Line Of Least Resistance Research Articles

Building research careers in a changing environment

Building research careers in a changing environment

The alignment between phenotypic plasticity, the major axis of genetic variation and the response to selection.

Phenotypic plasticity is the ability of a genotype to produce more than one phenotype in order to match the environment. Recent theory proposes that the major axis of genetic variation in a phenotypically plastic population can align with the direction of selection. Therefore, theory predicts that plasticity directly aids adaptation by increasing genetic variation in the direction favoured by selection and reflected in plasticity. We evaluated this theory in the freshwater crustacean Daphnia pulex, facing predation risk from two contrasting size-selective predators. We estimated plasticity in several life-history traits, the G matrix of these traits, the selection gradients on reproduction and survival, and the predicted responses to selection. Using these data, we tested whether the genetic lines of least resistance and the predicted response to selection aligned with plasticity. We found predator environment-specific G matrices, but shared genetic architecture across environments resulted in more constraint in the G matrix than in the plasticity of the traits, sometimes preventing alignment of the two. However, as the importance of survival selection increased, the difference between environments in their predicted response to selection increased and resulted in closer alignment between the plasticity and the predicted selection response. Therefore, plasticity may indeed aid adaptation to new environments.

Once upon Multivariate Analyses: When They Tell Several Stories about Biological Evolution.

Geometric morphometrics aims to characterize of the geometry of complex traits. It is therefore by essence multivariate. The most popular methods to investigate patterns of differentiation in this context are (1) the Principal Component Analysis (PCA), which is an eigenvalue decomposition of the total variance-covariance matrix among all specimens; (2) the Canonical Variate Analysis (CVA, a.k.a. linear discriminant analysis (LDA) for more than two groups), which aims at separating the groups by maximizing the between-group to within-group variance ratio; (3) the between-group PCA (bgPCA) which investigates patterns of between-group variation, without standardizing by the within-group variance. Standardizing within-group variance, as performed in the CVA, distorts the relationships among groups, an effect that is particularly strong if the variance is similarly oriented in a comparable way in all groups. Such shared direction of main morphological variance may occur and have a biological meaning, for instance corresponding to the most frequent standing genetic variation in a population. Here we undertake a case study of the evolution of house mouse molar shape across various islands, based on the real dataset and simulations. We investigated how patterns of main variance influence the depiction of among-group differentiation according to the interpretation of the PCA, bgPCA and CVA. Without arguing about a method performing ‘better’ than another, it rather emerges that working on the total or between-group variance (PCA and bgPCA) will tend to put the focus on the role of direction of main variance as line of least resistance to evolution. Standardizing by the within-group variance (CVA), by dampening the expression of this line of least resistance, has the potential to reveal other relevant patterns of differentiation that may otherwise be blurred.

Rate of evolutionary change in cranial morphology of the marsupial genus Monodelphis is constrained by the availability of additive genetic variation.

We tested the hypothesis that the rate of marsupial cranial evolution is dependent on the distribution of genetic variation in multivariate space. To do so, we carried out a genetic analysis of cranial morphological variation in laboratory strains of Monodelphis domestica and used estimates of genetic covariation to analyse the morphological diversification of the Monodelphis brevicaudata species group. We found that within-species genetic variation is concentrated in only a few axes of the morphospace and that this strong genetic covariation influenced the rate of morphological diversification of the brevicaudata group, with between-species divergence occurring fastest when occurring along the genetic line of least resistance. Accounting for the geometric distribution of genetic variation also increased our ability to detect the selective regimen underlying species diversification, with several instances of selection only being detected when genetic covariances were taken into account. Therefore, this work directly links patterns of genetic covariation among traits to macroevolutionary patterns of morphological divergence. Our findings also suggest that the limited distribution of Monodelphis species in morphospace is the result of a complex interplay between the limited dimensionality of available genetic variation and strong stabilizing selection along two major axes of genetic variation.

Return to Monte Cristo:

Return to Monte Cristo:

Return to Monte Cristo:

Return to Monte Cristo:

Speaking Truth to Power: “Not the Time … to Follow the Line of Least Resistance”

“Speaking Truth to Power” seeks to explore the experiences and possibilities that arise when educators speak Truth to power.

Quick divergence but slow convergence during ecotype formation in lake and stream stickleback pairs of variable age.

When genetic constraints restrict phenotypic evolution, diversification can be predicted to evolve along so-called lines of least resistance. To address the importance of such constraints and their resolution, studies of parallel phenotypic divergence that differ in their age are valuable. Here, we investigate the parapatric evolution of six lake and stream threespine stickleback systems from Iceland and Switzerland, ranging in age from a few decades to several millennia. Using phenotypic data, we test for parallelism in ecotypic divergence between parapatric lake and stream populations and compare the observed patterns to an ancestral-like marine population. We find strong and consistent phenotypic divergence, both among lake and stream populations and between our freshwater populations and the marine population. Interestingly, ecotypic divergence in low-dimensional phenotype space (i.e. single traits) is rapid and seems to be often completed within 100 years. Yet, the dimensionality of ecotypic divergence was highest in our oldest systems and only there parallel evolution of unrelated ecotypes was strong enough to overwrite phylogenetic contingency. Moreover, the dimensionality of divergence in different systems varies between trait complexes, suggesting different constraints and evolutionary pathways to their resolution among freshwater systems.

Speaking Truth to Power: Lou LaBrant: “Not the Time … to Follow the Line of Least Resistance”

This column seeks to explore the experiences and possibilities that arise when educators speak Truth to power.

The direction of main phenotypic variance as a channel to morphological evolution: case studies in murine rodents

How evolution can be channeled by intrinsic processes such as genetic and developmental networks is a key issue in evolution. Studying the phenotypic variation in a population can shed light on these constraints, because this variation, being the product of these genetic and developmental processes, is the target of both selective screening and random sampling. It could thus act as a “line of least resistance to evolution”. Based on morphometric analysis of molar and mandible shape in several fossil lineages and modern groups of murine rodents, we illustrate here the questions that can be addressed based on this framework. The role intrapopulational variation as line of least resistance to evolution is validated on several lineages. The existence of such preferential direction of evolution can contribute to explain cases of parallel evolution. The underlying mechanisms can be the sharing of similar genetic/developmental pathways but also common functional constraints limiting the range of phenotypic variation to be explored. Comparing directions of intrapopulation variance to the course of interpopulation evolution can thus be of help to bridge several evolutionary levels and contribute to an integrated vision of the phenotypic evolution. Download the complete Yellow Book on Virtual Morphology and Evolutionary Morphometrics in the new millenium.

Lines of least resistance and genetic architecture of house mouse (Mus musculus) mandible shape

Evolution along "lines of least resistance (LLR)" is a well-established phenomenon, which is ultimately based on variational properties of the developmental system. However, it has remained unclear which aspects of development are responsible for observed distributions of variation. This article suggests that house mouse mandible shape may present an opportunity for future research in this field. The genetic architecture of mouse mandible shape has been investigated in the laboratory, and its evolution has been surveyed in studies on natural variation. Here, I ask whether evolutionary diversification of mandible shape follows "LLR" by comparing principal directions of genetic and evolutionary variation, and I assess the potential contribution of specific genomic regions to evolutionary divergence along these directions. The role of two aspects of development, QTL number (presumably reflecting mutational target size) and canalization, is comparatively assessed. Overall, our results demonstrate a strong tendency of genetic and evolutionary systems to vary along similar directions, suggesting that mandible shape evolves along LLR at the level of populations, subspecies and species. At the level of genetic factors, effects bearing similarity to directions of evolution are significantly overrepresented, providing support for the mutational target size hypothesis. A role for canalization is not supported by a clear correlation between directions of evolution and size of genetic effects; however, the evidence for canalization remains ambiguous. These results provide some insights into how the developmental system may shape the variational properties of genetic systems and thus influence the direction of evolution.

Fracture through a Harris growth arrest line

Fractures occur when bone is overloaded and mechanical failure occurs with the fracture propagating along the lines of least resistance. We report the case of a 6-year-old boy who sustained a nondisplaced distal third tibial shaft fracture through a Harris growth arrest line of increased osseous density due to low-energy blunt trauma. This case is used as an opportunity to review the literature on Harris growth arrest lines and discuss a fracture pattern that has not been previously described in the literature.

Role-Play: Taking the Line of Least Resistance

Today, one of the main concerns in second language acquisition is to learn how to communicate orally with others. So speaking has played an increasingly essential role in second language settings. However, in many universities, ESL students rarely communicate effectively in English with other people. They would rather remain passive when a communicative task is assigned. Such a phenomenon has long left many ESL practitioners defeated. This had prompted the research to ascertain the effectiveness of role-play in eradicating the problem. Using Kolb (1984) model in the ESL classroom experimentally, after fourteen weeks, the outcomes showed that role-play is an effective technique to enhance the learners' confidence and their oral competency.

The evolution of waving displays in fiddler crabs (Uca spp., Crustacea: Ocypodidae)

Male fiddler crabs are commonly recognized by the presence of a single massive claw used in a variety of contexts, including territorial defence, agonistic interactions, and courtship behaviour. The most common behavioural context involving these enlarged chelipeds is their use in waving displays, which are remarkably diverse among species. Although the waving display is one of the most obvious behavioural features of male fiddler crabs, little is known about their main evolutionary trends during the diversification of the genus. The present study employed phylogenetic comparative methods to investigate the evolution of waving behaviour in a sample of 19 species of Uca from Central and North America. Digital recordings were used to quantify the temporal dynamics of waving behaviour in each species. Multivariate ordination methods were used to assess whether different elements of the display showed distinct evolutionary dynamics, particularly with respect to body size and the environment where species are most commonly found. Most of the interspecific variation in displays involves differences in the overall waving velocity, with no correspondence to their local environments, nor their body size. Interestingly, despite the strong concentration of variance in the first two ordination axes, there was no statistically significant evidence for phylogenetic signals in their respective scores. These results suggest that the overall structure of waving displays is evolutionarily labile, at the same time as being concentrated in a few particular axes of variation, possibly indicating evolution along lines of least resistance. The approach employed in the present study highlights the utility of phylogenetic comparative methods for elucidating the evolution of complex behavioural characteristics, such as the waving display in male fiddler crabs. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106, 307–315.

Study on Optimization of Blasting Parameters and its Effect on Anchoring Rock Beam of a Underground Workshop

The optimum model for blasting parameters of anchoring rock beam is established and its blasting parameters are optimized by making use of a strong mapped function of the neural networks technology with the typical samples of other practical smooth blasting parameters. The explosive types, the extent of joint development of rock mass, the diameter of bore-hole, the depth of bore-hole, the linear charge density, the burden line of least resistance and the spacing of bore-hole are considered as the primary effective factors in the excavation of anchoring rock beam. In the meantime, the experimental blasting parameters for anchoring rock beam are determined by the in-site blasting experiments of the protective layer and platform of rock mass in similar conditions. The results show that the in-site experimental blasting parameters are preferably identical to those of the optimum design. The acoustic wave examination for the blasting of the protective layer and platform of rock mass indicates that the blasting effect is satisfied and its smaller loose ring of surrounding rock mass is obtained.

Differential Evolvability Along Lines of Least Resistance of Upper and Lower Molars in Island House Mice

Variation within a population is a key feature in evolution, because it can increase or impede response to selection, depending on whether or not the intrapopulational variance is correlated to the change under selection. Hence, main directions of genetic variance have been proposed to constitute “lines of least resistance to evolution” along which evolution would be facilitated. Yet, the screening of selection occurs at the phenotypic level, and the phenotypic variance is not only the product of the underlying genetic variance, but also of developmental processes. It is thus a key issue for interpreting short and long term evolutionary patterns to identify whether main directions of phenotypic variance indeed constitute direction of facilitated evolution, and whether this is favored by developmental processes preferably generating certain phenotypes. We tackled these questions by a morphometric quantification of the directions of variance, compared to the direction of evolution of the first upper and lower molars of wild continental and insular house mice. The main phenotypic variance indeed appeared as channeling evolution between populations. The upper molar emerged as highly evolvable, because a strong allometric component contributed to its variance. This allometric relationship drove a repeated but independent evolution of a peculiar upper molar shape whenever size increased. This repeated evolution, together with knowledge about the molar development, suggest that the main direction of phenotypic variance correspond here to a “line of least developmental resistance” along which evolution between population is channeled.

Rhythm Control Should Be Better for the Management of Patients With Atrial Fibrillation and Heart Failure - Rhythm Control vs. Rate Control: Which Is Better in the Management of Atrial Fibrillation? (Rhythm-Side) -

The incidence of atrial fibrillation (AF) increases with advancing NHYA cardiac functional class, and it significantly affects the cardiac function of a failing heart. In such situations, clinicians should aim to maintain sinus rhythm in these patients with heart failure (HF) in order to improve their prognosis. However, according to various randomized clinical studies demonstrating the non-superiority of rhythm control over rate control, many clinicians seem to prefer to take the line of least resistance (ie, rate control). Curative catheter ablation mainly based on isolation procedure of the pulmonary veins in patients with AF and HF has demonstrated a significant improvement in left ventricular function, even in the presence of adequate ventricular rate control before the ablation. On the other hand, ablation and biventricular pacing therapy, which is an extreme rate control strategy, has not shown any beneficial effects for these patients. Therefore, a regular RR interval with an appropriate cycle length only is not sufficient to improve cardiac performance, and maintenance of sinus rhythm, which restores atrial contraction and the atrioventricular synchrony, is thought to be essential for an improvement in HF. Thoughtful clinicians should do their best to find a way to keep HF patients in sinus rhythm.

Ecology of plant speciation

Ecology of plant speciation

A healed echinococcus pathological femoral shaft non-union—A case report and a literature review

Hydatid disease is prevalent throughout much of the world, mainly in the developing world and unprivileged areas. There are twelve subtypes of Echinococcus known today. However, in humans there are two main types of infection—Echinococcus multilocularis causing alveolar and Echinococcus granulosus which causes the cystic echinococcosis. The incidence of bone disease, caused by echinococcus is rare as only 0.5–4.5% of cases of echinococcosis have bony involvement. Primary hydatid disease of bone, is caused by E. granulosus, occurs when a bloodborne scolex settles in bone. In bone involvement, pericyst formation of the echinococcus does not occur, thereby allowing aggressive proliferation in an irregular branching fashion along the line of least resistance, especially the bone canals. When this proliferation causes damage severe enough to create a compromise in the solidity of the bone, a pathological fracture may occur. However, very few reports deal with the treatment of pathological long bone fractures, especially as the sole presentation of the echinococcus usually with a grim outcome. We present a case of a pathological femur fracture non-union caused as an isolated bony infection of echinococcus, treated successfully with serial debridements, antibiotics and fixation with a locked plate construct.

SIZE AS A LINE OF LEAST RESISTANCE II: DIRECT SELECTION ON SIZE OR CORRELATED RESPONSE DUE TO CONSTRAINTS?

Evolutionary change in New World Monkey (NWM) skulls occurred primarily along the line of least resistance defined by size (including allometric) variation (g(max)). Although the direction of evolution was aligned with this axis, it was not clear whether this macroevolutionary pattern results from the conservation of within population genetic covariance patterns (long-term constraint) or long-term selection along a size dimension, or whether both, constraints and selection, were inextricably involved. Furthermore, G-matrix stability can also be a consequence of selection, which implies that both, constraints embodied in g(max) and evolutionary changes observed on the trait averages, would be influenced by selection. Here, we describe a combination of approaches that allows one to test whether any particular instance of size evolution is a correlated by-product due to constraints (g(max)) or is due to direct selection on size and apply it to NWM lineages as a case study. The approach is based on comparing the direction and amount of evolutionary change produced by two different simulated sets of net-selection gradients (beta), a size (isometric and allometric size) and a nonsize set. Using this approach it is possible to distinguish between the two hypotheses (indirect size evolution due to constraints or direct selection on size), because although both may produce an evolutionary response aligned with g(max), the amount of change produced by random selection operating through the variance/covariance patterns (constraints hypothesis) will be much smaller than that produced by selection on size (selection hypothesis). Furthermore, the alignment of simulated evolutionary changes with g(max) when selection is not on size is not as tight as when selection is actually on size, allowing a statistical test of whether a particular observed case of evolution along the line of least resistance is the result of selection along it or not. Also, with matrix diagonalization (principal components [PC]) it is possible to calculate directly the net-selection gradient on size alone (first PC [PC1]) by dividing the amount of phenotypic difference between any two populations by the amount of variation in PC1, which allows one to benchmark whether selection was on size or not.