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Haldane's rule (HR) and incipient speciation is studied in the beetle Tribolium castaneum. The results show that incipient speciation in flour beetles can occur with or without HR and that significant hybrid incompatibilities result from the accumulation of gene difference between populations without differentially affecting the heterogametic sex.

The contributions of additive, non additive and environmental effects to genetic divergence and incipient speciation among 12 populations of the beetle Tribolium castaneum were investigated. The results suggest that genetic incompatibilities responsible for postzygotic isolation might be a natural component of speciation.

While reproductive caste in eusocial insects is usually determined by environmental factors, in some populations of the harvester ants, Pogonomyrmex barbatus and P. rugosus, caste has been shown to have a strong genetic component. This system of genetic caste determination (GCD) is characterized by between-caste nuclear variation and high levels of mitochondrial haplotype variation between alternative maternal lineages. Two previous genetic models, involving a single nuclear caste-determining locus or interactions between two nuclear loci, respectively, have been proposed to explain the GCD system. We propose a new model based on interactions between nuclear and mitochondrial genes that can better explain the co-maintenance of distinct nuclear and mitochondrial lineages. In our model, females with coevolved cyto-nuclear gene complexes, derived from intra-lineage mating, develop into gynes, while females with disrupted cyto-nuclear complexes, derived from inter-lineage mating, develop into workers. Both haplodiploidy and inbreeding facilitate the buildup of such coevolved cyto-nuclear complexes within lineages. In addition, the opportunity for both intralineage and inter-lineage mating in polyandrous populations facilitates the accumulation of gyne-biasing genes. This model may also help to explain the evolution of workerless social parasites. We discuss similarities of GCD and cytoplasmic male sterility in plants and how worker production of males would affect the stability of GCD. Finally, we propose experiments and observations that might help resolve the origin and maintenance of this unusual system of caste determination. Key words: cyto-nuclear coevolution; genetic caste determination; hybrid breakdown; inbreeding; social parasitism.

The findings of the theoretical investigation of the effect of random genetic drift on the covariance of identity-by-descent of nuclear and cytoplasmic genes are described. It is found that the conversion is biased in species with separate sexes, so that the increment of additive variance added to the nuclear genome is more than that added to the cytoplasmic genome.

The experimental methods for measuring epistasis are reviewed, some that are commonly used but weak and others that are less frequently used but stronger. The statistical genetic methods are also reviewed based on analyses of variances and means as well as molecular genetic methods for detecting gene interactions. It is concluded how technologies for investigating genome-wide epistasis are bridging the gap between physiological and statistical epistasis for model organisms.

Inbreeding depression is expected to play an important but complicated role in evolution. If we are to understand the evolution of inbreeding depression (i.e., purging), we need quantitative genetic interpretations of its variation. We introduce an experimental design in which sires are mated to multiple dams, some of which are unrelated to the sire but others are genetically related owing to an arbitrary number of prior generations of selfing or sib-mating. In this way we introduce the concept of 'inbreeding depression effect variance,' a parameter more relevant to selection and the purging of inbreeding depression than previous measures. We develop an approach for interpreting the genetic basis of the variation in inbreeding depression by: (1) predicting the variation in inbreeding depression given arbitrary initial genetic variance and (2) estimating genetic variance components given half-sib covariances estimated by our experimental design. As quantitative predictions of selection depend upon understanding genetic variation, our approach reveals the important difference between how inbreeding depression is measured experimentally and how it is viewed by selection.

Research points out that female nest-site philopatry is sex-specific, culturally inherited in reptiles, influenced by environmental sex determination, and exhibits highly female-biased sex rations. Data indicate that these attributes facilitate the maternal manipulation of offspring sex ratios in favor of females.

Maternal effect genes are discussed relative to evolution of sociality in haplo-diploid organisms. In hymenoptera, maternal care and female-biased sex ratios are thought by many to be essential for the evolution of eusaocial behaviors. Haplo-diploidy has been found not only to be helpful to evolution of sister-sister altruism by kin selection, but also to facilitate evolution of female-biased sex rations and maternal care. These are prerequisites for eusociality.

A controversy about important differences in two views on the content of evolutionary theory and the experimental approaches used to test and investigate evolutionary hypotheses in laboratory and field studies is discussed. The two schools of thought have their roots in the Fisher-Wright debates. Empirical studies are formative for some. The relationship between interdemic and group selection and role of gene interactions, epistasis, in evolution are considered in the light of biologist S. Wright's shifting balance theory. Both theories, it is concluded, at least as idealized, have difficulty with important features of natural populations. That is because assumption differ and thus limit the application of each theory to other domains. Recent findings, both theoretical and empirical, are not explicit, strictly, in either theory and only enrich both. That is especially true of Wright's work.

Results from previous experiments in group selection show the relationship between mean demic and individual fitness is controlled by the experimenters. An interdemic selection protocol that includes random and phase 3 migration might happen in nature, but this disappears when all migration is random.

We investigated patterns of within-species genetic variation for traits observed in hybrids (hybrid numbers, hybrid sex ratios, and hybrid male deformities) between two species of flour beetles, Tribolium castaneum and T. freemani. We found genetic variation segregating among four natural populations of T. castaneum as well as within these populations. For some hybrid traits, we observed as much variation among populations 750 km apart as between populations on different continents, suggesting genetic differentiation at a local scale. Within natural populations, the variation segregating among sires is greater than that found in an earlier study for an outbred laboratory population and comparable to that observed between inbred lines derived from the outbred stock by eight generations of brother-sister mating. When sires from T. castaneum are mated to conspecific and heterospecific females, we do not observe a significant correlation at the level of the family mean between the intraspecific and interspecific phenotypes, suggesting the independence of the hybrid traits from comparable traits within species. We discuss our findings in relation to the evolutionary genetics of speciation and the expression of epistatic genetic variance in interspecific crosses.

Natural populations of many organisms experience 'bottlenecks,' periodic reductions in the numbers of breeding adults (Powell 1978; Carson and Templeton 1984; McCauley 1989; Whitlock 1992a): 'Founder events' in the colonization [...]

The hypothesis of speciation by drift-mediated peak shifts needs special assumptions taking into account the genetic conditions depending on the nature of genetic variation for reproductive isolation. A study analyzes the effect of random genetic drift and founder events in determining speciation showing that the speciation by founder events can occur to a greater extent with x-linked loci than equivalent autosomal genes. This accounts for the Haldane's rule.

Population genetic methods help propose the anticipated population dynamics of the selfish-gene chromosomal factor Medea in flour beetles. Medea factors extend to fixation for all positive degrees of maternal-effect lethality when there are no harmful effects on gross fertility at a rate that varies with the nature of the effect and with the density. A stable interior polymorphism occurs when medea adversely affects fertility, affecting all offspring genotypes.

Use of quantitative genetic techniques on a laboratory strain of Tribolium castaneum in a study of the genetic basis of variation for the expression of viability reveals genetic variation for two traits of T. castaneum male and T. freemani female hybrids. Variation in hybrid sex ratio and surviving hybrid male fraction with antennal morphological defects increase when T. castaneum animals are inbred. The two traits exhibit a minimal but significant correlation with each other in both the hybrid and inbred lines, indicating that the variation in their expression could arise from the pleiotropic effects of the same set of segregating genes.

The patterns of cytoplasmic diversity, as revealed by chloroplast and mitochondrial DNA (mtDNA) sequence variation within and among populations, can be different from that of nuclear DNA variation (Avise et [...]

The amount of genetic variation in a population is determined by the interaction of the fundamental processes of evolution: selection, drift, migration, and mutation. Whereas the roles of selection and [...]

The genetic and ecological effects of population subdividsion were investigated for two wild strains of Tribolium castaneum and two wild strains of T. confusum and compared with the effects of population subdivision on the synthetic laboratory strain of T. castaneum (c-SM), used extensively in earlier experiments. For the c-SM strain, it has been shown repeatedly, for a variety of different population structures (different combinations of effective numbers, [N.sub.c], and migration rates, m) that large heritable differences in population growth rate arise among demes during 10 to 15 generations of population subdivision. Because this laboratory strain was synthesized by mass mating several 'inbred' strains in 1973 (80 to 100 generations ago), it is possible that it has genetic variation for fitness (measured as the heritable variance among demes in the rate of population increase) unusually large compared to natural populations of flour beetles. In this paper, I report that natural populations of flour beetle exhibit as much or more phenotypic and genetic variation in the effects of population structure on fitness than the laboratory strain, c-SM. The observation of substantial heritable variation for fitness in natural populations is unexpected under additive theory and may be indicative of nonaddictive genetic variance. Key words.--Beetles, fitness, genetic variation, interdemic selection, Tribolium.

Two levels of selection have been shown to exist within and among families. They act in opposing directions in the Hedrick biallelic viability model based on human data for maternal-fetal interactions. The invasion of new alleles is favored. Inbreeding avoidance characterizes the human histocompatibility loci. With it, within-family selection is strengthened and among-family selection is weakened. The pattern of selection is much like that seen for the maternal effect selfish genes in four beetles, fire ants and mice.

Population genetic theory developed for maternal-effect genes is used for predicting the equilibrium polymorphism within species and sequence divergence among species for genes with social effects on fitness. The studies have shown that the relative increase in polymorphism is proportional to the inverse of the genetic relatedness between individuals expressing the gene and their social partners that experience the fitness effects of the gene.

Two mechanisms, inbreeding and kin selection, have allowed mitochondria to respond to selection on both male viability and fertility. When either male viability effects of mitochondria or the indirect fitness effects is sufficiently strong, the studies have shown that there are conditions that allow the spread of mitochondria with direct effects that are harmful to females.

The way sex differences in the strength of random genetic drift create different patterns of genetic diversity for maternally and paternally inherited haploid genes is described. The equilibrium model is applied to quantify the opportunity for sexual selection in Homo sapiens.

The effects of temperature and genotype-by-environment interactions in the expression of Haldane's rule for hybrids of flour beetles have been examined. Haldane's rule shows that hybrid dysfunction is an indirect result of divergent adaptation to different environments. Results indicate that temperature has a significant effect on hybrid phenotype and various phenotypes react to temperature differently. It has also been proven that genetic variation with no seeming effect in conspecific populations may affect hybrid viability and morphology.

A study was conducted to analyze two theories of adaptive evolution. S. Wright's shifting balance theory and R.A. Fisher's large population size theory were examined using the results of laboratory studies and theoretical research. The study also discussed controversies surrounding the theories, specifically the nature of evolutionary change and the refinement of existing adaptation. In addition, ways in which the population genetic structure of metapopulations promote the evolution of gene combinations were examined.