Evolution and speciation Flashcards
Define evolution.
Changes in the heritable characteristics of organisms over generations.
What are heritable characteristics?
Characteristics that can be inherited by, or passed on to, the next generation.
Do changes in non-heritable characteristics lead to evolution?
No, changes in characteristics that are not inherited, e.g., a plant having its leaves eaten, do not lead to evolution.
What determines heritable characteristics?
Heritable characteristics are determined by the alleles of genes that are present in an individual.
How can alleles change?
Alleles may change as a result of random mutation, causing them to become more or less advantageous.
Explain the process of natural selection.
Heritable characteristics that are advantageous are more likely to be passed on to offspring, leading to a gradual change in a species over time.
What can changes in heritable characteristics lead to?
Changes in the heritable characteristics of organisms can lead to the development of completely new species.
How has evolution contributed to species diversity on Earth?
The formation of new species via the process of evolution has resulted in a great diversity of species on Earth.
Describe the theoretical process of species diversification from the origin of life on Earth.
Theoretically, at the origin of life on Earth, there would have been just one single species. This species evolved into separate new species. These species would then have divided again, each forming new species once again. Over millions of years, evolution has led to countless numbers of these speciation events, resulting in the millions of species now present on Earth.
How does the definition of evolution as “changes in heritable characteristics” distinguish Darwinian evolution from Lamarckism, and why is evolution by natural selection considered a theory?
This definition distinguishes Darwinian evolution from Lamarckism because it emphasizes that only heritable (genetic) changes contribute to evolution, while acquired changes that are not genetic in origin are not regarded as evolution. This aligns with Darwin’s theory but contradicts Lamarck’s idea of inherited acquired characteristics.
The theory of evolution by natural selection is considered a pragmatic truth and referred to as a theory, despite substantial supporting evidence, because the nature of science makes it impossible to formally prove it true by correspondence. It predicts and explains a broad range of observations but, like all scientific theories, remains open to potential falsification.
What is Darwinian evolution?
A theory proposed by Charles Darwin based on natural selection, stating that individuals in a species show variation due to random DNA mutations, compete for survival, and those with advantageous characteristics are more likely to survive and reproduce, passing these traits to offspring. Over generations, advantageous alleles become more frequent in a population.
List the key points of Darwin’s theory of evolution by natural selection.
- Individuals in a species show a wide range of variation due to random mutations in their DNA
- Individuals within a population must compete for survival due to selection pressures
- Individuals with characteristics most suited to the environment have a higher chance of survival and reproduction
- Advantageous alleles are passed down to offspring
- Over many generations, the advantageous alleles become more frequent in a population
What is a crucial requirement for Darwinian evolution by natural selection?
Darwinian evolution by natural selection requires that characteristics are heritable.
Who proposed the theory of Lamarckian evolution and when?
French scientist Jean-Baptiste Lamarck developed the theory at the start of the 19th century, before Darwin announced his theory.
What is the main idea behind Lamarck’s theory of evolution?
Lamarck’s theory was based mainly on the idea that changes that occur in an organism during its lifetime can be inherited. Such changes are known as acquired characteristics.
Explain Lamarck’s theory of evolution.
Lamarck’s theory states that:
- A characteristic that is used frequently by an organism becomes better and stronger, whereas a characteristic that isn’t used gradually disappears
- The beneficial characteristics that are used frequently are passed to offspring
Provide an example of Lamarck’s theory of evolution.
Lamarck suggested that giraffes had a short-necked ancestor that would frequently stretch its neck to reach high branches for feeding. This repeated stretching could very slowly elongate the giraffe’s neck, and this elongated neck would be passed to the giraffe’s offspring. Over time and many generations, the giraffe would evolve to have the very long neck it has today.
Why is Lamarck’s theory of evolution considered incorrect?
Lamarck’s ideas were incorrect because they lack the component of heritability; acquired characteristics are not passed on to offspring.
What is the relationship between epigenetics and Lamarckian evolution?
The new science of epigenetics may provide an exception to the rule that acquired characteristics are not inherited. However, changes like these are unlikely to be major drivers of natural selection.
How does the definition of evolution as “change in the heritable characteristics of a population” distinguish Darwinian evolution from Lamarckism?
This definition helps to distinguish Darwinian evolution from Lamarckism because it emphasizes that only heritable (genetic) changes contribute to evolution. Acquired changes that are not genetic in origin are not regarded as evolution, which aligns with Darwin’s theory but contradicts Lamarck’s idea of inherited acquired characteristics.
Why is the theory of evolution by natural selection considered a “pragmatic truth” and referred to as a theory despite substantial evidence?
The theory of evolution by natural selection predicts and explains a broad range of observations and is unlikely ever to be falsified. However, the nature of science makes it impossible to formally prove that it is true by correspondence. It is therefore referred to as a theory, despite all the supporting evidence, because it remains open to potential falsification, as do all scientific theories.
How do scientists gather information about the world?
Scientists gather information about the world by observing events.
What do scientists do with the information gathered from observations?
They formulate theories that seek to explain observed events.
Why is the theory of natural selection widely accepted?
The theory of natural selection explains many observations, and no other reasonable theories have ever been proposed to explain species change over time.
What is a falsified aspect of Darwin’s original theory regarding the speed of evolution?
The idea that “Evolution by natural selection is always slow” has been falsified. We now know that, for example, antibiotic resistance can evolve in bacteria very quickly.
What is a falsified aspect of Darwin’s original theory regarding fossil evidence?
The idea that “The fossil record cannot provide evidence for evolution” has been falsified. There are multiple examples of fossils that appear to show intermediate species.
How have errors in Darwin’s original theory been addressed?
These errors have resulted in updates to Darwin’s theory, but not to its falsification.
Why is it not possible to formally prove that natural selection has given rise to the species we see today?
Due to the geological time periods over which evolutionary change has occurred, it is not possible to formally prove that natural selection has given rise to the species that we see today.
Why is the term ‘theory’ still used for evolution by natural selection?
The term ‘theory’ is still used because it is not possible to formally prove that natural selection has given rise to the species we see today, despite the strong evidence supporting it.
What is the significance of the theory of evolution by natural selection in terms of predictions and explanations?
The theory of evolution by natural selection predicts and explains a broad range of observations and is unlikely to ever be falsified.
What three types of sequence data provide evidence for evolution?
- DNA base sequences (nuclear, mitochondrial, chloroplast)
- RNA base sequences (from transcribed genes)
- Amino acid sequences in proteins
Why do similarities in sequence data between species suggest common ancestry?
Similarities in DNA, RNA, or protein sequences indicate shared genetic heritage, implying species evolved from a common ancestor.
Why compare data from multiple genes/sources?
Increases certainty about evolutionary relationships by reducing chance of coincidental similarities.
What are conserved sequences, and why are they used for comparisons in evolutionary studies?
Conserved sequences are sections of DNA or protein that have remained largely unchanged across species over evolutionary time. They are crucial for evolutionary studies because:
1) They help in constructing phylogenetic trees, showing relationships between species
2) They often indicate functionally important regions, as sequences vital for survival tend to resist change
3) They allow scientists to trace evolutionary history and relationships between diverse organisms
4) They aid in identifying essential genes and their functions.
By comparing these sequences, researchers can better understand the molecular basis of life and evolution across different species.
Describe the process of comparing DNA sequences to determine evolutionary relationships.
To determine evolutionary relationships, DNA is first extracted from cells or fossils. The extracted DNA is then processed and analyzed to obtain its base sequence. These sequences are compared between different organisms. The more similarities found in the DNA base sequences, the more closely related the members of different species are considered to be.
What key discovery was made when comparing human and chimpanzee genomes?
In 2005, when the chimpanzee genome was sequenced and compared to the human genome, it was discovered that humans and chimpanzees share almost 99% of their DNA sequences. This finding established chimpanzees as our closest living relatives.
How do amino acid sequences in proteins provide evolutionary evidence?
Amino acid sequences in proteins provide evolutionary evidence because proteins with similar amino acid sequences likely share a common ancestral gene. The fewer differences there are between the amino acid sequences of proteins in different species, the more recent their evolutionary divergence is likely to be.
What is an evolutionary tree, and how is sequence data used to build one?
An evolutionary tree is a diagram showing inferred evolutionary relationships between species. Sequence data is used to determine the branching patterns of these trees. Species with more matching sequences in their DNA, RNA, or proteins are placed closer together on the tree, indicating a more recent common ancestor.
Why might mitochondrial DNA be particularly useful for evolutionary studies?
- Unique inheritance: mtDNA is inherited only from the mother, making it easier to trace lineages without the complications of genetic recombination.
- Rapid mutation rate: mtDNA mutates about 10 times faster than nuclear DNA, allowing scientists to detect evolutionary changes over shorter time periods.
- Conserved structure: Despite its high mutation rate, mtDNA is well-conserved across species due to its critical role in cellular respiration.
- Easy to analyze: The small size and high copy number of mtDNA in cells make it easier to extract and study, even from ancient samples.
What is selective breeding?
Selective breeding is a process in which humans choose organisms with desirable characteristics and breed them together repeatedly to increase the expression of these characteristics over many generations.
How does selective breeding take advantage of naturally occurring variation?
Selective breeding utilizes natural variation between individuals. For example, some plants may have higher food yield or disease resistance, while some domestic animals may have thicker wool or higher milk production. Humans select these individuals with desirable traits for breeding.
What is another term for selective breeding, and how does it relate to natural selection?
Selective breeding is also known as artificial selection. It makes use of the principles of natural selection but is carried out by humans. In natural selection, advantageous alleles are more likely to be passed on because they increase an organism’s chances of survival. In artificial selection, desirable alleles are more likely to be passed on because humans decide which individuals will be used for breeding.
How does selective breeding provide evidence for evolution?
Selective breeding involves changes to heritable characteristics over many generations, making it an example of evolution in action. It provides evidence that evolution occurs due to the accumulation of small changes to the DNA of organisms over time.
How does the rate of change in selective breeding compare to natural selection?
Selective breeding leads to faster change than natural selection. This is because only the selected individuals are allowed to breed together, while in natural selection there will still be some breeding between individuals with less favorable alleles.
Describe the process of selective breeding in five steps.
- The population shows variation; there are individuals with different characteristics.
- Breeders select individuals with the desired characteristics.
- Two selected individuals are bred together.
- The offspring produced reach maturity and are then tested for the desirable characteristics; those that display the desired characteristics to the greatest extent are selected for further breeding.
- The process is repeated over many generations; the best individuals from the offspring are continually chosen for breeding until all offspring display the desirable characteristics.
How does variation between domesticated breeds and wild species provide evidence for evolution?
Variation between different domesticated animal breeds and varieties of crop plants, and between them and the original wild species, shows how rapidly evolutionary changes can occur. This demonstrates that significant changes can accumulate over relatively short periods through selective breeding, providing evidence for the process of evolution.
How does selective breeding of crop plants provide evidence for evolution?
Selective breeding of crop plants has resulted in varieties that differ significantly from their wild ancestors. These differences, achieved over relatively short time periods, demonstrate how quickly evolutionary changes can occur when selection pressure is strong. This provides evidence for the process of evolution and the plasticity of species.
Give examples of how selective breeding has changed domesticated animals and crop plants from their wild ancestors.
Selective breeding has led to significant changes in both animals and plants. For example:
- Dogs have been bred into numerous breeds with vastly different sizes, shapes, and behaviors.
- Corn (maize) has been bred from a wild grass (teosinte) into a high-yield crop with large, edible kernels.
- Cattle have been bred for increased milk or meat production.
- Wheat has been bred for higher yield, disease resistance, and specific baking qualities.
These examples show how human-directed selection can lead to rapid evolutionary changes, providing evidence for the mechanisms of evolution.
What are homologous structures?
Homologous structures are body parts that may look and function very differently but share structural similarities due to shared ancestry. Examples include the limbs of birds, bats, crocodiles, whales, horses, and monkeys, which are used differently but share similar bone arrangements.
What explains the existence of homologous structures across species?
Adaptive radiation explains homologous structures. Organisms with homologous structures evolved from a shared common ancestor but adapted to different environments, resulting in structural similarities despite functional differences.
What is a pentadactyl limb, and why is it significant?
A pentadactyl limb is any limb with five digits (fingers or toes). It is significant because it appears in mammals, birds, amphibians, and reptiles, with similar bone structures enabling diverse locomotion (e.g., human walking, whale swimming, bird flying), supporting common ancestry.
Provide examples of how the pentadactyl limb is adapted for different functions.
- Human foot: Evolved for upright walking and running.
- Whale flipper: Enables propulsion in water.
- Bird wing: Adapted for flight.
- Frog limb: Allows walking, jumping, and swimming.
Despite functional differences, the bone layout remains nearly identical.
Does adaptive radiation prove common ancestry?
No. Adaptive radiation does not prove common ancestry but provides a strong explanation for the existence of homologous structures across species with shared ancestry.
How do homologous structures support evolutionary theory?
Homologous structures (e.g., pentadactyl limbs) suggest species diverged from a common ancestor. Structural similarities in limbs across vertebrates, despite varied functions, imply inheritance of traits modified by natural selection over time.
What genetic evidence supports homology in limb structure?
Studies of Hoxa11 and Hoxa13 genes show their regulation is critical for pentadactyl limb development. Mutations in these genes in ancestral tetrapods likely drove the transition from polydactyl (many digits) to pentadactyl limbs, conserved in modern species.
Why are bird wings and bat wings not homologous?
Bird wings (modified forelimbs with feathers) and bat wings (membranous skin stretched over elongated finger bones) evolved independently for flight. They are analogous (similar function) but not homologous (different structures).
How does the pentadactyl limb refute Lamarckian evolution?
Lamarckism predicts acquired traits (e.g., stretched giraffe necks) are inherited. The pentadactyl limb’s conserved structure across species, despite no “use,” aligns with Darwinian evolution (heritable genetic changes), not Lamarck’s acquired characteristics.
What broader evolutionary conclusion do homologous structures support?
Homologous structures (e.g., pentadactyl limbs, vertebrate spines) imply all life shares a common ancestor. The more similar the structures, the more closely related the species (e.g., humans share 99% DNA with chimpanzees).
What do the pentadactyl limbs of humans, whales, birds, frogs and alligators all have in common?
The pentadactyl limbs of humans, whales, birds, frogs, and alligators all have the same basic layout despite having evolved for different functions.
What are analogous structures?
Analogous structures are characteristics with similar form and function but different evolutionary origins.
How do analogous structures differ from homologous structures?
Homologous structures share evolutionary origins but may differ in function, while analogous structures share function but have different evolutionary origins.
What process leads to the development of analogous structures?
Analogous structures arise through convergent evolution, where distantly related species evolve similar traits due to similar environmental pressures.
Why do analogous structures provide evidence for natural selection?
Analogous structures demonstrate that advantageous characteristics (e.g., streamlined bodies in aquatic animals) are selected independently in unrelated species facing similar selection pressures.
Explain the example of convergent evolution in dolphins and sharks.
Dolphins (mammals) and sharks (fish) evolved streamlined body shapes independently. Despite similar aquatic adaptations, they belong to different classes and lack a recent common ancestor.
Describe the convergent evolution example of cacti and euphorbia.
Cacti (Americas) and euphorbias (Africa) are desert plants with spiny leaves and succulent stems. They belong to different plant orders but evolved similar traits due to arid environments.
What is another example of analogous structures mentioned in the text?
Wings in butterflies (insects) and bats (mammals). Both enable flight but evolved independently from different ancestral structures.
How do analogous structures affect taxonomy?
Analogous structures historically confused taxonomy because superficial similarities can mask distant evolutionary relationships.
What environmental factor drives convergent evolution?
Similar selection pressures in habitats (e.g., aquatic life, desert survival) lead unrelated species to evolve analogous traits.
Why don’t analogous structures imply shared ancestry?
Analogous structures evolve separately in unrelated lineages adapting to similar challenges, unlike homologous structures inherited from a common ancestor.
Define speciation.
Speciation is the development of new species from pre-existing species over time. It is the only way in which new species have appeared on Earth.
How does speciation affect biodiversity?
Speciation increases the total number of species on Earth, contributing to the great diversity of species we see today.
Describe the theoretical process of species diversification from the origin of life on Earth.
Theoretically, at the origin of life on Earth, there would have been just one single species. This species evolved into separate new species. These species would then have divided again, each forming new species once again. Over millions of years, evolution has led to countless numbers of these speciation events, resulting in the millions of species now present on Earth.
What conditions can lead to speciation?
Speciation can occur when the exchange of genes, or gene flow, between populations of a species is prevented, e.g., due to them being separated on different islands. When gene flow stops, genetic differences can accumulate between the two populations, especially if different selection pressures are acting on them.
When has a speciation split occurred?
A speciation split has occurred when two populations can no longer interbreed to produce fertile offspring; at this point, the two populations are said to be reproductively isolated from each other.
Is gradual evolutionary change alone sufficient for speciation to occur?
No, gradual evolutionary change alone is not enough for speciation. There must be reproductive isolation between populations for speciation to have occurred.
How does extinction affect biodiversity?
Extinction reduces the number of species on Earth, decreasing biodiversity. Many species that have evolved over evolutionary time no longer exist today due to extinction.
Give examples of extinct species mentioned in the text.
The passenger pigeon and the woolly mammoth are examples of species that have gone extinct.
Why is it important to understand that speciation is the only way new species appear?
Understanding that speciation is the only way new species appear emphasizes the importance of evolutionary processes in creating biodiversity. It also highlights that all species are related through common ancestry.
How does the concept of speciation differ from gradual evolutionary change within a species?
Speciation results in the formation of new, reproductively isolated species, while gradual evolutionary change within a species does not lead to reproductive isolation or the formation of new species. Speciation increases the number of species, while gradual change only modifies existing species.
What is reproductive isolation, and how does it contribute to speciation?
Reproductive isolation occurs when genetic or phenotypic changes prevent individuals within a species from successfully interbreeding. This leads to speciation by creating distinct populations that can no longer produce fertile offspring together.
Name two mechanisms of reproductive isolation and provide examples.
- Prezygotic isolation: Prevents mating or fertilization (e.g., bonobos and chimpanzees diverging due to geographical separation by the Congo River).
- Postzygotic isolation: Hybrid inviability/sterility (e.g., Drosophila hybrids with lethal gene interactions).
What is differential selection, and how does it drive speciation?
Differential selection occurs when separated populations face distinct environmental pressures, leading to divergent adaptations. Over time, genetic differences accumulate, reinforcing reproductive isolation (e.g., bonobos and chimpanzees adapting to different habitats).
Explain geographical isolation as a mechanism for speciation.
Geographical isolation physically separates populations (e.g., rivers, mountains). Without gene flow, populations diverge due to differential selection. Example: The Congo River split bonobos (south) and chimpanzees (north), leading to distinct behaviors and traits.
How did the Congo River contribute to speciation in bonobos and chimpanzees?
The Congo River geographically isolated ancestral populations. Bonobos (south) evolved in stable forests with female-dominated societies, while chimpanzees (north) adapted to competitive environments with male dominance. Differential selection drove behavioral and genetic divergence.
Why are behavioral changes significant in reproductive isolation?
Behavioral differences (e.g., mating rituals, social structures) prevent interbreeding. Example: Bonobos use conflict resolution through social bonding, while chimpanzees exhibit aggression, reducing cross-species mating.
How do chromosomal changes reinforce reproductive isolation?
Chromosomal inversions/translocations (e.g., in Drosophila) cause hybrid sterility. For example, Nup96 gene incompatibilities disrupt nuclear pore formation in hybrids, ensuring postzygotic isolation.
What role do selection pressures play in parapatric speciation?
Strong differential selection (e.g., metal tolerance in Anthoxanthum grasses) overrides gene flow. Populations adapt to local conditions (e.g., polluted vs. non-polluted soils), leading to reproductive isolation despite partial overlap.
How does temporal isolation act as a prezygotic barrier?
Populations reproduce at different times (e.g., orchids flowering seasonally). For example, Three rainforest orchid species avoid hybridization by blooming in distinct months, preventing pollen transfer.
Why is gene flow critical in maintaining species boundaries?
Reduced gene flow allows genetic divergence. For example, Chromosomal inversions in Ficedula flycatchers suppress recombination, linking adaptive traits (plumage) to hybrid sterility genes, solidifying reproductive isolation.
What is reproductive isolation, and why is it critical for speciation?
Reproductive isolation occurs when genetic, behavioral, or physical barriers prevent interbreeding between populations. It is critical for speciation because it allows populations to diverge genetically, leading to the formation of distinct species.
How does geographical isolation contribute to speciation?
Geographical isolation physically separates populations (e.g., rivers, mountains), halting gene flow. Over time, differential selection pressures and genetic divergence lead to reproductive isolation. For example, The Congo River split bonobos and chimpanzees.
Describe the divergence of bonobos and chimpanzees due to the Congo River.
The Congo River geographically isolated ancestral populations:
- North (chimpanzees): Male-dominated societies, aggressive behaviors (intense resource competition).
- South (bonobos): Female-dominated societies, conflict resolution through social bonding.
Differential selection drove behavioral and genetic divergence, resulting in speciation.
What is differential selection?
Differential selection occurs when separated populations face distinct environmental pressures, leading to divergent adaptations. Example: Chimpanzees adapted to competitive northern habitats, while bonobos adapted to stable southern forests.
How did behavioral differences arise between bonobos and chimpanzees?
Behavioral differences (e.g., aggression in chimpanzees vs. social bonding in bonobos) arose due to differential selection pressures. These differences reinforced reproductive isolation by reducing interbreeding.
What role does gene flow play in speciation?
Gene flow maintains genetic similarity between populations. When geographical isolation stops gene flow (e.g., Congo River barrier), genetic differences accumulate, accelerating speciation.
How do prezygotic and postzygotic barriers differ?
- Prezygotic: Prevent mating/fertilization (e.g., geographical, behavioral, or temporal isolation).
- Postzygotic: Reduce hybrid fitness (e.g., sterility).
In bonobos/chimpanzees, behavioral differences act as prezygotic barriers.
Why is the Congo River example significant for understanding speciation?
It demonstrates how a geographical barrier (the river) led to reproductive isolation, differential selection, and speciation in closely related primates.
What evidence supports that bonobos and chimpanzees are separate species?
They are reproductively isolated (no interbreeding in the wild) and exhibit distinct social structures, behaviors, and genetic profiles due to millions of years of divergence.
How does this example align with the concept of allopatric speciation?
The Congo River caused allopatric speciation—geographical separation led to genetic divergence, differential selection, and eventual reproductive isolation, forming two distinct species.
What is geographical isolation?
Geographical isolation is the physical separation of populations by barriers such as rivers, mountains, or oceans. It prevents gene flow between populations but may be temporary.
How does geographical isolation differ from reproductive isolation?
Geographical isolation prevents gene flow but may be temporary. If populations reunite, they could potentially interbreed. Reproductive isolation means speciation has occurred, and populations cannot breed successfully even if they share the same habitat.
What is the key characteristic of reproductive isolation?
Reproductive isolation means that two populations have become separate species and can no longer breed together successfully, even if they live in the same habitat.
Can geographically isolated populations always interbreed if reunited?
Not necessarily. While geographically isolated populations may be able to interbreed if reunited, long periods of separation can lead to genetic divergence and eventual reproductive isolation.
How can geographical isolation lead to reproductive isolation?
Geographical isolation can lead to reproductive isolation if the separated populations experience different selection pressures, accumulate genetic differences, and develop mechanisms that prevent successful interbreeding over time.
In exams, how should you refer to species like bonobos?
In exams, it’s fine to use common names like “bonobos” rather than binomial Latin names such as “Pan paniscus”.
Define speciation.
Speciation is the formation of new species from pre-existing species over time, caused by evolution.
What are the two main types of speciation?
The two main types of speciation are:
- Allopatric speciation
- Sympatric speciation
What is allopatric speciation?
Allopatric speciation occurs when populations of a species become geographically isolated from each other, leading to reproductive isolation and the formation of new species.
What is sympatric speciation?
Sympatric speciation occurs when new species form from populations living in the same area, without geographical isolation.
What are examples of geographical barriers that can lead to allopatric speciation?
Geographical barriers can be natural (e.g., a body of water or a mountain range) or man-made (e.g., a motorway).
How does allopatric speciation occur?
- Populations become geographically isolated
- Gene flow between populations stops
- Allele frequencies change due to different selection pressures or genetic drift
- Phenotypes of the two populations change
- Reproductive isolation occurs, leading to separate species
What is genetic drift?
Genetic drift is the accumulation of random changes in allele frequencies within a population.
How can reproductive isolation occur?
Reproductive isolation can be:
- Geographic (physical separation)
- Behavioral (differences in mating rituals or preferences)
- Temporal (differences in breeding seasons or times)
Describe an example of allopatric speciation in trees.
- A tree population exists in a mountainous habitat
- A new mountain range forms, dividing the population
- Geographical barrier prevents interbreeding
- Different environments lead to differential selection
- Different alleles become more frequent in each population
- Over thousands of years, two distinct species form
What is the main difference between allopatric and sympatric speciation?
Allopatric speciation involves geographical isolation of populations, while sympatric speciation occurs without geographical separation.
What is sympatric speciation?
Sympatric speciation takes place without geographical barriers. It occurs when random changes in alleles and phenotypes prevent some individuals in a population from successfully breeding with others in the same area.
What are the three main types of reproductive isolation?
- Geographic isolation
- Behavioral isolation
- Temporal isolation
What is temporal isolation?
Temporal isolation occurs when some individuals in a population develop different mating or flowering seasons, so their reproductive timings no longer match up with the rest of the population.
What is behavioral isolation?
Behavioral isolation occurs when some individuals in a population develop changes in their courtship behaviors, meaning they can no longer attract individuals of the opposite sex for mating.
How does sympatric speciation lead to the formation of new species?
- Random allele changes cause phenotype differences
- Phenotype differences prevent interbreeding
- Gene flow stops between populations
- Allele frequencies change differently in each population
- Reproductive isolation occurs
- Two separate species form
Describe an example of sympatric speciation in fruit flies.
- A fruit fly population exists in a laboratory
- Random mutation causes allele change, leading to phenotype change (e.g., food preference)
- Phenotype difference prevents interbreeding
- No gene flow between populations
- Different alleles passed on in each population (due to selection pressure or random inheritance)
- Over time, two distinct species form that can no longer interbreed
How does sympatric speciation differ from allopatric speciation?
Sympatric speciation occurs without geographical barriers, while allopatric speciation requires geographical isolation. In sympatric speciation, populations live in the same habitat but don’t interbreed due to other isolating mechanisms.
What is the key similarity between sympatric and allopatric speciation?
Both sympatric and allopatric speciation result in reproductive isolation and the formation of new species through the accumulation of genetic differences over time.
Why is it important not to confuse isolation mechanisms with reproductive isolation?
Isolation mechanisms (e.g., temporal, behavioral, or geographical) are the causes that prevent gene flow, while reproductive isolation is the result of accumulated genetic differences that make interbreeding impossible, even if isolation mechanisms are removed.
How can selection pressures influence sympatric speciation?
Selection pressures can favor different alleles in subpopulations, such as enzymes advantageous for digesting different foods. This can reinforce genetic divergence and contribute to the speciation process.
What is adaptive radiation?
Adaptive radiation is the process by which a single ancestral species rapidly diversifies into multiple new species, each adapted to different ecological niches.
How does adaptive radiation contribute to biodiversity?
Adaptive radiation allows closely related species to coexist without competing, thereby increasing biodiversity in ecosystems where there are vacant niches.
What is a key characteristic of species formed through adaptive radiation?
Species formed through adaptive radiation are closely related but adapted to different ecological niches, allowing them to coexist without direct competition.
In what type of ecosystems is adaptive radiation most likely to occur?
Adaptive radiation is most likely to occur in ecosystems where there are vacant niches, such as newly formed islands or environments with reduced competition.
How does adaptive radiation relate to competition between species?
Adaptive radiation reduces competition between closely related species by allowing them to exploit different resources and occupy different ecological niches.
Give an example of adaptive radiation.
Darwin’s finches in the Galapagos Islands are a classic example of adaptive radiation, where different species evolved various beak shapes to exploit different food sources.
What is the relationship between adaptive radiation and vacant niches?
Adaptive radiation fills vacant niches in an ecosystem, allowing for increased biodiversity as closely related species evolve to occupy different ecological roles.
How does adaptive radiation impact ecosystem stability?
Adaptive radiation can enhance ecosystem stability by increasing the diversity of species and their ecological roles, making the ecosystem more resilient to changes.
What is the definition of a species?
A species is a group of organisms with similar characteristics that can interbreed to produce fertile offspring.
What is a hybrid?
A hybrid is the offspring of individuals of two different species.
Define hybridization.
Hybridization is the mechanism by which hybrids are produced, including the mating, fertilization, and development processes between different species.
Why are hybrids usually rare and infertile?
Hybrids are rare due to barriers to hybridization, and they are usually infertile due to incompatible chromosome numbers or other genetic incompatibilities.
How do incompatible chromosome numbers prevent hybridization?
Different species often have different chromosome numbers. When gametes fuse, the resulting zygote may have an uneven number of chromosomes, unable to pair up in homologous pairs. This leads to infertility as the hybrid cannot carry out meiosis.
What is an example of a sterile hybrid?
A mule, which is the offspring of a horse and a donkey, is an example of a sterile hybrid. Mule chromosomes cannot pair up during meiosis, so mules cannot produce gametes of their own.
How does courtship behavior prevent hybridization in animal species?
Incompatible courtship behaviors between different species can prevent mating, thus acting as a barrier to hybridization.
What are two reasons why individuals of different species cannot breed together to produce fertile offspring?
- Incompatible chromosome numbers
- Incompatible courtship behaviors
Why is preventing hybridization important for species?
Preventing hybridization helps maintain the genetic integrity of species by preventing the mixing of alleles between different species.
What happens when gametes from different species fuse?
The fusion of gametes from different species often leads to non-viable zygotes, or if viable, usually develops into infertile hybrids due to genetic incompatibilities.
What are two main barriers to hybridization?
- Incompatible chromosome numbers
- Incompatible courtship behaviors
How do incompatible chromosome numbers prevent fertile hybrids?
Different species often have different chromosome numbers. Hybrids may have an odd number of chromosomes, preventing proper meiosis and resulting in sterility.
What is an example of a sterile hybrid due to chromosome incompatibility?
A mule, which is the offspring of a horse and a donkey, has an odd number of chromosomes and cannot carry out meiosis, making it sterile.
What is courtship behavior in animals?
Courtship behavior is a ritual that eventually results in mating and reproduction. It can involve visual, chemical, or auditory stimuli and can range from simple to highly complex sequences of behaviors.
How does courtship behavior prevent hybridization?
If the courtship rituals of two individuals from different species do not match, no mating will occur, thus preventing hybridization.
Give an example of a species with complex courtship rituals.
Many birds of paradise have intricate and impressive courtship rituals.
Why is preventing hybridization important for species?
Preventing hybridization helps maintain the genetic integrity of species by preventing the mixing of alleles between different species.
How can courtship behavior vary between species?
Courtship behavior can range from simple processes involving a small number of stimuli to highly complex sequences of behaviors involving multiple individuals and modes of communication.
What is adaptive radiation?
Adaptive radiation is the rapid evolution of multiple species from a common ancestor through natural selection.
How does adaptive radiation contribute to biodiversity?
Adaptive radiation allows closely related species to coexist without competing, thereby increasing biodiversity in ecosystems where there are vacant niches.
What is an ecological niche?
An organism’s ecological niche is its role within its ecosystem, e.g., the food it eats, the environmental conditions it requires, and the predators it provides food for.
How do species resulting from adaptive radiation manage to coexist?
The differences that arise between the new species often enable them to live together in one habitat because they are able to fill different ecological niches.
Give two examples of species groups that show adaptive radiation.
- Darwin’s finches in the Galapagos Islands
- Hawaiian honeycreepers in the Hawaiian archipelago
Why do species resulting from adaptive radiation often have some similar features?
Species resulting from adaptive radiation often have some similar features due to their shared ancestry.
How does adaptive radiation relate to vacant niches in an ecosystem?
Adaptive radiation allows new species to evolve and fill vacant niches in an ecosystem, increasing biodiversity.
What role does natural selection play in adaptive radiation?
Natural selection drives the rapid evolution of multiple species from a common ancestor in adaptive radiation, allowing them to adapt to different ecological niches.
What is abrupt speciation in plants?
Abrupt speciation is when a new plant species forms within a single generation, also known as instant speciation. It can occur because plant cells remain viable even when polyploid.
Define polyploidy in plants.
Polyploidy is the condition where cells have more than two sets of chromosomes. Examples include:
- 3n = triploid
- 4n = tetraploid
- 6n = hexaploid
- 8n = octoploid
This contrasts with normal diploid (2n) body cells and haploid (n) gametes.
What are the two types of polyploidy in plants?
- Autopolyploidy: Arises within a single species
- Allopolyploidy: Arises between different species
How can autopolyploidy occur?
Autopolyploidy can occur through incorrect meiosis, specifically:
- Failure of homologous chromosomes to separate (nondisjunction)
- One daughter cell receives two sets of chromosomes
- The resulting diploid (2n) gamete fuses with a normal or another diploid gamete
What is allopolyploidy and how does it lead to speciation?
Allopolyploidy occurs when diploid gametes from different species fuse to produce a polyploid hybrid zygote. This can result in sympatric speciation if the offspring are so different from their parents that they cannot breed with them to produce fertile offspring.
Why are polyploid plant varieties often successful?
Polyploid plants may be successful due to advantages such as:
- Ability to carry out meiosis in hybrids that would otherwise be infertile
- Often larger and more vigorous than their diploid parents
- More copies of each gene, reducing the impact of negative mutations
What is the genus Persicaria, and how does it relate to polyploidy?
Persicaria, also known as knotweed or smartweed, is a plant genus that contains many species formed by hybridization and polyploidy. Examples include:
- Persicaria foliosa (diploid, 2n)
- Persicaria japonica (tetraploid, 4n)
- Persicaria puritanorum (hexaploid, 6n)
How might a tetraploid Persicaria species arise?
A tetraploid Persicaria species (4n) could arise through allopolyploidy between two diploid species.
What is chromosome nondisjunction?
Chromosome nondisjunction is the failure of chromosomes to separate fully during meiosis, which can lead to gametes with abnormal chromosome numbers and potentially result in polyploidy.
How does polyploidy contribute to sympatric speciation in plants?
Polyploid offspring may be so different from their parents that they are unable to breed with them to produce fertile offspring. This reproductive isolation results in sympatric speciation, as the new species forms within the same geographical area as its parent species.
What is the difference between using common names and scientific names for organisms in exams?
In examinations, either the common name or the scientific name is acceptable when referring to organisms. For example, you can use “knotweed” or “Persicaria” when discussing this genus.
How can polyploidy occur through meiosis?
- Separate meiosis events within an individual may produce either a 1n gamete OR a 2n gamete, which can result in a 3n zygote after self-fertilization.
- Meiosis with nondisjunction in individuals from two different species can result in 2n gametes, which can lead to a 4n zygote if fertilization occurs.
What are some advantages of polyploidy in plants?
- May allow otherwise infertile hybrids to carry out meiosis due to additional chromosomes
- Often results in larger and more vigorous plants than diploid parents
- More copies of each gene reduce the impact of negative mutations as harmful alleles are masked
Give examples of polyploidy in the genus Persicaria (smartweeds).
- Persicaria foliosa: diploid (2n)
- Persicaria japonica: tetraploid (4n)
- Persicaria puritanorum: hexaploid (6n)
How might tetraploid and hexaploid Persicaria species have arisen?
- Tetraploid species: possibly by allopolyploidy between two diploid species
- Hexaploid species: possibly by hybridization between a diploid and a tetraploid species
Give examples of polyploidy in the genus Fallopia (knotweeds).
- Japanese knotweed (Fallopia japonica): octoploid (8n)
- Giant knotweed (Fallopia sachalinensis): tetraploid (4n)
- Bohemian knotweed (Fallopia xbohemica): hexaploid (6n)
How did Bohemian knotweed arise, and what is its ploidy level?
Bohemian knotweed is a hexaploid (6n) hybrid of Japanese knotweed and giant knotweed. It likely formed when Japanese knotweed (8n) produced 4n gametes and giant knotweed (4n) produced 2n gametes through normal meiosis.
How does polyploidy contribute to the invasiveness of Japanese knotweed?
The polyploid nature of Japanese knotweed is thought to aid its vigorous growth, making it a famously invasive species. Bohemian knotweed, a polyploid hybrid, is thought to be even more vigorous.
