Generations Of Full-sib Mating Research Articles

Detecting purging of inbreeding depression by a slow rate of inbreeding for various traits: the impact of environmental and experimental conditions.

Inbreeding depression (ID) has since long been recognized as a significant factor in evolutionary biology. It is mainly the consequence of (partially) recessive deleterious mutations maintained by mutation-selection balance in large random mating populations. When population size is reduced, recessive alleles are increasingly found in homozygous condition due to drift and inbreeding and become more prone to selection. Particularly at slow rates of drift and inbreeding, selection will be more effective in purging such alleles, thereby reducing the amount of ID. Here we test assumptions of the efficiency of purging in relation to the inbreeding rate and the experimental conditions for four traits in D. melanogaster. We investigated the magnitude of ID for lines that were inbred to a similar level, F ≈ 0.50, reached either by three generations of full-sib mating (fast inbreeding), or by 12 consecutive generations with a small population size (slow inbreeding). This was done on two different food media. We observed significant ID for egg-to-adult viability and heat shock mortality, but only for egg-to-adult viability a significant part of the expressed inbreeding depression was effectively purged under slow inbreeding. For other traits like developmental time and starvation resistance, however, adaptation to the experimental and environmental conditions during inbreeding might affect the likelihood of purging to occur or being detected. We discuss factors that can affect the efficiency of purging and why empirical evidence for purging may be ambiguous.

High genetic load in an old isolated butterfly population

We investigated inbreeding depression and genetic load in a small (N(e) ∼ 100) population of the Glanville fritillary butterfly (Melitaea cinxia), which has been completely isolated on a small island [Pikku Tytärsaari (PT)] in the Baltic Sea for at least 75 y. As a reference, we studied conspecific populations from the well-studied metapopulation in the Åland Islands (ÅL), 400 km away. A large population in Saaremaa, Estonia, was used as a reference for estimating genetic diversity and N(e). We investigated 58 traits related to behavior, development, morphology, reproductive performance, and metabolism. The PT population exhibited high genetic load (L = 1 - W(PT)/W(ÅL)) in a range of fitness-related traits including adult weight (L = 0.12), flight metabolic rate (L = 0.53), egg viability (L = 0.37), and lifetime production of eggs in an outdoor population cage (L = 0.70). These results imply extensive fixation of deleterious recessive mutations, supported by greatly reduced diversity in microsatellite markers and immediate recovery (heterosis) of egg viability and flight metabolic rate in crosses with other populations. There was no significant inbreeding depression in most traits due to one generation of full-sib mating. Resting metabolic rate was significantly elevated in PT males, which may be related to their short lifespan (L = 0.25). The demographic history and the effective size of the PT population place it in the part of the parameter space in which models predict mutation accumulation. This population exemplifies the increasingly common situation in fragmented landscapes, in which small and completely isolated populations are vulnerable to extinction due to high genetic load.

Growth and Short Term Egg Production of Two Exotic (Layer Type) and the Local Chickens Compared with Their F1 Inbred Progenies

The objective of this study was to compare the growth and short term egg production of two exotic and the local chicken with those of their F1 inbred progenies in order to determine the effect of one generation of full sib mating on these traits. The two exotic chickens were H and N Brown Nick (strain 1) and Black Olympia (strain 2) while the local chicken was strain 3. The experimental birds were raised in deep litter pens from day old to 40 weeks of age. The coefficient of inbreeding of the three strains were as follows: strain 1 (10.80%), strain 2 (9.00%) and strain 3 (11.80%). Body weight, weight gain, age at first egg, age at peak egg production, egg weight, hen day rate and feed per dozen eggs were significantly (p<0.01) depressed in the two exotic (strains 1 and 2) but not in the local chicken except age at peak egg production. The parent consumed significantly (p<0.01) more feed to first egg compared with the inbred progeny of strain 1. The reverse was the case in strain 2. Total feed to first egg was similar in both generations of strain 3. The inbred progeny generation of the two exotic strains recorded more mortality compared with the parents. Both generations of strain 3 did not record any mortality during the laying period. It was concluded that generating replacement stock through inbreeding should be avoided in the exotic chicken but not in the local type.

Inbreeding depression affects life-history traits but not infection by Plasmodium gallinaceum in the Asian tiger mosquito, Aedes albopictus

Emerging and re-emerging vector-borne diseases represent an increasingly significant public health challenge. While geographic variation among populations of vector species for susceptibility to pathogen infection and vector competence has been thoroughly documented, relatively little attention has been devoted to understanding the ultimate evolutionary causes of this intraspecific variation. Local genetic drift is known to influence genetic differentiation among populations for a variety of container-inhabiting mosquito species, including Aedes albopictus. Because genetic drift is expected to reduce genetic variation and lead to the accumulation of (partially) recessive deleterious alleles, we hypothesized that reduced genetic variation might affect susceptibility to pathogen infection in a model pathogen-vector system. We therefore created replicate inbred (two generations of full-sib mating, expected f = 0.375) and control (expected f ≈ 0.07) lines of Ae. albopictus and measured life-history traits including larval survivorship, adult longevity, and female wing length (body size) as well as susceptibility to infection by a model pathogen, Plasmodium gallinaceum. Inbred mosquitoes had significantly reduced larval survivorship and female adult longevity but inbreeding did not affect male adult longevity or female wing length (body size). Furthermore, there was no effect of inbreeding on susceptibility to infection by P. gallinaceum. Therefore, while our results did not support the hypothesis that reduced genetic variation influences susceptibility to pathogen infection in this system, we did find evidence for an effect of reduced genetic variation on female adult longevity, an important component of vectorial capacity. We suggest that additional research is needed to elucidate the genetic underpinnings of intraspecific variation in traits related to disease transmission and discuss the implications of our results for the efficacy of creating transgenic strains refractory to disease transmission.

Effects of inbreeding on fitness components of Cotesia glomerata, a parasitoid wasp with single-locus complementary sex determination (sl-CSD)

Abstract In many hymenopteran species with single-locus complementary sex determination (sl-CSD) system, inbreeding will lead to an increase in the proportion of male offspring due to the production of diploid sons. Since diploid males are normally inviable or sterile, their production generates a genetic load to the population. Although it has been well documented that many sl-CSD species suffer sever inbreeding depression in sex ratio, the impact of inbreeding on other fitness components in such species is rarely known. In this study we pursue this issue in Cotesia glomerata, a gregarious parasitoid species with sl-CSD, by comparing three fitness traits (i.e., development time, brood size and body size), as well as sex ratio, between experimentally imposed inbred and outbred populations. Results of breeding experiments showed that one generation of full-sib mating in C. glomerata resulted in a significantly higher proportion of males (43%) compared with outbred control (29%), and the sex ratio shifts are largely in agreement with sl-CSD model. When the inbreeding level increased over four consecutive generations, brood sex ratios became more male-biased. However, no significant differences were found in the egg-to-adult development time and brood size between inbred and outbred groups. Inbreeding had no negative effect on the body size (measured as hind tibia length) of both female and male wasps. When the relationship of body size and brood size was analyzed with a general linear model, a significantly negative correlation was found for wasps of both sexes. These findings may have implications for the laboratory rearing of C. glomerata and the evolution of gregariousness and inbreeding in the parasitoids species with sl-CSD.

Reduced inbreeding depression due to historical inbreeding in Drosophila melanogaster: evidence for purging

An important issue in conservation biology and the study of evolution is the extent to which inbreeding depression can be reduced or reversed by natural selection. If the deleterious recessive alleles causing inbreeding depression can be 'purged' by natural selection, outbred populations that have a history of inbreeding are expected to be less susceptible to inbreeding depression. This expectation, however, has not been realized in previous laboratory experiments. In the present study, we used Drosophila melanogaster as a model system to test for an association between inbreeding history and inbreeding depression. We created six 'purged' populations from experimental lineages that had been maintained at a population size of 10 male-female pairs for 19 generations. We then measured the inbreeding depression that resulted from one generation of full-sib mating in the purged populations and in the original base population. The magnitude of inbreeding depression in the purged populations was approximately one-third of that observed in the original base population. In contrast to previous laboratory experiments, therefore, we found that inbreeding depression was reduced in populations that have a history of inbreeding. The large purging effects observed in this study may be attributable to the rate of historical inbreeding examined, which was slower than that considered in previous experiments.

Effect of inbreeding on salinity tolerance in the guppy ( Poecilia reticulata)

This experiment was designed to study the relationship between different levels of inbreeding and observed inbreeding depression for salinity tolerance, one of the most important tolerances to environmental conditions, in the guppy ( Poecilia reticulata). Two generations of full-sib mating and six generations of mating in the n=10 produced individuals with an expected level of inbreeding coefficient of 0.375 and 0.265, respectively. A significant decrease in the mean value of salinity tolerance, expressed by survival time in 35-ppt seawater, was observed in both the full-sib mated line and the closed line of n=10, indicating inbreeding depression for salinity tolerance. The mean and coefficient of variation (C.V.) of salinity tolerance decreased linearly with the increase in inbreeding coefficient with a rate of 9.1% and 10.1% per 10% increase in the inbreeding coefficient, respectively. Analyses among seven lines of the full-sib matings indicated that inbreeding caused the larger reduction of the means observed in the lines having higher salinity tolerance at the P generation and decreased both deviations of the means among the lines and C.V. within each line. The linear decrease in salinity tolerance with an increase in inbreeding coefficient suggests that inbreeding depression for salinity tolerance results from additive combination among the loci responsible for inbreeding depression.

Effects of population structures and selection strategies on the purging of inbreeding depression due to deleterious mutations.

Stochastic simulations were run to compare the effects of nine breeding schemes, using full-sib mating, on the rate of purging of inbreeding depression due to mutations with equal deleterious effect on viability at unlinked loci in an outbred population. A number of full-sib mating lines were initiated from a large outbred population and maintained for 20 generations (if not extinct). Selection against deleterious mutations was allowed to occur within lines only, between lines or equal within and between lines, and surviving lines were either not crossed or crossed following every one or three generations of full-sib mating. The effectiveness of purging was indicated by the decreased number of lethal equivalents and the increased fitness of the purged population formed from crossing surviving lines after 20 generations under a given breeding scheme. The results show that the effectiveness of purging, the survival of the inbred lines and the inbreeding level attained are generally highest with between-line selection and lowest with within-line selection. Compared with no crossing, line crossing could lower the risk of extinction and the inbreeding coefficient of the purged population substantially with little loss of the effectiveness of purging. Compromising between the effectiveness of purging, and the risk of extinction and inbreeding coefficient, the breeding scheme with equal within- and between-line selection and crossing alternatively with full-sib mating is generally the most desirable scheme for purging deleterious mutations. Unless most deleterious mutations have relatively large effects on fitness in species with reproductive ability high enough to cope with the depressed fitness and thus increased risk of extinction with inbreeding, it is not justified to apply a breeding programme aimed at purging inbreeding depression by inbreeding and selection to a population of conservation concern.

A general algorithm to compute multilocus genotype frequencies under various mating systems.

This paper provides a general method to derive algebraic expressions of genotype frequencies for multiple loci under various mating systems, including random mating, back-crossing, selfing, and full-sib mating. For each mating system, general equations are presented. In the case of three loci, comprehensive tables provide recurrence equations for genotype frequencies under random or self mating, and expected genotype frequencies after two generations of full-sib mating. Our results should prove useful in genetic linkage analysis.

GENETIC VARIATION IN INBREEDING DEPRESSION IN THE RED FLOUR BEETLE TRIBOLIUM CASTANEUM.

Inbreeding depression varies among species and among populations within a species. Few studies, however, have considered the extent to which inbreeding depression varies within a single population. We report on two experiments to provide evidence that inbreeding depression is genetically variable, such that within a single population some lineages suffer severe inbreeding depression, others suffer only mild inbreeding depression, and some lineages actually increase in phenotypic value at higher levels of inbreeding. We examine the effects of population structure on inbreeding depression for two traits in the first experiment (adult dry weight and female relative fitness), and for seven traits in the second experiment (female and male adult dry weight, female and male relative fitness, female and male developmental time, and egg-to-adult viability). In the first experiment, we collected data from 4 families within each of 38 lineages derived from a single ancestral stock population and maintained for four generations of full-sib mating. Both traits demonstrate significant inbreeding depression and provide evidence that even within a single lineage there is significant genetic variability in inbreeding depression. In the second experiment, we collected data from 5 replicates for each of 15 lineages derived from the same ancestral population used in the first experiment; these lineages were maintained for four generations of full-sib mating. We also collected data on outbred control beetles in each generation and incorporated these data into the analyses to account for environmental effects in an unbiased manner. All traits except female and male developmental time show significant inbreeding depression. All traits showing inbreeding depression are genetically variable in inbreeding depression, as is evident from a significant linear lineage-×-f component. For both experiments, the effect of population structure on inbreeding depression is further evident from the increasing amount of variation that can be explained by the models used to measure inbreeding depression when additional levels of population structure are included. Genetic variation in inbreeding depression has important implications for conservation biology and may be an important factor in mating-system evolution.

Isozyme polymorphisms maintained by lethal loci in inbred strains of Aedes triseriatus.

We analyzed the progeny of brother-sister matings of two inbred strains of the treehole mosquito, Aedes triseriatus, at several isozyme loci to determine which factors were maintaining heterozygosity at these loci after prolonged inbreeding. The triseriatus Kramer (TK) lines were polymorphic for the Odh and Hbd loci after 12 generations of full-sib mating, and the triseriatus Vero Beach (TV) lines were polymorphic for the Odh, Hk-4, Pgm, and Hbd loci after 14 generations of full-sib mating. Genetic analysis of 22 TK F13 matings and nine TV F15 matings showed that heterozygosity was enforced by lethal loci to which all the polymorphic isozyme loci were linked. The lethal loci formed a balanced lethal system. We determined the relative positions and map distances of lethals and enzyme loci.

Effect of rate of inbreeding on inbreeding depression in Drosophila melanogaster

This experiment was designed to study the relationship between rate of inbreeding and observed inbreeding depression of larval viability, adult fecundity and cold shock mortality in Drosophila melanogaster. Rates of inbreeding used were full-sib mating and closed lines of N=4 and N=20. Eight generations of mating in the N=20 lines, three generations in the N=4 lines and one generation of full-sib mating were synchronised to simultaneously produce individuals with an expected level of inbreeding coefficient (F) of approximately 0.25. Inbreeding depression for the three traits was significant at F=0.25. N=20 lines showed significantly less inbreeding depression than full-sib mated lines for larval viability at approximately the same level of F. A similar trend was observed for fecundity. No effect of rate of inbreeding depression was found for cold shock mortality, but this trait was measured with less precision than the other two. Natural selection acting on loci influencing larval viability and fecundity during the process of inbreeding could explain these results. Selection is expected to be more effective with slow rates of inbreeding because there are more generations and greater opportunity for selection to act before F=0.25 is reached. Selection intensities seem to have been different in the three traits measured. Selection was most intense for larval viability, less intense for fecundity and, perhaps, negligible at loci influencing cold shock mortality.

THE EFFECT OF INBREEDING ON COMPETITIVE MALE-MATING ABILITY IN DROSOPHILA MELANOGASTER

The effect of full-sib inbreeding on competitive male-mating ability (CImale symbol) in Drosophila melanogaster was investigated in two experiments. In the first, five inbred lines (with reserves) were assessed up to 18 generations. Linear inbreeding depression, of 5.9% per 10% increase in homozygosity, was observed. In a second experiment, 21 inbred lines were tested after three generations of full-sib mating (without reserves), and the decline with inbreeding was more severe, the male competitive index (CImale symbol) decreasing by 10.7% per 10% increase in F. The difference between these results is attributed to natural selection acting on variation within the inbred lines in extent of homozygosity, which can arise because of the peculiarly strong influence of linkage in Drosophila. Furthermore, differentiation between the lines may have reflected this variation rather than the various effects of different alleles fixed.-These results imply that the genetic variation in male-mating ability is largely due to dominance (no epistasis was detected) and are consonant with the proposition that intermale sexual selection is a very important component of fitness in D. melanogaster . There was no evidence of a positive correlation between male body size and competitive mating ability.

Genetic correlations of abdominal fat with production traits of Leghorn hens based on inbred line averages.

Data from 16 inbred lines derived by three generations of full sib mating from a common outbred base population were used to estimate genetic correlations between body weight, abdominal fat content, follicle number, liver weight, egg weight and egg number using between-line variances and covariances. High genetic correlations were found between body weight, fat content and egg weight. Low genetic correlations were found between follicle number and all traits other than egg weights. Theoretical expectations and low correlations within lines led to the conclusion that environmental correlations among the traits considered were very low.

Inbreeding and heterogamic mating: an alternative to Averhoff and Richardson.

An alternative explanation to the pheromonal control of mating through chemoreceptor saturation proposed by Averhoff and Richardson (1974) is offered for the apparent rise in heterogamic mating in their experiments, after several generations of full-sib mating. In a multiple-choice mating between two genotypic strains differing in their level of sexual vigor, there is a sequence from heterogamic to homogamic mating. It is proposed that, by reducing mating speed, inbreeding changes the rate of this sequence but not its pattern, so the apparent level of heterogamic mating will increase during inbreeding, for a fixed observation period. This hypothesis was tested using the Kence-Bryant model of mating success.

Effects of Inbreeding on Rainbow Trout Populations

Abstract An approach for measuring inbreeding depression on the basis of differences between inbred and outbred half-sib family groups is described. Using this method, estimates of inbreeding depression in populations of rainbow trout (Salmo gairdneri) following one generation of brother-sister mating was calculated for three production traits–percent egg hatchability, percent fry survival from swim-up to 150 days, and weight at 150 days. The inbreeding depression estimates obtained from male and female half-sib families were 1.7 and 4.4% for percent egg hatchability, 22.2 and 16.1% for percent fry survival, and 12.0 and 9.8% for weight at 150 days, respectively. Estimates for fry survival and weight at 150 days were significant at P < 0.01 while egg hatchability estimates were nonsignificant. Following one generation of full-sib mating, the calculated effect of inbreeding on the number of live fish and total weight of fish at 150 days of age showed a reduction of 16.1 and 24.4% in female families and 22....

Heterosis, sex and maternal interactions in crosses among inbred lines of mice.

All possible crosses and reciprocals were made among four inbred lines (F = 92%) developed from 12 generations of full-sib mating. All lines originated from a common outbred base population of ICR-albino mice. Data were obtained from 356 litter containing 2,734 mice to evaluate heterosis, reciprocal effects, sex effects and their interactions as they affect body weight and weight gain. Heterosis was significant for most of the postweaning traits (42- and 56-day weight and gain from 21 to 42 days). Nonadditive gene action may have included overdominance and epistasis since both reciprocal linecrosses were generally heavier than those of the better inbred lines. Although significant differences in reciprocals and inbred lines were not frequent, there were sufficient differences to indicate that lines varied in the fixation of loci during inbreeding. Sex-heterosis interactions were significant for 12 of 30 possible cases. However, eight of the 12 significant interactions occurred in crosses involving only one of the lines. The interactions were of the divergent type and arose from males exhibiting more heterosis than females. Overdominance in genes on the sex chromosomes modified by other loci (epistasis) was proposed as a possible explanation for these results. Some sex-linkage affecting growth was evident from the interaction of sex with reciprocal effects.

Genetic and Environmental Sources of Variation in Length and Weight of Rainbow Trout (Salmo gairdneri)

Rainbow trout (Salmo gairdneri) of three-year-classes (1967–1969) were produced from random mating, and one-year-class (1970) from inbreeding. The two first-year-classes were fullsib groups. Intraclass-correlations for body length in the 1967-year-class were: 0.16, 0.15, 0.09, and 0.17 at 90, 130, 355, and 485 days of age, respectively. The corresponding estimate for the 68-year-class was 0.25 at age 110 days. Phenotypic correlations between body length at different ages were high within seasons, but low between seasons.For the 1969-year-class the sire x dam interaction component was negative at ages 150 and 280 days, indicating that nonadditive gene effects were unimportant. Estimated heritabilities ranged from 0.0 to 0.40, those from the sire component being generally higher. Environmental differences between tanks were low, but not ignorable. The 1970-year-class, produced from first generation of fullsib mating, showed significant differences between inbred and control (noninbred) for mortality of eggs and fry, but not for body weight at age 75 days.

Abnormal Body Curvatures of Rainbow Trout (Salmo gairdneri) Inbred Fry

In an inbreeding experiment with rainbow trout (Salmo gairdneri), a special type of deformed fry was found. The deformity appeared after one generation of fullsib mating in one of nine fullsib groups. The deformed fry were observed soon after the resorption of the yolk sac and showed different forms of body curvatures. The deformity was lethal. Significant differences between inbred groups and the noninbred control groups indicate that the deformity is at least partly heritable.

GENETIC EFFECTS OF GAMMA-IRRADIATION ON EGG PRODUCTION AND ADULT EMERGENCE OF DROSOPHILA MELANOGASTER.

Newly emerged male and female flies from one inbred and one randombred population were subjected to 0, 500, 1000, or 1500 r of gamma-radiation and then mated in all possible combinations within populations, resulting in a four x four factorial arrangement of treatments. Daily egg production over a ten-day period was determined from two replicated experiments for the treated flies, their untreated progeny (Generation 1) and grand-progeny (Generation 2). Generation 2 resulted from full-sib matings of members of Generation 1. Eggs laid each day which resulted in viable adults were determined for Generations 1, 2, and 3 (Generation 3 resulting from two generations of full-sib mating). Mean daily egg production was not significantly affected by irradiating males or females with 1500 r or less of gamma rays; however irradiation of the female parent with 2000 r or more of x rays had a marked depressing effect on egg production. Irradiation of the male parent did not affect egg production appreciably. The partial linear and quadratic regression coefficients of daily egg production on day of oviposition for each pair of flies indicated no significant differences associated with levels of irradiation of males or females. Large linear depressing effects associated with irradiationmore » of both male and female parents were found in Generation 1 for mean daily percent adult emergence. Treatment of the females had no appreciable effect on the percent of eggs deposited by their progeny or grand-progeny which resulted in viable adults; however, treatment of the males had a significant effect on descendants. The weighted partial linear and quadratic regression coefficients of percent adult emergence on day of oviposition were determined for each pair of flies, Analyses of the differences of these coefficients indicated that secondary spermatocytes and early spermatids were more sensitive to radiation induced genetic damage than were spermatozoa, later spermatids, primary spermatocytes, and spermatogonia. Less differential effect was found for irradiation of females than males. Nevertheless, gametes treated as primary oocytes were more susceptible to damage than those treated as oogonia. Irradiation of male Drosophila resulted in four to flve times as much genetic damage in the gametes as did irradiation of the female. Evidence of this greater damage is also present in the gametes produced by the progeny and grand- progeny of irradiated males, the extent of the damage being approximately halved each generation. (auth)« less