Outcome Of Selection Research Articles

What determines the evolutionary trajectories of wild plant species? Approaches to the study of quantitative fitness-related traits.

Wild plant species provide excellent examples of qualitative traits that evolve in response to environmental challenges (e.g., flower color, heavy metal tolerance, cyanogenesis, and male sterility). In addition to such discrete characters, a dazzling array of continuously distributed, quantitative traits are expressed at every phase of the life cycle. These traits are known or suspected to have evolved by natural selection because they are heritable, differ among populations or closely related taxa occupying distinct habitats, and have individual phenotypes associated with survival and reproductive success. This special issue [American Journal of Botany 109(11)] focuses on the tools and approaches for detecting or inferring the ecological and genetic factors contributing to changes in genetically based variation of quantitative traits within or among populations, or causing their divergence among taxa. The assembled articles use one or more of three primary approaches to detect the process or outcome of natural selection on morphological, life history, reproductive, chemical, and physiological quantitative traits: the analysis of phenotypic or artificially imposed selection to detect direct and indirect selection on traits whose function is well-understood; common garden experiments, including reciprocal transplants and "resurrection" experiments; and quantitative genetic analyses designed to detect and to estimate the environmental and genetic sources of phenotypic variation or to forecast short-term evolutionary change. Together, these articles examine and reveal the adaptive capacity of quantitative traits and the genetically based constraints that may limit their directional evolutionary change, thereby informing and testing inferences, hypotheses, and predictions concerning the evolutionary trajectories of wild plant species.

Life-history traits and fitness of plateau pika (Ochotona curzoniae) in alpine meadow ecosystem.

Plateau pika (Ochotona curzoniae) is an endemic mammal living in the alpine meadow ecosystem in Qinghai–Tibet Plateau. We studied life history of plateau pika by mark–recapturing method. The research results showed that fitness of plateau pika to its habitat was lower than those of many other mammal species; plateau pika adopted quick growth strategy; the life‐history features of plateau pika were accorded with Charnov (Evolutionary Ecology Research, 2002, 4, 749)'s formula about life‐history classification, that is, E/α ≈ 1.35, C·E ≈ 1.7, I/m ≈ 0.3, in which E stands for average adult life span; α stands for age at first reproduction; C is reproductive effort; I is the size of an offspring at independence from the parent; m is average adult body mass. There does not exist dimorphism in plateau pikas. The configurations of females and males are similar; the average body mass of males is a little heavier than that of females, but the difference is not significant (F = 1.0854, df = 154, p > .3058). The juveniles exhibit a J‐form growth curve before 30‐day age and grow slower between 30 and 65‐day age and reach body mass equilibrium at about 65 days old. So, 65 days is the maturity age of plateau pika. There are 3 mortality peaks in plateau pika population. The first time is in neonate period, when only one half of juveniles can pass through this period, which implies that juvenile period is influenced strongly by natural selection; the second time is in fecundity peak period, which reflects the cost of reproduction; the third time is in the old age of plateau pika, a significant loss occurs during this period, which is the result of natural selection. The average longevity of females is longer than that of males. A female reaches the maximum life span recorded, that is, 931 days. The average longevity of all individuals is 16.33 months ≈ 490 days. The survival rate of females is higher than that of males, which reflects the cost of reproduction and society role of males. It is the outcome of natural selection. The sex ratio of neonates is 1:1; however, the sex ratio of adults is female: male = 1.31:1, which is caused by higher mortality of males over females in life history. Plateau pikas reproduced two times every year. The average gestation period of females is 18–20 days. The average litter size is 4.57 individual. The average body mass of neonates is 9.28 g. The average litter size of adult female plateau pika does not variate with age. Breeding season is between April and June. The reproductive value and fertility of 15–18 months age females are highest. The reproductive value and fertility increased with age before reproductive value and fertility peak age; however, the reproductive value and fertility decreased with age after peak age. The fitness of plateau pika (r = .1125) was lower than that of American pikas (O. princeps) (r = 2.172). The survival rate was the main factor influencing fitness. The dynamic trend of plateau pika population was coincident with r, that is, the plateau pika population was stable.

Evidence of economical territory selection in a cooperative carnivore.

As an outcome of natural selection, animals are probably adapted to select territories economically by maximizing benefits and minimizing costs of territory ownership. Theory and empirical precedent indicate that a primary benefit of many territories is exclusive access to food resources, and primary costs of defending and using space are associated with competition, travel and mortality risk. A recently developed mechanistic model for economical territory selection provided numerous empirically testable predictions. We tested these predictions using location data from grey wolves (Canis lupus) in Montana, USA. As predicted, territories were smaller in areas with greater densities of prey, competitors and low-use roads, and for groups of greater size. Territory size increased before decreasing curvilinearly with greater terrain ruggedness and harvest mortalities. Our study provides evidence for the economical selection of territories as a causal mechanism underlying ecological patterns observed in a cooperative carnivore. Results demonstrate how a wide range of environmental and social conditions will influence economical behaviour and resulting space use. We expect similar responses would be observed in numerous territorial species. A mechanistic approach enables understanding how and why animals select particular territories. This knowledge can be used to enhance conservation efforts and more successfully predict effects of conservation actions.

Fixation probabilities in graph-structured populations under weak selection.

A population’s spatial structure affects the rate of genetic change and the outcome of natural selection. These effects can be modeled mathematically using the Birth-death process on graphs. Individuals occupy the vertices of a weighted graph, and reproduce into neighboring vertices based on fitness. A key quantity is the probability that a mutant type will sweep to fixation, as a function of the mutant’s fitness. Graphs that increase the fixation probability of beneficial mutations, and decrease that of deleterious mutations, are said to amplify selection. However, fixation probabilities are difficult to compute for an arbitrary graph. Here we derive an expression for the fixation probability, of a weakly-selected mutation, in terms of the time for two lineages to coalesce. This expression enables weak-selection fixation probabilities to be computed, for an arbitrary weighted graph, in polynomial time. Applying this method, we explore the range of possible effects of graph structure on natural selection, genetic drift, and the balance between the two. Using exhaustive analysis of small graphs and a genetic search algorithm, we identify families of graphs with striking effects on fixation probability, and we analyze these families mathematically. Our work reveals the nuanced effects of graph structure on natural selection and neutral drift. In particular, we show how these notions depend critically on the process by which mutations arise.

Multiple Realization and Evolutionary Dynamics: A Fitness-Based Account

ABSTRACT Multiple realization occurs when a natural kind is variably realized at more basic levels and the common physical structure of the realizers is not essential for supporting nomological statements. It has been suggested that this phenomenon may be an outcome of natural selection acting over multiple realizers that perform an adaptive function. In this paper, we make the following contributions. First, we present a revision of this model, characterized by stricter equilibrium conditions and superior explanatory power. Second, we present a typology of multiple realization that provides a plausible account of the differences between across- and within-species multiple realization. Third, we perform a formal analysis of the dynamics of multiple realization that sheds light on the differences between multiple realization at different levels of organization.

An analysis of elasticity vector distribution specific to semelparous species using randomly generated population projection matrices and the COMPADRE Plant Matrix Database

The elasticity of population growth rate λ is a notable statistic in population projection matrix models and has been used by many empirical researchers. Silvertown and his collaborators published a paper in 1996 in which they mapped elasticity vectors of stasis, growth and fecundity for 84 plant species in a ternary plot and reported that the elasticity vector distribution of semelparous species (10 species) was located in the upper-left region of the ternary plot. To understand and clarify why the elasticity vectors of semelparous species were distributed in the upper-left region, we conducted three analyses. First, we used 68 matrices of semelparous species populations in the COMPADRE Plant Matrix Database and plotted their elasticity vectors in the ternary plot. Second, we constructed randomly generated population projection matrices for three archetypes, where several biological assumptions were made, and obtained their elasticity vector distributions. We showed that the high fecundity and/or immediate death after reproduction shifted the elasticity vector distribution to the upper-left region of the plot. Third, we examined the evolutionary change in the distribution using a population projection matrix model in which the trade-off between fecundity and adult survival was incorporated. The evolutionary trajectory derived from the trade-off model showed that the evolutionary consequence of semelparity was located in the upper-left more than was that of iteroparity in the ternary plot. Synthesizing the results derived from the three analyses, we concluded that the distinctive distribution of the elasticity vectors of semelparous species is the outcome of natural selection under the trade-off with low convexity, and the outcome of the resultant big-bang reproduction and immediate death after reproduction.

Natural Selection Towards Wild-Type in Composite Cross Populations of Winter Wheat.

Most of our crops are grown in monoculture with single genotypes grown over wide acreage. An alternative approach, where segregating populations are used as crops, is an exciting possibility, but outcomes of natural selection upon this type of crop are not well understood. We tracked allelic frequency changes in evolving composite cross populations of wheat grown over 10 generations under organic and conventional farming. At three generations, each population was genotyped with 19 SSR and 8 SNP markers. The latter were diagnostic for major functional genes. Gene diversity was constant at SSR markers but decreased over time for SNP markers. Population differentiation between the four locations could not be detected, suggesting that organic vs. non-organic crop management did not drive allele frequency changes. However, we did see changes for genes controlling plant height and phenology in all populations independently and consistently. We interpret these changes as the result of a consistent natural selection towards wild-type. Independent selection for alleles that are associated with plant height suggests that competition for light was central, resulting in the predominance of stronger intraspecific competitors, and highlighting a potential trade-off between individual and population performance.

Dispatches

Dispatches

A biological market analysis of the plant-mycorrhizal symbiosis.

It has been argued that cooperative behavior in the plant-mycorrhizal mutualism resembles trade in a market economy and can be understood using economic tools. Here, we assess the validity of this "biological market" analogy by investigating whether a market mechanism--that is, competition between partners over the price at which they provide goods--could be the outcome of natural selection. Then, we consider the conditions under which this market mechanism is sufficient to maintain mutualistic trade. We find that: (i) as in a market, individuals are favored to divide resources among trading partners in direct relation to the relative amount of resources received, termed linear proportional discrimination; (ii) mutualistic trade is more likely to be favored when individuals are able to interact with more partners of both species, and when there is a greater relative difference between the species in their ability to directly acquire different resources; (iii) if trade is favored, then either one or both species is favored to give up acquiring one resource directly, and vice versa. We then formulate testable predictions as to how environmental changes and coevolved responses of plants and mycorrhizal fungi will influence plant fitness (crop yields) in agricultural ecosystems.

Epistasis and natural selection shape the mutational architecture of complex traits.

The evolutionary trajectories of complex traits are constrained by levels of genetic variation as well as genetic correlations among traits. Because the ultimate source of all genetic variation is mutation, the distribution of mutations entering populations profoundly affects standing variation and genetic correlations. Here, we use an individual-based simulation model to investigate how natural selection and gene interactions (i.e., epistasis) shape the evolution of mutational processes affecting complex traits. We find that the presence of epistasis allows natural selection to mold the distribution of mutations, such that mutational effects align with the selection surface. Consequently, novel mutations tend to be more compatible with the current forces of selection acting on the population. These results suggest that in many cases mutational effects should be seen as an outcome of natural selection rather than as an unbiased source of genetic variation that is independent of other evolutionary processes.

The Evolution of Altruistic Preferences: Mothers versus Fathers.

What can evolutionary biology tell us about male-female differences in preferences concerning family matters? Might mothers be more solicitous toward offspring than fathers, for example? The economics literature has documented gender differences-children benefit more from money put in the hands of mothers rather than fathers, for example-and these differences are thought to be partly due to preferences. Yet for good reason family economics is mostly concerned with how prices and incomes affect behavior against a backdrop of exogenous preferences. Evolutionary biology complements this approach by treating preferences as the outcome of natural selection. We mine the well-developed biological literature to make a prima facie case for evolutionary roots of parental preferences. We consider the most rudimentary of traits-sex differences in gamete size and internal fertilization-and explain how they have been thought to generate male-female differences in altruism toward children and other preferences related to family behavior. The evolutionary approach to the family illuminates connections between issues typically thought distinct in family economics, such as parental care and marriage markets.

A comparative analysis of the evolution of imperfect mimicry

Although exceptional examples of adaptation are frequently celebrated, some outcomes of natural selection seem far from perfect. For example, many hoverflies (Diptera: Syrphidae) are harmless (Batesian) mimics of stinging Hymenoptera. However, although some hoverfly species are considered excellent mimics, other species bear only a superficial resemblance to their models and it is unclear why this is so. To evaluate hypotheses that have been put forward to explain interspecific variation in the mimetic fidelity of Palearctic Syrphidae we use a comparative approach. We show that the most plausible explanation is that predators impose less selection for mimetic fidelity on smaller hoverfly species because they are less profitable prey items. In particular, our findings, in combination with previous results, allow us to reject several key hypotheses for imperfect mimicry: first, human ratings of mimetic fidelity are positively correlated with both morphometric measures and avian rankings, indicating that variation in mimetic fidelity is not simply an illusion based on human perception; second, no species of syrphid maps out in multidimensional space as being intermediate in appearance between several different hymenopteran model species, as the multimodel hypothesis requires; and third, we find no evidence for a negative relationship between mimetic fidelity and abundance, which calls into question the kin-selection hypothesis. By contrast, a strong positive relationship between mimetic fidelity and body size supports the relaxed-selection hypothesis, suggesting that reduced predation pressure on less profitable prey species limits the selection for mimetic perfection.

Teaching About Adaptation: Why Evolutionary History Matters

Adaptation is one of the central concepts in evolutionary theory, which nonetheless has been given different definitions. Some scholars support a historical definition of adaptation, considering it as a trait that is the outcome of natural selection, whereas others support an ahistorical definition, considering it as a trait that contributes to the survival and reproduction of its possessors. Finally, adaptation has been defined as a process, as well. Consequently, two questions arise: the first is a philosophical one and focuses on what adaptation actually is; the second is a pedagogical one and focuses on what science teachers and educators should teach about it. In this article, the various definitions of adaptation are discussed and their uses in some textbooks are presented. It is suggested that, given elementary students’ intuitions about purpose and design in nature and secondary students’ teleological explanations for the origin of adaptations, any definition of adaptation as a trait should include some information about its evolutionary history.

Darwin's Saussure: Biosemiotics and Race in Expression

Charles Darwin's The Expression of the Emotions in Man and Animals (1872) theorizes expressions as biological signs based on the physiological signifier's arbitrary nature as an outcome of natural selection. Darwin's biosemiotic thinking in advance of Saussurian linguistics produces a correlated reading of race as a biologically incoherent sign. While Darwin's methodological modernism remains implicit in his writings, the Darwinian biosemiotics that emerges in Expression offers a promising means to bridge the natural and human sciences.

Random Boolean nets and features of language

Describes an attempt to cast several abstract properties of natural languages in the framework of Kauffman's (1993, 1995) random Boolean nets (RBN). The properties are complexity, interconnectedness, stability, diversity, and underdeterminedness. A language is modeled as a Boolean net attractor. (Groups of) net nodes are linguistic principles or parameters as posited by Chomskyan theory, according to which the language learner sets parameters to appropriate values on the basis of very limited experience of the language. The setting of one parameter can have a complex effect on the settings of others. A RBN is generated to find an attractor. A state from this attractor is degraded, which represents the degenerate input of language to the learner, and this state is then input to a net with the same connectivity and activation functions as the original net to see whether it converges on the same attractor. Many nets degenerate into attractors representing complete uncertainty. Others settle at intermediate levels of uncertainty, and some manage to overcome the incompleteness of input and converge on attractors identical to that from which the original inputs were (de)generated. Finally, an attempt was made to select a population of such successful nets, using a genetic algorithm where fitness was correlated with an ability to acquire several different languages faithfully. This has so far proved impossible, supporting the Chomskyan suggestion that the human language acquisition capacity is not the outcome of natural selection.

Nesting Success of Forest Birds in Southeast Alaska and Adjacent Canada

AbstractPredation caused 78% of nest failures in coastal forests of southeast Alaska and interior forests of adjacent Canada. Nest success tended to be better in coastal than interior forests. Mayfield daily nest survival from predation on open-cup nests was higher in egg than nestling phase for most species. Species building large (thrush-sized) nests had lower Mayfield daily survival from predation than species building smaller (warbler-sized) nests, but there was no difference in daily survival (total and from predation only) among species nesting in different vegetation strata. Nesting success differed little with nest cover or nest site diversity for most species. Total nest success within species was only sometimes higher in commonly used nest sites than in less frequently used sites. Nest survival from predation did not generally decrease with increasing nest density within guilds of species with similar nests or with nest-site similarity. We emphasize the likelihood of varied outcomes of natural selection on nest-site selection in differing circumstances.

Length of tail streamers in barn swallows

Both natural and sexual selection affect the expression of secondary sexual characters1, so any secondary sexual character will be affected by a mixture of selection pressures. Evans2 has compared the flight performance of male barn swallows (Hirundo rustica) whose tail lengths have been altered with that of controls, and concludes that the outermost tail feathers of these birds are mainly the outcome of natural selection.

On the relationship between evolutionary and psychological definitions of altruism and selfishness

I examine the relationship between evolutionary definitions of altruism that are based on fitness effects and psychological definitions that are based on the motives of the actor. I show that evolutionary altruism can be motivated by proximate mechanisms that are psychologically either altruistic or selfish. I also show that evolutionary definitions do rely upon motives as a metaphor in which the outcome of natural selection is compared to the decisions of a psychologically selfish (or altruistic) individual. Ignoring the precise nature of both psychological and evolutionary definitions has obscured many important issues, including the biological roots of psychological altruism.

Functional explanation in linguistics and the origins of language

In these remarks, I shall place scare quotes around the terms relating to ‘function’ (‘functional’, ‘functionalist’, etc.), because it is misleading to present this term as in some way opposed to ‘formal’ (etc.), and I do not accept Newmeyer’s lumping strategy in regard to those linguists whose central project is not the formal calculus of ‘an autonomous grammar’. Furthermore, when referring to Newmeyer’s sense of the word ‘grammar’, I shall likewise bracket it with quote marks and shall always supply the indefinite article ‘a’ and the adjective ‘autonomous’ (viz. ‘an autonomous grammar’). I do this because there is a constant danger of silently moving from his understanding of ‘grammar’ as an independent, discrete, mentally represented, innate entity to a more fuzzy conception of grammar as a mass noun, a cover term for a wide and heterogeneous spectrum of regularities in speech as noticed by a linguist. By slipping back and forth between these two radically different conceptions (‘a grammar’ versus ‘grammar’), Newmeyer is sometimes able to make it seem as if there is or should be agreement where there is none and cannot be any. Much of Newmcyer’s position paper is devoted to the speculative hypothesis that ‘an autonomous grammar’ is an outcome of natural selection. Since any number of evolutionary scenarios might be constructed for language with equal validity, each compatible with a radically different set of assumptions about evolution, language, innateness, etc. it is highly unlikely that sufficient agreement about the meaning and use of terms could be reached to even debate this proposition. For example, in his assertion: ‘ . . . studies of ape intclligcnce suggest that prchominids possessed a surprisingly sophisticated level of mental representation’, one is hard put to find a single content-word that is not open to dispute. With such fundamental disagreement over vocabulary, I cannot see that the controversy over ‘an autonomous grammar’ is illuminated in any way by conjecture of this kind. Newmeyer’s version of natural selection offers nothing over Chomsky’s version of creationism. What is most disturbing to me is Newmeyer’s unwillingness to understand that in the eyes of the diverse linguists whom he lumps together as ‘functionalists’ or ‘functional grammarians’ many or all of the tacit assumptions he works with are suspect. In fact, Newmeyer’s view of ‘functionalism’ would render it distinct only in directionality from standard autonomous grammar: in this view, the forms of a language would be isomorphic to functions, and it would not matter much whether you described the functions first and then matched forms to them, or proceeded by developing a calculus of a grammar first and then (if you felt like it) showing how the previously arrived at forms were used in real-life situations. No paradigmatic gulf would separate formalists from ‘functionalists’, only disagreement as to the degree to which statements about functional correlates of

Species of thought: A comment on evolutionary epistemology

The primary outcome of natural selection is adaptation to an environment. The primary concern of epistemology is the acquistion of knowledge. Evolutionary epistemology must therefore draw a fundamental connection between adaptation and knowledge. Existing frameworks in evolutionary epistemology do this in two ways; (a) by treating adaptation as a form of knowledge, and (b) by treating the ability to acquire knowledge as a biologically evolved adaptation. I criticize both frameworks for failing to appreciate that mental representations can motivate behaviors that are adaptive in the real world without themselves directly corresponding to the real world. I suggest a third framework in which mental representations are to reality as species are to ecosystems. This is a many-to-one relationship that predicts a diversity of adaptive representations in the minds of interacting people. As “species of thought”, mental representations share a number of properties with biological species, including isolating mechanisms that prevent them from blending with other representations. Species of thought also are amenable to the empirical methods that evolutionists use to study adaptation in biological species. Empirical studies of mental representations in everyday life might even be necessary for science to succeed as a normative “truth-seeking” discipline.