Fertility of triploid hybrids of Prussian carp (<Emphasis Type="Italic">Carassius gibelio</Emphasis>) with common carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis> L.)

Fertility of backcross triploid hybrids containing one genome of Prussian carp and two genomes of common carp is investigated. The females of hybrids of Prussian carp and common carp (Prussian × common carp) are prolific and produce diploid gametes. Since males of such hybrids are sterile, their reproduction is realized by means of induced gynogenesis. Triploid progeny is obtained by backcrossing female Prussian × common carp with carp males. Among triploids obtained from hybrids F₁ and among hybrids of the first gynogenetic generation, there were no prolific specimens. However, in reproduction of diploid hybrids by means of gynogenesis during six generations, the female fertility in the backcross progeny is restored. From backcross triploid females (daughters of Prussian × common carp of the sixth gynogenetic generation), a viable triploid gynogenetic progeny and a tetraploid backcross (by carp) progeny are obtained. The obtained data may be considered as the experimental proof of the hypothesis of reticular speciation.     

Quantitative trait loci affecting the difference in pigmentation between Drosophila yakuba and D. santomea

Using quantitative trait locus (QTL) mapping, we studied the genetic basis of the difference in pigmentation between two sister species of Drosophila: Drosophila yakuba, which, like other members of the D. melanogaster subgroup, shows heavy black pigmentation on the abdomen of males and females, and D. santomea, an endemic to the African island of S?o Tomé, which has virtually no pigmentation. Here we mapped four QTL with large effects on this interspecific difference in pigmentation: two on the X chromosome and one each on the second and third chromosomes. The same four QTL were detected in male hybrids in the backcrosses to both D. santomea and D. yakuba and in the female D. yakuba backcross hybrids. All four QTL exhibited strong epistatic interactions in male backcross hybrids, but only one pair of QTL interacted in females from the backcross to D. yabuka. All QTL from each species affected pigmentation in the same direction, consistent with adaptive evolution driven by directional natural selection. The regions delimited by the QTL included many positional candidate loci in the pigmentation pathway, including genes affecting catecholamine biosynthesis, melanization of the cuticle, and many additional pleiotropic effects.     

甘蓝型油菜Ogura 雄性不育×白菜的回交杂种后代与亲本之间蕾期基因表达差异比较研究*

以甘蓝型油菜（Brassica napus L, AACC,2n＝38）Ogura细胞质雄性不育材料为母本,以不同白菜（B campestris ssp. chinensis Makino, AA, 2n＝20） 自交系‘新选一号’和‘矮脚黄’为父本进行杂交,获得了杂种F1、BC1、BC2代。利用cDNA-AFLP技术对两种材料的不同回交世代BC1、BC2代与其亲本在蕾期的基因表达进行分析。结果表明,两种白菜回交世代与其亲本的基因表达有明显差异,在质和量上都存在差异。基因表达模式有5类共7种：（1）单亲沉默型（2种）,（2）单亲一致型（2种）,（3）双亲共沉默型,（4）杂种特异型,（5）表达一致型。随着回交世代的增加,回交杂种和亲本的基因表达在单亲沉默型、双亲共沉默型呈增加趋势。而在母本一致型、父本一致型、杂交种特异型、表达一致型呈下降的趋势。两种白菜在F1、BC1、BC2 3个世代与回交亲本花蕾间的基因差异表达有15种类型,其中以在轮回亲本、F1、BC1、BC2中共同出现表达的带的比例最高。Abstract: Crosses between female parent of Ogura male sterility Brassica napus L. and male parents of B. campestris ssp. chinensis Makino were made and F1, BC1 and BC2 generations produced. Gene expression of two Chinese cabbage backcross hybrid BC1, BC2 and their parents at bud stage was analyzed by means of cDNA-AFLP technique. The results indicated that the patterns of gene expression differ significantly between BC1 and BC2 generations and their parents. There were many patterns of gene expression, including gene overexpression and gene silencing. Five patterns (seven kinds) of gene expression were observed, which include: (1) bands occurring in only one parent (two kinds); (2) bands observed in hybrids and one parent (two kinds); (3) bands occurring in only parents (one kind); (4) bands visualized in only hybrids (one kind); (5) bands observed in parents and hybrids (one kind). In accompany with the addition of backcross, the increase trend in backcross hybrids and their parents were described in the aspects of differential gene expression, bands expressed only in one parent and bands expressed only in both parents. The declined trend in backcross hybrids and their parents were observed in the aspects of bands expressed in both hybrids and one parent (two kinds), bands visualized in only hybrids and bands observed in parents and hybrid. Fifteen patterns of gene expression were observed in F1、BC1、BC2 and backcross parents. The percent of bands expressed in F1、BC1、BC2 and backcross was highest.     

HETEROSIS AND OUTBREEDING DEPRESSION IN INTERPOPULATION CROSSES SPANNING A WIDE RANGE OF DIVERGENCE

The intertidal copepod Tigriopus californicus was used as a model organism to look at effects of crossing distance on fitness and to investigate the genetic mechanisms responsible. Crosses were conducted between 12 pairs of populations spanning a broad range of both geographic distance (5 m to 2007 km) and genetic distance (0.2% to 22.3% sequence divergence for a 606-bp segment of the mitochondrial COI gene). For each pair of populations, three fitness components (hatching number, survivorship number, and metamorphosis number) were measured in up to 16 cohorts including parentals, reciprocal F₁, F₂, F₃, and first-generation backcross hybrids. Comparisons of each set of cohorts allowed estimation of within- and between-locus gene interaction. Relative to parentals, F₁ hybrids showed a trend toward increased fitness, with no correspondence with population divergence, and a decrease in variance, which in some cases correlated with population divergence. In sharp contrast, F₂ hybrids had a decrease in fitness and an increase in variance that both corresponded to population divergence. Genetic interpretation of these patterns suggests that both the beneficial effects of dominance and the detrimental effects of breaking up coadaptation are magnified by increasing evolutionary distance between populations. Because there is no recombination in T. californicus females, effects of recombination can be assessed by comparing F₁ hybrid males and females backcrossed to parentals. Both recombinant and nonrecombinant backcross hybrids showed a decline in fitness correlated with population divergence, indicating that segregation among chromosomes contributes to the breakup of coadaptation. Although there was no difference in mean fitness between the two backcross types, recombinational backcrosses showed greater variance for fitness than nonrecombinational backcrosses, suggesting that the breakup of parental gene ombinations within chromosomes has both beneficial and detrimental effects.     

Model for genetic control of Heliothis virescens

Summary A model was developed which corrects and extends an earlier one proposed for the control of the tobacco budworm, Heliothis virescens (F.), through hybrid male sterility. Population suppression is effected through the release into natural populations of the backcross progeny of a hybrid between H. virescens and a related species. Thereafter, the system perpetuates itself in nature through continual backcrossing of the fertile backcross females to native H. virescens males. When the proportion of backcross hybrid females in the total population is large enough to draw off the insemination potential of the native males, the native females fail to replace themselves. The present model demonstrated that the ratio of released backcross hybrids to natural H. virescens remains constant in a closed population. Furthermore it was shown that the release ratio necessary to achieve extinction of a closed population is related to the number of females that a male can inseminate and to the population growth rate. Release ratios required to slow natural population growth and to lessen the impact damage of releases on crop plants were also examined. Effects of selection against the backcross females on the predictions of the model were explored.     

Features of recombination of nuclear genome in back crossed offspring of barley-wheat hybrids Hordeum vulgare L. (2n=14) x Triticum aestivum L. (2n+42) with the use of SSR-analysis

The backcross progenies of the barley-wheat hybrids Hordeum vulgare L. (2n = 14) x Triticum aestivum L. (2n = 42) and two alloplasmic lines derived from them were studied using microsatellite markers of barley and wheat. The F1 hybrids and first backcross plants BC1 contained the genetic material of both cultivated barley and the cultivars of common wheat involved in developing of these hybrid genotypes. The genomes of BC3, BC4, and alloplasmic lines contained no microsatellite markers of the cultivated barley, whereas chromosomes of each homeologous group of common wheat were identified. In chromosomes of backcross progenies BC3, BC4, and alloplasmic lines yielded by backcrosses of hybrids and various common wheat cultivars, microsatellite markers of the parental wheat cultivars were shown to undergo recombination.     

Dominance effects strengthen premating hybridization barriers between sympatric species of grasshoppers (Acrididae,Orthoptera)

Sexual selection can lead to the rapid evolution of premating hybridization barriers and allows accelerated diversification and speciation within an evolutionary lineage. Especially during early stages of divergence, hybridization may impede further divergence, which strongly depends on the reproductive success of hybrids. Behavioural sterility of hybrids can limit or even prevent homogenizing gene flow. In this study, we investigated the attractiveness of male courtship songs for females of the grasshopper species Chorthippus biguttulus and C. brunneus and their interspecific F1 and F2 hybrids. Song preferences of females of both species are highly species specific and differ in three parameters: shape of the preference function, preference for syllable pattern and phrase duration. F1 hybrid females of both reciprocal crosses as well as F2 hybrid females resembled closely pure C. biguttulus females in respect of shape of the preference function and preference for syllable pattern, while preference for phrase duration showed an intermediate expression. This resulted in song preferences of hybrid females that closely resembled those of one parental species, that is C. biguttulus females. Such strong dominance effects were rarely reported so far. They represent an effective barrier limiting gene flow between the two species, since hybrid females will backcross to only one parental species and discriminate against hybrid males, which are behaviourally sterile. Such taxon‐specific modes of inheritance may have facilitated the rapid divergence of acoustically communicating grasshoppers of the species group of Chorthippus biguttulus. Our findings have novel implications on the expression of neuronal filters and the evolution of complex courtship signals.     

Behavioral sterility of hybrid males in acoustically communicating grasshoppers (Acrididae,Gomphocerinae)

The effectiveness of hybridization barriers determines whether two species remain reproductively isolated when their populations come into contact. We investigated acoustic mating signals and associated leg movements responsible for song creation of hybrids between the grasshopper species Chorthippus biguttulus and C. brunneus to study whether and how songs of male hybrids contribute to reproductive isolation between these sympatrically occurring species. Songs of F1, F2, and backcross hybrids were intermediate between those of both parental species in terms phrase number and duration. In contrast, species-specific syllable structure within phrases was largely lost in hybrids and was produced, if at all, in an irregular and imperfect manner. These divergences in inheritance of different song parameters are likely the result of incompatibility of neuronal networks that control stridulatory leg movements in hybrids. It is highly probable that songs of hybrid males are unattractive to females of either parental species because they are intermediate in terms of phrase duration and lack a clear syllable structure. Males of various hybrid types (F1, F2, and backcrosses) are behaviorally sterile because their songs fail to attract mates.     

Slug herbivory on hybrids of the crop Brassica napus and its wild relative B. rapa

Some plant species can cross with each other but stay nevertheless distinct with little gene flow between them. Selective herbivory could explain this pattern when hybrids are more susceptible or intermediate between their parents. We performed choice and no-choice experiments with the slug Arion lusitanicus to test this hypothesis for the crop Brassica napus, wild B. rapa and their backcross hybrids. In both experiments slugs greatly preferred B. napus over B. rapa while average herbivory on backcross hybrids was intermediate. Concentrations of aliphatic glucosinolates in the hybrids were intermediate between the parental species. Slug herbivory potentially reduces establishment of backcross hybrids. This hypothesis needs to be tested in the field.     

Interspecific genetics of mate recognition: inheritance of female acoustic preference in Hawaiian crickets

Abstract. Female mating behavior plays a fundamental role in the divergent evolution of mate recognition systems that may lead to speciation. Despite this important role, the phenotypic and genetic bases of female mating behavior remain poorly understood. In this study, I examine the shape of the female acoustic preference function and estimate values for pulse rate preference in two species of Hawaiian crickets, Laupala kohalensis and L. paranigra . In addition, I examine how preference differences are inherited in hybrid crosses between these species. Females expressed unimodal preference functions and were generally more attracted to pulse rates characterizing their own species. Unimodal preference functions also characterized F1 and backcross generations, with hybrid females expressing preferences for intermediate pulse rates. Pulse rate preferences segregated in the backcross generation. Mean pulse rate preference matched mean pulse rate in both parental and hybrid generations. Based on F1 hybrids and segregation patterns in backcross females, I show that changes in both signal and receiver components of the mate recognition system are consistent with a multilocus model of change through incremental steps. The results therefore suggest that ancestors of the current species also expressed unimodal preference functions and that changes in acoustic communication signals occurred through shifts in mean pulse rates and pulse rate preferences among populations.     

Paternal inheritance of mitochondria and chloroplasts in Festuca pratensis-Lolium perenne intergeneric hybrids

Organelle inheritance in intergeneric hybrids of Festuca pratensis and Lolium perenne was investigated by restriction enzyme and Southern blot analyses of chloroplast DNA (cpDNA) and mitochondrial DNA (mtDNA). All F₁ hybrids exhibited maternal inheritance of both cpDNA and mtDNA. However, examination of backcross hybrids, obtained by backcrossing the intergeneric F₁ hybrids to L. Perenne, indicated that both uniparental maternal organelle inheritance and uniparental paternal organelle inheritance can occur in different backcross hybrids.     

Genetics of Male and Female Sterility in Hybrids of Drosophila pseudoobscura and D. persimilis

The genetic basis of male and female sterility in hybrids of Drosophila pseudoobscura-Drosophila persimilis was studied using backcross analysis. Previous studies indirectly assessed male fertility by measuring testis size; these studies concluded that male sterility results from an X chromosome-autosome imbalance. By directly scoring for the production of motile sperm, male sterility is shown to be largely due to an incompatibility between genes on the X and Y chromosomes of these two species. These species have diverged at a minimum of nine loci affecting hybrid male fertility. Semisterility of hybrid females appears to result from an X chromosome-cytoplasm interaction; the X chromosome thus has the largest effect on sterility in both male and female hybrids. This is apparently the first analysis of the genetic basis of female sterility, or of sterility/inviability affecting both sexes, in an animal hybridization.     

Genetics of dystrophic epicardial mineralization in DBA/2 mice

The genetics of dystrophic epicardial mineralization in mice was studied using 6 to 8-week-old hybrids and recombinant inbred strains derived from DBA/2J (high prevalence) and C57B1/6J (low prevalence) mice. DBA/2J mice of both sexes were uniformly affected. No cases were seen among 32 F1 mice and 82 F2 mice. Six out of 31 backcross progeny obtained from F1 females backcrossed to DBA/2J males were affected. Two out of 25 recombinant inbred strains were affected. These results suggest that dystrophic epicardial mineralization is determined by three or four unlinked autosomal recessive alleles.     

Hybrid bridges to gene flow: a case study in milkweeds (Asclepias)

Natural hybridization occurs throughout areas of sympatry for the North American milkweeds Asclepias exaltata and A. syriaca (Asclepiadaceae), even though the formation of F1 hybrid seed is a rare event. For introgressive hybridization to proceed, F1 and advanced hybrids must be released from reproductive barriers and successfully mate with one or both parental species. I investigated the mating system of natural hybrids between A. exaltata and A. syriaca in three populations in Shenandoah National Park, Virginia. Allozyme data and a maximum-likelihood procedure were used to estimate the frequency of six genotypic classes (parentals, F1, F2, and backcrosses) of the hybridizing populations, the pollinia received by hybrid plants, and the paternal parents of seeds produced by hybrids. F1 hybrids, backcross A. syriaca, and parental A. syriaca individuals were common in three hybrid populations. Even though self-pollinations and interhybrid pollinations were common, F2 seed production and the occurrence of F2 individuals were rare in hybrid populations. Hybrid plants received more pollen from A. syriaca than A. exaltata, which resulted in the production of more backcross-A. syriaca seed than backcross-A. exaltata seed. Asclepias exaltata was rare in the hybrid populations, but A. exaltata pollinia were received by hybrids and this species sired between 15% and 36% of the seeds produced on hybrids. The potential for introgression with A. exaltata populations is lower because this species is unsuccessful as the maternal parent in interspecific and backcross hand-pollinations. The asymetry of hybridization with A. syriaca as the maternal parent is further supported by the incorporation of maternally inherited chloroplast DNA markers in hybrids. Hybrid milkweeds frequently backcross with both parental species and may be released from the reproductive barriers that limit the formation of F1 hybrids in natural populations. The direction of interspecific gene flow and introgression in milkweeds is influenced by the reproductive biology of hybrids, the constituency of the surrounding population, and failure of some crosses to produce seeds. Finally, introgressive hybridization remains an important evolutionary force even when the initial formation of F1 hybrids in natural populations is rare.     

Fertility in first-generation hybrids of roach, Rutilus rutilus (L.), and silver bream, Blicca bjoerkna (L.)

Fertility in first‐generation hybrids of roach, Rutilus rutilus, and silver bream, Blicca bjoerkna, was investigated. Sperm and egg production of hybrids at first sexual maturity were examined. Eggs from female hybrids were artificially fertilized with the sperm of a corresponding hybrid male; a hybrid male from the reciprocal crossbreeding; a parental species male R. rutilus; and a parental species male B. bjoerkna. The results revealed that gametogenesis was normal in female hybrids. However, in male hybrids, a low efficiency of gametogenesis was observed. The semen of male hybrids was extremely dilute, with spermatozoa concentration lower than that in parental species. Nevertheless, these F1 hybrids (males and females) from reciprocal crossbreeding were fertile. F2 and backcross generations were produced, but F2 crosses from the female hybrid and corresponding hybrid male displayed a drastically slower hatching rate. Also higher proportions of deformed embryos were hatched than in other post‐F1‐generation crosses.     

Genetic analysis for insulitis in NOD mice

Non-obese diabetic (NOD) mice spontaneously develop diabetic signs akin to those of Type I diabetes in man. Insulitis, i.e., lymphocytic infiltration around and into the pancreatic islets is one of the characteristics of such mice. It is also the etiologic pathological lesion in the development of diabetes mellitus in NOD mice. Thus, we chose insulitis as a marker for genetic analysis of the development of diabetes mellitus in NOD mice and clarified the mode of its inheritance. In breeding studies between NOD and C57BL/6J mice, insulitis was not observed in the F1 and (F1 X C57BL/6J) backcross generations, but was found with incidences of 3.9% in females and 1.4% in males in the F2 generation and 23.7% in females and 12.1% in males in the (F1 X NOD) backcross generation. These incidences in the F2 and (F1 X NOD) backcross females corresponded approximately to 1/16 and 1/4 of the incidences of 89.7% in the NOD females, respectively. A similar relationship was observed between the F2 and (F1 X NOD) backcross males and the NOD males. When the gene expressivity of both sexes for a double recessive homozygote was assumed to be the incidences of insulitis in 9-week-old NOD females and males, respectively, the expected numbers of both sexes with and without insulitis in the F2 and backcross generations agreed well with the observed ones. These observations suggest that two recessive genes on independent autosomal chromosomes are necessary for the development of insulitis in NOD mice.     

Genetics, experience, and host-plant preference in Eurosta solidaginis: implications for host shifts and speciation

Host-associated mating is crucial in maintaining the partial reproductive isolation between the host races of Eurosta solidaginis (Diptera: Tephritidae), a fly that forms galls on Solidago altissima and S. gigantea. (We refer to flies reared from S. gigantea as gigantea flies and those reared from S. altissima as altissima flies.) We measured the host preference of males and females of both host races, F1 hybrids between the host races, F2, and backcrosses to both host races. Male and female altissima flies and female gigantea flies had high host fidelity, whereas male gigantea flies had low host fidelity. This result suggests that there may be gene flow between the host races due to nonassortative mating that occurs when male gigantea mate with altissima females on S. altissima. This indicates assortative-mating mechanisms in addition to host-associated mating are required to produce the partial reproductive isolation between the host races that has been observed. Nongenetic factors had no influence on host preference. Larval conditioning did not influence host preference: reciprocal F1 hybrids reared in S. altissima and S. gigantea both preferred S. gigantea. Adult experience had no impact on host preference: females preferred their natal host plant regardless of which host they encountered first as an adult. The hypothesis that maternal effects influence preferences was rejected because male and female flies did not show a consistent preference for the host plant of their mother. We also found no evidence that preference was a sex-linked trait because F1 and backcrosses to the host races with different combinations of X chromosomes from the two host races preferred S. gigantea. Our results indicate that host preference is not determined by a large number of genes because preference of hybrids did not correspond to the proportion of the genome derived from each host race. The strength of the ovipuncture preference for S. gigantea by gigantea females, the females of both reciprocal F1 hybrids, the backcross to gigantea, and F2s indicates that preference is inherited nonadditively at a limited number of loci. The F1 female hybrids, however, had a weaker host preference for S. gigantea than the pure gigantea host race, indicating that there may be incomplete dominance or modifier loci. Males had different host preference patterns than females, with individual male gigantea and male F1 hybrids usually exhibiting preference exclusively for S. gigantea or S. altissima. One hypothesis explaining the difference in host preference between males and females is that the same gene influences both female and male host preference, but it is a sex-influenced gene. Thus, males carrying the gene for S. gigantea preference have an intermediate host preference, whereas females have a strong host preference to S. gigantea. In summary, we found that the host preference that produces host-associated mating is inherited nonadditively at a relatively small number of loci on autosomal genes. This mode of inheritance meets the assumptions of models of sympatric speciation, indicating that the host races could have evolved in sympatry.     

Wild rats (Rattus norvegicus) for mapping of disease-resistant genes

Wild rat representing a disease-resistant phenotype and genotype, was used in a crossing study with spontaneously hypertensive rat (SHR) to search for quantitative trait loci (QTL) affecting blood pressure. Therefore, one male wild rat was crossed with SHR females and F1 hybrids were transferred in a pathogen free environment by wet-hysterectomy and backcrossed onto hypertensive SHR rats resulting in first backcross hybrids (BC1). Considering that the F1 hybrids are not uniform, as are the cross hybrids of inbred rat strains, we selected 72 BC1 progeny of one F1 female, which were characterised for systolic blood pressure, measured by tail cuff method and were genetically analysed using 200 microsatellites covering the whole genome. We found suggestive linkage of blood pressure to region on chromosome 2 flanked by D2Mit8 and Fgg loci (lod score 2.3). In addition, possible interaction between genes on chromosomes 7 and 3, X and 3, 14 and 3, 13 and 11 was described, indicating that blood pressure development in the SHR might be the result of interacting genes.     

Intergeneric hybridization between Diplotaxis siettiana and crop brassicas for the production of alloplasmic lines

Summary Intergeneric hybrids were produced between Diplotaxis siettiana and Brassica campestris through embryo rescue. The hybrids were completely pollen sterile and backcrosses with pollen of B. campestris did not yield any seeds. Induction of colchiploidy restored pollen fertility and backcross pollinations yielded viable seeds. Cytological details of the hybrid, amphidiploid and backcross progenies were studied. Both pollen-sterile and pollen-fertile plants have been obtained in backcross 2 progeny. This hybrid (D. siettiana x B. campestris) was used as a bridge cross to transfer the cytoplasm of D. Siettiana to two other incompatible cultivars of Brassica — B. juncea and B. napus. Pollinations of the amphidiploid (D. siettiana x B. campestris, 2n = 36) with pollen of B. juncea/B. napus readily produced seeds without embryo rescue. These hybrids were grown to flowering and their cytological details were studied. Seeds have been produced from backcross pollinations of both these hybrids with the pollen of the respective cultivars. The results clearly show the feasibility of producing alloplasmic lines in all the three oilseed brassicas.