Chapter 24 The Origin of Species

Which would be most useful for identifying species in teh field? Explain.

Morphological species concept would be most useful in the field because it distinguishes species using morphological criteria which can be observed in the field without requiring extensive gene or reproductive analysis.

Example of fusion in world

Murky water pollution lessened the effects of behavioral reproductive barriers and females were not able to see the males as well in the water. The two species of fish, therefore, merged into one.

Hybrids

Offspring resultant from interspecific meeting. Reproductive isolation limits the formation of these.

How does allopatric speciation actually happen?

Once two species are separated, gene pools diverge and different mutations arise. Natural selection and genetic drift ten alter allele frequencies in different ways in the separate population and then evolve as a byproduct of such selection or drift.

Sister species

Pairs whose member species are each other's closest relative.

Allopolyploid

A sterile hybrid sometimes reproducing asexually can eventually change to a fertile hybrid through many mechanisms, one of which is through a mitotic or meiotic error doubling chromosome number.

Prezygotic barriers

Barriers that prevent fertilization from occurring.

Does polyploid happen in plants or animals?

Both, but is much more common in plants.

Limitations of the Biological Species Concept

Cannot evaluate reproductive isolation of fossils, asexual organisms, or certain organisms which are morphologically and ecologically distinct still have offspring.

Phylogenetic species concept

Defines a species as the smallest group of individuals who share a common ancestor. This can be vague however, as it is difficult to determine the degree of difference needed to define a species.

Ecological species concept

Defines species in the context of their ecological environment. Can differentiate for disruptive natural selection also.

How formidable must a geographic barrier be to promote allopatric speciation?

Depends on organisms ability to cross such barriers. Pollen can blow across rivers, rodents cannot.

Morphological species concept

Distinguishes a species by body shape and other structural features, which can be applied to both sexual and asexual organisms. Researchers, however, might disagree on which structural features distinguish a species.

Full example of allopatric speciation

Fish moved to different lakes which have since become isolated. As a result of natural selection, the body type of the mosquito fish differed to suit its pond. Upon being brought together, the fish prefer to mate with those of a similar body type. This equals behavioral barrier.

Suppose you are studying two bird species that live in a forest and are not known to interbreed. One species feeds and mates in the treetops and the other on the ground. But in captivity, the birds can interbreed and produce viable, fertile offspring. What type of reproductive barrier likely keeps these species separate in nature?

Habitat isolation because one species lives in the trees while the other lives in a similar environment but on the ground so they rarely encounter one another.

Reinforcement

Hybrid species are less fit than their parent species and are thus selected against. This reinforces reproductive barriers.

What are hybrid zones, and why can they be viewed as natural laboratories in which to study speciation?

Hybrid zones are areas where members of different species mate creating new offspring as a hybrid of each species. They are considered natural laboratories because they can give rise to new species or diminish old ones shedding light on how barriers to reproduction between closely related species change over time.

Describe the concept of stability in relation to hybrid zones.

Hybrids continue to form even if they are selected against because both parent species continue to pass gene flow to the hybrid species and travel into the hybrid zone.

Speciation

Process by which one species splits into two or more species.

In simplest terms, how does speciation begin?

Interruption in gene flow.

Autopolyploid

A cell division error results in a tetraploid cell where chromosome numbers are different from parent species which creates reproductive isolation. These tetraploid cells can produce their own offspring through self-pollination or by mating with other tetraploids.

Genetic drift

A change in the allele frequency of a population as a result of chance events rather than natural selection.

Species

A group of populations whose members have the potential to interbreed in nature and produce viable fertile offspring within the species but with no other groups.

Habitat differentiation

A population of a species exploits a particular resource that is not available to its parent source giving this population an advantage. This advantage source facilitates habitat isolation and they slowly develop their own characteristics. Natural selection helps to provide postzygotic barriers to reproduction as it changes its alleles.

Hybrid zone

Region in whch members of different species meet and mate, producing offspring of mixed ancestry.

Three outcomes of hybrid zones

Reinforcement of barriers, fusion of species, or stability.

Why might reinforcement be more prevalent amongst sympatric populations than allopatric populations?

Since reinforcement is occurring, species in a sympatric population are more likely to sexually select for members of their own species rather than with hybrids or other species as indicated by the study of male and female flycatchers.

How many genes influence the formation of new species?

Speciation can be driven by few or many genes.

Speciation can occur rapidly between diverging populations, yet the time between speciation events is often more than a million years. Explain this apparent contradiction.

Speciation can occur rapidly between diverging populations, however it may take millions of years for such divergence to begin.

Temporal Isolation

Species breed during different times of the day, seasons, or years and therefore do not mix gametes.

Behavioral Isolation

Species have unique mating calls which they can identify and thus only mate if such a mating ritual is performed.

Gametic Isolation

Sperm of one species cannot fertilize that of another.

How do prezygotic barriers occur?

Stopping members of a species from trying to mate, stopping an attempted mating from being completed successfully, or by stopping fertilization if mating is completed successfully.

What happens genetically within a hybrid zone?

The allele frequency of yellow-bellied toads and fire bellied toads is 50%.

Macroevolution

The broad pattern of evolution above the species level like the development of mammals or a flower plants through multiple speciation changes.

Polyploidy

The condition by which a species originates accidently during cell division resulting in extra sets of chromosomes.

Speciation clock

The fallacy that organisms have some sort of internal clock causing them to produce new species at regular intervals.

Why are alleles not passed from one species to another across a hybrid zone?

The hybrid animals produced in the hybrid zone are less competitive having a poorer survival and reproduction than either parent species. Consequently, hybrid animals do not serve as a conduit for gene passage from the yellow to the fire bellied toads. Yellow-bodied toads also are selected for in higher altitudes while the reverse are selected in lower altitudes.

How does speciation rate vary?

The time between speciation averaged between 500,000 years and 6.5 million years.

How can plant geneticists create new species through polyploids?

They can apply chemicals to induce meiotic and mitotic errors and produce a new species with desired qualities, like a hybrid combining high wheat yield with the hardiness of rye.

Examples of allopatric speciation

Two fish populations are separated into different environments and a new species arises. River divides a species, species migrate to remote area and are geographically isolated from parent population.

Fusion

Two species joining together.

Reduced hybrid fertility

Where the hybrid is sterile because the parent chromosomes differ in number and hybrids cannot produce normal gametes.

Mechanical Isolation

Where two species attempt to mate, but due to anatomical differences are not able to reproduce.

Hybrid breakdown

While an organism may be developmentally okay and be fertile, however these offspring are less fit and thus don't develop into a new species.

How can reproductive barriers form between sympatric populations while their members remain in contact with each other?

While no geographic isolation facilitates gene flow interspecies, factors such as polyploidy, sexual selection, and habit differentiation can create reproductive barriers.

Reproductive isolation

existence of biological factors impeding members of two species from interbreeding and producing viable, fertile offspring blocking the gene flow between species.

Habitat isolation

prezygotic barrier whereby species who occupy different habitats in the same area do not encounter each other thus do not mate.

Evidence of sexual selection

Females of cichlid fish species prefer to mate with males of a certain color pattern. This behavior isolation can eventually give rise to a new species through the blockage of gene flow.

Which species concept's could you apply to both asexual and sexual species?

All except biological species concept

Summarize key differences between allopatric and sympatric speciation. Which type of speciation is more common, and why?

Allopatric speciation is the process of a new species arising as a result of geographic isolation. This geographic isolation creates a reproductive barrier to the species blocking gene flow to the parent population. As a result of natural selection, this population eventually becomes its own species. Sympatric speciation, in contrast, is less common because it requires the spontaneous emergence of a reproductive barrier which brings rise to a new species. Allopatric reproduction is more common because geographic splits between species happen more often than a spontaneous mutation resultant in a reproductive barrier.

Is allopatric speciation more likely to occur on an island close to a mainland or on a more isolated island of the same size?

Allopatric speciation would more likely occur on an isolated island where there is a greater chance gene flow between parent species and the island population is stopped. This reproductive barrier combined with natural selection and environmental adaptations makes allopatric speciation more likely to occur on an isolated island.

Punctuated equilibria

Evolutionary change occurs in rapid bursts separated by large periods of no change

Sexual selection

Female preference of certain characteristics in males when mating.

What if female cichlids living in the murky waters of a polluted lake could not distinguish colors well. In such waters, how might the gene pools of these species change over time?

Gene flow between the two species would be reinstituted as the female could not distinguish between the two species. This reinstituted gene flow would eventually combine the genes of both species merging them into one

What holds the gene pool of a species together, causing its members to resemble each other more than they resemble members of other species?

Gene flow, or the transfer of alleles between populations genetically holds populations of species together.

Reduced hybrid viability

Genes of two parents react in a manner that it impairs the hybrid's ability to survive and reproduce.

Describe two mechanisms that can decrease gene flow in sympatric populations, thereby making sympatric speciation more likely to occur.

Habitat differentiation happens when a population of a species exploits a new resource which the parents do not exploit. This creates habitat isolation. Polyploidy, by which new species arise as a result of genetic mutations and eventually, upon the offspring's ability to reproduce instills reproductive barriers as the new species can no longer reproduce with their ancestor.

Postzygotic barriers

If mating is completed successfully, these barriers prevent the zygote from being formed. Examples are developmental errors or infertility from the hybrid species.

How does fusion occur?

If two species contact one another in a hybrid zone and barriers to reproduction are not strong, gene flow may be overwhelmingly strong and thus the two gene pools of species become increasingly alike. The two species eventually merge into one over time.