Polymorphism in sexual versus non-sexual disease transmission

Pathogens causing sexually transmitted diseases (STDs) often consist of related strains that cause non-sexually transmitted, or ''ordinary infectious'', diseases (OIDs). We use differential equation models of single populations to derive conditions under which a genetic variant with one (e.g. sexual) transmission mode can invade and successfully displace a genetic variant with a different (e.g. non-sexual) transmission mode. Invasion by an STD is easier if the equilibrium population size in the presence of an OID is smaller; conversely an OID can invade more easily if the equilibrium size of the population with the STD is larger. Invasion of an STD does not depend on the degree of sterility caused by the infection, but does depend on the added mortality caused by a resident OID. In contrast, the ability of an OID to invade a population at equilibrium with an STD decreases as the degree of sterility caused by the STD increases. When equilibrium population sizes for a population infected with an STD are above the point at which non-sexual contacts exceed sexual contacts (the sexual–social crossover point) and when equilibrium population sizes for an OID are below this point, there can be a stable genetic polymorphism for transmission mode. This is most likely when the STD is mildly sterilizing, and the OID causes low or intermediate levels of added mortality. Because we assume the strains are competitively equivalent and there are no heterogeneities associated with the transmission process, the polymorphism is maintained by density-dependent selection brought about by pathogen effects on population size.     

Inheritance of Fusarium wilt resistance introgressed from Solanum aethiopicum Gilo and Aculeatum groups into cultivated eggplant (S. melongena) and development of associated PCR-based markers

The two eggplant relatives Solanum aethiopicum gr. Gilo and Solanum aethiopicum gr. Aculeatum (=Solanum integrifolium) carry resistance to the fungal wilt disease caused by Fusarium oxysporum f. sp. melongenae, a worldwide soil-borne disease of eggplant. To introgress the resistance trait into cultivated eggplant, the tetraploid somatic hybrids S. melongena + S. aethiopicum and S. melongena + S. integrifolium were used. An inheritance study of the resistance was performed on advanced anther culture-derived androgenetic backcross progenies from the two somatic hybrids. The segregation fitted a 3 resistant (R): 1 susceptible (S) ratio in the selfed populations and a 1R:1S ratio in the backcross progenies for the trait derived from S. aethiopicum and S. integrifolium. These ratios are consistent with a single gene, which we designated as Rfo-sa1, controlling the resistance to Fusarium oxysporum f. sp. melongenae. The allelic relationship between the resistance genes from S. aethiopicum and S. integrifolium indicate that these two genes are alleles of the same locus. Bulked Segregant Analysis (BSA) was performed with RAPD markers on the BC₃/BC₅ resistant advanced backcross progenies, and three RAPD markers associated with the resistance trait were identified. Cleaved Amplified Polymorphic Sequences (CAPSs) were subsequently obtained on the basis of the amplicon sequences. The evaluation of the efficiency of these markers in predicting the resistant phenotype in segregating progenies revealed that they represent useful tools for indirect selection of Fusarium resistance in eggplant.     

Evolution of insecticide resistance in Culex pipiens populations: The Corsican paradox

Culex pipiens mosquitoes from Corsica have been subject to insecticide treatments since 1971, using temephos (an organophosphate). After 17 years, resistance has not developed beyond a 14-fold level. This relatively low resistance is due to the presence of several identified resistance genes, including the insensitive target ( Ace^R ) and overproduced esterases (A1, A4 and B4). The fact that only a low resistance has developed after 17 years of treatment and that this low resistance level is the result of a relatively large number of resistance genes constitute a paradox. To understand this situation and explain why a higher temephos resistance level has not evolved in Corsica as in other parts of the world, it is proposed that the occurrence (through mutation or migration) of efficient resistance genes was a limiting step, and that the only resistance genes available at that time through migration from the surrounding Mediterranean countries had a low cross-resistance to temephos. The local situation of Corsica is discussed in the light of recent data on the world distribution of the known organophosphate resistance genes in this species, and the relative role of mutation and migration in the evolution of insecticide resistance in natural populations.     

Expected early genetic gain from selection for milk yield in dairy cattle

Summary A matrix program to predict short term genetic gain from single trait selection for milk yield was developed. Rate of genetic gain was calculated as the annual change in the mean breeding value of all producing females. Several parameters sets representing various selection policies were used to examine situations pertinent to dairy populations of the United States. Approach to the asymptotic rates of genetic gain within the model varied with the choice of parameters, but even with consistent selection policies, predicted total genetic gain in the first 10 years was only half of the expected from classical theory. Considerable year to year variation in the rate of gain occurred. Early gains were more dependent on female selection decisions than gains during the steady state. In a two-phase model, the approach to the linear rate of gain in the second phase was accelerated by starting with an ongoing improvement program, but considerable delays still existed. Selection for sex- limited traits such as milk yield, which require pedigree selection and a waiting time for progeny test results reached asymptotic rates more slowly than previously assumed.     

Computing the selection gradient and evolutionary response of an infinite-dimensional trait

 Following the results developed in a previous paper, an equation describing the evolutionary response to selection is extended from finite- to infinite-dimensional traits. The selection gradient and evolutionary response are then computed for a large class of infinite-dimensional traits of broad biological interest. In this framework, traits are modeled as Gaussian processes, and reproducing kernel Hilbert spaces constitute a primary tool. Received 12 September 1996     

Genotype by environment interaction for index traits that combine growth and wood density in loblolly pine

 Genotype×environment interactions of individual traits have been assessed in numerous experiments with forest trees. However, since breeding programs rarely aim at the improvement of a single trait, the impact of G×E on index or composite traits must also be assessed. In a study with 12-year-old loblolly pine families in the southeastern U.S., G×E variance was of relatively little importance compared to genetic variance for wood density but was of greater significance for several growth traits. An index that combined stem volume and wood density to improve dry weight but maintain wood density constant (restricted selection index) resulted in substantially greater G×E variance compared to either of the component traits. The interaction variance of an index trait is shown to be a function of the index coefficients and the G×E variances and covariances for its constituent traits. As a result, for some conditions it surpasses the magnitude of G×E variance for each component trait. Received: 5 September 1996 / Accepted: 25 October 1996     

Construction of Selection Indexes with Restrictions

In this paper the problem of unistage selection with inequality constraints is formulated. If the predictor and criterion variables are all normally distributed, this problem can be written as a convex programming problem, with a linear objective function and with linear constraints and a quadratic constraint. Using the duality theory, for convex nonlinear programming it is proved, that its dual problem can be transformed into a convex minimization problem with non-negativity conditions. Good computational methods are known for solving this problem. By the help of the dual problem sufficient conditions for a solution of the original primal problem are derived and illustrated by an example of practical interest.     

The value of indirect selection

Summary Conditions are developed under which progeny-testing using indirect selection can give more rapid genetic improvement than using direct selection. Analogous conditions for mass selection are given in Searle [1954].Paper No. BU-335 in the Biometrics Unit, Cornell University.     

A variable selection index for the compensation of correlated genetic change

Summary A selection index for two traits has been constructed which allows partial restriction for one of the traits. The index is used in a situation where correlated response to selection in one sex is compenstated for by selection for other traits in the opposite sex. A numerical example is given.     

Human biology in Tlaxcala, Mexico: demography

A demographic survey was conducted as part of an ongoing population study of large Mestizo and Indian communities in Tlaxcala, Mexico. Comparative data on population structure and movement, mate selection, age at marriage, differential fertility, and mortality were collected through the administration of a standardized demographic proforma, and then cross-tabulated by computer analysis. The resulting differences between the Indian and Mestizo populations are interpreted in terms of the relative importance of hybridization, natural selection, and genetic drift. Sizeable variance in achieved reproduction and the high neonatal mortality suggest the operation of natural selection in these two populations. Observed patterns of population movement and mate selection indicate that the Mestizo population of the city of Tlaxcala is highly hybridized, in contrast to the endogamous Indian community of San Pablo del Monte.