Inbreeding Experiments Research Articles

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.

MEASURES OF PHENOTYPIC SELECTION ARE BIASED BY PARTIAL INBREEDING.

When populations are partially inbred due to the population structure or to a mixed mating system like partial self-fertilization, some individuals will be more inbred than others. This heterogeneity among individuals in the history of inbreeding can greatly complicate the interpretation of measures of quantitative genetic variability when the traits studied exhibit inbreeding depression. Partial inbreeding can also bias measures of phenotypic selection toward the detection of strong directional and stabilizing selection. In this paper, data are presented from several inbreeding experiments conducted on two partially selfing, annual populations of the monkeyflower Mimulus guttatus that show that the means of many of the morphological and phenological traits measured were affected by inbreeding. These findings imply that estimates of heritabilities and additive genetic covariances would not reflect the potential for these populations to respond to selection. Phenotypic selection analyses conducted on naturally occurring plants, involving linear regressions of relative seed production on the traits, revealed significant directional selection on many of the same quantitative traits measured in the inbreeding studies. However, when the same selection analyses were performed on plants with known histories of inbreeding, part of the statistical relationship between relative seed number and the traits was found to be due to the mating system: inbred individuals had both lower seed production and different mean values for the traits than outcrossed individuals. It is also shown, with a hypothetical example, that partial inbreeding can bias measures of stabilizing selection toward the detection of strong stabilizing selection. Partial inbreeding therefore tends to make directional and stabilizing selection appear stronger than it is, and it may be that natural selection in the wild is actually weaker than many studies of partially inbred species suggest.

Experimental tests of sex determination in Goniozus nephantidis (Hymenoptera: Bethylidae)

Single locus complementary sex determination (CSD) occurs in several species of Hymenoptera. Individuals that carry two different alleles (heterozygotes) are female while those with one and two copies of the same allele (hemizygotes and homozygotes) are haploid and diploid males, respectively. A multilocus model, in which diploids are only male if homozygous at all sex loci, has been proposed for species with regular but not exclusive inbreeding. To date, the only explicit test of the multilocus model is for Nasonia vitripennis. The latter is an inbreeding species in the Infra-order Parasitica and was shown not to conform to the multilocus model. In this study, inbreeding experiments are used to refute single and multilocus sex determination in a second inbreeding hymenopteran, Goniozus nephantidis (Infra-order Aculeata). Single locus CSD has been demonstrated in five other aculeates and G. nephantidis is the first aculeate species shown not to have CSD. The absence of CSD in G. nephantidis is probably a derived condition, favoured by the penalty of increased diploid male production under inbreeding.

Effects of a change in the level of inbreeding on the genetic load

"The effects of inbreeding may not be as noticeable in the first generation as the invigoration immediately apparent after crossing". This statement, published in 1919, has received little attention, and has apparently never been tested empirically, although the reduction of the genetic load of populations by inbreeding is well known in theoretical terms. Because inbreeding increases homozygosity, and hence the effectiveness of selection against recessive or partially recessive detrimental alleles, changes in levels of inbreeding can lead to a reduction in the frequencies of such mutant alleles. This results in equilibration at higher population mean fitness and is referred to as 'purging' populations of their genetic load. Severe inbreeding can also reduce genetic load due to overdominant alleles, provided selection coefficients are not symmetrical at all loci, because alleles giving lower fitness will be reduced in frequency at equilibrium. With either fitness model, however, reduction in genetic load takes time, and the initial effect of an increase in inbreeding is reduced fitness due to homozygosity. There are few data relating to the extent to which fitness is reduced during inbreeding in a set of lines and to how long the reduction lasts before increasing again to the initial level, or higher. Inbreeding experiments involving sib mating in mice and Drosophila subobscura, and successive bottlenecks in house flies have yielded some evidence consistent with the purging hypothesis. Here, we report results of an experiment demonstrating a prolonged time-course of recovery of mean fitness under self-fertilization of a naturally outcrossing plant, and also compare our results with expectations derived by computer calculations. Our results show that the genetic load present in an outcrossing population can be explained only with a high mutation rate to partially recessive deleterious alleles, and that inbreeding purges the population of mutant alleles.

Mechanisms of kin recognition

Although kin recognition mechanisms are necessary neither for the operation of kin selection nor for optimal mate selection (e.g. inbreeding avoidance), once established, such mechanisms may accelerate the evolution of kin-directed behaviors. Aside from spatially-based recognition, in which organisms adjust their behavior principally in response to their immediate location, several behavioral mechanisms originally suggested by Hamilton recently have generated discussion and controversy. Familiar kin can be identified individually, but individual recognition mechanisms alone cannot serve to distinguish between closely and more distantly related kin, or to identify novel relatives. These kin can be identified through group recognition mechanisms that evaluate the extent of trait overlap among individuals to determine their probable genetic relatedness. Precisely whom an organism recognizes as kin using either type of mechanism may be dependent on its past social experience. Individual recognition permits discrimination of previously encountered conspecifics, whereas group recognition generally leads to discrimination of individuals sharing traits with previously encountered conspecifics. Individual and group recognition mechanisms are not mutually exclusive, and they may operate concurrently. Furthermore, they are not distinct, separable processes. Mistaken individual identifications become more likely as conspecifics show increasing phenotypic resemblance, and hence kin discrimination can result directly from individual recognition mechanisms. The extent to which kin are identified depends on a criterion rule which may fluctuate in response to social, spatial, and temporal factors. When favored by natural selection, kin recognition may be facilitated by the process of stimulus generalization, as trait matching is achieved within wider tolerance ranges. But such generalization may occur even in the absence of selection per se . Recognition effected through the action of hypothetical “recognition alleles” does not constitute a logical alternative to individual or group kin recognition mechanisms. In common with those processes, recognition allels must operate by the effective matching of phenotypes. Unlike kin recognition mechanisms, which assess similarity by generalized phenotypic comparisons, the phenotype compared by a recognition allele (or linkage group) is that it itself generates, leading to the possibility of intragenomic conflict. As suggested by Hamilton, alleles might be expected to induce their bearers to favor behaviorally conspecifics that share thier copies, regardless of the overall genetic relatedness of those conspecifics. Hence, recognition alleles, if they exist, would not invariably lead to kin identifications. Moreover, such alleles need not act in a manner that necessarily excludes learning. Through inbreeding experiments, a genetic component to the labels that elicit kin recognition has been demonstrated in some invertebrates. Genetically determined kin recognition templates, with which the labels are compared, have yet to be established. A “genetic recognition system” cannot be safely inferred when experiments fail to demonstrate experiential effects on recognition abilities. Kin recognition mechanisms can be characterized through detailed examination of the ontogenetic and sensory processes underlying recognition abilities, and of the ecological and social contexts in which kin-directed behaviors are expressed.

Settlement requirements of molluscan larvae: New data on chemical and genetic roles

Recent studies in the author's laboratory and elsewhere indicate that a high degree of substratum chemical specificity is necessary to induce settlement and metamorphosis in a number of molluscan species. The chemical nature of natural and artificial inducers, as well as the nature of inducer-larval interactions, provides insights into both stimulus and response aspects of the metamorphic process. Larvae of Phestilla sibogae undergo rapid and complete metamorphosis in response to a soluble, coral-produced substance. These larvae undergo slow but complete metamorphosis in response to choline, GABA, and some related compounds; they exhibit partial metamorphosis in the presence of certain catecholamines. Reversible inhibition of metamorphosis (habituation) occurs when larvae are exposed to an inducer prematurely. Analysis of these observations allows the formulation of new models for molluscan metamorphic induction. It may be that a single model will not be appropriate for all marine molluscs. Both age at metamorphic competence and concentration of natural inducer necessary to elicit metamorphosis in competent larvae of Phestilla are known to show wide variance among larvae. Long-term selective inbreeding experiments have failed to indicate obvious genetic components of the observed variances. High variance in age at competence occurs even among the egg masses of a single, highly inbred individual with a single mate.

Comparative results of selection in the early and late stages of an inbreeding programme

Selection for final height using three different selection criteria has been applied retrospectively to the records of two inbreeding experiments, using pedigree and single-seed-descent breeding programmes, carried out without selection within crosses of varieties 1 and 5 of Nicotiana rustica. In the pedigree programme the results of individual and family selection imposed at the F3, F4 and F6 generations on the performance of the inbred families from the F9 generation onwards are compared. In the single-seed-descent programme the results of individual selection in the F2 are compared with those of delaying selection until the F7/F8 generations. The results show that selection is considerably more successful if it is delayed and that family selection is more successful than individual selection in the early generations.

Frequency of chlorophyll-deficient and other detrimental genes in Japanese populations of buckwheat, Fagopyrum esculentum Moench.

The frequency of chlorophyll-deficient genes and other detrimentals per gamete was estimated by conducting more than 1, 000 full-sib matings in six Japanese populations of buckwheat. The following types of abnormalities were observed in cotyledons; albinos 0.2%, yellows 3.7%, pale yellows 4.5%, pale green 5.6%, variegateds 3.4% and morphological abnormalities 1.9%. Each type of abnormality was also found in the foliage leaves at about a half the frequency in the cotyledons. The total frequencies were not very different among the populations, they ranged from 22 to 34%, except in the Togakushi population where the frequency was very low, 12%. The frequencies of all the abnormalities except the morphological one were also examined in random mating populations in farmer's fields. The total frequency of homozygotes was very low, around 0.02-0.05% in the cotyledons and not much different in the foliage leaves, probably because the population sizes are large and breeding is by insect pollination.-Based on the frequencies of abnormalities in the inbreeding experiment and those in random mating populations, the mechanism whereby detrimental genes are maintained in buckwheat populations was discussed. It seems that such detrimental genes are maintained by mutation-selection balance.-Information on the contribution of other factors to genetic loads, such as female sterility genes and cytoplasmic factors, were also given.

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.

Effect of Selection and Linkage on Inbreeding

Gill and Clemmer performed an inbreeding experiment by using Monte Carlo simulation techniques and reported that both selection and linkage significantly increased the rate of inbreeding in a population of a given size. The results could not be explained by the theoretical explanation that linkage should not affect in� breeding coefficient in the absence of selection. A programme was written to repeat Gill's and Clemmer's experiment ..

Frequency of occurrence of diploid bovine spermatozoa.

semen smears was twice the normal level. Similar observations on bovine spermatozoa have been made by Gledhill (1964, 1965) who also studied such cells by ultraviolet fight absorption and by interferometric mass determinations. All three of the techniques used by Gledhill support the hypothesis that the exceptionally large and densely staining sperm nuclei are diploid. The incidence of diploid spermatozoa is low, is characteristic of the semen of individual bulls and may be genetically determined. This paper presents evidence on the inci¬ dence of diploid spermatozoa in a special population of bulls and suggests the reality of genetic influence on the incidence within this population. The data are derived from the examination of single Feulgen-stained semen smears from eighty bulls from the San Juan Basin Branch Experiment Station, Hesperus, Colorado. Most of the bulls are involved in an inbreeding experiment and include inbred Hereford lines, line crosses, an outbred control line, some breed crosses and a few dairy bulls. Inbreeding coefficients in the inbred lines range from 0-14 to 0-50. The diploid spermatozoa in 1000 spermatozoa were counted on each smear with the exception of two thin smears, where the counts

Some differences between two strains of rats developed by selection of differ in their response to equine gonadotrophin.

SOME of the causes of variation in the response of the ovaries of 21- day-old rats to a standard dose of equine gonadotrophin have been reported by Chapman (1946). Heredity was estimated on his random-bred stock as responsible for 40% of the variance in the weight of the stimulated ovaries after the variability due to body weight and to temporal factors was eliminated. Selection and inbreeding experiments have since been carried out on the descendents of this stock to develop lines that differ markedly in their quantitative response to the gonadotrophic hormone (Kyle and Chapman, 1948). The ability of a rat ovary to respond to gonadotrophic stimulation is associated with the presence of vesicular follicles (Corey, 1930 and Hargitt, 1930). It may be suspected that the larger the number of vesicular follicles present, within limits, the greater will be the response to a given amount of hormone and that differences in number of vesicular follicles might account for differences between lines in the degree of ...

The sex ratio and the occurrence of mutations in cultures of the blow-fly (Calliphora erythrocephala)

1. The sex ratio in pure-line cultures of strains of a white-eyed mutant ofCalliphora erythrocephala varied from strain to strain. The average for 49, 161 flies was 46% females and 54% males. Different strains varied in the ratio of females to males. The lowest was 40% females to 60% males and the highest 50% females to 50% males. 2. In cultures of wild-typeC. erythrocephala it was found that on the average more males than females were produced. Of 27,880 flies, 46% were females and 54% males. Different strains gave different ratios of females to males, varying from 50% females to 50% males to 45% females to 55% males. 3. During extensive inbreeding experiments with pure-line cultures a number of possible mutations occurred, including some mosaics in which only part of the insect showed the mutant character. 4. In two cases when females heterozygous for the white-eyed mutant gene were crossed with males bearing the mutant gene in theirX-chromosome, the progeny consisted of wild-type males and only wild-type females, instead of white-eyed and wild-type females and males in the proportion 1∶1∶2. Possibly these cases were due to the fertilization of the parent females by males with non-disjunction of theXY-chromosomes.

A Comparison of the Effects of Inbreeding and Selection on Performance in Swine

Factors responsible for changes in merit of inbred lines have been identified and their net effect expressed symbolically. The rate at which inbreeding can proceed without loss of merit when selection is of the intensity practiced over a period of years in lines at Minnesota has been estimated for litter size. and average daily gains. These estimates are subject to considerable error, but the theoretical and actual results were in reasonable agreement. It is concluded that litter size is much more difficult to maintain in lines being inbred than is growth rate, which is in agreement with the published results of other inbreeding experiments. Suggestions are advanced for making selection for fertility more effective. The results of this report emphasize the necessity for maximum attention to selection in the development of inbred lines of swine.

Proof for Multiple Allelism of Sex-Differentiating Factors in Habrobracon

Evidence is presented showing that sex-differentiating factors in Habrobracon are allelic to each other in a single series (multiple alleles) rather than occurring in separately segregating pairs (multiple factors). Backcross breeding tests of the composition of F2 males proves that quadruple alleles are involved in the crosses reported in this paper. Bostian's proof of triple alleles in his inbreeding experiment and Whiting's evidence for nine alleles linked with fused are discussed. In contrast to a multiple factor hypothesis, the theory of multiple alleles is regarded as more consistent with general principles of the evolution of sex differentiation in the entire group of Hymenoptera.

Genetic Aspects of Egg Weight Observed During Inbreeding Experiments

THE present paper considers certain genetic aspects of egg weight in the domestic fowl. Poultrymen as a group fully recognize the importance of this character to the poultry industry. Every egg produced which weighs less than two ounces is arbitrarily discriminated against when placed on the market. For some reason, certainly not a sound biological reason, the poultry industry has accepted the 56.7 gram, or two ounce egg as a standard by which an egg is judged to be large or small. Previous publications by different investigators have frequently raised the question as to whether egg weight is a dominant or recessive character. The answer probably lies somewhere between with a multiplicity of other factors both genetic and environmental. The most important question to the poultry industry is how can egg weight be improved through the application of breeding methods. In so far as the practical breeder is concerned, any .

A Ten Year Inbreeding Experiment in the Domestic Fowl

THE analysis of the problem of inbreeding may well be classed as among the recent major achievements of biology. Thanks to the well known inbreeding experiments in plants and laboratory animals, and as a result of the masterful analysis of the Mendelian consequences of inbreeding by Wright (1921), the theoretical aspects of this problem have been largely solved.From the applied standpoint, however, much remains to be done. While a mild degree of inbreeding has been used extensively by animal breeders as a tool for fixing certain traits in their herds, probably the greatest practical use of inbreeding has been made by corn geneticists, who have built the present program of corn improvement around a program of intensive inbreeding following by cross-breeding. In animals, intensive inbreeding has been done with considerable success in laboratory rodents, but few successful inbreeding experiments have been reported for larger animals. This is especially true .

AN INBREEDING EXPERIMENT WITH POLAND CHINA SWINE

Journal Article AN INBREEDING EXPERIMENT WITH POLAND CHINA SWINE Get access HUGH C. MCPHEE, HUGH C. MCPHEE Bureau of Animal Industry, U. S. Department of Agriculture Search for other works by this author on: Oxford Academic PubMed Google Scholar E. Z. RUSSEL, E. Z. RUSSEL Bureau of Animal Industry, U. S. Department of Agriculture Search for other works by this author on: Oxford Academic PubMed Google Scholar JOHN ZELLER JOHN ZELLER Bureau of Animal Industry, U. S. Department of Agriculture Search for other works by this author on: Oxford Academic PubMed Google Scholar Journal of Heredity, Volume 22, Issue 12, December 1931, Pages 393–403, https://doi.org/10.1093/oxfordjournals.jhered.a103423 Published: 01 December 1931

Chick Mortality and Sex-Ratio in the Domestic Fowl

Previous articleNext article No AccessChick Mortality and Sex-Ratio in the Domestic FowlWalter Landauer and Anna B. LandauerWalter Landauer Search for more articles by this author and Anna B. Landauer Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The American Naturalist Volume 65, Number 701Nov. - Dec., 1931 Published for The American Society of Naturalists Article DOIhttps://doi.org/10.1086/280395 Views: 3Total views on this site Citations: 26Citations are reported from Crossref PDF download Crossref reports the following articles citing this article:T. H. CLUTTON-BROCK Sex ratio variation in birds, Ibis 128, no.33 (Apr 2008): 317–329.https://doi.org/10.1111/j.1474-919X.1986.tb02682.x Bibliography, (Jan 1977): 392–418.https://doi.org/10.1016/B978-0-12-673260-3.50017-XK. F. Laughlin, H. Lundy, J. A. 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