Fecundity Selection Research Articles

Selection for prolificacy in the Cambridge sheep

Selection for prolificacy in the Cambridge sheep

Selection for prolificacy in the Cambridge sheep

Selection for prolificacy in the Cambridge sheep

Selection component analysis of natural polymorphisms using population samples including mother-offspring combinations, II

Population samples including mother-offspring combinations provide information on the selection components: zygotic selection, sexual selection, gametic seletion and fecundity selection, on the mating pattern, and on the deviation from linkage equilibrium among the loci studied. The theory for the analysis of a sample consisting of adult individuals including combinations of a mother and one randomly chosen offspring in the case of n polymorphic autosomal loci with m a alleles at the ath locus, a = 1, 2,…, n, is developed for an organism with discrete non-overlapping generations. In this general analysis complete determination of the genotypes is assumed. The modifications in the analysis for the case n = 2 and m 1 = m 2 = 2 when the two double heterozygotes cannot be separated are discussed, and the analysis is illustrated by data from a population of Zoarces viviparus (a marine teleost).

Genetics of life history in Drosophila melanogaster. II. Exploratory selection experiments.

two types of small-scale selection experiments were performed. (1) Artificial selection experiments were performed on age-specific female fecundity. Selection for early fecundity over three generations produced a statistically detectable direct response. There was no detectable indirect response in other life-history characters. Selection for late fecundity over three generations did not produce any detectable direct response. Indirect responses were detected: early egg-laying decreased and longevity increased. (2) Natural selection for late-age fitness components increased late fecundity, female longevity, and the duration of female reproduction, while early fecundity and mean egg-laying rate decreased.

The evolution and socioecology of dominance in primate groups: A theoretical formulation, classification and assessment

Dominance hierarchies are presumed to evolve by individual selection from an evolutionary compromise between intraspecific competition for resources and for mates. The hypothesis is put forward that when competition in “stable” habitats leads to “niche breadth,” a species is preadapted to life in heterogeneous environments and the consequent selection for fecundity. Status patterns are viewed as systems of signals communicating differential tendencies among individuals to attack or retreat, and a simple graphical model is presented which relates the costs or benefits to fitness of aggressive or appeasement behavior and interindividual distance. Primate societies are classified on the basis of their dominance hierarchies, and the ecological correlates of these patterns are discussed. Based on hypotheses presented in the paper, topics for future research are suggested.

Selection for prolificacy in the pig : results of a 10 generation selection experiment

Selection for prolificacy in the pig : results of a 10 generation selection experiment

Population trajectories for single locus additive fecundity selection and related selection models

A selection model which comprises models of additive fecundities as well as models of viability, fecundity, or differential mating selection acting only in one sex, is investigated for an autosomal gene locus in a population reproducing in nonoverlapping generations. The recurrence equations and basic properties of the genotypic population trajectories and equilibrium points are formulated for the multiallelic case. For the diallelic case, the trajectory development is discussed in more detail, and it is proven that every population trajectory converges to a Hardy-Weinberg equilibrium point.

Fecundity Selection and Maximization of Equilibrium Number

Simultaneous recurrence equations for the dynamics and the genetics of a population are derived for two mating systems, random mating of gametes and random mating of individuals. In the last mating system, two expressions for fecundity per mating are used. For random mating of gametes, it has been shown that natural selection at equal male and female fitnesses leads to maximum equilibrium population size (ROUGHGARDEN, 1976). With random mating of individuals no such ecological analogue to the Fundamental Theorem of Natural Selection is generally valid. This can be ascribed to a violation of the assumption of independence of individuals throughout the life cycle.

Habitat Preference and Reproduction of Feral House Mice, Mus musculus, during Plague and Non-Plague Situations in Western Australia

In Western Australia feral Mus musculus are well established in the southern half of the State, including remote, arid desert situations. In the South West Division Mus have a distinct spring-summer breeding period, with some breeding in autumn after favourable climatic conditions. A plague in autumn 1975 is described and abundance, fecundity, trapping behaviour and habitat selection are compared between plague and non-plague situations. It is considered that abundant rainfall during the two preceding years caused the plague. Decline of the plague coincided with the onset of winter; there is some evidence to suggest that shelter more than food limited numbers, but the decline was probably also influenced by intrinsic factors. In wheatbelt areas of Western Australia Mus are most abundant in samphire heaths.

Selection for prolificacy in sheep in relation to meat production characters

Selection for prolificacy in sheep in relation to meat production characters

Some Models of Genetic Selection

This paper begins with a description of the classical theory of viability selection in which probabilities that individuals of various genotypes survive are in proportions that do not change with time and are independent of population structure. Salient features of viability selection with one and two loci are reviewed. This theory is intimately connected with the usual theory of mass selection in quantitative genetics. It is well known that the mean of the relative viabilities does not necessarily increase if there is viability selection at more than one locus. It also turns out that if there is selection for fecundity with one locus, the mean fecundity may steadily decrease or oscillate rather than increase. This and the fact that a Hardy-Weinberg structure may no longer exist at any stage of life may have a bearing on predicting progress from artificial selection on reproductive characters. Classical viability selection theory does not completely describe natural selection. Other possibilities are discussed. Among these is the density and frequency dependent selection induced when the population lives in a limited habitat. Implications in quantitative genetics are discussed.

Response to partial selection for fecundity in Merino sheep

Divergent selection for fecundity in a South Australian Merino flock was carried out over a 10 year period at Roseworthy Agricultural College, South Australia. Comparisons were made between two flocks of sheep in which selection was restricted to ram replacements. Analyses showed that very little response was achieved. Pooled estimates of repeatability by analysis of variance were 0.04 for lambs born per ewe joined (LBJ) and 0.14 for lambs born per ewe lambing (LBP). Pooled half-sib estimates of heritability were 0,10 for LBJ and 0.10 for LBP. The realized heritability of LBP was 0.03, averaged over age groups. The lack of response was due to limited selection pressure and the time taken for improvement to pass through the breeding flock.

On Intraspecific Competition for Avian Dispersers in Tropical Trees

Two models are developed which predict life-history adaptations resulting from intraspecific competition for avian dispersers. One suggests stabilizing selection for a rate of fruit production necessary to maintain a limited and specialized guild of dispersers. The other suggests directional selection for high fecundity which is mediated by intraspecific competition for a variety of opportunistic birds drawn from alternative sources of plant or animal food. Operational procedures are suggested which would test for the applicability of either model. Relevant literature is discussed.

Selection component analysis of natural polymorphisms using population samples including mother-offspring combinations

Abstract Population samples including mother-offspring combinations provide information on the selection components: zygotic selection, sexual selection, gametic seletion and fecundity selection, on the mating pattern, and on the deviation from linkage equilibrium among the loci studied. The theory for the analysis of a sample consisting of adult individuals including combinations of a mother and one randomly chosen offspring in the case of n polymorphic autosomal loci with ma alleles at the ath locus, a = 1, 2,…, n, is developed for an organism with discrete non-overlapping generations. In this general analysis complete determination of the genotypes is assumed. The modifications in the analysis for the case n = 2 and m1 = m2 = 2 when the two double heterozygotes cannot be separated are discussed, and the analysis is illustrated by data from a population of Zoarces viviparus (a marine teleost).

Dynamics of polymorphisms. I. Selection components in an experimental population of Drosophila melanogaster.

Abstract The total dynamics of a fourth chromosome polymorphism in Drosophila melanogaster is studied in an experimental population in which it is possible to measure various selection components simultaneously in each generation. It is demonstrated that although zygotic selection operates in the system, the component of major importance for the dynamics is sexual selection, and it is this component that is responsible for the stability of the polymorphism. Fecundity selection is of very minor importance. Both zygotic and sexual selection components behave in a frequency-dependent way. The results are discussed in relation to genetic load and the detection of selection in natural and experimental populations.

Semen Characteristics as Influenced by Selection for Divergent Growth Rate in Chickens

PROGRESS through selection has been partially responsible for the tremendous advances which have come about in the poultry industry during the last fifty years. The process of selection, however, is often conducted on a quantitative basis and problems of linkages, epistasis and other genetic properties may not only limit the rate of progress, but may also result in a reduction of other desirable traits. Genetic experiments which have been designed to study the effects of intense selection for one trait on other traits have been limited.Jones and Lamoreux (1942) studied the effect of intense selection for high and low fecundity in the female on semen characteristics in the males of these lines. Males from the high fecundity line exhibited earlier sexual maturity, larger testes weights, better semen quality and greater fertilizing capacity than the males from the low fecundity line. The authors concluded that the production of eggs and…

The effect of inbreeding on potato cyst‐nematode, Heterodera rostochiensis

SUMMARYTwo populations, Duddingston and Feltwell, of potato cyst‐nematode were inbred for seven and six generations respectively. The Duddingston population maintained a high fecundity in some lines for three generations, but in subsequent generations the fecundity as measured by cyst production declined in spite of selection for high fecundity. By selecting for fecundity, some lines of the Feltwell population still produced many cysts after five generations of inbreeding. In the Duddingston population it was possible to increase the number of cysts produced by an inbred line of poor fecundity by using paired cysts plus selection for fecundity. A similar change may have been obtained for unprolific lines of the Feltwell population. Selection for production of few cysts quickly produced lines with poor fecundity. One cause of poor fecundity was the small number of larvae in cysts used for inoculations. Yellow eggs were found in large numbers in some cysts but these were not a cause of loss of fecundity following repeated inbreeding.

Mass selection for prolificacy in maize

Results of 5 generations of selection for improved productivity in corn by selecting for prolificacy, a correlated trait, are reported. The regression for gain in yield per cycle of selection relative to the parental variety, Hays Golden, was 6.28%. This compares favorably with a previously reported gain from mass selection in the same variety using weight of grain per plant as the selection trait. The greater effectiveness of selection where prolificacy was the primary trait is believed due to higher selection intensity used as well as higher heritability.

Part record selection for fecundity in Turkeys

Synopsis Production records from 3 flocks of turkeys comprising 2 strains are analysed to determine the heritabilities of, and genetic correlation between, egg production during the 6 weeks following flock attainment of 20 per cent production, and total poult production over 24 weeks of lay. Part record and full record selection are compared, taking into consideration the difference in selection intensity obtainable under the two methods. Practical problems involved in part record selection are discussed and it is concluded that, when, as appears probable in large flocks, neither system exhibits a clear genetic advantage over the other, practical considerations will weigh in favour of full record selection.

The Relative Emphasis Placed on Components of a Selection Index under Two Nutritional Environments

The data from two lines of swine, descended from a common stock, that were maintained as closed populations for six generations were used in this study. One line (H) was full-fed from weaning to 150 lb., hand-fed from 150 lb. to parturition at levels which permitted gains of 1.5–2.0 lb. daily and again full-fed during lactation. The other line (L) received 70% as much feed as the H group throughout. All selections were made as each pig reached 150 lb. using the following index: I=B+2W+35G, where B is the number farrowed alive and W is the number weaned in the litter in which the individual pig was born, and G is the average rate of daily gain of the individual pig from weaning to 150 lb. There was no significant difference between H and L in average number of pigs farrowed alive per litter (8.85 vs. 9.26). However, there was a highly significant difference between H and L in average number of pigs weaned per litter (5.65 vs. 6.63), average weaning weight of the individual pig (36.5 lb. vs. 28.5 lb.) and average rate of daily gain from weaning to 150 lb. (1.31 lb. vs. 0.89 lb.). Selection apparently was ineffective in increasing litter size in either line. However, selection for rate of daily gain appeared to be effective in both lines. As determined by the method of path coefficients, approximately equal emphasis was placed on prolificacy (B+2W) as on average daily gain in H, while in L more emphasis was placed on prolificacy than on average daily gain. Using weighted selection differentials expressed in terms of standard deviations, somewhat less selection was practiced for prolificacy than for average daily gain in H, while in L there was considerably more selection for prolificacy than for average daily gain.