bluuebunny/crossref_metadata_2025 huggingface dataset:
The paternal-sex-ratio (PSR) chromosome in natural populations of Nasonia (Hymenoptera: Chalcidoidea)
Authors: Beukeboom L. W. , Werren J. H.
Published: March 2003

Selfish genetic elements may be important in promoting evolutionary change. Paternal sex ratio (PSR) is a selfish B chromosome that causes all-male families in the haplodiploid parasitic wasp Nasonia vitripennis, by inducing paternal genome loss in fertilized eggs. The natural distribution and frequency of this chromosome in North American populations of N. vitripennis was investigated using a combination of phenotypic and molecular assays. Sampling throughout North America failed to recover PSR except from populations in the Great Basin area of western North America. Extensive sampling of Great Basin populations revealed PSR in frequencies ranging from 0 to 6% at different collection sites, and extended its distribution to Idaho and Wyoming. Intensive sampling in upstate New York did not detect the chromosome. Frequencies of the maternal-sex ratio distorter (MSR), son killer (SK) and virgin females ranged from 0 to 12%. Paternal sex ratio may be restricted to the Great Basin because its spread is hampered by geographical barriers, or because populations in other areas are not conducive to PSR maintenance. However, it cannot be ruled out that PSR occurs in other regions at very low frequencies. The apparent limited distribution and low frequency of PSR suggest that it will have relatively little impact on genome evolution in Nasonia.
Experimental analysis of an early life-history stage: avian predation selects for larger body size of hatchling turtles
Authors: Janzen F. J. , Tucker J. K. , Paukstis G. L.
Published: March 2003

One common life-history pattern involves an elevated rate and nonrandom distribution of neonatal mortality. However, the mechanisms causing this pattern and the specific traits that confer a survival benefit are not always evident. We conducted a manipulative field experiment using red-eared slider turtles to test the hypothesis that diurnal avian predators are a primary cause of size-specific neonatal mortality. Body size was a significant predictor of recapturing hatchlings alive and of finding hatchlings dead under natural conditions, but was unimportant when diurnal predators were excluded from the field site. Overall recapture rates also more than doubled when predators were excluded compared to natural conditions (72.4 vs. 34.9%). We conclude that birds are an important cause of size-specific mortality of recently emerged hatchling turtles and that ‘bigger is better’ in this system, which has important implications for life-history evolution in organisms that experience size-specific neonatal mortality.
Macroevolution of hoverflies (Diptera: Syrphidae): the effect of using higher-level taxa in studies of biodiversity, and correlates of species richness
Authors: Katzourakis A. , Purvis A. , Azmeh S. , Rotheray G. , Gilbert F.
Published: March 2003

We test a near-complete genus level phylogeny of hoverflies (Diptera: Syrphidae) for consistency with a null model of clade growth having uniform probabilities of speciation and extinction among contemporaneous species. The phylogeny is too unbalanced for this null model. Importantly, the degree of imbalance in the phylogeny depends on whether the phylogeny is analysed at the genus level or species level, suggesting that genera ought not to be used uncritically as surrogates for species in large-scale evolutionary analyses. Tests for a range of morphological, life-history and ecological correlates of diversity give equivocal results, but suggest that high species-richness may be associated with sexual selection and diet breadth. We find no correlation between species-richness and either body size or reproductive rate.
Genotype-by-environment interaction and the Dobzhansky–Muller model of postzygotic isolation
Authors: Bordenstein S. R. , Drapeau M. D.
Published: March 2003

The Dobzhansky–Muller (D–M) model of reproductive isolation (RI) posits that hybrid sterility and inviability result from negative epistatic interactions between alleles at a minimum of two genes. This standard model makes several implicit assumptions, including a lack of environmental effects and genotype-by-environment interactions (GEI) involving hybrid sterility and hybrid inviability loci. Here we relax this assumption of the standard D–M model. By doing so, several patterns of the genetic architecture of RI change. First, a novel single-locus model of postzygotic RI emerges. Several indirect lines of evidence are discussed in support of the model, but we conclude that this new single-locus model is currently no more supported than previous ones. Second, when multilocus D–M models incorporating GEI are considered, we find that the number of potential negative epistatic interactions increases dramatically over the number predicted by the standard D–M model, even when only the most simple case of two-allele interactions are considered. Third, these multilocus models suggest that some previous generalizations about the evolutionary genetics of postzygotic RI may not necessarily hold. Our findings also suggest that the evolution of postzygotic RI may be more likely when the expression of traits driving speciation is affected by the environment, since there appears to be a greater spectrum of potential hybrid incompatibilities under the D–M model incorporating GEI.
DNA variation at the rp49 gene region in Drosophila madeirensis and D. subobscura from Madeira: inferences about the origin of an insular endemic species
Authors: Khadem M. , Rozas J. , Segarra C. , Aguadé M.
Published: March 2003

An ~1.6-kb fragment spanning the rp49 gene was sequenced in 16 lines of Drosophila subobscura from Madeira and in 22 lines of the endemic species D. madeirensis. Nucleotide diversity in D. subobscura from Madeira (π=0.0081) was similar to that in lines from Spain carrying the O3+4 chromosomal arrangement (π=0.0080). No significant genetic differentiation was detected between insular and continental O3+4 lines of D. subobscura. These results are compatible both with a rather recent and massive colonization, and with multiple colonization events from the continent. Nucleotide diversity in D. madeirensis (π=0.0076) was similar to that in D. subobscura, which deviates from the expectation, under strict neutrality, of a lower level of variation in an insular species with a small population size. The observed numbers of shared polymorphisms and of fixed differences between D. madeirensis and D. subobscura are compatible with the isolation model of speciation, where shared polymorphisms are due to common ancestry.
Combining mitochondrial DNA sequences and morphological data to infer species boundaries: phylogeography of lanceheaded pitvipers in the Brazilian Atlantic forest, and the status of Bothrops pradoi (Squamata: Serpentes: Viperidae)
Authors: Puorto G. , Da Graça Salomão M. , Theakston R. D. G. , Thorpe R. S. , Warrell D. A. , Wüster W.
Published: March 2003

Phylogeographic studies using mitochondrial DNA sequence information are frequently used as the principal source of evidence to infer species boundaries. However, a critical analysis of further evidence is essential to test whether different haplotype clades identify different species. We demonstrate a hypothesis-testing approach, using a combination of phylogeographic methods, multivariate morphometrics and matrix association tests, to investigate species boundaries in eastern Brazilian pitvipers conventionally assigned to the species Bothrops leucurus and B. pradoi. Two basal haplotype clades with partly overlapping geographical distributions are identified, which could either represent two partly sympatric species, or multiple haplotypes within one organismal lineage. We use partial Mantel matrix association tests to verify whether generalized morphology, or any of four supposedly diagnostic characters for the two species, show any association with mtDNA variation. Negative results lead to the conclusion that the haplotype clades do not denote independently evolving organismal lineages, and do not constitute separate species under any criterion.
Sexual selection on phenotypic traits in a hybrid zone of Littorina saxatilis (Olivi)
Authors: Cruz R. , Rolán-Álvarez E. , García C.
Published: March 2003

Step clinal transitions in inherited character(s) between genetically distinct populations are usually referred to as hybrid zones. An example is found in the population of the intertidal snail Littorina saxatilis in Galicia (NW Spain). We studied the shape of the overall fitness surface for sexual selection in this hybrid zone, and the position of hybrids and pure morphs on this surface. We found that sexual divergent selection acted on a combination of phenotypic traits separating the pure morphs, and therefore that sexual selection contributed to morph differentiation. The average fitness of hybrids as a group was not significantly different from that of the pure morphs, but they did show divergent sexual selection in some traits. These results are in agreement with a model of divergent selection favouring both the pure morph as well as those hybrids most resembling each morph. The finding of divergent selection is remarkable because quadratic selection gradients are usually weak in nature.
Host preference and survival in selected lines of a Drosophila parasitoid, Asobara tabida
Authors: Rolff J. , Kraaijeveld A. R.
Published: March 2003

Host selection behaviour of parasitoids has important fitness consequences, if hosts of different quality are available. Here the host selection behaviour, the ability to distinguish between hosts differing in their suitability, of the Drosophila parasitizing wasp Asobara tabida was studied. Females from five lines selected for higher survival in the encapsulating host species D. melanogaster (Kraaijeveld et al., 2001) were compared with females from control lines. Females from all five selected lines more readily accepted the encapsulating host species for oviposition when offered together with a nonencapsulating host species than females from the control lines. We found no evidence for pleiotropic effects and suggest that host selection behaviour evolved parallel to the ability to escape encapsulation in the hosts. Our results also suggest that given the appropriate selection pressures, host selection behaviour can quickly evolve in parasitoids, enabling them to adapt fast to changing circumstances.
Sexual selection and peripatric speciation: the Kaneshiro model revisited
Authors: Ödeen A. , Florin A.-B.
Published: March 2003

The Kaneshiro model proposes a role for sexual selection in peripatric speciation. During population bottlenecks, derived males lose attractive traits and become discriminated against by ancestral females, whereas derived females are selected to be less choosy. This permits novel mate choice cues to evolve in derived populations. In a quantitative analysis of laboratory experiments, we show that bottlenecked males have indeed become less attractive, but females have not lost their ancestral preferences. Contrary to the model, mating asymmetries were not limited to bottlenecks, but regularly occurred between derived and ancestral populations. The simplest explanation for the observed mating asymmetries is loss of genetic variation and inbreeding in the derived populations. The Kaneshiro process is unlikely to isolate small daughter populations from their ancestor but with slight modifications it may become a strong candidate for speciation in allopatry manifested as isolation between daughter populations in secondary contact.
Geographical distribution and genetic relatedness of sympatrical thelytokous and arrhenotokous populations of the parasitoid Venturia canescens (Hymenoptera)
Authors: Schneider M. V. , Beukeboom L. W. , Driessen G. , Lapchin L. , Bernstein C. , Van Alphen J. J. M.
Published: March 2003

Theory predicts that asexual reproduction has a competitive advantage over sexual reproduction because of the twofold cost of producing males. Few systems are suitable for directly testing this prediction. In the solitary parasitoid wasp Venturia canescens both arrhenotokously (sexual) and thelytokously (asexual) reproducing individuals occur sympatrically. We sampled 922 wasps from 22 localities along the coast of south-eastern France. Thelytokous wasps were less abundant (23%) than arrhenotokous wasps and were almost always found in sympatry with arrhenotokous ones. An analysis of genetic relatedness using amplified fragment length polymorphism (AFLP) markers showed the existence of a widespread thelytokous clone. In addition, a few thelytokous individuals were found to be closely related to arrhenotokous ones and vice versa. These data suggest the occurrence of occasional gene flow between both reproductive modes and/or recurrent origin of thelytokous clones from coexisting arrhenotokous populations in the area. The results are discussed in the context of the paradox of sex.
A simple covarion-based approach to analyse nucleotide substitution rates
Authors: Siltberg J. , Liberles D. A.
Published: March 2003

Using the ratio of nonsynonymous to synonymous nucleotide substitution rates (Ka/Ks) is a common approach for detecting positive selection. However, calculation of this ratio over a whole gene combines amino acid sites that may be under positive selection with those that are highly conserved. We introduce a new covarion-based method to sample only the sites potentially under selective pressure. Using ancestral sequence reconstruction over a phylogenetic tree coupled with calculation of Ka/Ks ratios, positive selection is better detected by this simple covarion-based approach than it is using a whole gene analysis or a windowing analysis. This is demonstrated on a synthetic dataset and is tested on primate leptin, which indicates a previously undetected round of positive selection in the branch leading to Gorilla gorilla.
The effects of spontaneous mutation on competitive fitness in Drosophila melanogaster
Authors: Ávila V. , García-Dorado A.
Published: March 2003

We have analysed the effect of 288 generations of mutation accumulation (MA) on chromosome II competitive fitness in 21 full-sib lines of Drosophila melanogaster and in a large control population, all derived from the same isogenic base. The rate of mean log-fitness decline and that of increase of the between-line variance were consistent with a low rate (λ ≈ 0.03 per gamete and generation), and moderate average fitness effect [E(s) ≈ 0.1] of deleterious mutation. Subsequently, crosses were made between pairs of MA lines, and these were maintained with effective size on the order of a few tens. In these crosses, MA recombinant chromosomes quickly recovered to about the average fitness level of control chromosomes. Thus, deleterious mutations responsible for the fitness decline were efficiently selected against in relatively small populations, confirming that their effects were larger than a few percent.
Sanctions and mutualism stability: when should less beneficial mutualists be tolerated?
Authors: West S. A. , Kiers E. Toby , Pen I. , Denison R. F.
Published: March 2003

Why do mutualists perform costly behaviours that benefit individuals of a different species? One of the factors that may stabilize mutualistic interactions is when individuals preferentially reward more mutualistic (beneficial) behaviour and/or punish less mutualistic (more parasitic) behaviour. We develop a model that shows how such sanctions provide a fitness benefit to the individuals that carry them out. Although this approach could be applied to a number of symbioses, we focus on how it could be applied to the legume-rhizobia interaction. Specifically, we demonstrate how plants can be selected to supply preferentially more resources to (or be less likely to senesce) nodules that are fixing more N2 (termed plant sanctions). We have previously argued that appreciable levels of N2 fixation by rhizobia are only likely to be selected for in response to plant sanctions. Therefore, by showing that plant sanctions can also be favoured by natural selection, we are able to provide an explanation for the stability of the plant-legume mutualism.
Female mate choice in relation to heterozygosity in Tribolium castaneum
Authors: Pai A. , Yan G.
Published: March 2003

Female mate choice, both before and after copulation, is pervasive among insect species. It is often hypothesized that females would preferentially mate with males that are genetically dissimilar to promote the genetic variability of the offspring. We used various strains of red flour beetle, Tribolium castaneum, and tested the effect of male and female genetic backgrounds on precopulatory and post-copulatory female mate choice. Simultaneous mate choice experiments using previously well established pheromone assays did not detect female preference for males of different strains. Post-copulatory female mate choice was examined through paternity analysis. Two parameters were used to measure post-copulatory female mate choice, including male defence capacity (P1, proportion of offspring sired by the first male when a female mated with two males consecutively) and offence capacity (P2, proportion of offspring sired by the second of two males to mate with a female). When female and male beetle strains were same, defence capacity was significantly higher than when female and male strains were different. However, such a pattern was not observed for offence capacity. The results suggest that female precopulatory mate choice is not affected by genetic background, but the outcome of post-copulatory processes depends on the genetic background of male and female beetles.
Genetic loads under fitness-dependent mutation rates
Authors: Agrawal A. F.
Published: March 2003

Although much theory depends on the genome-wide rate of deleterious mutations, good estimates of the mutation rate are scarce and remain controversial. Furthermore, mutation rate may not be constant, and a recent study suggests that mutation rates are higher in mildly stressful environments. If mutation rate is a function of condition, then individuals carrying more mutations will tend to be in worse condition and therefore produce more mutations. Here I examine the mean fitnesses of sexual and asexual populations evolving under such condition-dependent mutation rates. The equilibrium mean fitness of a sexual population depends on the shape of the curve relating fitness to mutation rate. If mutation rate declines synergistically with increasing condition the mean fitness will be much lower than if mutation rate declines at a diminishing rate. In contrast, asexual populations are less affected by condition-dependent mutation rates. The equilibrium mean fitness of an asexual population only depends on the mutation rate of the individuals in the least loaded class. Because such individuals have high fitness and therefore a low mutation rate, asexual populations experience less genetic load than sexual populations, thus increasing the twofold cost of sex.
Phenotypic plasticity and the evolution of trade-offs: the quantitative genetics of resource allocation in the wing dimorphic cricket, Gryllus firmus
Authors: Roff D. A. , Gélinas M. B.
Published: March 2003

In the wing dimorphic sand cricket, Gryllus firmus, there is a pronounced trade-off between flight capability and fecundity. This trade-off is found both between morphs and within the macropterous morph, in which fecundity is negatively correlated with the mass of the principle flight muscles, the dorso-longitudinal muscles (DLM). In this paper, we examine how this trade-off is affected by a reduction in food and its genetic basis. We find that the relative fitness of the two wing morphs is not changed although both fecundity and DLM mass are decreased. A quantitative genetic analysis shows that the trade-off function is genetically variable but that most of the variation occurs in the intercept rather than the slope of the function. Analysis further indicates a very high genetic correlation between environments (food ration) supporting the hypothesis of a strong functional constraint between reproduction and flight capability.
Maternal control of offspring sex and male morphology in the Otitesella fig wasps
Authors: Pienaar J. , Greeff J. M.
Published: March 2003

Models concerning the evolution of alternative mating tactics commonly assume that individuals determine their own strategies. Here we develop a computer-based ESS model that allows mothers, ovipositing in discrete patches, to choose both the sex and the male mating tactics (natal-patch mating or dispersing) of their offspring based only on how many other mothers have used the specific patch before them. Data for three species of nonpollinating fig wasps from the Otitesella genus agree quantitatively with the model's assumptions and predictions. This suggests that females respond to population densities at the level of individual figs. The alternative male tactics in the species we studied are probably a result of a conditional strategy exercised by the mother that laid them. In addition, as females were only allowed to lay one egg per patch, our results suggest a new mechanism that can skew population sex ratios towards a female bias.
The origin of interlocus sexual conflict: is sex-linkage important?
Authors: Andrés J. A. , Morrow E. H.
Published: March 2003

Sexual conflict has been proposed as a potential selective agent in the evolution of a variety of traits. Here, we present a simple model that investigates the initial conditions under which sex-linked and sex-limited harming alleles can invade a population. In this paper, we expand previous threshold models to study how sex-linkage and sex determination mechanisms affect the spreading conditions of a harming allele. Our models provide new insights into how sexual conflict could originate, showing that in diploid organisms the probability of a new harming allele spreading is independent of both the genetic sex determination system and the dominance relationships. However, the incidence of interlocus sexual conflicts in the initial steps of the invasion critically depends on the inheritance system.
Establishment of the first World Health Organization International Standard for human parvovirus B19 DNA nucleic acid amplification techniques
Authors: Saldanha J. , Lelie N. , Yu M. W. , Heath A. ,   the B19 Collaborative Study Group
Published: March 2003

Background and ObjectivesA collaborative study, involving 26 laboratories from 14 countries, was carried out in order to establish a World Health Organization (WHO) International Standard for human parvovirus B19 (B19) DNA nucleic acid amplification techniques (NAT).

Materials and methodsFour samples: AA, BB (which were lyophilized), CC and DD (which were liquid preparations) were analysed using several different NAT assays. The mean B19 DNA content of each sample was determined for each laboratory using an end‐point dilution method.

ResultsThere was good agreement between the overall mean ‘equivalents’/ml obtained by the different assays. The mean log10‘equivalents’/ml were 5·76 for sample AA, 5·73 for sample BB, 5·82 for sample CC and 7·70 for sample DD. The differences in titre among samples AA, BB and CC were not statistically significant, but the titre of DD was significantly higher.

ConclusionsDespite the range of NAT assays used in the study, it was possible to calculate the mean B19 DNA concentrations in the four preparations. Lyophilized preparation AA was established as the first International Standard for B19 DNA NAT assays and was assigned a concentration of 106international units (IU)/ml.
Differential Drought Responses of Faba Bean (Vicia faba L.) Inbred Lines
Authors: Amede T. , Kittlitz E. V. , Schubert S.
Published: March 2003

Drought responses of 19 inbred faba bean lines of different origin were studied in the field under rain shelters with and without irrigation. Inbred lines differed significantly in response to drought (P < 0.01): those with a lower drought sensitivity index (SI) (more resistant) originated from the drought‐prone regions characterized by smaller plant size (r = 0.93), and more pods and seeds per plant (r ≥ 0.90) regardless of seed size, while lines with higher SI (more sensitive) were those which mainly exhibited higher yield under favourable conditions accompanied by a greater biomass. In a greenhouse experiment under mild drought (−0.15 MPa soil water potential), comparisons between relatively drought‐sensitive (Adriewaalse) and drought‐resistant (L7) inbred lines showed that Adriewaalse used 38 % more water than L7 and also produced 40 % more biomass. There was a stress‐induced decrease in osmotic potential (ψs) in both lines (by 0.72 and 0.50 MPa for Adriewaalse and L7, respectively) accompanied by decreased turgor in Adriewaalse and increased turgor in L7. The difference in drought‐induced solute accumulation between lines was diminished when solute accumulation due to water loss and growth inhibition was considered, which indicates that solute accumulation was the result of a concentration effect. Similarly, lower SI in the field was not the result of osmotic adjustment, as the relationship between SI and drought‐induced decrease in ψs was negative. The water use efficiency of both inbred lines increased markedly with increasing water deficit, though there was no difference between the lines. It was concluded that differences in drought resistance between these inbred faba bean lines were manifested through plant size‐induced water demand (avoidance) but were not associated with osmotic adjustment (tolerance).
Effect of Elevated CO2 and Nitrogen Nutrition on Photosynthesis, Growth and Carbon‐Nitrogen Balance in Brassica juncea
Authors: Uprety D.C , Mahalaxmi V.
Published: March 2003

The response of Brassica juncea var. Bio‐183‐92 to elevated CO2 under increased nitrogen treatment was studied. There was an interactive effect of CO2 and nitrogen nutrition, indicating that, on the addition of more nitrogen, the plants sustained the positive effect of CO2 enrichment by utilizing additional carbohydrates for the development of new sinks. Excess carbohydrate enables plants to be flexible and responsive to additional nitrogen application to sustain the CO2 enrichment effect.
Konkurrenz und Ertragsvorteile in Gemengen aus Erbsen (Pisum sativum L.) und Hafer (Avena sativa L.)
Authors: Rauber R. , Schmidtke K. , Kimpel‐Freund H.
Published: March 2003

Competition and yield advantage in mixtures of pea (Pisum sativum L.) and oats (Avena sativa L.)

In field trials on a fertile fluvisol in 1995 and 1996 near Göttingen, Germany, pea (Pisum sativum; cv. Messire/conventional leafed, cv. Profi/semileafless) and oats (Avena sativa; cv. Alf) were grown as sole crops and in substitutive mixtures. The sole crops were established at 80 pea seeds m−2 and 300 oat seeds m−2. The mixtures consisted of 67 % (pea) and 33 % (oats) of the monoculture densities, respectively. Interactions of cv. Messire or cv. Profi and oats were similar in 1995 and 1996. The mixtures outyielded the monocultures with respect to total above ground dry matter (RYT = 1.15) and grain yield (RYT = 1.09). Grain yield of pea and oats averaged 4.9 t ha−1 in monocultures and 5.5 t ha−1 in mixtures. Oats was relatively the stronger of the two competitors. Decreasing number of pods per plant could be highlighted as the factor for a lower pea seed frequency in the yield of the mixtures. For oats the number of panicles per plant and kernels per panicle were higher in the mixtures compared with the oat monocultures. The average amount of the harvest index (HI) was 0.52 for pea and 0.46 for oats. Favourable growth conditions increased HI values however, prolific vegetative growth in the mixtures resulted in lower HI values. The predicted RYT‐values estimate the maximum combined grain yield of 6.3 t ha−1 in the mixture of 87 % pea (70 seeds m−2) and 13 % oats (39 kernels m−2).
Effects of Salicylic Acid on the Development and Root Nodulation of Soybean Seedlings
Authors: Lian B. , Zhou X. , Miransari M. , Smith D. L.
Published: March 2003

Salicylic acid (SA) is recognized as an endogenous regulator of plant metabolism, mainly involved in induction of systemic acquired resistance (SAR). Exogenous SA can also induce a SAR reaction and SAR gene expression. Excessive SAR‐related activity can be an overall cost to the plant in terms of energy and materials expended unnecessarily. Elicitation of plant defence responses might also block beneficial plant‐microbe interactions and result in negative effects on plant growth. The objective of this study was to investigate the effects of SA concentration (5, 1, 0.5, 0.1 and 0 m m) on soybean seedling growth and nodulation by watering of soybean seedling roots or soaking of seedling leaves with SA solutions. It was found that 5 m
m SA had negative effects on soybean seedling development, but other concentrations of SA did not affect the development of soybean seedlings. In addition, there were no negative effects on seedling development due to SA soaking of seedling leaves. Soybean seedling growth in sterile soil was reduced due to repressed nitrogen uptake following addition of 5 m
m SA, indicating that some concentrations of SA can alter the N nutrition of seedlings. A model is presented that ties SA to nodule formation and plant growth.
Water Relations, Abscisic Acid and Yield of Wheat Plants in Relation to the Interactive Effect of Seawater and Growth Bioregulators
Authors: Aldesuquy H. S. , Ibrahim A. H.
Published: March 2003

Irrigation of wheat plants with seawater (10 and 25 %) led to significant increases in free and bound abscisic acid (ABA) in leaves, especially at 25 %. The relative water content (RWC) and water use efficiency (calculated from grain yield, WUEG, or from biomass yield, WUEB) of the seawater‐irrigated plants were lower than those of the control. Grain pre‐soaking in gibberellic acid (GA3), indole‐3‐acetic acid (IAA) or ABA reduced the levels of accumulated ABA (free and bound) produced by seawater irrigation. The stress imposed by seawater generally reduced yield and yield components of wheat plants and the effect was more pronounced at the higher level of seawater irrigation (25 %). Furthermore, seawater treatments decreased the carbohydrate content and increased the protein content of the developing grains. The effect of seawater treatments on ion concentrations in the developing grains was not consistent. The application of growth bioregulators appeared to mitigate the effect of seawater salinity stress on wheat productivity. GA3 was the most effective hormone in this regard. The economic yield (grain yield) had a strong positive correlation with RWC, WUEG, WUEB, plant height, shoot fresh and dry weight, grain number/main spike, kernel weight and harvest index.
Effects of Nitrogen on Dry Matter Accumulation and Productivity of Three Cropping Systems and Residual Effects on Wheat in Deep Vertisols of Central India
Authors: Ramesh P. , Ghosh P. K. ,   Ajay, Ramana S.
Published: March 2003

A field experiment was conducted on deep vertisols of Bhopal, India to study the effects of three levels of nitrogen (N), namely 0, 75 and 100 % of the recommended dose of nitrogen (RDN), on the dry matter accumulation (DMA) and productivity of three cropping systems (sole soybean, sole sorghum and soybean + sorghum intercropping) during the rainy season and their residual effect on the subsequent wheat crop during the post‐rainy season. During the rainy season, sole sorghum was found to have significantly higher DMA and productivity in terms of soybean equivalent yield (SEY) than sole soybean or soybean + sorghum intercropping. Increasing the N dose from 0 to 100 % RDN significantly improved the DMA and SEY. At a low fertility level (N0), soybean + sorghum intercropping was found to be more productive, while at a high fertility level (100 % RDN), sole sorghum was more productive than the other two cropping systems. However, during the post‐rainy season, sole soybean as the preceding crop gave the highest DMA and seed yield of wheat, which were similar to those found with soybean + sorghum intercropping. Sorghum followed by wheat gave the lowest DMA and seed yield of wheat. Application of 100 % RDN irrespective of cropping system during the preceding crop improved the DMA of wheat but not its seed yield. However, N applied to the wheat crop significantly increased its DMA and seed yield.
Effects of Ozone on Tobacco (Nicotiana tabacumL.) Varieties
Authors: Saitanis C. J. , Karandinos M. G.
Published: March 2003

The well‐known ozone bioindicator tobacco (Nicotiana tabacumL.) variety Bel‐W3 and six varieties cultivated in Greece were tested for their relative sensitivities to ozone by exposures conducted in controlled‐environment chambers (0, 90, 135 and 180 p.p.b. for 20 days at 8 h day−1). Based on the extent of macroscopic symptoms, Bel‐W3 was found to be the most sensitive variety, followed by Zichnomirodata (KK6/5), while K63 was the most resistant. There was a differentiation between Bel‐W3 and KK6/5, in terms of both magnitude and visual appearance of symptoms. Ozone reduced the plant height, leaf area and dry weights of leaves, stems and roots. The root dry weight reduction was greater than that of leaves and stems. Moreover, gross photosynthesis was reduced by ozone exposure, mainly in the lower leaves. The ozone‐related sensitivity could not be attributed to greater stomatal density because (a) the most tolerant and the most resistant varieties had almost the same number of stomata per mm2and (b) the most resistant leaves (upper) had greater stomatal density than the most sensitive (lower) ones, even in the same plant. Stomatal conductance was greater in the abaxial surface (P < 0.001) than in the adaxial surface and in the upper leaves (P=0.013) than in the lower leaves, but it did not differ significantly between the Bel‐W3 and K63 varieties (P=0.3417). The fumigation of grafted plants – Bel‐W3 (ozone‐sensitive) on K63 (ozone‐resistant) and vice versa – suggested that stocks did not affect the ozone sensitivity of scions.
Contributions to the Analysis of Genotype × Environment Interactions: Experimental Results of the Application and Comparison of Clustering Techniques for the Stratification of Field Test Sites
Authors: Truberg B. , Hühn M.
Published: March 2003

The results from multienvironment field performance trials of cultivars are usually analysed as two‐way classification data with rows=genotypes/cultivars and columns=environments (locations and/or years). To reduce the impact of genotype × environment interaction effects, one commonly stratifies genotypes/cultivars or environments by cluster analysis techniques into homogeneous groups so that interactions within groups are minimized. By such a stratification, for example of test sites, with regard to similarity of genotype × environment interactions and the selection of only one representative test site from each group, the overall number of necessary test sites for yield trials can be reduced. In the literature, many clustering techniques have been proposed. Systematic comparisons between different cluster methods, however, are rather rare. A single cluster method is characterized by `measure of distance', `stopping criterion', `algorithm' and `level of significance'. In this paper, 11 clustering techniques were applied to extensive yield data sets of several agricultural crops (faba bean, fodder beet, oat, winter oilseed rape and sugar beet) from the official registration trials of the German `Bundessortenamt'. The results were compared with each other using two proposed parameters: measure of resemblance (for two classifications) and cluster size (for one classification). Neither the level of significance nor the algorithm has a substantial impact on the resulting clusters. The final results of clustering are therefore mainly determined by the stopping criterion with its associated measure of distance. If one uses tests for crossover interactions as stopping criteria, the resulting clusters are larger than the resulting clusters for theF‐test of conventional interactions in an analysis of variance. The cluster size decreases with increasing sensitivity of the tests that are used as stopping criteria. Finally, recommendations for the choice and handling of clustering techniques for practical applications are given.
Recovery Strategy Following the Imposition of Episodic Soil Moisture Deficit in Stands of Peanut (Arachis hypogaea L.)
Authors: Awal M. A. , Ikeda T.
Published: March 2003

Peanut stands often face water deficits in the tropics and subtropics, especially in drought‐prone areas of India. The effect of drought on peanut production has previously been studied. However, there is a lack of information on the post‐stress recovery mechanism. The objective of this study was to investigate the recovery mechanism after relief of water stress. The effect of short‐term drought applied (for 12 days) at the pre‐flowering, peak flowering and pod‐filling stages on chlorophyll (Chl) pigments, water use efficiency (Wue), quantum yield (Qy), root/shoot ratio (R:S), relative growth rate (RGR), net assimilation rate (NAR) and flower production during stress and subsequent post‐stress recovery was examined. The leaf water potential (ψleaf) and leaf relative water content (RWC) in plants subjected to water deficit were reduced to 1/10 and 2/3, respectively, of the corresponding control values. Moisture deficit significantly reduced Chl a and b concentrations, the Chl a/b ratio, stomatal conductance, photosynthesis, Wue and Qy. However, a strong recovery of these traits was noted after rewatering, which led to onset of fresh growth on post‐stress, with a marked increase in RGR and NAR and a flush of flowering. Drought significantly enhanced R:S, which accelerated post‐stress recovery. Peanut stands exhibited excellent ecophysiological recovery with the post‐stress onset of fresh growth. This strong recovery mechanism found in peanut stands suggests that peanut has high environmental plasticity.
The Effect of Lead and Zinc on Mentha spicata
Authors: Bekiaroglou P. , Karataglis S.
Published: March 2003

Clones of Mentha spicata were cultivated in nutrient solution, to which lead and zinc were added in soluble form. The plants remained in a controlled environment for 2 weeks in this solution. The root lengths of the plants and the chlorophyll content of the upper and lower leaves were measured. The lead and zinc contents of the plant tissue were also determined. It was found that the increased concentration of metals resulted in a decrease in root growth and chlorophyll content. The relation that connects the concentration of the heavy metal to the decrease in root growth is logarithmic. It was also found that more lead than zinc entered the plant tissues, but unlike zinc did not reach the leaves.
Comparative Effects of NaCl and Polyethylene Glycol on Germination, Emergence and Seedling Growth of Cowpea
Authors: Murillo‐Amador B. , López‐Aguilar R. , Kaya C. , Larrinaga‐Mayoral J. , Flores‐Hernández A.
Published: March 2003

Seeds of Paceño and Cuarenteño cultivars of cowpea (Vigna unguiculata L. Walp.) were tested for salt and drought tolerance at germination, seedling emergence and early seedling growth in NaCl and PEG‐8000 solutions of different osmotic potentials (0, −0.2, −0.4, −0.6, and −0.8 MPa). Daily and final germination and emergence percentage, as well as germination and seedling emergence rate, and seedling growth were recorded under controlled conditions. Results showed that germination and emergence rate were delayed by both solutions in both cultivars, with differences between cultivars among growth stages, given that cultivar Cuarenteño, showed a higher germination rate than Paceño in NaCl, but Paceño was less affected by NaCl and PEG solutions at the emergence stage. Sodium chloride had a lesser effect on both cultivars in terms of germination rate, emergence rate and the final germination and emergence percentage than did PEG‐8000. This conclusively proves that the adverse effect of PEG‐8000 on germination, emergence and early seedling growth was due to the osmotic effect rather than the specific ion. Seedling growth was reduced by both stresses, but NaCl usually caused less damage than PEG to cowpea seedlings, suggesting that NaCl and PEG acted through different mechanisms.
Hermetically Sealed Storage of Cereal Seeds and its Influence on Vigour and Germination
Authors: Guberac V. , Maric S. , Lalic A. , Drezner G. , Zdunic Z.
Published: March 2003

Investigations of the influence of hermetic cereal seed storage on germination were carried out in the laboratory of the Faculty of Agriculture in Osijek (Croatia) over 5 years (1992–96). Seeds of four species (winter wheat, winter barley, spring oat, and maize) were stored in hermetic glass containers at an air temperature of 20 °C and a relative humidity of 65 %. The moisture level in stored seeds was 13 %. After 5 years, statistically highly significant associations (P < 0.01) were found between storage longevity (five researched years) and seed germination of the four cereals. Germination of all investigated cereals was high (between 97.25 % for maize and 93 % for winter wheat) after harvest. The germination level decreased for all cereals, on average by 38 %, over the 5 years of storage. The highest germination values were found for wheat seeds (84.75 %) and the lowest germination values for maize seeds (36.0 %). The results showed that germination of all investigated cereals seeds was negatively correlated with storage longevity. The differences in germination found amongst the cereals were statistically highly significant (P < 0.01).
Synaptonemal complex investigations on lamas (Lama glama) with differing fertility recordings
Authors: Kova By B. ZS. ,   CS, Gauly M. , Stranzinger G.
Published: March 2003

The present study involved three male lamas (Lama glama). Mitotic preparations from fibroblast culture and an electron microscopic observation on the synaptonemal complexes (Scs) were reported. Special attention was given to the morphology and behaviour of the chromosomes at the zygotene and pachytene substages of prophase I in primary spermatocytes from lamas. Analysis of mitotic preparations show diploid and triploid cells, with a relatively high frequency of polyploidy. Analyses of synaptonemal complexes in primary spermatocytes were carried out on 89 cells. Pairing abnormalities were only recorded in an average of 63% of the cells of the animal Tabasco. The other two animals were normal. The photographed cells give an upper limit estimate of the existing abnormalities, as there was a deliberate tendency towards selecting abnormal cells for photography. The presence of degenerating primary spermatocytes in SC preparations as well as in testicular sections, and the absence of spermatozoa in ejaculates confirm the chromosomally derived male sterility of one animal.
Microsatellite variation between an African and five European taurine breeds results in a geographical phylogenetic tree with a bison outgroup
Authors: Mommens By G. , Peelman L. J. , Van Zeveren A. , D G. , ’Ieteren . , Wissocq N.
Published: March 2003

Introduction

Genetic variation is being used extensively for individual identification and linkage analysis, and may be useful for interpopulation studies. Previously, blood groups and biochemical variants in blood cell and serum proteins have been used to study (evolutionary) relationships in mammals. But genetic divergence and gene flow among closely related populations are difficult to measure with these classical markers because their mutation rate is so low that new mutations have not had sufficient time to appear and become fixed. So they have a small number of alleles and a relatively low level of heterozygosity. These markers are now replaced by DNA markers, mostly microsatellites. These microsatellite loci are useful genetic markers at which alleles differ in length due to differences in the number of short sequence motifs arranged adjacent to one another. They are abundantly distributed throughout the mammalian genome. They have a large number of alleles, a high level of heterozygosity and are inherited in true Mendelian fashion. These characteristics make them valuable for parentage control, linkage analysis, genome mapping and phylogenetic studies. In terrestrial vertebrates with limited mobility, genetic differentiation often increases with the distance between populations or corresponds to the extent of geographic and habitat barriers (R oy et al. 1994). Investigations of short tandem repeats yield a considerable volume of genetic data regarding the similarities and divergence times of different cattle populations. Microsatellite markers are suitable for the estimation of these parameters as they are not generally subject to direct selection and environmental influences. Computation of genetic distances based on data from several loci can be used to evaluate the taxonomic relationship between populations. The aim of this study was to estimate the relative genetic variability between Belgian cattle breeds and to reconstruct the evolutionary relationship among them, also using two small genetically isolated cattle‐like populations.
Quantitative trait locus mapping based on selective DNA pooling
Authors: Dekkers J. C. M.
Published: March 2003

Concepts of a simple method to map quantitative trait loci (QTL) based on selective DNA pooling in half‐sib family, backcross, and F2 designs were developed. It is shown that the position of a QTL can be estimated from differences in allele frequencies for two flanking markers between individuals with high and low phenotypes and does not depend on the phenotypic means of the selected groups. An estimate of the QTL effect was obtained by relating group differences in phenotypic means to differences in QTL frequencies, which can be estimated from the QTL position and marker allele frequencies. Simulation of a half‐sib family and a F2 family of 2000 individuals showed that the method gives close to unbiased results when power is high. Biases increased when measurement errors on marker allele frequencies increased and when the effect of the QTL was small. Similarities of QTL mapping based on selective DNA pooling data and on individual genotyping data are discussed, as are opportunities to extend the selective DNA pooling method to the use of multiple markers and multiple half‐sib family designs. This study shows that the use of selective DNA pooling can be extended from the detection of marker associations to the mapping of QTL. Selective DNA pooling can greatly reduce the number of genotypings required.
Genetic and phenotypic parameters for monthly egg production in White Leghorn hens
Authors: Anang A. , Mielenz N. , Schüler L.
Published: March 2003

This article reports genetic and phenotypic parameters of monthly egg production and the influence of Box‐Cox transformation on the parameters from a population of White Leghorns, selected for feed efficiency. A total of 6450 daughters of 180 sires and 1335 dams were analysed by restricted maximum likelihood (REML) using a multivariate animal model. The traits considered were monthly egg productions, cumulative production of the first 5 months (S5), cumulative production of first 10 months (S10), and survivor egg production in the first cycle (S12). Two sets of data were analysed: the original data and with the Box‐Cox method transformed data. The results indicated that there were no great differences in the estimates between untransformed and transformed data. The estimates of heritability for monthly egg production were high for the first period, decreased to reach the lowest during peak production, and increased to the end of lay. The estimates of heritability for cumulative records were generally higher than monthly records. Genetic and phenotypic correlations among monthly egg production totals were generally high for contiguous periods and then decreased as the interval between months increased. The highest genetic correlation between monthly records and S5 was for the second month of production, whereas the correlations between monthly production totals and S10 and S12 reached their peak at the sixth and eighth months of production, respectively.