Chapter 22 Continue 2

Darwin's finches

- are a group of about fifteen species of passerine birds.[1] They often are classified as the subfamily Geospizinae or tribe Geospizini. It is still not clear to which bird family they belong, but they are not related to the true finches. They were first collected by Charles Darwin on the Galápagos Islands during the second voyage of the Beagle.

How do population become allopatric?

1. the first is dispersal in which some individuals colonize a distant place, such as an island far from the main source population 2. the second is by vicariance in which a geographic barrier arises within a single population separating it into two or more isolated population

Evolutionary species concept

: A species is a lineage (an ancestral-descendant sequence of populations) evolving separately from others and with its own unitary evolutionary roles and tendencies (Simpson, 1961). Evolutionary species concept: A species is a single lineage of ancestor-descendant populations which maintain its identity from other such lineages and which has it own evolutionary tendencies and historical fate (Wiley, 1981). Evolutionary species concept: A species is a population or group of populations that shares a common evolutionary fate through time (Templeton, 1989).

postzygotic barrier example

A mule is a hybrid between a horse and a donkey. Mules nearly always display hybrid sterility.

Given a group of organisms, describe how you would test whether they all belong to one species or whether they belong to two separate species.

According to the morphospecies concept, organisms of the same species often have very similar appearances, so careful observation of the phenotypic characteristics of the organisms could provide insight into how many species were represented in the group. If possible, a more rigorous test would be to determine whether the organisms could breed with one another to produce viable, fertile offspring.

Given a group of organisms describe how you would test whether they all belong to one species or whether they belong to two separate species

According to the morphospeices concept, organisms of the same species often have very simliar appearances, so careful observation of the phenotypic characteristics of the organisms could provide insight into how species were represented in the group.

Differentiate between allopatric speciation by dispersal and by vicariance and give one example of each.

Allopatric speciation can occur if a subset of a population moves to a new location far from the original population (dispersal), like if a hurricane blew a group of beetles to a distant island off the coast of the mainland. Allopatric speciation can also occur by vicariance, which is when a change in the environment effectively separates a population into two distinct groups. An example of allopatric speciation by vicariance would be if a lake receded and began to dry out leaving only smaller, isolated ponds behind. Fish from a single species might be split among several different ponds, each of which would be subject to genetic divergence based on the conditions in their respective pond and genetic drift, which over time could lead to speciation.

Allopatric VS Sympatric

Allopatric speciation means that speciation occured in different regions.The key with allopatric speciation is geographical separation. For example, say you have a squirrel population in a mountain, and over years a canyon forms a physical barrier between the two sides so that what was once 1 species of squirrel is split up into two different populations on different sides Over time, each population will adapt to its region and eventually speciate. This actually took place in I beleive the grand canyon between Abert and Kaibab squirrels. You can look that up if you would like. Sympatric speciation means that one population of one species became two species while in the same geographic region with no physical separation. This usually occurs because different inviduals of the same species begin to occupy a distinct niche and eventually become specifically adapted for that role. Look up African tilapia which is a good example if you want to know more.

Differentiate between allopatric and sympatric speciation, and state which is thought to be more common.

Allopatric speciation, which is thought to happen more often than sympatric speciation, occurs after a geographic barrier physically separates two populations from one another, which limits gene flow and promotes genetic divergence of the two populations as they adapt to their different environments. Sympatric speciation is the divergence of one group of organisms into distinct species within the same geographical area, so that although the organisms inhabit the same area and come in contact with one another, gene flow is limited because of strong selection against hybrid offspring.

Define the term "species.

Although no one definition is able to perfectly describe the genetic boundaries between different organisms, the biological species concept defines a species as a group of organisms that can share genetic material by interbreeding with one another to generate viable, fertile offspring. By this definition, organisms that cannot successfully reproduce with one another are therefore considered different species.

difference between directional selection, disruptive selection, and stabilizing selection

Directional Selection occurs when selection favors one extreme trait value over the other extreme. This typically results in a change in the mean value of the trait under selection. Disruptive Selection occurs when selection favors the extreme trait values over the intermediate trait values. In this case the variance increases as the population is divided into two distinct groups. Disruptive selection plays an important role in speciation. Stabilizing Selection occurs when selection favors the intermediate trait value over the extreme values. Populations under this type of selection typically experience a decrease in the amount of additive genetic variation for the trait under selection. -Stabilizing selection results in a decrease of a population's genetic variance when natural selection favors an average phenotype and selects against extreme variations. In directional selection, a population's genetic variance shifts toward a new phenotype when exposed to environmental changes. Diversifying or disruptive selection increases genetic variance when natural selection selects for two or more extreme phenotypes that each have specific advantages. In diversifying or disruptive selection, average or intermediate phenotypes are often less fit than either extreme phenotype and are unlikely to feature prominently in a population.

Describe how genetic divergence

Genetic divergence is the process in which two or more populations of an ancestral species accumulate independent genetic changes (mutations) through time, often after the populations have become reproductively isolated for some period of time. In some cases, subpopulations living in ecologically distinct peripheral environments can exhibit genetic divergence from the remainder of a population, especially where the range of a population is very large (see parapatric speciation). The genetic differences among divergent populations can involve silent mutations (that have no effect on the phenotype) or give rise to significant morphological and/or physiological changes. Genetic divergence will always accompany reproductive isolation, either due to novel adaptations via selection and/or due to genetic drift, and is the principal mechanism underlying speciation.

Describe how Genetic Drift can result in speciation

Genetic drift depends strongly on population size as a consequence of the law of large numbers. When many individuals carry a particular allele, and all face equal odds, the number of offspring they collectively produce will only slightly differ from the expected value, which is the expected average per individual times the number of individuals. But with a small effective breeding pool, a departure from the norm in even one individual can cause a disproportionately greater deviation from the expected result. Therefore small populations are more subject to genetic drift than large ones. This is also the basis for the founder effect, a proposed mechanism of speciation.

Describe how genetic divergence and reproductive isolation are related to each other.

In order for populations to genetically diverge from one another, they must have limited gene flow between them. Reproductive isolation limits the production of hybrid offspring, so genetic exchange between populations is reduced and divergence continues as each population is subjected to the selective pressures of their environment and genetic drift. In addition, if populations begin to diverge through genetic drift or disruptive selection, these differences can result in establishment of a reproductive barrier, which would then work to limit further genetic exchange and promote reproductive isolation.

How are new alleles created?

Occasionally, DNA mutations occur in germ cells - cells destined to become eggs or sperm. In this case, the DNA mutation is copied into every new cell of the growing embryo following fertilization. In this way, new DNA variants are passed on to the next generation. If the mutation affects a gene, it will result in a new version of that gene - a new allele.

Name four reproductive barriers and indicate whether each is pre-or post-zygotic.

Reproductive barriers that prevent fertilization (pre-zygotic) include differences in mating behaviors like courtship rituals, mechanical blocks to fertilization such as differences in the genitalia required for mating, and biochemical incompatibilities in the gametes that can limit the fusion of sperm and egg. After fertilization has occurred, post-zygotic barriers limit the ability of the zygotes formed from gametes of different species to develop into fertile adults because of differences at the genomic level such as an improper number of chromosomes.

What role does natural selection play in speciation

Selection against hybrids is essential to the definition of biological species. Alleles will be eliminated from a population if they find themselves in unfit heterozygotes or recombinants, and similarly, sexual selection will act against alleles that make males unattractive, or make it harder for females to find a mate. The fundamental opposition of selection to the evolution of reproductive isolation has long been seen as the major obstacle to speciation

Describe how genetic drift can result in speciation.

Since genetic drift acts randomly to alter allele frequencies, the alleles that become fixed or extinct in a given population will be different in each population. These differences, accumulated over time, can result in genetic incompatibility, which will limit gene flow and lead to the establishment of two different species.

Explain how ecological and evolutionary considerations can help inform whether or not a group of organisms represents a single species.

Since resources are limited in every habitat, each species must have a unique niche within its environment in order to avoid competition with other species, thus organisms with overlapping ecological requirements are likely members of a single species. In addition, organisms of a single species will have a high degree of genetic identity due to a shared ancestral lineage, so information about the evolutionary history of an organism can suggest whether a group of organisms is indeed a single species or whether they have genetically diverged from one another to form two separate species.

Name two types of organisms that do not fit easily into the biological species concept

Since the biological species concept defines species based on their ability to interbreed to generate viable, fertile offspring those organisms that reproduce asexually such as bacteria and that are extinct cannot be easily characterized

Name two types of organisms that do not fit easily into the biological species concept.

Since the biological species concept defines species based on their ability to interbreed to generate viable, fertile offspring, those organisms that reproduce asexually (such as bacteria) and those that are extinct cannot be easily characterized by this definition.

Describe how natural selection can result in speciation.

Speciation is the result of genetic divergence between two populations to the point where they are no longer capable of producing fertile offspring. Natural selection can drive genetic divergence of populations based on the characteristics that are favorable in each population's environment, which may also influence their reproductive compatibility with other populations. The characteristics that allow for optimal survival and reproduction in one population will be specific for its environment, so two populations that have lived in different locations for a long time, both being adapted to their environments by natural selection, will likely encounter reproductive barriers, limiting gene flow between the populations and reinforcing speciation.

limitations of biological species concept define a species

The biological species concept cannot be applied to fossils or asexual organisms (including all prokaryotes)

Reproductive selection

The environment may impose an external barrier to reproduction, such as a river or mountain range, between two incipient species but that external barrier alone will not make them separate, full-fledged species. Allopatry may start the process off, but the evolution of internal (i.e., genetically-based) barriers to gene flow is necessary for speciation to be complete. If internal barriers to gene flow do not evolve, individuals from the two parts of the population will freely interbreed if they come back into contact. Whatever genetic differences may have evolved will disappear as their genes mix back together. Speciation requires that the two incipient species be unable to produce viable offspring together or that they avoid mating with members of the other group.

Genetic Divergence

The separation of a population's gene pool from the gene pools of other populations due to mutation, genetic drift, and selection. Continued divergence can lead to speciation.

difference between prezygotic and postzygotic barriers

When prezygotic isolation mechanisms fail to keep species in reproductive isolation from each other, the postzygotic isolations will take over and ensure that speciation is the preferred route for evolution and diversity among species will continue to increase as natural selection acts. In postzygotic isolation, hybrids are produced, but tend not to be viable. They may not survive long enough to be born or have major defects. If the hybrid makes it to adulthood, it is often sterile and cannot produce its own offspring. These isolation mechanisms ensure that hybrids are not the most prevalent and species remain separate. The main weakness of postzygotic isolation mechanisms is that they must rely on natural selection to correct the convergence of species. There are times this does not work and the hybrid actually makes a species regress in their evolutionary timeline and revert to a more primitive stage. While this sometimes is a desirable adaptation, more often than not it is actually a set back on the evolution scale. -Both prezygotic isolations and postzygotic isolations are necessary to keep species separate and on divergent paths of evolution. These types of reproductive isolations increase biological diversity on Earth and help drive evolution. Even though they are still dependent upon natural selection to work, it ensures that the best adaptations are kept and species do not regress back to a more primitive or ancestral state through hybridization of once related species. These isolation mechanisms are also important to keep very different species from mating and producing weak or not viable species from taking up important resources for individuals that actually should reproduce and pass down their genes to the next generation.

Explain the process of allopatric speciation

Whenever a population is split due to a geographical barrier (mountain, canyon, river ect) and one population is exposed to different environmental pressures than the other for a long period of time one population will diverge from the other and become another species. This could be true when there is no real difference in selective presure and the changes that cause the species to diverge arise from only genetic events but that kind of allopatric speciation would take a much larger amount of time.

sympatric speciation process

You may be wondering how one species can become two separate species, even though they still live in the same area. This can happen in a variety of ways, but let's look at a hypothetical example to understand the process better. In the image below, we start with a group of flies that are all the same species. There are two sources of food for them to choose from: red apples and green apples. Originally, all of the flies feed on red apples, but at some point some of the flies begin to prefer green apples. Sympatric speciation occurs if interactions are so limited between these groups that mating no longer occurs between them. Each new population of flies will have genetic variation in its gene pool (the collective genetic information for the group), and as they continue to mate with other members of their new group, these variations become more prevalent in the population. Over a long enough period of time, a new species may develop.

Tetraploid

double diploid

Genetic incompatibilities

are commonly observed between hybridizing species. . We investigated the evolution of two loci involved in a classic example of a Bateson-Dobzhansky-Muller (BDM) incompatibility in Xiphophorus, a genus of freshwater fishes from northern Central America. Hybrids develop a lethal melanoma due to the interaction of two loci, an oncogene and its repressor. We cloned and sequenced the putative repressor locus in 25 Xiphophorus species and an outgroup species, and determined the status of the oncogene in those species from the literature. Using phylogenetic analyses, we find evidence that a repeat region in the proximal promoter of the repressor is coevolving with the oncogene. The data support a hypothesis that departs from the standard BDM model: it appears the alleles that cause the incompatibilities have coevolved simultaneously within lineages, rather than in allopatric or temporal isolation.

hybridization

capable of exchanging genes with other species in their genera through interbreeding between species

Instantaneous speciation

caused by hybridization between two species in which the offspring are reproductively isolated from both parents

population genetics

examines the amount of genetic variation within populations and the processes that influence this variation. A population is defined as a group of interbreeding individuals that exist together at the same time. Genetic variation refers to the degree of difference found among individuals, for instance in height, coat color, or other less observable traits. The particular set of genes carried by an individual is known as his or her genotype, while all the genes in a population together comprise the "gene pool." -study the interrelated patterns of phenotypic, genotypic and allelic frequencies within populations. These frequencies are generally expressed in relatively formal statistical notation. -begins with the concept of a "perfect" population in which all allelic frequencies are constant, and in which all mating is random. This ideal population is called a Hardy-Weinberg population, after the statisticians responsible for developing the concept. A population which simulates this ideal population is often described as being "in equilibrium." The relationship between the allelic and genotypic frequencies in this ideal population is described by the Hardy-Weinberg equation (H-W equation).

Partially reproductively isolated

if we trey to cross members of two population that have genetically diverged but not diverged far enough for full reproductive isolation that is speciation to have arisen, we may find that the pop. are

Some examples of prezygotic barriers

include sexual organs that don't physically fit together (mechanical isolation), having different mating seasons (temporal isolation), having different mating behaviors so the 2nd species isn't attracted to the 1st (behavioral isolation), living in different places (habitat isolation), or having eggs and sperm that won't physically join together even if mating does occur (gametic isolation).

ecological species concept

is a concept of species in which a species is a set of organisms adapted to a particular set of resources, called a niche, in the environment. According to this concept, populations form the discrete phenetic clusters that we recognize as species because the ecological and evolutionary processes controlling how resources are divided up tend to produce those clusters.

Reproductive isolation

is a mechanism that keeps species from mating with others. Prezygotic isolation prevents the fertilization of eggs while postzygotic isolation prevents the formation of fertile offspring. Prezygotic mechanisms include habitat isolation, mating seasons, "mechanical" isolation, gamete isolation and behavioral isolation. Postzygotic mechanisms include hybrid inviability, hybrid sterility and hybrid "breakdown."

Ring species

is a situation in which two populations which do not interbreed are living in the same region and connected by a geographic ring of populations that can interbreed. -Consider a species that is geographically distributed in a straight line from east to west across America: it is possible that the forms in the east and west are so different that they could not interbreed. Now imagine taking the line and bending it into a circle, such that the end points (formerly in the east and west) come to overlap in space. If they do not interbreed then the geographic distribution of the species will be in the shape of a ring, and they will be 'ring species': the extreme forms do not interbreed in the region of overlap. A ring species has an almost continuous set of intermediates between two distinct species, and these intermediates happen to be arranged in a ring. At most points in the ring, there is only one species; but there are two where the end-points meet. The image opposite is of the herring and lesser black-backed gulls in northern Europe: while they are two reproductively isolated species, there is a continuous set of interbreeding forms between them. -here we find that some population within a species are reproductively isolated from reach other but others are not

Peripatric speciation

is a special version of the allopatric speciation mode and happens when one of the isolated populations has very few individuals. Here's a very hypothetical example of how the peripatric speciation mode works, returning to our intrepid fruit flies venturing off the mainland on a bunch of rotting bananas. We pick up their story as their banana bunch is washed up on an island: 1. Double disaster: Not only are the island fruit flies now geographically isolated from their mainland relatives, but only a few larvae have survived the harrowing journey to end up colonizing the island. 2. Rare genes survive: These few survivors just by chance carry some genes that are rare in the mainland population. One of these rare genes happens to cause a slight variation in the mating dance. Another causes a slight difference in the shape of male genitalia. This is an example of the founder effect. The rare genes become fixed in the island population. 3. Gene frequencies drift: These small differences, which are rare on the mainland, drift to fixation in the small population on the island over the course of a few generations (i.e., the entire island population ends up having these genes). The population grows and changes. 4. More changes: As the island population grows, the unique reproductive features on the island result in a cascade of changes caused by sexual selection. These changes optimize, or at least improve, the fit of male and female genitalia to one another and female sensitivity to nuances of the mating ritual. Flies also experience natural selection that favors individuals better suited to the climate and food of the island. Peripatric speciation has occurred. 5. Speciation: After some generations, the island flies become reproductively isolated from the mainland flies. Peripatric speciation has occurred.

Plasmodium falciparum

is the deadliest of five human malaria species and responsible for the majority of malaria related deaths. There are around 300 million clinical cases occur each year resulting in at least one million deaths annually, predominantly in sub-saharan Africa. An estimated 3,000 children, under the age of five, fall victim to malaria each day and around 40% of the worlds population are at risk of infection.

Species Concepts/morphospecies concept

is the oldest species concept and uses differences in morphological characters to distinguish species. In former times species were considered as inalterable units. After Charles Darwin published his book "On the Origin of Species by Means of Natural Selection" (1859), the morphospecies concept has been applied under the assumption that similar to identical morphological characters would reflect relatedness and therefore result in a natural systematics.

ecological niche

is the role and position a species has in its environment - how it meets its needs for food and shelter, how it survives, and how it reproduces. A species' niche includes all of its interactions with the biotic and abiotic factors of its environment.

Polymorphisms

literally many forms

Species

members of populations that actually or potentially interbreed (the biological species concept). In this sense, a species is the largest gene pool possible under natural conditions. -organisms that cannot successfully reproduce with one another are therefore considered different species

sympatric speciation

occurs when two individuals pop. diverge from an ancestral species without being separated geographically.

Allele

one of the versions of a gene that may exist at a locus. For example, the pea color locus may have either the yellow allele or the green allele. Different alleles of the same locus are often symbolized by capital and lowercase letters (e.g., the Y and y alleles).

Pre-zygotic

prevents fertilization from taking place -important in reproductive isolation

Post-zygotic

results in the failure of the fertilized egg to develop into a fertile individual

Morphospecies concept

species traditionally have been described and identified on the basis of morphological criteria a classification system referred to as the morphological. -species are groups of individuals that are morphologically simliar and clearly distinguishable from individuals of other groups -usually any geographic variation among members of the group was not detected or simply ignored -if they look alike, they are considered the same species

Lock and Key

systems that require both components, whether physical or biochemical to match for successful interaction to take place

polyploidy,

the condition in which a normally diploid cell or organism acquires one or more additional sets of chromosomes.

What is speciation

the formation of new and distinct species in the course of evolution.

Sympatric

the term we use to describe a pop. that are in the same geographic location is

Morphosepcies vs BSC concept

these chromosomal differences prevent the formation of interspecies hybrids so those butterflies meet the BSC criterion they are different species, but they do not meet the morphospecies criterion because they look so much alike

Subspecies

this genetic distinctness is sometimes recognized by taxonomists who deem each geographic form

Disadvantages of morphospecies species concept

very subjective; doesn't count cryptic species (look identical but have different traits such as birds and their songs) -memebers of a species may not always look alike, but instead show different phenotypes called polymorphisms literally many forms for example color differences in some species of birds.