Chapter 24

Define sympatric speciation

groups from the same ancestral population evolve into separate species without any geographical separation.

Explain the Phylogenetic Species Concept

identifies species based on the evolutionary hisotry of populations. The reasoning behind this concept begins with Darwin's theory that all species are realted by common ancestry. In modern species, all species form a monphyletic group-the tree of life

Explain sympatric speciation by polyploidzation

in which an offspring or group of offspring will be produced with twice the normal number of chromosomes. Where a normal individual has two copies of each chromosome (diploidy), these offspring may have four copies (tetraploidy). A tetraploid individual cannot mate with a diploid individual, creating reproductive isolation.

Describe the methods of prezygotic isolation

prevents individuals of different species from mating successfully

explain the morphospecies concept

researchers identify evolutionary indepedent lineages by difference in size, shape, or other morphological features. The logic behind the morphospecies concept is that distinguishing features are most likely to arise if populations are independent and isolated from gene flow

Explain the biological species concept

the main criterion for identifying species is reproductive isolation. This is logical because no gene flow occurs between populations that are reproductively isolated from each other- pre&post zygotic come from this concept

Explain allopatric speciation by vicariance

vicariance occurs when a natural situation arises to physically divide organisms

Disadvantages of Phylogenetic Species Concept

- Carefully estimated phylogenies available only for tiny subset of populations on tree of life - Will lead to recognition of many more species than morphospeices- sibnce it makes slight differences amoung groups easier to detect - While this might better reflect the extent the life's diversity, it compicates the naming of species

Explain allopatric speciation by dispersal

-The movement of individuals from one palce to another -few members of a species move to a new geographical area -resulting in differentiation of the original group into new varieties or species

disadvantage of biological species concept

-cannot be applied to fossils or asexual species -difficult to apply when closely realted populations don't overlap with each other geographically, therefore biologists are left to guess whether interbreeding would occur if the populations happened to come into contact -reproductive isolation can sometimes be a complex gradient rather than an all-or-nothing scenario

Disadvantages of Morphological species concept

-may lead to the naming of two or more species when there is only one polymorphic species with differing phenotypes, such as the spotted and black morphs of jaguars -it cannot identify cryptic species, which differ in traits other than morphology, such as the songs in some songbirds .morphological features used to distinguish species are subjective

Explain how new species can arise via hybridization

Hybrid speciation can be broadly defined as the hybridization between two or more distinct lineages that contributes to the origin of a new species. More specifically, hybridization must result in a hybrid population that is at least partially reproductively isolated from the parental species. if two species interbreed and produce hybrid offspring that can not only survive and reproduce, but also possess a unique combination of traits that are adaptive in their particular environment, a new species may occur

Explain sympatric speciation by disruptive selection

Selective pressures that might not have factored into a low-density population can take effect, and the resulting disruptive selection can drive a population apart. In doing so, the populations are often pushed to different niches, lowering the competition between them. A new species, perhaps based on a different food source or characteristic, seems to develop spontaneously. The theory is that some individuals become dependent on certain aspects of an environment—such as shelter or food sources—while others do not.

Define Allopatric Speciation

Speciation that begins with geographic isolation

Advantages of morphological species concept

Widley applicable, works for asexual and extinct species, and useful when biologists have no data on the extent of gene flow

Explain what hybrid zones are

an area where the ranges of two interbreeding species meet and interbreed

advantage of biological species concept

evolutionary indepence

Explain what reinforcement means in the context of speciation

Hybrids can have less fitness, more fitness, or about the same fitness level as the purebred parents. Usually, hybrids tend to be less fit; therefore, reproduction to produce hybrids will diminish over time, which nudges the two species to diverge further in a process called reinforcement. This term is used because the low success of the hybrids reinforces the original speciation. If the hybrids are less fit than the parents, reinforcement of speciation occurs, and the species will continue to diverge until they can no longer mate and produce viable offspring.

Explain what fusion means when isolated populations come into contact

If the hybrids are as fit or more fit than the parents, or the reproductive barriers weaken, the two species may fuse back into one species (reconnection). For a hybrid form to persist, it will generally have to be able to exploit the available resources better than either parent species, with which, in most cases, it will have to compete.

Explain how extinction can occur when isolated populations come into contact

If the isolating mechanisms between these populations are only partially complete, extensive hybridization may occur. This can result in fusion back into a single population, or in the swamping of one population's gene pool by the genes of the other (extinction).

Advantages of Phylogenetic Speceis Concept

Its widely applicable; based on testable criteria. It can be applied to any population (fssil, sexual, or asexual). it is also logical because different speceis have different synamorphies only if they are isolated from gene flow and have evolved independently

Explain how the processes of evolution affect speciation

One of these is natural selection, which is a process that increases the frequency of advantageous gene variants, called alleles, in a population. Natural selection can result in organisms that are more likely to survive and reproduce and may eventually lead to speciation. A second process called genetic drift describes random fluctuations in allele frequencies in populations, which can eventually cause a population of organisms to be genetically distinct from its original population and result in the formation of a new species.

Examples of prezygotic isolation What is habitat isolation? What is temporal isolation? What is behavorial isolation? What is gametic isolation? What is mechanical isolation?

Two species might prefer different habitats and thus be unlikely to encounter one another. This is called habitat isolation. Two species might reproduce at different times of the day or year and thus be unlikely to meet up when seeking mates. This is called temporal isolation. Two species might have different courtship behaviors or mate preferences and thus find each other "unattractive". This is known as behavioral isolation. Two species might produce egg and sperm cells that can't combine in fertilization, even if they meet up through mating. This is known as gametic isolation. Two species might have bodies or reproductive structures that simply don't fit together. This is called mechanical isolation. These are all examples of prezygotic barriers because they prevent a hybrid zygote from ever forming.

Describe methods of postzygotic reproductive isolation

keeps hybrid zygotes—one-celled embryos with parents of two different species—from developing into healthy, fertile adults. Postzygotic barriers are often related to the hybrid embryo's mixed set of chromosomes, which may not match up correctly or carry a complete set of information. In some cases, the chromosomal mismatch is lethal to the embryo or results in an individual that can survive but is unhealthy. In other cases, a hybrid can survive to adulthood in good health but is infertile because it can't split its mismatched chromosomes evenly into eggs and sperm. For example, this type of mismatch explains why mules are sterile, unable to reproduce 1. Hybrid inviability. Development of the zygote proceeds abnormally and the hybrid is aborted. (For instance, the hybrid egg formed from the mating of a sheep and a goat will die early in development.) 2. Hybrid sterility. The hybrid is healthy but sterile. (The mule, the hybrid offspring of a donkey and a mare, is sterile; it is unable to produce viable gametes because the chromosomes inherited from its parents do not pair and cross over correctly during meiosis (cell division in which two sets of chromosomes of the parent cell are reduced to a single set in the products, termed gametes - see Figure). Hybrid is healthy and fertile, but less fit, or infertility appears in later generations (as witnessed in laboratory crosses of fruit flies, where the offspring of second-generation hybrids are weak and usually cannot produce viable offspring).