Probabilities of negative estimates of genetic variances

Summary The probability of negative analysis of variance estimates of genetic variance components due to sampling error (Ps) was investigated. The objectives were to evaluate the magnitude of Ps, to compare Ps for estimates of _A ² and _D ² , and to compare Ps for genetic variance component estimates from the nested and factorial mating designs. Ps was defined in terms of ratios of mean squares and the F distribution was used to calculate probabilities of the negative estimates. The results indicated that Ps is often greater than 0.20 for _D ² . It is generally lower for _A ² than for _D ² , and lower for the factorial mating design than the nested mating design.Technical Contribution No. 2589 from the South Carolina Agricultural Experiment Station, Clemson University     

EVOLUTIONARY PREDICTABILITY IN NATURAL POPULATIONS: DO MATING SYSTEM AND NONADDITIVE GENETIC VARIANCE INTERACT TO AFFECT HERITABILITIES IN PLANTAGO LANCEOLATA?

Quantitative genetics has been an immensely powerful tool in manipulating the phenotypes of domesticated plants and animals. Much of the predictive power of quantitative genetics depends on the breeder's control over the context in which phenotype and mating are being expressed. In the natural world, these contexts are often difficult to describe, let alone control. We are left, therefore, with a poor understanding of the limits of quantitative genetics in natural populations. One of the crucial contextual elements for assessing breeding value is the genetic background in which an individual's genes are being assessed. When interacting genes are polymorphic within a population, the degree of mating among relatives can influence the correlations among mates and the predictions of a response to selection. Population structure can strongly influence the degree to which dominance and epistasis influences additive genetic variance and heritability. The extent of inbreeding can also influence heritabilities through its effect on the environmental component of phenotypic variance. The applicability of standard quantitative genetic breeding designs to the measurement of heritabilities in natural populations therefore depends in part on: (1) the mating system of the population; and (2) the importance of gene interactions in determining phenotypic variation. We tested for an effect of mating structure on the partitioning of phenotypic variance and heritability by comparing two breeding designs in a common environment. Both breeding designs used 139 pollen parents taken from mapped locations in a population of Plantago lanceolata L., and crossed to 280 seed parents from the same population. One design was random-mating, the second was biased toward near-neighbor matings to an extent determined by field measure of pollen-mediated gene flow distances. The offspring were grown randomly mixed in a common garden. Nine traits were measured: central corm diameter, number of leaves, area of the most recently fully expanded leaf, density of hairs (cm^-2) on the leaves, dry weight per unit leaf area, photosynthetic capacity, transpiration rates, water use efficiency, and reproductive dry weight. Heritabilities and variance components from the two designs were compared using randomization tests. None of the variance components or the heritabilities differed significantly between breeding designs at the 0.05 level. The test could distinguish differences between the heritabilities measured in the two breeding designs as small as 0.11, on average. Thus, for the degree of inbreeding normally exhibited in P. lanceolata there is insufficient gene interaction present within populations to influence the partitioning of variance between additive and nonadditive components or to influence heritability estimates to a meaningful extent. We suggest that for Plantago other sources of variation in heritability estimates, such as maternal effects and genotype × environment interactions, are more important influences than the interaction between inbreeding and gene interactions, and standard heritability estimate based on random breeding is as accurate as one taking the natural mating structure into account.     

Mating frequency in dispersing potato tuber moth, Phthorimaea operculella, and its influence on the design of refugia to manage resistance in Bt transgenic crops

Mating of potato tuber moth, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), was investigated in relation to the dispersal of males in laboratory and field trials. The effect of stimulating the flight of males to light sources in a large cage on their mating ability was estimated for three age groups, and compared with similar estimates for confined moths. Although the mating of males declined with ages of up to 15 days, simulated dispersal had no effect on subsequent mating when the males were paired with virgin females. The dispersal of male moths was also categorised by the initial flight activity of untethered moths to a light source. Scores for poor, moderate, and good flight provided a repeatable measure of initial male flight activity, but the degree of activity was not related to their subsequent mating ability. In the field, virgin female potato tuber moths were tethered at various distances from the edge of isolated potato crops and then dissected to determine their mating status. Female mating frequency averaged 75% at the crop margin, remained above 50% up to 200 m, and then declined to 19% at 360 m from the margin. Derivation of the mating probability for an individual male potato tuber moth confirmed earlier work by other researchers that has indicated a tendency for dispersal prior to mating, and that males retain their ability to mate as they disperse from a crop. The influence of dispersal and mating on gene flow between crops, and its potential effects on refuge size required to minimise the development of resistance to Bt transgenic potato crops was examined.     

Male Mate Choice in Lemur catta

Though females are generally more selective in mate choice, males may also derive reproductive benefits from exercising mate selectivity if one or more factors limit male reproductive success and females differ in reproductive potential. I used male mating effort as a proxy for male mate choice in ring-tailed lemurs (Lemur catta). I calculated mating effort as the rate of male-male agonism during each female's estrous period 30 min before and 30 min after the first and last mountings with intromission. I collected data on 1 free-ranging Lemur catta troop during 2 consecutive breeding seasons on St. Catherines Island, USA. In both yrs, male mating effort differed significantly among troop females once I adjusted male-male agonistic rates to reflect agonistic intensity, and I corrected for the number of observed mates per female (2000: χ² = 27.43, df = 3, p < 0.0001; 2001: χ² = 21.10, df = 3, p < 0.001). Results strongly suggest male mate choice. Contrary to expectation, males did not expend the greatest mating effort for females with the highest dominance status nor the highest reproductive success. Males preferred females that either: (1) belonged to the age class in which fecundity and infant survival is the highest at this site (4–9 yrs), or 2) were older females (≥10 yrs) with high reproductive success. Female reproductive potential appears to be an important variable determining male mating effort in Lemur catta.     

Search behavior of pheromone-stimulated potato tuber moth males (Lepidoptera: Gelechiidae)

The processes of female searching by male potato tuber moths,Phthorimaea operculella, were analyzed. The behavioral components to copulation were antennal cleaning, quiescence, walking, wing fanning, contact with female, hair brush display, copulation attempt, and copulation. Males did not always succeed in mating on their first attempt. Searching behavior of males changes to “area-restricted searching” after contact with a female. Males could, therefore, find females efficiently and copulate.     

The effects of mating design on introgression between chromosomally divergent sunflower species

Population genetic theory suggests that mating designs employing one or more generations of sib-crossing or selfing prior to backcrossing are more effective than backcrossing alone for moving alleles across linkage groups where effective recombination rates are low (e.g., chromosomally divergent linkages). To test this hypothesis, we analyzed the effects of chromosomal structural differences and mating designs on the frequency and genomic distribution of introgressed markers using the domesticated sunflower, Helianthus annuus, and one of its wild relatives, H. petiolaris, as the experimental system. We surveyed 170 progeny, representing the end products of three different mating designs (design I, P-F₁-BC₁-BC₂-F₂-F₃; design II, P-F₁-F₂-BC₁-BC₂-F₃; and design III, P-F₁-F₂-F₃-BC₁-BC₂), for 197 parental RAPD markers of known genomic location. Comparison of observed patterns of introgression with expectations based on simulations of unrestricted introgression revealed that much of the genome was protected from introgression regardless of mating design or chromosomal structural differences. Although the simulations indicated that all markers should introgress into multiple individuals in each of the three mating designs, 20 of 58 (34%) markers from collinear linkage groups, and 112 of 139 (81%) markers from rearranged linkage groups did not introgress. In addition, the average size of introgressed fragments (12.2 cM) was less than half that predicted by theoretical models (26–33 cM). Both of these observations are consistent with strong selection against introgressed linkage blocks, particularly in chromosomally divergent linkages. Nonetheless, mating designs II and III, which employed one and two generations of sib-mating, respectively, prior to backcrossing, were significantly more effective at moving alleles across both collinear and rearranged linkages than mating design I, in which the backcross generations preceded sib-mating. Thus, breeding strategies that include sib-crossing, in combination with backcrossing, should significantly increase the effectiveness of gene transfer across complex genic or chromosomal sterility barriers.     

Author index for volume 219

Proteinase inhibitors I and II were purified to electrophoretic homogeneity from leaves of tomato plants induced by either wounding intact plants or by supplying excised plants with the proteinase inhibitor inducing factor. Affinity chromatography with chymotrypsin-Sepharose was employed as a final purification step for each inhibitor. The tomato leaf inhibitors are very similar to potato tuber inhibitors I and II in subunit molecular weight, composition, and inhibitory activities against chymotrypsin, trypsin, and subtilisin. However, unlike the potato tuber which contains multiple isoinhibitors by isoelectric focusing, the tomato leaf exhibits only two isoinhibitor forms of inhibitor I and a single form of inhibitor II. The molecular weight of native potato inhibitor I was reevaluated by rigorous ultracentrifugal analysis and compared with data from previous analyses. The data confirm that native inhibitor I has a native M_r of about 41,000 and is a pentamer. Inhibitor II has a molecular weight of near 23,000 and is a dimer.     

Efficiency of check-plot designs in unreplicated field trials

Check-plot designs have a lower selection intensity than unreplicated non-check-plot designs if both the number of test lines to be selected (s) and of total plots in the trial (N) are kept constant. For a check-plot design to be more efficient, local control must effectively reduce the plot error variance and increase heritability to such a level that it compensates for the corresponding loss in selection intensity and makes the expected gain from selection at least equal to that in the non-check-plot design. To realize this goal, the required minimum reduction in plot error variance in a checkplot design (relative to that in a non-check-plot design) depends on (1) check-plot frequencyf _c , (2) fractionk = s/N, and (3) ratiow ₀= ₀ ² / _g ² of non-check-plot design plot error variance ₀ ² to genetic variance _g ² among test lines. Lowerw ₀ and higherf _c andk are found to require a relatively higher reduction in plot error variance in check-plot designs. A condition is derived to show when a check-plot design may never be more efficient.     

How multiple mating by females affects sexual selection

Multiple mating by females is widely thought to encourage post-mating sexual selection and enhance female fitness. We show that whether polyandrous mating has these effects depends on two conditions. Condition 1 is the pattern of sperm utilization by females; specifically, whether, among females, male mating number, m (i.e. the number of times a male mates with one or more females) covaries with male offspring number, o. Polyandrous mating enhances sexual selection only when males who are successful at multiple mating also sire most or all of each of their mates'' offspring, i.e. only when Cov_♂(m,o), is positive. Condition 2 is the pattern of female reproductive life-history; specifically, whether female mating number, m, covaries with female offspring number, o. Only semelparity does not erode sexual selection, whereas iteroparity (i.e. when Cov_♀(m,o), is positive) always increases the variance in offspring numbers among females, which always decreases the intensity of sexual selection on males. To document the covariance between mating number and offspring number for each sex, it is necessary to assign progeny to all parents, as well as identify mating and non-mating individuals. To document significant fitness gains by females through iteroparity, it is necessary to determine the relative magnitudes of male as well as female contributions to the total variance in relative fitness. We show how such data can be collected, how often they are collected, and we explain the circumstances in which selection favouring multiple mating by females can be strong or weak.     

Genetic variation in Solanum tuberosum group Andigena haploids

Summary A random sample of haploids, derived from 28 parental introductions from Solarium tuberosum Gp. Andigena, was used to estimate the quantitative genetic variation for six traits within this group. The six traits analyzed on a plot mean basis were: total tuber weight, fresh vine weight, total fresh weight (tuber+vine), dry vine weight, total dry matter (tuber+vine) and specific gravity. Progenies were obtained following the North Carolina mating Design I and were evaluated along with the female parental clones at two locations. Components of variance and narrow sense heritabilities were calculated by two methods: Design I and female parent-offspring regression. Heritability estimates calculated by the two procedures were in close agreement for most traits. The estimates for total tuber weight from the Design I procedure were twice that from parent offspring regression. The genetic coefficient of variation for these traits indicated a large amount of total genetic variance in this population. Genetic variability for total tuber weight was mostly additive, while both additive and dominant genetic variances were equally important for the remaining traits.     

蝇蛹金小蜂的交配行为及雄蜂交配次数对雌蜂繁殖的影响

多数昆虫能够进行多次交配,随寄生蜂雄蜂交配次数的增加,雄蜂体内精子减少,雌蜂获得的精子数量减少,产下更多的单倍体卵,发育为雄性后代;一些单寄生性的寄生蜂雌蜂一生仅能够交配1次。描述了蝇蛹金小蜂雌雄蜂的交配行为,探讨了雄蜂交配次数对雌蜂后代产量等的影响以及雌蜂的可交配次数。结果表明,交配过程包括求偶、交尾前期、交尾和交尾后期;雄蜂已交配的次数并不能够显著影响其配偶的寿命、产卵期和后代总数量,但显著影响到其配偶的雌、雄后代数量和性比。随雄蜂交配次数的增加,与之交配的雌蜂的后代雄性百分比显著增大,雌蜂在产卵期内更早地出现较多雄性后代,体内精子不足的现象更加明显。无论已交配的蝇蛹金小蜂雌蜂在产卵期中是否出现精子不足,均不能再次完成交配。     

Statistical epistasis between candidate gene alleles for complex tuber traits in an association mapping population of tetraploid potato

Association mapping using DNA-based markers is a novel tool in plant genetics for the analysis of complex traits. Potato tuber yield, starch content, starch yield and chip color are complex traits of agronomic relevance, for which carbohydrate metabolism plays an important role. At the functional level, the genes and biochemical pathways involved in carbohydrate metabolism are among the best studied in plants. Quantitative traits such as tuber starch and sugar content are therefore models for association genetics in potato based on candidate genes. In an association mapping experiment conducted with a population of 243 tetraploid potato varieties and breeding clones, we previously identified associations between individual candidate gene alleles and tuber starch content, starch yield and chip quality. In the present paper, we tested 190 DNA markers at 36 loci scored in the same association mapping population for pairwise statistical epistatic interactions. Fifty marker pairs were associated mainly with tuber starch content and/or starch yield, at a cut-off value of q ≤ 0.20 for the experiment-wide false discovery rate (FDR). Thirteen marker pairs had an FDR of q ≤ 0.10. Alleles at loci encoding ribulose-bisphosphate carboxylase/oxygenase activase (Rca), sucrose phosphate synthase (Sps) and vacuolar invertase (Pain1) were most frequently involved in statistical epistatic interactions. The largest effect on tuber starch content and starch yield was observed for the paired alleles Pain1-8c and Rca-1a, explaining 9 and 10% of the total variance, respectively. The combination of these two alleles increased the means of tuber starch content and starch yield. Biological models to explain the observed statistical epistatic interactions are discussed.     

Effect of cadmium on glutathione reductase in potato tubers

Short-term treatment of potato tuber (Solanum tuberosum L.) discs with CdCl₂ changed glutathione reductase (GR) activity depending on cadmium ions concentrations, kind of tuber and time of incubation. The increase of GR activity at 10 and 100 μmol·dcm⁻³ of CdCl₂ solutions was marked in less resistant tissues of cv. Bintje after 24 hrs, and was slight in more resistant tissues of cv. Bzura after 72 hrs. At 1 mmol·dcm⁻³ concentration of CdCl₂ rapid and total inactivation in both kind of tissues was observed, which disappeared after a few days. However this elevation was faster in more resistant tissues. These inhibition effects come from the inactivation process of GR by cadmium. The values of K_I for cadmium and K_M for GSSG of GR from potato tuber tissues indicated that enzyme from more resistant tissues possessed lower affinity to toxic metal and higher affinity to substrate.     

Quantification of Superoxide Radical in the Brain of Rats with Experimentally Induced Obstructive Jaundice

The study aimed to directly measure in vivo superoxide radical (O₂⁻) a direct indicator of oxidative stress, in the brain of rats with experimentally induced obstructive jaundice by employing a new quantitative ultrasensitive fluorescent assay requiring minimum sample. O₂⁻ anion is specific for dihydroethidine (DHE) and upon reaction gives a characteristic product, namely 2-OH-ethidium. Ten male rats underwent laparotomy and were divided into two groups: I, sham operated and II bile duct ligation. Ten days later, following injection with DHE (a O₂⁻ trap), all animals were killed and samples from cerebral cortex, midbrain and cerebellum were removed for analysis. It was shown that compared to group I, in group II the O₂⁻ was increased by 67% in the cerebral cortex and by 37% in the midbrain as a consequence of experimental obstructive jaundice, while its levels were unaffected in the cerebellum. The data in this experimental obstructive jaundice model imply a region-specific increase of O₂⁻ formation rate, being higher in cerebral cortex, less so in the midbrain and not at all in cerebellum.     

Isoenzymatic identification of quantitative traits in crosses between heterozygous parents: mapping tuber traits in diploid potato (Solanum spp.)

Eleven isozyme markers were utilized for quantitative trait loci (QTL) analysis in diploid potato. These markers are distributed among 7 of the 12 chromosomes and therefore give a representative, though sparse, survey of the potato genome. Tuber specific gravity and tuder dormancy were studied. Two segregating diploid populations were constructed from heterozygous self-incompatible parents. These two populations, TRP132 (127 individuals) and TRP133 (110 individuals), have a common maternal parent and combine genomes of Solanum tuberosum (haploid), S. chacoense, and S. phureja. The populations were planted at two locations in Michigan in 1990 using a randomized complete block design with three replications per location. After harvest they were characterized with the isozymes and evaluated for specific gravity and tuber dormancy. To test for QTLs, one-way analyses of variance were conducted for each locus by trait combination. Significant associations between markers and quantitative trait variation were identified, which accounted for a range from 4% to 15% of the phenotypic variation for specific gravity, and from 4.5% to 20.4% for tuber dormancy. Two-way analyses of variance between significant markers were used to identify epistatic interactions between markers. Multiple regression analyses were used to estimate the overall effect of the significant markers on the phenotypic variation for these traits. These values ranged from 15.3% and 32.3% for specific gravity. For dormancy, the significant loci accounted for 8.5% and 36.9% of the total phenotypic variation for each of the populations. We find that isozyme analysis is a useful tool for preliminary QTL studies in potato.     

CROWN GALL TUMORIGENESIS IN POTATO TUBER TISSUE

Potato tuber discs were examined as a possible quantitative bioassay for studying tumor induction by Agrobacterium tumefaciens. Discs from two potato varieties, Pontiac and Russett Burbank, were inoculated and cultured on water agar plates. Tumors appeared within 10 days. Both the number and weight of tumors per disc increased linearly for inoculum concentration between 1 × 10⁷–1 × 10⁹ cells per ml. Polarity, position of the disc relative to tuber epidermis, potato variety and the light conditions did not influence the tumor formation. The simplicity of the procedure and the homogeneity of the tissue, together with the fact that it is a quantitative bioassay, makes the potato tuber disc an ideal system for the investigation of biochemical step(s) associated with the transformation process.     

Genetic evidence for the mating system and reproductive success of black sea bream (Acanthopagrus schlegelii)

Understanding the mating system and reproductive success of a species provides evidence for sexual selection. We examined the mating system and the reproductive success of captive adult black sea bream (Acanthopagrus schlegelii), using parentage assignment based on two microsatellites multiplex PCR systems, with 91.5% accuracy in a mixed family (29 sires, 25 dams, and 200 offspring). Based on the parentage result, we found that 93.1% of males and 100% of females participated in reproduction. A total of 79% of males and 92% of females mated with multiple partners (only 1 sire and 1 dam were monogamous), indicating that polygynandry best described the genetic mating system of black sea bream. For males, maximizing the reproductive success by multiple mating was accorded with the sexual selection theory while the material benefits hypothesis may contribute to explain the multiple mating for females. For both sexes, there was a significant correlation between mating success and reproductive success and the variance in reproductive success of males was higher than females. Variation in mating success is the greatest determinant to variation in reproductive success when the relationship is strongly positive. The opportunity for sexual selection of males was twice that of females, as well as the higher slope of the Bateman curve in males suggested that the intensity of intrasexual selection of males was higher than females. Thus, male–male competition would lead to the greater variation of mating success for males, which caused greater variation in reproductive success in males. The effective population number of breeders (N_b) was 33, and the N_b/N ratio was 0.61, slightly higher than the general ratio in polygynandrous fish populations which possibly because most individuals mated and had offspring with a low variance. The relatively high N_b contributes to the maintenance of genetic diversity in farmed black sea bream populations.     

Double hydroperoxidation of α-linolenic acid by potato tuber lipoxygenase

The potato tuber lipoxygenase preparations convert α-linolenic acid not only to 9(S)-HPOTE, but also to some more polar metabolites. Two of these polar products, I and II, with ultraviolet absorbance maxima at 267 nm were purified by HPLC. It was found that metabolites I and II have, respectively, one and two hydroperoxy groups. Products of NaBH₄ reduction of both I and II were identified by their chemical ionization and electron impact mass spectra and by ¹H-NMR spectra as 9,16-dihydroxy-10(E), 12(Z), 14(E)-octadecatrienoic acid. The obtained results suggest that compound II is 9,16-dihydroperoxy-10(E), 12(Z), 14(E)-octadecatrienoic acid and product I is a mixture of two positional isomers, 9-hydroxy-16-hydroperoxy-10(E),12(Z),14(E)-octadecatrienoic and 9-hydroperoxy-16-hydroxy-10(E),12(Z), 14(E)-octadecatrienoic acids. Lipoxygenase converts efficiently [¹⁴C]9-HOTE into product I. Also, both metabolites I and II are the products of double dioxygenation. The second oxygenation at C-16 position as well as the first one at C-9 is controlled by lipoxygenase.     

QTL mapping for resistance against the European corn borer (Ostrinia nubilalis H.) in early maturing European dent germplasm

The European corn borer (ECB, Ostrinia nubilalis Hübner) is a major pest of maize in Central Europe. We mapped and characterized quantitative trait loci (QTLs) involved in resistance of maize against ECB damage, compared them with QTLs for agronomic traits, and evaluated the usefulness of marker-assisted selection (MAS) for improving ECB resistance in early maturing European maize germplasm. A total 226 F₃ families from the cross D06 (resistant) × D408 (susceptible), together with 93 RFLP and two SSR markers were used for the QTL analyses. For each F₃ family we measured the length of tunnels produced by larval stalk mining (TL), stalk damage ratings (SDR), and relative grain yield (RGY) in field experiments, with two replications in two environments in 1 year. The agronomic traits comprised grain yield under insecticide protection (GYP) and manual ECB larval infestation (GYI), the date of anthesis (ANT), and the in vitro digestibility of organic matter (IVDOM) of stover. Estimates of genotypic variance (σ² _g) were highly significant for all traits. Six QTLs for TL and five QTLs for SDR were detected, explaining about 50.0% of σ² _g. Most QTLs showed additive gene action for TL and dominance for SDR. No QTL was found for RGY. The number of QTLs detected for the agronomic traits ranged from two for GYI to 12 for ANT, explaining 12.5 to 57.3% of σ² _g, respectively. Only a single QTL was in common between the two resistance traits, as expected from the moderate trait correlation and the moderate proportions of σ² _g explained. Based on these results, MAS for improving ECB resistance can be competitive when cost-effective PCR-based marker systems are applied. However, it remains to be established whether the putative QTL regions for ECB resistance detected in the population D06 × D408 are consistent across other early maturing European maize germplasms. Received: 20 December 1999 / Accepted: 6 June 2000     

Seasonal variation of reproductive success under female philopatry and male-biased dispersal in a common vole population

Variation of reproductive success, an important determinant of the opportunity for sexual selection, is an outcome of competition within one sex for mating with members of the other sex. In promiscuous species, males typically compete for access to females, and their reproductive strategies are strongly related to the spatial distribution of females. I used 10 microsatellite loci and the mtDNA control region to determine seasonal differences in the reproductive success of males and females of the common vole (Microtus arvalis), one of the most numerous mammals in Europe. The sex-related spatial structure and bias in dispersal between genders were also assessed. Standardized variance of the reproductive success of females did not vary seasonally due to the continuity of female philopatry throughout the breeding season and to the constancy of the number of females reproducing successfully in each season. The males are the dispersing sex, undergoing both natal and breeding dispersal. Their standardized variance of reproductive success was significantly higher than that for females in July, when only two males monopolized 80% of the females in the population and when variance of male reproductive success was highest (I_m = 7.70). The seasonally varying and high standardized variance of male reproductive success may be explained by male-male competition for matings, coupled with seasonal changes in the age structure of the population.