Biological Constraint Research Articles

Realized niche analysis of phytoplankton communities involving HAB: Phaeocystis spp. as a case study

The link between harmful algal blooms, phytoplankton community dynamics and global environmental change is not well understood. To tackle this challenging question, a new method was used to reveal how phytoplankton communities responded to environmental change with the occurrence of an harmful algae, using the coastal waters of the eastern English Channel as a case study. The great interannual variability in the magnitude and intensity of Phaeocystis spp. blooms, along with diatoms, compared to the ongoing gradual decrease in anthropogenic nutrient concentration and rebalancing of nutrient ratios; suggests that other factors, such as competition for resources, may also play an important role. A realized niche approach was used with the Outlying Mean Index analysis and the dynamics of the species’ realized subniches were estimated using the Within Outlying Mean Indexes calculations under low (L) and high (H) contrasting Phaeocystis spp. abundance. The Within Outlying Mean Indexes allows the decomposition of the realized niche into realized subniches, found within the subset of habitat conditions and constrained by a subset of a biotic factor. The two contrasting scenarios were characterized by significantly different subsets of environmental conditions and diatom species (BV-step analysis), and different seasonality in salinity, turbidity, and nutrients. The subset L environmental conditions were potentially favorable for Phaeocystis spp. but it suffered from competitive exclusion by key diatom species such as Skeletonema spp., Thalassiosira gravida, Thalassionema nitzschioides and the Pseudo-nitzchia seriata complex. Accordingly, these diatoms species occupied 81% of Phaeocystis spp.'s existing fundamental subniche. In contrast, the greater number of diatoms, correlated with the community trend, within subset H exerted a weaker biological constraint and favored Phaeocystis spp. realized subniche expansion. In conclusion, the results strongly suggest that both abiotic and biotic interactions should be considered to understand Phaeocystis spp. blooms with greater consideration of the preceeding diatoms. HABs needs must therefore be studied as part of the total phytoplankton community.

Estimating Aging Effects in Running Events

This paper uses world running records by age to estimate a biological frontier of decline rates. Two models are compared: a linear/quadratic (LQ) model and a non-parametric model. Two estimation methods are used: 1) minimizing the squared difference between the observed records and the modeled biological frontier and 2) using extreme value theory to estimate the biological frontier that maximizes the probability of observing the existing world records by age. The results support the LQ model and suggest there is linear percentage decline up to the late 70’s and quadratic decline after that. The extreme value estimates suggest that the true biological frontier is on average about 8 percent below the existing world records. The estimated age factors are also compared to the World Master Athletics (WMA) age factors. The two sets of age factors are close except at the old ages, where the WMA factors are noticeably smaller. Also, the WMA age factors do not meet an important biological constraint.

Totipotency segregates between the sister blastomeres of two-cell stage mouse embryos

Following fertilization in mammals, it is generally accepted that totipotent cells are exclusive to the zygote and to each of the two blastomeres originating from the first mitotic division. This model of totipotency was inferred from a minority of cases in which blastomeres produced monozygotic twins in mice. Was this due to experimental limitation or biological constraint? Here we removed experimental obstacles and achieved reliable quantification of the prevalence of dual totipotency among mouse two-cell stage blastomeres. We separated the blastomeres of 1,252 two-cell embryos, preserving 1,210 of the pairs. Two classes of monozygotic twins became apparent at the blastocyst stage: 27% formed a functional epiblast in both members (concordant), and 73% did so in only one member of the pair (discordant) – a partition that proved insensitive to oocyte quality, sperm-entry point, culture environment and pattern of cleavage. In intact two-cell embryos, the ability of sister blastomeres to generate epiblast was also skewed. Class discovery clustering of the individual blastomeres’ and blastocysts’ transcriptomes points to an innate origin of concordance and discordance rather than developmental acquisition. Our data place constraints on the commonly accepted idea that totipotency is allocated equally between the two-cell stage blastomeres in mice.

Within outlying mean indexes: refining the OMI analysis for the realized niche decomposition.

The ecological niche concept has regained interest under environmental change (e.g., climate change, eutrophication, and habitat destruction), especially to study the impacts on niche shift and conservatism. Here, we propose the within outlying mean indexes (WitOMI), which refine the outlying mean index (OMI) analysis by using its properties in combination with the K-select analysis species marginality decomposition. The purpose is to decompose the ecological niche into subniches associated with the experimental design, i.e., taking into account temporal and/or spatial subsets. WitOMI emphasize the habitat conditions that contribute (1) to the definition of species’ niches using all available conditions and, at the same time, (2) to the delineation of species’ subniches according to given subsets of dates or sites. The latter aspect allows addressing niche dynamics by highlighting the influence of atypical habitat conditions on species at a given time and/or space. Then, (3) the biological constraint exerted on the species subniche becomes observable within Euclidean space as the difference between the existing fundamental subniche and the realized subniche. We illustrate the decomposition of published OMI analyses, using spatial and temporal examples. The species assemblage’s subniches are comparable to the same environmental gradient, producing a more accurate and precise description of the assemblage niche distribution under environmental change. The WitOMI calculations are available in the open-access R package “subniche.”

Weed management in direct seeded rice: A review

Weeds are the major biological constraint in direct seeded rice (DSR) due to the concurrent emergence of competitive weeds, absence of water to suppress weeds at the time of seedling emergence and emergence of difficult to control weeds. Strategies on weed management in direct seeded rice depend on critical period of weed control, weed flora and method to be adopted. In order to achieve the long term and sustainable management of weeds in DSR an integration of different weed management strategies like integrated weed management (IWM) are essential. The literature regarding the critical period of weed control, weed flora and different methods for the sustainable management of weeds in direct seeded rice are reviewed in this paper.

Seeding rate and genotype effects on weeds and yield of dry-seeded rice

Weeds are the main biological constraint to wide spread adoption of dry-seeded rice (DSR). Research analyzing the effects of seeding rate on weeds and yield of DSR using newly developed genotypes adapted to DSR is not well documented in Asia. The objective of this study was to investigate the relative performance of selected genotypes in relation to seeding rate and weed infestation levels on weeds and yield of DSR in the rainy seasons of 2014 and 2015. Four selected genotypes [two cultivars (PR-115 and Dhan-202), and two recombinant inbred lines (RIL-367 and RIL-1646)], were grown in a split-split plot arrangement in a randomized complete block, with weed infestation levels (weed-free and partial weedy) in the main plots, seeding rate (100 and 200 seeds m−2) in the subplots, and genotypes in the sub-subplots. Total weed biomass was lower at the high seed rate (HSR; 200 seeds m−2) as compared to the low seeding rate (LSR; 100 seeds m−2), and the reduction in weed biomass varied from 40 to 72% depending on genotypes. At the LSR, the weed-competitive index (WCI) of RIL-1646 (1.13) was higher than PR-115 (0.44), but remained similar to RIL-367 and Dhan-202. At the HSR, the WCI of RIL-367 (1.57), RIL-1646 (2.24), and Dhan-202 (2.89) was higher than PR-115 (0.95). The WCI of newly developed genotypes (RIL-367, RIL-1646 and Dhan-202) increased with increased seeding rate, while for PR-115; no such increase was found. In the weed-free plots, RIL-367 at both the seeding rates had higher grain yield (5.97 t ha−1) than other genotypes and the lowest yield was recorded with Dhan-202, and the trend was similar at both the seeding rates. However, in the partial weedy plots, at both the seeding rates, the lowest yield was recorded for PR-115. In the partial weedy plots, the grain yield of RIL-367 was increased using the HSR. In the partial weedy plots, the plant height of RIL-367 at HSR was higher than that at LSR, and a similar trend was observed for panicle weight. There was a negative relationship between early plant height and relative grain yield loss due to weed infestation. This study indicates that the newly developed genotypes for DSR have variations in WCI, and weed control in DSR could be improved by increasing the seeding rate for these genotypes.

Caractérisation Physiologique Et Évaluation Du Comportement Germinatif De Semences De Rottboellia Cochinchinensis, Euphorbia Heterophylla, Et Porophyllum Ruderale, Trois Adventices Des Rizières De Côte d’Ivoire

Weeds are the most important biological constraint reducing rice production. This study was conducted to know the physiological characteristics and the germinative behavior of the seeds of Rottboellia cochinchinensis, Euphorbia heterophylla and Porophyllum ruderale, three major weeds of rice field in Côte d'Ivoire. Seed characteristics were determined according to ISTA’s standards. These three weeds had orthodox seeds with low moisture content (< 15%). These weeds raise better when they were sown on the surface (0-0.5 cm) or slightly buried in the ground. E. heterophylla and P. ruderale germinated well when their seeding density is high (150 seeds/Petri dish). For R. cochinchinensis, when the seedling density is low (25 seeds/Petri dish). The germination was maximum after five to nine days.

Evolution of gremlin 2 in cetartiodactyl mammals: gene loss coincides with lack of upper jaw incisors in ruminants

Understanding the processes that give rise to genomic variability in extant species is an active area of research within evolutionary biology. With the availability of whole genome sequences, it is possible to quantify different forms of variability such as variation in gene copy number, which has been described as an important source of genetic variability and in consequence of phenotypic variability. Most of the research on this topic has been focused on understanding the biological significance of gene duplication, and less attention has been given to the evolutionary role of gene loss. Gremlin 2 is a member of the DAN gene family and plays a significant role in tooth development by blocking the ligand-signaling pathway of BMP2 and BMP4. The goal of this study was to investigate the evolutionary history of gremlin 2 in cetartiodactyl mammals, a group that possesses highly divergent teeth morphology. Results from our analyses indicate that gremlin 2 has experienced a mixture of gene loss, gene duplication, and rate acceleration. Although the last common ancestor of cetartiodactyls possessed a single gene copy, pigs and camels are the only cetartiodactyl groups that have retained gremlin 2. According to the phyletic distribution of this gene and synteny analyses, we propose that gremlin 2 was lost in the common ancestor of ruminants and cetaceans between 56.3 and 63.5 million years ago as a product of a chromosomal rearrangement. Our analyses also indicate that the rate of evolution of gremlin 2 has been accelerated in the two groups that have retained this gene. Additionally, the lack of this gene could explain the high diversity of teeth among cetartiodactyl mammals; specifically, the presence of this gene could act as a biological constraint. Thus, our results support the notions that gene loss is a way to increase phenotypic diversity and that gremlin 2 is a dispensable gene, at least in cetartiodactyl mammals.

The nuclear higher-order structure defined by the set of topological relationships between DNA and the nuclear matrix is species-specific in hepatocytes

During the interphase the nuclear DNA of metazoan cells is organized in supercoiled loops anchored to constituents of a nuclear substructure or compartment known as the nuclear matrix. The stable interactions between DNA and the nuclear matrix (NM) correspond to a set of topological relationships that define a nuclear higher-order structure (NHOS). Current evidence suggests that the NHOS is cell-type-specific. Biophysical evidence and theoretical models suggest that thermodynamic and structural constraints drive the actualization of DNA-NM interactions. However, if the topological relationships between DNA and the NM were the subject of any biological constraint with functional significance then they must be adaptive and thus be positively selected by natural selection and they should be reasonably conserved, at least within closely related species.We carried out a coarse-grained, comparative evaluation of the DNA-NM topological relationships in primary hepatocytes from two closely related mammals: rat and mouse, by determining the relative position to the NM of a limited set of target sequences corresponding to highly-conserved genomic regions that also represent a sample of distinct chromosome territories within the interphase nucleus. Our results indicate that the pattern of topological relationships between DNA and the NM is not conserved between the hepatocytes of the two closely related species, suggesting that the NHOS, like the karyotype, is species-specific.

Storage of Blood in the Mammalian Spleen: an Evolutionary Perspective

Splenic blood storage is usually considered a characteristic restricted to Carnivora, Perissodactyla, and Ruminantia. In these mammals, the red pulp comprises the major part of the organ and – within it – the cords show a vast extension, allowing the storage of a great quantity of erythrocytes. Moreover, well-muscularized capsule and trabeculae permit a strong contractility. In this way, a significant quantity of erythrocytes can be poured into the circulation in response to an increased demand of oxygen. These spleens are usually classified as the “storing type,” in contrast to the “defensive type,” characterized by negligible quantity of blood stored. Past evolutionary interpretations have seen the former type as derived from the latter one. This explanation was based on some ontogenetic observations, thus deriving from the approach of Haeckel’s biogenetic law, and caused some contradictions that remained unsolved. An in-depth examination of the literature reveals that almost all mammalian species can store erythrocytes in their spleen. What changes is the quantity of this storage and the efficiency of its release. This means that the dichotomy between “storage” and “defensive” types is just an approximation – and not very useful. Splenic storage, indeed, is not a recently acquired character by some mammals, rather a primitive one, that underwent different quantitative and qualitative changes during the evolution of the different mammalian lineages. This review offers a new hypothesis on the evolution of this function (viewing the presence of splenic erythropoiesis as a biological constraint) and proposes it as a case of exaptation.

Structural asymmetry of the human cerebral cortex: Regional and between-subject variability of surface area, cortical thickness, and local gyrification

Structural asymmetry varies across individuals, brain regions, and metrics of cortical organization. The current study investigated regional differences in asymmetry of cortical surface area, thickness, and local gyrification, and the extent of between-subject variability in these metrics, in a sample of healthy young adults (N=200). Between-subject variability in cortical structure may provide a means to assess the extent of biological flexibility or constraint of brain regions, and we explored the potential influence of this variability on the phenotypic expression of structural asymmetry. The findings demonstrate that structural asymmetries are nearly ubiquitous across the cortex, with differing regional organization for the three cortical metrics. This implies that there are multiple, only partially overlapping, maps of structural asymmetry. The results further indicate that the degree of asymmetry of a brain region can be predicted by the extent of the region's between-subject variability. These findings provide evidence that reduced biological constraint promotes the expression of strong structural asymmetry.

Extreme sensitivity of reservoir computing to small network disruptions

Recent computational models based on reservoir computing (RC) are gaining attention as plausible theories of cortical information processing. In these models, the activity of a recurrently connected population of neurons is sent to one or many read-out units through a linear transformation. These models can operate in a chaotic regime which has been proposed as a possible mechanism underlying sustained irregular activity observed in cortical areas [1,2]. Furthermore, models based on RC replicate the neural dynamics involved in decision making [3], interval timing [2], and motor control [1]. However, one biological constraint that has been overlooked in these models is their resistance to small connectivity perturbations such as failures in synaptic transmission, a phenomenon that occurs frequently in healthy circuits without causing any drastic functional changes. Here, we show that different implementations of RC display very little resistance to small synaptic disruptions and discuss the implications of such fragility for RC mechanisms that may be present in neural coding. With the FORCE [1] procedure, networks lost their ability to replicate a jagged sinusoidal signal after a single neuron was removed from the reservoir (Figure ​(Figure1A).1A). Networks with innate training [2] showed a similar effect on a timing task (Figure ​(Figure1B).1B). The lag in the timing and the noise in the output both increased monotonically as further neurons were removed (Figure 1C,D); networks reached random performance after ~1.5% of neurons were eliminated. After the suppression of a single neuron, the spectrum of the weight matrix was greatly disturbed and repeated trials displayed unreliable trajectories, as assessed with principal components analysis. When individual synapses were removed instead of neurons, networks reached random performance after ~0.5% of synapses from the reservoir were eliminated. While living neuronal circuits can withstand small synaptic disruptions without compromising task performance, our results suggest that such disruptions have a catastrophic impact on the behaviour of RC models. Retraining the read-out unit seems to be futile as it results as a completely new solution post retraining instead of a finer restructuration. These results cast doubt on the validity of a large class of models that claim to capture the neuronal mechanisms of cognitive and behavioral tasks. Figure 1 Performance of damaged reservoirs of 1,000 neurons with FORCE and innate learning algorithms. A. Target signal (green, perfectly replicated with the originally trained network) and the trace of the same network after the removal of one neuron in its reservoir. ...

Distribution of Alkaloides and Allelopathismof Selelected Weeds from a Post Harvest CropField

Though beneficial the weeds always pose an important biological constraint to crop productivity. The economic losses that are caused by these weeds globally costs billions of rupees every year. Allelopathic potentialities of plants are considered as an alternative natural way of weed management strategy for crop production as well as environmental benefits.Although the plants like the weeds are the great reservoirs of many new & potential phytochemicals,majority of them still remains unexplored either due to restricted habitat or because of being wild in nature.Hence the present survey was carried out taking ten (10) selected weeds of various stages of development from post harvest crop fields of Rice and Mustard in the OUAT Farm campus which have been left open for around two months. The Botanical authentication of the weeds were done by following the Texonomic literatures.They are Cardus nutans L, Cerastium fontanum Baumg., Cleome viscosa L., Euphorbia maculata L. ,Helianthus tuberosus L., Lactuca serriola L., Phyllanthus niruri L. ,Sinapsis arvensis L. ,Vernonia cinerea Scherb., Veronica arvensis L.Weeds were collected between January and February 2014 . Their crude alkaloidal contents were extracted and estimated from the dried powder of the whole plant following the standard methods (Harborne et al 1992). All plant samples indicate the presence of good amount of Alkaloid, highest being in Veronica persica Poiret.(17.35%) and lowest in Cardus nutans (3.07%). Variation of alkaloidal contents with variation in stage of development maximum reaching at the flowering stage, was indicated within the individuals of the same family. The quantity of the alkaloid was species specific.The allelopathic effect of the crude alkaloidal extract tested against the seed germination of Rice,Mung(Green gram ) and Mustard , indicates that the alkaloids are not so effective towards the growth of Rice but quite inhibitory towards the growth of Mung.This result is interpreted basing upon their chi-scquare values.

Hedonics and the “Selective Associations” Biological Constraint on Learning

Research concerned with visual dominance in appetitive and auditory dominance in aversive learning situations (selective associations) is reviewed. The present analysis stresses that the dominant sensory modality of stimulus control is determined by the relative affective valence acquired by a compound auditory-visual stimulus through reinforcement contingencies, rather than by whether the primary reinforcer is appetitive or aversive. For example, take two groups of rats or pigeons on exactly the same shock-avoidance contingency in a tone-light compound (TL), but with different contingencies when the compound is absent (TL). Responding came predominantly under (1) auditory control when conditions in TL were hedonically negative relative to those in (TL), and (2) visual control when conditions in (TL) made TL relatively positive. Selective associations here are a product of the relative hedonic state, positive or negative, established to the auditory-visual compound. Therefore, this constraint reflects a high level of functioning by a hedonic comparator -- with TL’s hedonic value contextually determined by the totality of the events encountered, and reinforcement contingencies, operating in its world. The physical particulars of the reinforcer in TL here, shock avoidance, clearly were not responsible for the hedonic psychological state TL produced. Weiss, Panlilio, and Schindler (1993a, 1993b) went on to show that these proclivities can be (1) reversed, and (2) overcome by a blocking design when the biologically-contingency-disadvantaged stimulus is first pretrained on its own. Relating the “hedonic model” to evolution is speculative. But, the hedonic model is scientifically integrative by relating this biological constraint to a variety of phenomena that involve incentive-motivational states. These include choice behavior, conditioned preference, behavioral contrast and appetitive-aversive interactions.

Mapping the distribution of maize streak virus genotypes across the forest and transition zones of Ghana.

Throughout sub-Saharan Africa, maize streak virus strain A (MSV-A), the causal agent of maize streak disease (MSD), is an important biological constraint on maize production. In November/December 2010, an MSD survey was carried out in the forest and transition zones of Ghana in order to obtain MSV-A virulence sources for the development of MSD-resistant maize genotypes with agronomic properties suitable for these regions. In 79 well-distributed maize fields, the mean MSD incidence was 18.544% and the symptom severity score was 2.956 (1=no symptoms and 5=extremely severe). We detected no correlation between these two variables. Phylogenetic analysis of cloned MSV-A isolates that were fully sequenced from samples collected in 51 of these fields, together with those sampled from various other parts of Africa, indicated that all of the Ghanaian isolates occurred within a broader cluster of West African isolates, all belonging to the highly virulent MSV-A1 subtype. Besides being the first report of a systematic MSV survey in Ghana, this study is the first to characterize the full-genome sequences of Ghanaian MSV isolates. The 51 genome sequences determined here will additionally be a valuable resource for the rational selection of representative MSV-A variant panels for MSD resistance screening.

Running Up Against Nature's Limits?

Does Darwinian evolutionary biology have the resources to explain art and its place in our lives? This is the question Stephen Davies sets himself in The Artful Species. There are, Davies explains, only three positions one might take. An affirmative answer requires that one hold that art—or rather our disposition to make, enjoy and value art—is an adaptation or that it is a non-adaptive side effect of adaptations (a spandrel). A negative answer requires one to hold that art is a cultural product that floats free of biological constraint (a technology). Davies rejects all three options. Adaptationist accounts of art have defects, says Davies, stemming from the fact that they ‘search for a common underlying function for art, which leads to simplification and to ignoring many of the diverse functions art can serve’ (117). He is ‘skeptical of the likely success of theories that attempt to bind the various, disparate arts to a single, biologically adaptive tree’ (117). Moreover, Davies is mindful that whatever adaptive function art behaviours might have served in our remote ancestral past, they could serve different adaptive functions now, or have no function at all.

Optimal Recall from Bounded Metaplastic Synapses: Predicting Functional Adaptations in Hippocampal Area CA3

A venerable history of classical work on autoassociative memory has significantly shaped our understanding of several features of the hippocampus, and most prominently of its CA3 area, in relation to memory storage and retrieval. However, existing theories of hippocampal memory processing ignore a key biological constraint affecting memory storage in neural circuits: the bounded dynamical range of synapses. Recent treatments based on the notion of metaplasticity provide a powerful model for individual bounded synapses; however, their implications for the ability of the hippocampus to retrieve memories well and the dynamics of neurons associated with that retrieval are both unknown. Here, we develop a theoretical framework for memory storage and recall with bounded synapses. We formulate the recall of a previously stored pattern from a noisy recall cue and limited-capacity (and therefore lossy) synapses as a probabilistic inference problem, and derive neural dynamics that implement approximate inference algorithms to solve this problem efficiently. In particular, for binary synapses with metaplastic states, we demonstrate for the first time that memories can be efficiently read out with biologically plausible network dynamics that are completely constrained by the synaptic plasticity rule, and the statistics of the stored patterns and of the recall cue. Our theory organises into a coherent framework a wide range of existing data about the regulation of excitability, feedback inhibition, and network oscillations in area CA3, and makes novel and directly testable predictions that can guide future experiments.

Effect of tillage systems, seeding rates, and herbicides on weed growth and grain yield in dry-seeded rice systems in the Philippines

In Asia, dry-seeded rice (DSR) production systems are increasing because of water and labour scarcities. DSR can be sown under zero-till (ZT) or after conventional tillage (CONT) operations. In these seeding systems, however, weeds are the main biological constraint. A study was conducted during the wet season of 2012 and the dry season of 2013 at the International Rice Research Institute to evaluate the effect of the tillage systems (ZT and CONT), seeding rate [low seeding rate (LSR) at 50 kg ha−1, and high seeding rate (HSR) at 100 kg ha−1], and weed control treatments (oxadiazon applied as pre-emergence, oxadiazon applied as pre-emergence followed by a commercial mixture of fenoxaprop + ethoxysulfuron as post-emergence at 21–24 days after sowing, and weedy) on weed growth and grain yield in DSR systems. The efficacy of herbicides 14 days after the application of post-emergence herbicide was similar between the tillage systems and between seeding rates. At crop harvest, weed biomass was higher in the ZT plots than in the CONT plots, and higher at LSR than at HSR. At the same time, herbicide applications decreased weed biomass by 73–96%, compared with the weedy plots. Compared with the ZT plots, CONT plots had 9–18% higher grain yield. Similarly, plots sown at HSR had 17–19% higher grain yield than at LSR. Weedy plots had 81–84% less yield than the herbicide-treated plots (3060–3380 kg ha−1 in the wet season and 5820–5950 kg ha−1 in the dry season).

The Critical Period of Weed Control in Faba Bean and Chickpea in Mediterranean Areas

Weeds are often the major biological constraint to growing legume crops successfully, and an understanding of the critical period of weed control (CPWC) is important for developing environmentally sustainable weed management practices to prevent unacceptable yield loss. Therefore, we carried out two field experiments to identify the CPWC for two grain legume crops traditionally grown in Mediterranean areas: chickpea and faba bean. The experiments were conducted at two sites both located in the Sicilian inland (Italy). In chickpea, when weeds were left to compete with the crop for the whole cycle, the grain yield reduction was on average about 85% of the weed-free yield, whereas in faba bean the reduction was less severe (on average about 60% of the weed-free yield). The onset of the CPWC at a 5% yield loss level varied by species, occurring later in faba bean than in chickpea (on average, 261 and 428 growing degree days after emergence for chickpea and faba bean, respectively). In both species, the end of the CPWC occurred at the early full-flowering stage when the canopy of each crop enclosed the interrow space. On the whole, the CPWC at a 5% yield loss level ranged from 50 to 69 d in chickpea and from 28 to 33 d in faba bean. The results highlight the fact that faba bean has a higher competitive ability against weeds than chickpea. This could be attributable both to more vigorous early growth and to the plant's greater height, both factors related to a greater shading ability and, consequently, to a better ability to suppress weeds.

Specific‐gene studies of evolutionary mechanisms in an age of genome‐wide surveying

The molecular tools of genomics have great power to reveal patterns of genetic difference within or among species, but must be complemented by the mechanistic study of the genetic variants found if these variants' evolutionary meaning is to be well understood. Central to this purpose is knowledge of the organisms' genotype-phenotype-environment interactions, which embody biological adaptation and constraint and thus drive natural selection. The history of this approach is briefly reviewed. Strategies embracing the complementarity of genomics and specific-gene studies in evolution are considered. Implementation of these strategies, and examples showing their feasibility and power, are discussed. Initial generalizations emphasize: (1) reproducibility of adaptive mechanisms; (2) evolutionary co-importance of variation in protein sequences and expression; (3) refinement of rudimentary molecular functions as an origin of evolutionary innovations; (4) identification of specific-gene mechanisms as underpinnings of genomic or quantitative genetic variation; and (5) multiple forms of adaptive or constraining epistasis among genes. Progress along these lines will advance understanding of evolution and support its use in addressing urgent medical and environmental applications.