While classical strain selection and evolutionary adaptations have been performed for a long time, it is the emergence of next generation sequencing technologies that are providing an unprecedented resolution of strain/mutant characterization and have stimulated a substantial increase in experimental evolution studies over the last decade. To illustrate the impact of the …
By evolutionary adaptation to the temporal program of day and night, eucariothic organisms have developed endogenous periodic processes whose natural frequency approximates that of the earth's rotation and which persist in the absence of any periodic input to the organism.
Adaptation. An adaptation is a feature that arose and was favored by natural selection for its current function. Adaptations help an organism survive and/or reproduce in its current environment. Adaptations can take many forms: a behavior that allows better evasion of predators, a protein that functions better at body temperature, or an ...
For a trait to undergo positive selection, it must have two characteristics. First, the trait must be beneficial; in other words, it must increase the organism 's probability of surviving and ...
An understanding of evolution has been essential in finding and using natural resources, such as fossil fuels, and it will be indispensable as human societies strive to establish sustainable relationships with the natural environment. Such examples can be multiplied many times.
Importance of Adaptation Adaptation is essential for the survival of living organisms. Animals, which are unable to adapt to changing environmental changes die. These adaptations are a result of genetic changes. The animals that survive pass on the mutated genes to their offsprings.
In scientific terms, these hazards are referred to as selection pressures. They put pressure on us to adapt in order to survive the environment we are in and reproduce. It is selection pressure that drives natural selection ('survival of the fittest') and it is how we evolved into the species we are today.
All organisms need to adapt to their habitat to be able to survive. This means adapting to be able to survive the climatic conditions of the ecosystem, predators, and other species that compete for the same food and space.
Adaptations are inheritable characteristics that increase an organism's ability to survive and reproduce in an environment. Adaptations can help an organism find food and water, protect itself, or manage in extreme environments.
Natural selection is still happening in humans As much as we have made things easier for ourselves, there are still selection pressures around us, which mean that natural selection is still happening. Like all mammals, humans lose the ability to digest milk when they stop breastfeeding.
If something caused low-lying shrubs to die out, the giraffes with shorter necks would not get enough food. They would not survive to produce offspring. After a few generations, the surviving giraffes would have longer necks, because that body type is more suited to survive in the environment.
Individuals with adaptive traits—traits that give them some advantage—are more likely to survive and reproduce. These individuals then pass the adaptive traits on to their offspring. Over time, these advantageous traits become more common in the population.
Environmental adaptations include the ability to deal with an enormous range of pressures (from about one to hundreds of atmospheres), temperatures (from −1.8°C in polar waters to about 40°C in hot springs, tolerated by some tilapias), and salinities (from close to distilled water preferred by the discus fish, Symphysodon discus, of Amazonia to about 10%, e.g., in West African hypersaline coastal lagoons inhabited by the blackchin tilapia, Sarotherodon melanotheron), to list only three environmental factors.
By evolutionary adaptation to the temporal program of day and night, eucariothic organisms have developed endogenous periodic processes whose natural frequency approximates that of the earth's rotation and which persist in the absence of any periodic input to the organism. Since the period of the rhythm slightly deviates from 24 h under artificially constant conditions, the prefix circa has been introduced by Halberg (1959). Circadian rhythms, then, are characterized a) by their capability to freerun in constant conditions like self-sustaining oscillations, and b) by the way in which they are synchronized (entrained) by periodic factors in the environment, the Zeitgebers. The two examples provided in Fig. 1 show rhythms in oxygen uptake of two chaffinches, kept initially in light-dark cycles of 12 h light and 12 h darkness (LD 12:12) and thereafter in conditions of constant dim illumination (LL). As dayactive animals, the birds have a high level of oxygen uptake during L, and a low one during D. In LL, the rhythm persists undamped with a period, τ, which is longer than 24 h in the upper record, and shorter than 24 h in the lower record. This difference indicates that there can be a substantial interindividual variability in τ. In addition, τ is known to depend on the physiological state of the organism e.g. with regard to its reproductive functions, as well as on external factors such as intensity of illumination or ambient temperature. The effects of external factors show systematic differences between dayactive and nightactive species. (For a review, cf. Aschoff 1979a ).
When entrained by a Zeitgeber, the circadian rhythm maintains a distinct phase-relationship with the entraining signals. This phase-angle difference ψ might be measured between an arbitrary phase of the rhythm, e.g. a minimal value, and the time of ‘light-on’ of a LD-cycle. If in case of the records reproduced in Fig. 1 one takes as phase reference the point where oxygen starts to increase from its low d -level, it becomes evident that ψ has a small positive value (i.e. a leading phase) in the upper record, and a large positive value in the lower record. This difference in ψ is correlated with the difference in the τ-values (24.8 h in the upper record, 23.1 h in the lower record) and reflects the general rule that ψ depends on the ratio between the τ of a rhythm (as measured in constant conditions) and the period T of the entraining Zeitgeber. In consequence of this rule, ψ also changes when a rhythm becomes entrained by Zeitgebers with periods other than 24 h (cf. Fig. 3 ). (For a discussion of these rules, cf. Aschoff 1965a, 1981a ).
Biotechnology also offers an economically efficacious and environmentally durable and sustainable approach to control of insects and other plant pests (see Chapter 23 ). The prime example is insect-resistant crops that are obtained by gain-of-function expression of the bacterial Bt endotoxin gene in transgenic plants of cotton and maize. The Bt endotoxin inhibits insect digestion, which impairs survival and fecundity.
In addition, high salinity negatively influences water available for agriculture. Predicted global population increases and climate changes are major factors exacerbating the water use versus replenishment imbalance. Combining and synergizing classical and high-throughput (omics) technologies is an efficient and effective way to develop water and salt stress tolerant crops (see Chapter 18 ). After studying genes involved in water and salt stress tolerance for more than 10 years, it is now feasible to introgress better stress tolerance alleles from genetically distant relatives. Systems approaches will facilitate pyramiding loci and alleles for multiple traits that must be linked in combination with stress tolerance to maintain yield stability of stress-tolerant germplasm.
Plant adaptation to environmental stresses, both abiotic (e.g., drought, salinity, and temperature extremes) and biotic (e.g., bacterial, fungal, and viral diseases, and insect and other pests), is controlled by cascades of genes and molecular networks . These activate numerous stress responsive mechanisms necessary to re-establish homeostasis and to protect and repair damaged proteins and membranes. Plant engineering strategies for environmental stress tolerance rely on the expression of genes that are involved in signaling and regulatory pathways or genes that encode proteins conferring stress tolerance or enzymes present in pathways leading to the synthesis of functional and structural metabolites (see Chapters 2 and 18Chapter 2Chapter 18 ). Present efforts to improve plant stress tolerance by genetic transformation resulted in several important achievements; however, the genetically complex mechanisms involved in abiotic stress tolerance have made it difficult to achieve substantive effects in crops without side effects on yield. For this reason, biotechnology should be fully integrated with classical physiology and breeding.
In most species the fertile period starts about 10 days before the first egg is fertilized and ends when the final egg of the clutch is fertilized ( Birkhead and Møller 1992b ). Although data on the duration of sperm storage and hence the onset of the fertile period are lacking for most wild birds, field observations show that mate guarding occurs mainly in the middle portion of the female's fertile period, starting about 5 days or less before the first egg is laid and usually terminating before the last ovum is fertilized ( Birkhead 1982; Møller 1987a ). The fact that mate guarding does not cover the entire time females are fertile suggests that it is costly for males and that they concentrate their efforts during the time when the risks of extra-pair fertilization are greatest.
An adaptation is a feature that arose and was favored by natural selection for its current function. Adaptations help an organism survive and/or reproduce in its current environment.
Teach your students about adaptations with Form and function, a classroom activity for grades K-2.
Echolocation in bats is an adaptation for catching insects.
Positive natural selection, or the tendency of beneficial traits to increase in prevalence ( frequency) in a population, is the driving force behind adaptive evolution. For a trait to undergo positive selection, it must have two characteristics. First, the trait must be beneficial; in other words, it must increase the organism 's probability of surviving and reproducing. Second, the trait must be heritable so that it can be passed to an organism's offspring. Beneficial traits are extremely varied and may include anything from protective coloration, to the ability to utilize a new food source, to a change in size or shape that might be useful in a particular environment. If a trait results in more offspring who share the trait, then that trait is more likely to become common in the population than a trait that arises randomly. At the molecular level, selection occurs when a particular DNA variant becomes more common because of its effect on the organisms that carry it.
Under natural selection, a new beneficial mutation will rise in frequency (prevalence) in a population . A schematic shows polymorphisms along a chromosome, including the selected allele, before and after selection. Ancestral alleles are shown in grey and derived (non-ancestral) alleles are shown in blue. As a new positively-selected allele (red) rises to high frequency, nearby linked alleles on the chromosome ‘hitchhike’ along with it to high frequency, creating a ‘selective sweep.’
The domestication of plants and animals roughly 10,000 years ago profoundly changed human diets, and it gave those individuals who could best digest the new foods a selective advantage. The best understood of these adaptations is lactose tolerance (Sabeti et al., 2006; Bersaglieri et al., 2004). The ability to digest lactose, a sugar found in milk, usually disappears before adulthood in mammals, and the same is true in most human populations. However, for some people, including a large fraction of individuals of European descent, the ability to break down lactose persists because of a mutation in the lactase gene ( LCT ). This suggests that the allele became common in Europe because of increased nutrition from cow's milk, which became available after the domestication of cattle. This hypothesis was eventually confirmed by Todd Bersaglieri and his colleagues, who demonstrated that the lactase persistence allele is common in Europeans (nearly 80% of people of European descent carry this allele), and it has evidence of a selective sweep spanning roughly 1 million base pairs (1 megabase). Indeed, lactose tolerance is one of the strongest signals of selection seen anywhere in the genome. Sarah Tishkoff and colleagues subsequently found a distinct LCT mutation also conferring lactose tolerance, in this case in African pastoralist populations, suggesting the action of convergent evolution (Tishkoff et al ., 2007).
As advantageous alleles that are under positive selection increase in prevalence, these alleles leave distinctive signatures, or patterns of genetic variation, in the DNA sequence. Consider a population of individuals for which, before selection, there are hundreds of thousands of varied chromosomes in the population, all with different combinations of genetic variants. Now, say that an advantageous allele arises as a mutation on one copy of a chromosome. Through succeeding generations, the descendants of this copy, including the selected allele and nearby " hitchhiking " alleles, become more and more common through a process called a " selective sweep " (Figure 1). Note that the entire chromosome is not passed down as a unit, however; rather, because of recombination, segments of the chromosome are inherited. Thus, while the selected allele and hitchhiking alleles increase in prevalence in a selective sweep, at the same time, the segment that includes the selected allele is slowly reduced in size by recombination. Investigators are interested in the types of signals that can be detected in a selective sweep, as well as their properties and technical challenges (Nielsen, 2005; Sabeti et al., 2006).
The development of agriculture also changed the selective pressures on humans in another way: Increased population density made the transmission of infectious diseases easier, and it probably expanded the already substantial role of pathogens as agents of natural selection. That role is reflected in the traces left by selection in human genetic diversity; multiple loci associated with disease resistance have been identified as probable sites of selection. In most cases, the resistance is to the same disease—malaria (Kwiatkowski, 2005).
Three significant forces that have been identified thus far include changes in diet, changes in climate, and infectious disease.
With these new data, it is now possible to scan the entire human genome in search of signals of natural selection.
An adaptation is a feature produced by natural selection for its current function. Based on this definition we can make specific predictions (“If X is an adaptation for a particular function, then we’d predict that…”) and see if our predictions match our observations. As an example, we’ll consider the hypothesis: feathers are an adaptation for bird flight. Is the evidence consistent with this hypothesis? There are several relevant lines of evidence that must be examined:
Feathers meet three of the necessary requirements to be considered an adaptation for flight, but fail one of them. So the basic form of feathers is probably not an adaptation for flight even though it certainly serves that function now.
If a trait has been shaped by natural selection, it must be genetically encoded — since natural selection cannot act on traits that don’t get passed on to offspring. Are feathers heritable? Yes. Baby birds grow up to have feathers like those of their parents.
Did the trait arise when the current function arose? Did feathers arise when flying arose? The answer to this is probably no . The closest fossil relatives of birds, two-legged dinosaurs called theropods, appear to have sported feathers but could not fly.
If a trait has been shaped by natural selection, it must increase the fitness of the organisms t hat have it — since natural selection only increases the frequency of traits that increase fitness. Are birds more fit with feathers than without? Yes. Birds without feathers aren’t going to leave as many offspring as those with feathers.
To find the adaptation signal, Petrov and his colleagues looked for regions of the genome that "hitchhiked" along with an adaptation. When a genetic adaptation occurs and is passed on to offspring, other genes on both sides of the adaptation typically accompany it.
The result is a whole region of the genome where all humans are unusually similar to each other, referred to as a "selective sweep," that researchers can identify and trace through human genetic history. "Adaptation becomes widespread in the population very quickly," Petrov said.
Petrov hopes that researchers can now do a much better job of finding the regions within the genome responsible for specific human adaptations and relate them to changes in human history or past environments. For example, one could trace the arrival of lactose tolerance to the domestication of cattle and the introduction of milk into our adult diet.
This paper follows similar work in bacteria and fruit flies indicating adaptation is a significant contribution to evolution as a whole.
All genetic mutations start out random, but those that are beneficial to an organism's success in their environment are directly selected for and quickly perpetuate throughout the population, providing a uniform, traceable signature.
Adaptation is key in human evolution. By Cassandra Brooks. For years researchers have puzzled over whether adaptation plays a major role in human evolution or whether most changes are due to neutral, random selection of genes and traits. Geneticists at Stanford now have laid this question to rest.
The theory of evolution explains how primitive life forms have changed and adapted over millions of years to become the complex living organisms living on Earth today.
When are children taught about evolution and adaptation in primary school? 1 Learn that fossils provide information about the past 2 Explore how animals and plants are adapted to suit their natural environment 3 Understand that parents pass on characteristics to their offspring
Over time, animals and plants change and evolve because offspring have slightly different characteristics to their parents. Living things born with adaptations that make their lives easier in specific habitats are more likely to survive; the process of advantageous adaptations being passed on to future generations is known as natural selection.
Evolution is the process of change to animal and plant species over long periods of time, or how plant species and animals have developed from generation to generation.
As part of their study of evolution children may learn about famous scientists who explored evolutionary concepts and ideas (Charles Darwin, Thomas Huxley, Alfred Russel Wallace and Mary Anning ).
Living creatures (animals and plants) adapt or evolve to survive in their environment and to live amongst a specific group of other living things.
It is the relative fitness of a genotype that almost always matters in evolutionary genetics. The reason is simple. Natural selection is a differential process: there are winners and losers. It is, therefore, the difference in fitness that typically matters.
In the crudest terms, fitness involves the ability of organisms— or, more rarely, populations or species— to survive and reproduce in the environment in which they find themselves 6–9. The consequence of this survival and reproduction is that organisms contribute genes to the next generation. To get any further, we need to analyze these ideas into sharper ones. Fitness is commonly analyzed in two ways. One involves the actual “components” that give rise to differences in fitness among organisms and the other involves mathematical measures of fitness.
If only two genotypes segregate in a haploid population, mean absolute fitness is W̄= pW1+ qW2, where pis the frequency of genotype 1, qis the frequency of genotype 2 (p+ q= 1), and W1and W2are , respectively, the absolute fitnesses of genotypes 1 and 2. It is easy to show mathematically that mean absolute fitness equals mean individual fitness. This is also easy to see intuitively. The mean absolute viability is the chance that an individual having a randomly chosen genotype survives; but this must be the same as the probability that a randomly chosen individual survives, regardless of information on genotype. We can also calculate the variance in absolute fitness. This quantity is less than or equal to the variance in individual fitness. The reason is that the variance in absolute fitness takes into account only variation in fitness due to differences in genotype, whereas the variance in individual fitness takes into account variation in fitness due to genotype and to chance differences in the environment.
Absolute fitness is a statistic that is usually assigned to a genotype and it typically refers to a genotype’s expected total fitness, that complex mix of viability, mating success, fecundity, etc. As such, absolute fitness, symbolized W, is a quantity that can be greater than or equal to zero11. But if we continue to restrict attention to viability selection with all else equal, individuals of a given genotype have some probability of surviving. We can think of this probability as the absolute viability of the genotype.
If they do, adults attempt to court and mate. If all goes well, these adults produce some number of offspring and the cycle begins anew. Differences in fitness among individuals can arise from differences in “performance” at any of these stages . Each of these “fitness components”— in this case, viability, mating success, fecundity— can contribute to differences in total fitness among individuals, i.e., can cause different individuals to leave different numbers of progeny.
Evolutionary biologists have introduced various measures of fitness for good reason: fitness does work for us. In particular, only by defining fitness mathematically can we construct selection equations, equations that allow us to predict how rapidly allele frequencies will change under natural selection. To see this, consider again a haploid species with two alleles, A1and A2. If W1> W2, A1will become relatively more common through time and A2will become relatively less common. To say anything further, however, requires mathematics. Fortunately the necessary mathematics is straightforward.
We conclude, therefore, that change in allele frequency by natural selection depend s only on the difference in relative fitness between two alleles (and starting allele frequency). The absolute magnitudes of W1and W2are irrelevant. If we iterate Eq. 1over many generations, the difference in fitness lets us predict how A1will increase from an initial low frequency to higher frequencies. As Figure 1shows, the path of allele frequency through time is sigmoidal.