Epigenetic Programming： The Challenge to Species Hybridization

In many organisms, the genomes of individual species are isolated by a range of reproductive barriers that act before or after fertilization. Successful mating between species results in the presence of different genomes within a cell （hybridization）, which can lead to incompatibility in cellular events due to adverse genetic interactions. In addition to such genetic interactions, recent studies have shown that the epigenetic control of the genome, silencing of transposons, control of non-additive gene expression and genomic imprinting might also contribute to reproductive barriers in plant and animal species. These genetic and epigenetic mechanisms play a significant role in the prevention of gene flow between species. In this review, we focus on aspects of epigenetic control related to hybrid incompatibility during species hybrid- ization, and also consider key mechanism（s） in the interaction between different genomes.

Nutrient element contents of cutting seedlings of hybrid species (Liriodendron chinense x tulipifera)

The cutting seedlings of Liriodendron chinense x tulipifera were treated with the different concentrations of auxin (treatment1: IBA of 50 gkg-1 + NAA of 300 gkg-1; treatment2: IBA of 100 gkg-1 + NAA of 300 gkg-1). The biomass and the nutrient element contents for different organs (root, stem, leaf) of cutting seedling of Liriodendron chinense x tulipifera were measured by the dry method, Kjeldahl method and Atomic Absorption Spectroscopy method. The result showed that the biomass of root, stem, and leaf of the cutting seedling treated with auxin was all remarkably increased. The contents of element C in root, stem and leaf had no significant difference between the control and auxin treatments, while the contents of N, P, K and Ca in stem were much lower than that in leaf and root. Variance analysis showed that for the same organ with different concentration treatment of auxin, the four nutrient elements (N, P, K, and Ca) had no significant difference in contents, while there existed significant or very significant difference in contents of the four nutrient elements in different organs with the same concentration auxin treatment. The N, P, K and Ca contents were very low in cutting seedlings; as a result, additional fertilizer should be applied to the seedlings when they were planted in the field.

The Influence of Inbreeding Depression and Hybrid Superiority on Wood Property and Tree Growth of Eucalypt

With F1 of self pollinated Eucalyptus urophylla, F1 of inter tree pollinated E.urophylla, F1of open pollinated E.urophylla and F1 of E.urophylla×grandis as materials,inbreeding depression and hybrid superiority in growth and wood traits are analyzed and discussed.The results are as follows.①There was a regularity for E.urophylla that F1 of self pollinated was subjected to more intense depression than F1 of open pollinated,and growth traits showed more signifcant depression than wood traits.②As to F1 of self pollinated E.urophylla, height,DBH and volume showed significant or extremely significant depression,while water content of green wood,wood density and bark thickness showed no significant depression.③As to F1 of open pollinated E.urophylla, height,DBH and volume showed depression to a certain degree,but not significant;Here again,water content of green wood,wood density and bark thickness showed no significant depression.④F1 of E.urophylla×grandis showed significant hybrid superiority in height,DBH and volume,but the hybrid superiority percentage of different cross pairs varied greatly;It showed no hybrid superiority in water content of green wood,wood density and fiber length;Its bark thickness and content of 1% NaOH extractives decreased evidently.

Impacts of climate warming on hybrid zone movement： Geographically diffuse and biologically porous ＂species borders＂

The ecology and evolutionary biology of insect-plant associations has real- ized extensive attention, especially during the past 60 years. The classifications （categorical designations） of continuous variation in biodiversity, ranging from global patterns （e.g., lat- itudinal gradients in species richness/diversity and degree of herbivore feeding specialization） to localized insect-plant associations that span the biospectrum from polyphenisms, polymorphisms, biotypes, demes, host races, to cryptic species, remain academically contentious. Semantic and biosystematic （taxonomical） disagreements sometimes detract from more important ecological and evolutionary processes that drive diversification, the dynamics of gene flow and local extinctions. This review addresses several aspects of insect specialization, host-associated divergence and ecological （including ＂hybrid＂） speciation, with special reference to the climate warming impacts on species borders of hybridiz- ing swallowtail butterflies （Papilionidae）. Interspecific hybrid introgression may result in collapse of multi-species communities or increase species numbers via homoploid hybrid speciation. We may see diverging, merging, or emerging genotypes across hybrid zones, all part of the ongoing processes of evolution. Molecular analyses of genetic mosaics and genomic dynamics with ＂divergence hitchhiking＂, combined with ecological, ethological and physiological studies of＂species porosity＂, have already begun to unveil some answers for some important ecological/evolutionary questions. （i） How rapidly can host-associated divergence lead to new species （and why doesn＇t it always do so, e.g., resulting in ＂incom- plete＂ speciation）？ （ii） How might ＂speciation genes＂ function, and how/where would we find them？ （iii） Can oscillations from specialists to generalists and back to specialists help explain global diversity in herbivorous insects？ （iv） How could recombinant interspecific hybridization lead to divergence and speciation？ From ancient phytochemically defined angiosperm affiliations to recent and very local geographical mosaics, the Papilionidae （swallowtail butterflies） have provided a model for enhanced understanding of ecological patterns and evolutionary processes, including host-associated genetic divergence, ge- nomic mosaics, genetic hitchhiking and sex-linked speciation genes. Apparent homoploid hybrid speciation in Papilio appears to have been catalyzed by climate warming-induced interspecific introgression of some, but not all, species diagnostic traits, reflecting strong divergent selection （discordant）, especially on the Z （= X） chromosome. Reproductive isolation of these novel recombinant hybrid genotypes appears to be accomplished via a delayed post-diapause emergence or temporal isolation, and is perhaps aided by the thermal landscape. Changing thermal landscapes appear to have created （and may destroy） novel recombinant hybrid genotypes and hybrid species.

Natural hybridization and reproductive isolation between two Primula species

Natural hybridization frequently occurs in plants and can facilitate gene flow between species, possibly resulting in species refusion. However, various reproductive barriers block the formation of hybrids and maintain species integrity. Here, we conducted a field survey to examine natural hybridization and reproductive isolation （RI） between sympatric populations of Primula secundiflora and P. poissonii using ten nuclear simple sequence repeat （SSR） loci. Although introgressive hybridization occurred, species boundaries between P. secundiflora and P. poissonii were maintained through nearly complete reproductive isolation. These interfertite species provide an excellent model for studying the RI mechanisms and evolutionary forces that maintain species boundaries.

Hybrid Isothermal Model for the Ferrohydrodynamic Chemically Reactive Species

A hybrid isothermal model for the homogeneous-heterogeneous reactions in ferrohydrodynamic boundary layer ?ow is established. The characteristics of Newtonian heating and magnetic dipole in a ferro?uid due to a stretchable surface is analyzed for three chemical species. It is presumed that the isothermal cubic autocatalator kinetic gives the homogeneous reaction and the ?rst order kinetics gives the heterogeneous(surface) reaction. The analysis is carried out for equal diffusion coe?cients of all autocatalyst and reactions. Heat ?ux is examined by incorporating Fourier's law of heat conduction. Characteristics of materialized parameters on the magneto-thermomechanical coupling in the ?ow of a chemically reactive species are investigated. Further, the heat transfer rate and friction drag are depicted for the ferrohydrodynamic chemically reactive species. It is evident that the Schmidt number has increasing behavior on the rate of heat transfer in the boundary layer. Comparison with available results for speci?c cases is found an excellent agreement.

Differential effects of short term winter thermal stress on diapausing tiger swallowtail butterflies （Papilio spp.）

It is generally thought that insects inhabiting lower latitudes are more severely impacted by changes in their thermal environment than are high latitude species. This is attributed to the wider range of temperatures to which high-latitude species are exposed. By contrast, low-latitude species have typically evolved in more thermally stable environments with a narrower range of temperature variation. However, deviation from this pattern can occur and here we report that under variable winter conditions a higher latitude species may be more sensitive to thermal variation than its lower latitude sister species. Using split broods, we examined the survival and adult emergence success of diapausing pupae of Papilio canadensis and P. glaucus, as well as a unique, recombinant hybrid population （＂late-flight＂） to short periods of mid-winter cold and heat stress. Our results indicate that the higher latitude, univoltine populations （P. canadensis and late-flights） exhibit lower pupal survival than the lower latitude, facultative diapauser （P. glaucus） for all mid-winter thermal stress treatments, both high and low. Size differences alone do not appear to account for the observed differences in survival or metabolic costs in these three pheno- types, as late-flight individuals are similar in size to R glaucus. We attribute the observed differences in survival and weight loss to potential metabolic differences and variation in the intensity of diapause, in addition to divergent adaptation to winter precipitation levels （e.g. snow cover） and the influences this may have on microhabitat temperature moderation.