Bulls that passed had a higher percentage (P < 0.0001) of normal and motile sperm as well as a larger (P < 0.0001) scrotal circumference than bulls that failed. No bulls failed the BSE for physical soundness traits or other health reasons. The incidence of testicular hypoplasia was 2.5 and 3.3% and the incidence of cryptorchidism was 1.4 and 0.9% in 12- and 16-month-old bulls, respectively, with no occurrence in bulls >20 months. The proportion of all bulls that failed the BSE and received an Unsatisfactory rating for scrotal circumference or sperm motility decreased (P < 0.0001) from >90 to <25% with age. The proportion of all bulls that failed the BSE and received an Unsatisfactory rating for sperm morphology decreased (P < 0.0001) from 99 to 83.3% with age. The inbreeding coefficient was higher (P < 0.03) in bulls that failed the BSE than in those that passed (2.24 +/- 0.19% versus 1.40 +/- 0.32%, respectively). There was a tendency for bulls with testicular hypoplasia or cryptorchidism to have a higher (P = 0.09) inbreeding coefficient than bulls with normal testes (2.90 +/- 0.46% versus 2.13 +/- 0.11%, respectively). In conclusion, Senepol bulls raised under tropical conditions had a low probability of passing the BSE at young ages, but the passing rate increased with age. Older Senepol bulls were more likely to fail the BSE due to abnormal sperm morphology than due to inadequate testicular size or sperm motility. To prevent unnecessary culling, a BSE should not be performed on Senepol bulls <16 months old.

Animals↗
PubMed2002

Partial male sterility and the evolution of nuclear gynodioecy in plants.

Gynodioecy, a genetic dimorphism of females and hermaphrodites, is pertinent to an understanding of the evolution of plant gender, mating and genetic variability. Classical models of nuclear gynodioecy attribute the maintenance of the dimorphism to frequency-dependent selection in which the female phenotype has a fitness advantage at low frequency owing to a doubled ovule fertility. Here, I analyse explicit genetic models of nuclear gynodioecy that expand on previous work by allowing partial male sterility in combination with either fixed or dynamically evolving mutational inbreeding depression. These models demonstrate that partial male sterility causes fitness underdominance at the mating locus, which can prevent the spread of females. However, if partial male sterility is compensated by a change in selfing rate, overdominance at the mating locus can cause the spread of females. Overdominance at introduction of the male sterility allele can be caused by high inbreeding depression and a lower selfing rate in the heterozygote, by purging of mutations by a higher selfing rate in the heterozygote, and by low inbreeding depression and a higher selfing rate in the heterozygote. These processes might be of general importance in the maintenance of mating polymorphisms in plants.

Biological Evolution↗
PubMed2005

Lethals in subdivided populations.

The fate of lethal alleles in populations is of interest in evolutionary and conservation biology for several reasons. For instance, lethals may contribute substantially to inbreeding depression. The frequency of lethal alleles depends on population size, but it is not clear how it is affected by population structure. By analysing the case of the infinite island model by numerical approaches and analytical approximations it is shown that, like population size, population structure affects the fate of lethal alleles if dominance levels are low. Inbreeding depression caused by such alleles is also affected by the population structure, whereas the mutation load is only weakly affected. Heterosis also depends on population structure, but it always remains low, of the order of the mutation rate or less. These patterns are compared with those caused by mildly deleterious mutations to give a general picture of the effect of population structure on inbreeding depression, heterosis, and the mutation load.

Alleles↗
PubMed1996

A dispersive morph in the naked mole-rat.

Close inbreeding is known for a variety of small mammal species for which a high probability of mortality during dispersal makes helping and delayed maturation a relatively secure fitness option. Prolonged inbreeding, however, is usually associated with lowered fitness, and it has been shown that most highly inbred small mammals and social insects have inbreeding-avoidance mechanisms that promote some degree of outbreeding. However, previous field and laboratory research on the naked mole-rat (Heterocephalus glaber) suggested that this cooperatively breeding rodent is highly inbred, with new colonies forming by fission. Here we report the discovery of a dispersal phenotype that may occasionally promote outbreeding in naked mole-rats. These dispersers are morphologically, physiologically and behaviourally distinct from other colony members. They are laden with fat, exhibit elevated levels of luteinizing hormone, have a strong urge to disperse, and only solicit matings with non-colony members. These findings suggest that, although rare, a dispersive morph exists within naked mole-rat colonies.

Animals↗
PubMed2006

Outbred embryos rescue inbred half-siblings in mixed-paternity broods of live-bearing females.

Females commonly mate with more than one male, and polyandry has been shown to increase reproductive success in many species. Insemination by multiple males shifts the arena for sexual selection from the external environment to the female reproductive tract, where sperm competition or female choice of sperm could bias fertilization against sperm from genetically inferior or genetically incompatible males. Evidence that polyandry can be a strategy for avoiding incompatibility comes from studies showing that inbreeding cost is reduced in some egg-laying species by postcopulatory mechanisms that favour fertilization by sperm from unrelated males. In viviparous (live-bearing) species, inbreeding not only reduces offspring genetic quality but might also disrupt feto-maternal interactions that are crucial for normal embryonic development. Here we show that polyandry in viviparous pseudoscorpions reduces inbreeding cost not through paternity-biasing mechanisms favouring outbred offspring, but rather because outbred embryos exert a rescuing effect on inbred half-siblings in mixed-paternity broods. The benefits of polyandry may thus be more complex for live-bearing females than for females that lay eggs.

Animals↗
PubMed2003

Genetic diversity and population structure of the Italian fungi belonging to the taxa Pleurotus eryngii (DC.:Fr.) Quèl and P. ferulae (DC.:Fr.) Quèl.

A study using allozymes and PCR fingerprinting was conducted to estimate the genetic diversity of Italian populations of two economically important cultivated fungal taxa, Pleurotus eryngii and P. ferulae. Very little is known about the genetic diversity distribution pattern of these taxa. Heterozygote deficiency was observed at few loci; in fact the inbreeding coefficients were not high, which demonstrates that mechanisms restrain the inbreeding act at the local level. Estimates of genetic differentiation indicated a pattern of greater variation within, rather than between, populations. These results were supported by AMOVA analysis, which attributed a low proportion of the total genetic variation to large geographical scale divergence, and indicated that most of the genetic diversity was because of differences within populations. This distribution pattern of genetic variation of P. eryngii and P. ferulae populations seems to be the result of high gene flow, by efficient basidiospore dispersal, and outcrossing mechanisms, which restrain inbreeding within populations.

DNA Fingerprinting↗
PubMed2004

Mating patterns and genetic diversity in the wild daffodil Narcissus longispathus (Amaryllidaceae).

Despite the importance of Narcissus to ornamental horticulture, there have been no population genetic studies of wild species, many of which have narrow distributions. Here, we measure selfing rates and levels of genetic diversity at allozyme loci in six populations of Narcissus longispathus, a self-compatible daffodil endemic to a few mountain ranges in southeastern Spain. The populations were distributed among four distinct river valleys encompassing two main watersheds in the Sierra de Cazorla mountains. Selfing rates averaged 0.37 (range 0.23-0.46), resulting in significant inbreeding coefficients for the progeny (f = 0.324). In contrast, estimates of inbreeding in parental genotypes were not significantly different from zero (f = 0.001), indicating that few selfed offspring survive to maturity because of inbreeding depression. Species-wide estimates of genetic diversity for the six populations were P(s) = 0.38, H(es) = 0.119 and A(s) = 1.27 with significant genetic differentiation among populations theta = 0.15. The observed patterns of genetic differentiation among populations are likely influenced by the mating system, and a combination of local topography, watershed affinities and gene flow.

Genetic Variation↗
PubMed2005

Mating system of wild Phaseolus lunatus L. and its relationship to population size.

Using isozyme variation in a naturally pollinated seed family for 10 wild Phaseolus lunatus L. (Lima bean) populations, ranging in sizes from 10 to 60 reproductive individuals, we estimated levels of outcrossing (t) and parental inbreeding coefficient (F). We also examined the relationship between outcrossing rate and population size. Average estimates of the single-locus outcrossing rate (ts) ranged from 0.024 to 0.246 (mean=0.091+/-0.065). Estimates of the multilocus outcrossing rate (tm) ranged from 0.027 to 0.268, and averaged 0.096+/-0.071. Inbreeding coefficients based on genotypic frequencies of maternal plants were positive and significantly greater than zero (F=0.504), suggesting an excess of homozygotes in all the populations studied. There was indirect evidence of nonrandom mating for outcrosses and this was mainly attributed to self-fertilisation since the averaged difference between tm and ts, which provides a measure of biparental inbreeding, represents only 1% of the autogamy rate. No significant correlation was observed between outcrossing rate and population size. Estimates of t showed significant heterogeneity among populations and factors explaining this tendency are suggested.

Electrophoresis, Starch Gel↗
PubMed2000

Absence of single-locus complementary sex determination in the braconid wasps Asobara tabida and Alysia manducator.

In species with single-locus complementary sex determination (sl-CSD), sex is determined by multiple alleles at a single locus. In the haplodiploid Hymenoptera, sl-CSD results in females, if individuals are heterozygous at the sex locus, and in males, if individuals are hemizygous (haploid males) or homozygous (diploid males). Several hymenopteran species have been shown to have sl-CSD, but in several others sl-CSD is absent and the phylogenetic distribution remains unclear. In the family Braconidae, all four species tested so far were shown to possess sl-CSD. In this study, inbreeding experiments were used to test for the presence of sl-CSD in two species belonging to a subfamily of the Braconidae, Asobara tabida and Alysia manducator (Alysiinae). In both species inbreeding experiments showed no difference in brood size or sex ratio compared to the (outbred) control group. Furthermore, the sex ratios found in the inbreeding treatment differed significantly from the sex ratios expected under sl-CSD. Therefore, we conclude that sl-CSD is absent in these species. This study is the first to show the lack of sl-CSD in species of the Braconidae family and that hymenopteran sex-determining mechanisms can vary, even within a family.

Alleles↗
PubMed2005

Low levels of linkage disequilibrium in wild barley (Hordeum vulgare ssp. spontaneum) despite high rates of self-fertilization.

High levels of inbreeding cause populations to become composed of homozygous, inbred lines. High levels of homozygosity limit the effectiveness of recombination, and therefore, retard the rate of decay of linkage (gametic phase) disequilibrium (LD) among mutations. Inbreeding and recombination interact to shape the expected pattern of LD. The actual extent of nucleotide sequence level LD within inbreeding species has only been studied in Arabidopsis, a weedy species whose global range has recently expanded. In the present study, we examine the levels of LD within and between 18 nuclear genes in 25 accessions from across the geographic range of wild barley, a species with a selfing rate of approximately 98%. In addition to examination of intralocus LD, we employ a resampling method to determine whether interlocus LD exceeds expectations. We demonstrate that, for the majority of wild barley loci, intralocus LD decays rapidly, i.e., at a rate similar to that observed in the outcrossing species, Zea mays (maize). Excess interlocus LD is observed at 15% of two-locus combinations; almost all interlocus LD involves loci with significant geographic structuring of mutational variation.

DNA, Plant↗
PubMed2003

Delayed selfing and resource reallocations in relation to mate availability in the freshwater snail Physa acuta.

We study the influence of mate availability on the mating behavior of the self-fertile, preferentially outcrossing freshwater snail Physa acuta. Previous optimization theory indicated that mating system interacts with life-history traits to influence the age at first reproduction, providing three testable predictions. First, isolated individuals should reproduce later than individuals with available mates in the expectancy of finding a partner and avoiding the cost of inbreeding. Second, resource reallocation to future fecundity is needed for such reproductive delays to evolve. Third, the reproductive delay can be optimized with respect to life-history traits (e.g., survival, growth) and the mating system (inbreeding depression). Our results largely validate these predictions. First, reproduction is significantly delayed in isolated individuals ("selfers") as compared with individuals frequently exposed to mates ("outcrossers"). Second, delayed reproduction is associated with reallocation to future growth, survival, and fecundity, although fecundity is also affected by the mating system (selfing vs. outcrossing). Third, the reproductive delay found (approximately 2 wk) is consistent with quantitative predictions from optimization models. The delay is largely heritable, which might be partly explained by among-family differences in the amount of inbreeding depression (mating system) but not growth or survival.

Animals↗
PubMed1997

Quantitative genetics of sperm precedence in Drosophila melanogaster.

To assess the genetic basis of sperm competition under conditions in which it occurs, I estimated additive, dominance, homozygous and environmental variance components, the effects of inbreeding, and the weighted average dominance of segregating alleles for two measures of sperm precedence in a large, outbred laboratory population. Both first and second male precedence show significant decline on inbreeding. Second male precedence demonstrates significant dominance variance and homozygous genetic variance, but the additive variance is low and not significantly different from zero. For first male precedence, the variance among homozygous lines is again significant, and dominance variance is larger than the additive variance, but is not statistically significant. In contrast, male mating success and other fitness components in Drosophila generally exhibit significant additive variance and little or no dominance variance. Other recent experiments have shown significant genotypic variation for sperm precedence and have associated it with allelic variants of accessory-gland proteins. The contrast between sperm precedence and other male fitness traits in the structure of quantitative genetic variation suggests that different mechanisms may be responsible for the maintenance of variation in these traits. The pattern of genetic variation and inbreeding decline shown in this experiment suggests that one or a few genes with major effects on sperm precedence may be segregating in this population.

Animals↗
PubMed1975

Population size and selection intensity effects on long-term selection response in mice.

Long-term response to within full-sib family selection for increased postweaning gain was evaluated in lines having different effective population sized (Ne) and selection intensities (i). Line designations were I4(4), I8(2), I16(2), M4(4), M8(2) and M16(2), where I and M indicate selection of the top 50% and 25%, respectively; 4, 8 and 16 represent the number of parental pairs per replicate and number of replicates is given in parentheses. Realized within full-sib family heritabilities (hR-2) in the first phase of selection (0-14 generations) were larger in 16-pair lines than in 4- and 8-pair lines. In the second phase of selection (greater than 14 generations), hR-2 declined significantly (P smaller than .01) in all lines, and only the I16 and M16 lines had hR-2 values significantly (P smaller than .01) greater than zero. Realized genetic correlations involving number born, 12-day litter weight, weaning weight and six-week weight tended to decline in the second phase of selection. The I16, M16 and control (C16) replicates were crossed in all combinations at generation 14. Crosses were then selected within litters for high postweaning gain. The hR-2 values in the crossbred lines were all larger than those in the second selection phase for M16-1. M16-2 and I16-1, but not for I16-2. Within each Ne level, total response was significantly (P smaller than .01) less for I lines compared with M lines. Total response increased as Ne increased, within each level of i. Relatively small differences in realized i values among Ne lines could not account for this result. The difference in total response among the Ne lines at a given selection intensity may be due to inbreeding depression and a combination of interactions involving "drift" and selection. By crossing replicates of the M lines with the C16 control, the effects of inbreeding depression were removed. Inbreeding depression and genetic drift, as defined herein, were equally important in accounting for differences among Ne lines in total response.

Animals↗
PubMed1977

Genetic analysis of a strain of mice plateaued for litter size.

A strain of mice (S1) was successfully selected for large litter size for 31 generations, increasing the mean by 4.2 young per litter. After generation 31, there was no further progress and it was concluded that a selection plateau had been reached. Realized heritability decreased during the course of the experiment from 0.16+/-0.06 for the first 15 generations to 0.00+/-0.03 for generations 30 through 45.--In order to explore the nature of the selection plateau, the following groups were derived from line S1 at generation 34 or 35: Upward selection with inbreeding (SF), random (relaxed) selection (SO), and downward selection (SR). Selections were carried out for 10 to 11 generations. The means of SO and SF were similar to those of S1, ruling out any major effect of natural selection or overdominance. SR decreased, the mean averaging 2.3 young per litter below that of S1 during the last three generations. The fact that SR responded to selection indicates that genetic variance was still present in the plateaued population. The SF sublines were crossed when the inbreeding was 95% and a new line, SX, was formed. SX was maintained for three generations and the difference of +0.7 young per litter above the contemporary generations of S1 was significant. The results from this experiment suggest that the selection plateau in line S1 was caused by reduction of additive genetic variance to a very low level. Some nonadditive genetic variance remained, however, and was attributed to recessive alleles at low frequency. In agreement with results reported by Falconer (1971), inbreeding with selection followed by crossing of the inbred sublines proved to be effective in overcoming a selection plateau in litter size.

Animals↗
PubMedDate not supplied

Outcrossing rates and relatedness estimates in pecan (Carya illinoinensis) populations.

Estimates of single and multilocus outcrossing rates as well as relatedness among progeny of individual seed trees were obtained for 14 populations of pecan [Carya illinoinensis (Wangenh.) K. Koch]. Mean outcrossing estimates were not significantly different from 1.0 and relatedness values indicate that most progeny within families are half sibs. Biparental inbreeding was insignificant in all study sites, and inbreeding coefficients indicated that populations were close to inbreeding equilibrium.

Crosses, Genetic↗
PubMed2026

Ex situ reared black-footed ferrets exhibit altered sperm DNA methylation.

Many endangered species rely on ex situ management for survival when external threats exist on the landscape. Yet, ex situ settings pose challenges through space limitation, altered environment, and diet. This can lead to environmentally determined inbreeding depression, where ex situ animals exhibit reduced reproductive fitness compared with their in situ counterparts, despite originating from the same genetic stock. We investigated epigenetic differences as a potential mechanism underlying environmentally determined inbreeding depression in black-footed ferrets (Mustela nigripes), a North American endemic species reliant on ex situ conservation. More specifically, we explored how environmental context may influence sperm DNA methylation in samples collected from 12 ex situ and 5 in situ males. Average sperm DNA methylation was significantly higher in ex situ individuals. We additionally identified more than&#x2009;500 differentially methylated regions between ex situ and in situ sperm samples that were enriched for gene ontology terms pertaining to reproduction and development. Putative genes of interest included NPR2, WEE2, SLC15A1, PDE10A, PIP5K1B, CACNA1E, and CACNA1A, all of which have previously been linked to spermatogenesis, sperm motility, or fertilization in mammals. Results suggest that environmental conditions may alter sperm DNA methylation in black-footed ferrets, with possible links to decreased reproductive success in ex situ settings. These findings provide valuable insights into the molecular mechanisms underlying environmentally determined inbreeding depression in black-footed ferrets and other conservation-reliant species, and can serve as a foundation for future research on improving reproductive health in endangered wildlife.

Animals↗
PubMedDate not supplied

Origin of the B/J, R/J, and Y/J strains of rabbits.

The inbreeding of strains B/J, Y/J, and R/J, formerly designated ACCR(B), ACCR(Y), and ACCR(R), was started by full brother X sister inbreeding by C. Cohen to test the effect of inbreeding on the selective value of the different blood group genes.

Animals↗
PubMed1997

Microsatellite variation and evolution in the Mimulus guttatus species complex with contrasting mating systems.

Mutational variability at microsatellite loci is shaped by both population history and the mating system. In turn, alternate mating systems in flowering plants can resolve aspects of microsatellite loci evolution. Five species of yellow monkeyflowers (Mimulus sect. Simiolis) differing for historical rates of inbreeding were surveyed for variation at six microsatellite loci. High levels of diversity at these loci were found in both outcrossing and selfing taxa. In line with allozyme studies, inbreeders showed more partitioning of diversity among populations, and diversity in selfing taxa was lower than expected from reductions in effective population size due to selfing alone, suggesting the presence of either population bottlenecks or background selection in selfers. Evaluation of the stepwise mutation model (a model of DNA replication slippage) suggests that these loci evolve in a stepwise fashion. Inferred coalescent times of microsatellite alleles indicate that past bottlenecks of population size or colonization events were important in reducing diversity in the inbreeding taxon.

Alleles↗