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The process by which one species splits into two or more species.
Speciation fascinated Darwin because it is responsible for the tremendous diversity of life, repeatedly yielding new species that differ from existing ones. Speciation explains not only difference between species, but also similarities between them (the unity of life).
Changes over time (relatively short time periods) in allele frequencies in a population.
Microevolutionary mechanisms include mutation, natural selection, genetic drift, and gene flow.
The broad pattern of evolution over long time spans.
An example of macroevolutionary change is the origin of new groups of organisms such as mammals or flowering plants, through a series of speciation events.
What does species mean in latin?
Latin for "kind" or "appearance".
Although it is common to distinguish between various "kinds" of organisms through their appearance, they are truly divided into the discrete units we call species with differences in physiology, biochemistry, and DNA sequences.
Define Species based on the biological species concept.
A group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring - but do not produce viable, fertile offspring with members of other such groups.
Originated from the biological species concept by Ernst Mayr.
What is gene flow?
The transfer of alleles between populations, resulting from the movement of fertile individuals or their gametes.
Members of a species often resemble each other because their populations are connected by gene flow.
Gene flow has the potential to hold the gene pool of a species together, so long as it is not outweighed by effects of selection or drift (either of which can result in populations diverging).
What is reproductive isolation?
The existence of biological factors (barriers) that impede members of two species from producing viable, fertile offspring. Such barriers block gene flow between the species and limit the formation of hybrids, offspring that can result from an interspecific mating.
The barriers are categorized as prezygotic barriers and postzygotic barriers.
What is a hybrid?
Offspring that results from the mating of individuals from two different species.
What is a prezygotic barrier?
- "Before the zygote"
- A reproductive barrier that impedes mating between species or hinders fertilization if interspecific mating is attempted.
- The barriers typically act in one of three ways:
- a) By impeding members of different species from attempting to mate
- b) By preventing an attempted mating from being completed successfully
- c) By hindering fertilization if mating is completed successfully
What is a postzygotic barrier?
- "After the zygote"
- A reproductive barrier that prevents hybrid zygotes produced by two different species from developing into viable, fertile adults.
- These include:
- a) Developmental errors may reduce survival among hybrid embryos.
- b) Problems after birth may cause hybrids to be infertile or may decrease their chance of surviving long enough to reproduce.
What is habitat isolation?
A prezygotic barrier where two species occupy different habitats within the same area and may encounter each other rarely, if at all, even though they are not isolated by obvious physical barriers, such as mountain ranges.
Two species may live in the same geographic area but one may live in the water while the other lives primarily terrestrial.
What is temporal isolation?
A prezygotic barrier where species that breed during different times of the day, different seasons, or different years cannot mix their gametes.
One species may breed in the summer while the other breeds in the fall thus preventing them from interbreeding.
What is behavioral isolation?
A prezygotic barrier that prevents two species from interbreeding as courtship ritutals and other behaviors unique to a species are effective reproductive barriers. These behavioral rituals enable mate recognition, a way to identify potential mates of the same species.
What is mechanical isolation?
A prezygotic barrier after mating has been attempted between two species. Morphological differents prevent the successful completion of mating.
What is gametic isolation?
A prezygotic barrier after mating has been attempted but the sperm of one species may not be able to fertilize the eggs of another species.
For instance, sperm may not be able to survive in the productive tract of females of the other species, or biochemical mechanisms may prevent the sperm from penetrating the mebrane surrounding the other species' egg.
What is "reduced hybrid viability"?
A postzygotic barrier (after fertilization of the egg) where the genes of different parent species may interact in ways that impair the hybrid's development or survival in its environment.
The hybrid may be very frail and may not mature to adulthood or complete development.
What is "reduced hybrid fertility"?
A postzygotic barrier (after development of the zygote) where the hybrid is virgorous but may be sterile.
If the chromosomes of the two parent species differ in number or structure, meiosis in the hybrids may fail to produce normal gametes. Since infertile hybrids cannot produce offspring when they mate with either parent species, genes cannot flow freely between the species.
What is "hybrid breakdown"?
A postzygotic barrier (after development of the zygote) where some of the first-generation hybrids are viable and fertile, but when they mate with one another or either parent species, offspring of the next generation are feeble or sterile.
One strength of the biological species concept is that it directs our attention to how speciation occurs: by the evolution of repoductive isolation.
(T/F) However, the number of species that this concept may be applied to is limited. The biological species concept does not apply to fossils and organisms that reproduce asexually.
True. Page 492
The biological species concept emphasizes the _________ of species from one another due to reproductive barriers.
Awesome word - I know.
What is the morphological species concept?
A concept that characterizes a species by body shape and other structural features.
It has several advantages as it can be applied to asexual and sexual organisms, and can be useful without information on the extent of gene flow.
What is the ecological species concept?
A concept that characterizes a species in terms of its ecological nich, the sum of how members of the species interact with the nonliving and living parts of their envornment.
It may accommodate asexual as well as sexual species and emphasizes the role of disruptive natural selection as organisms adapt to different environmental conditions.
What is the phylogenetic species concept?
A concept that characterizes a species as the smallest group of individuals that share a common ancestor, forming one branch on the tree of life.
It is difficult in determining the degree in differences required to indicate separate species. The phylogenetic history of a species may be done by comparing its characteristics such as morphology or molecular sequences with those of other organisms.
What is allopatric speciation?
- allos - other
- partra - homeland
Gene flow is interrupted when a population is divided into geographically
Once geographyic separation has occured, the separated gene pools may diverge through different mutations, natural selection and genetic drift may occur. Reproductive isolation may then arise as a by-product of natural selection or drift having caused the populations to diverge genetically.
(T/F) Reproductive isolation between two populations generally increases as the distance between them decreases.
Reproductive isolation between two populations generally increases as the distance between them increases.
1) Which species concept(s) could you apply to both asexual and sexual species?
a) Biological species concept
b) Morphological species concept
c) Ecological species concept
d) Phylogenetic species concept
2) Which would be the most useful for identifying species in the field?
- 1) b, c, d
- 2) a - It is classification based on the morphological aspects of an organism.
What is sympatric speciation?
- syn - together
- patra - homeland
Speciation that occurs in populations living in the same geographic area due to a reduction of gene flow by factors such as polyploidy, habitat differentiation,
and sexual selection
. (It should be noted that these factors may also promote allopatric speciation).
A chromosomal alteration in which the organism possesses more than two complete chromosome sets. It is the result of an accident of cell division.
What is an autopolyploid?
- autos - self
- An individual that has more than two chromosome sets that are all derived from a single species.
For example, a failure of cell division could double a cell's chromosome number from the diploid number (2n) to a tetraploid number (4n).
What is an allopolyploid?
A fertile individual that has more than two chromosome sets as a result of two different species interbreeding and combining their chromosomes
Most hybrids are sterile because the set of chromosomes from one species cannot pair during meiosis with the set of chromosomes from the other species. However, an infertile hybrid may be able to propagate itself asexual (this is more common in plants than animals).
In subsequent generations, various mechanisms can change a sterile
hybrid into a fertile
What is habitat differentiation?
The occurance of sympatric speciation due to genetic factors enabling a subpopulation to exploit a habitat or resource not used by the parent population.
What is a population?
A localized group of individuals of the same species that can interbreed, producing fertile offspring.
What is sexual selection?
A form of natural selection, that may also cause sympatric speciation, in which individuals with certain inherited characteristics are more likely to mate than other individuals to obtain mates.
Contrast allopatric speciation and sympatric speciation.
Allopatric specation - A new species forms in geographic isolation from its parent populations, restricting gene flow and other reproductive barriers may arise as a byproduct of genetic changes that occur within the isolated population.
- Sympatric speciation - Speciation occurs due to an emergence of a reproductive barrier that isolates a subset of a population from the remainder of the population in the same area. Though it is rare than allopatric speciation, sympatric speciation can occur when geneflow to and from the isolated subpopulation is blocked as a result of one of the following:
- A Polyploidy - a condition in which an organism has extra sets of chromosomes
- Habitat differentiation - A population becomes reproductively isolated because of natural selection resulting from a switch to a habitat or food source not used by the parent population
- Sexual selection- The selection of mates due to genetically inherited factors
What is a hybrid zone?
A region in which members of different species meet and mate, producing at least some offspring of mixed ancestry.
- Hybrid zones may be narrow bands or thick bands.
What are the three possible outcomes for the hybrid zone over time? Which one of these occurs the most?
Reinforcement, Fusion, and Stability.
- Reinforcement - Stengthening of reproductive barriers - hybrids gradually cease to be formed
- Fusion - Weakening of reproductive barriers - the two species fuse
- Stability - Continued production of individuals
For speciation to occur, a barrier to _______ must be established.
What occurs in the following example of a hybrid zone:
When hybrids are less fit than members of their parent species, we would expect natural selection to ________ prezygotic barriers to reproduction, thus reducing the formation of unfit hybrids. The reproductive barriers are __________.
Reinforcement is the strengthening of reproductive barriers.
What occurs in the following example of a hybrid zone:
When two species come in contact with another in a hybrid zone where the barriers to reproduction are not strong, gene flow may occur where the reproductive barriers _____ further and the gene pools of the two species become increasingly _________. There is a ______ of reproductive barriers and a ________ of the species.
Weaken, Alike, Weakening, Fusion.
When the reproductive barriers are not very strong, the fusion of species may occur.
What occurs in the following example of a hybrid zone:
Production of hybrid individuals continue.
Stability occurs when there is a continuation in the production of hybrid individuals.
This occurs unexpectedly as one would expect the strengthening of the reproductive barriers in the hybrid zone.
What is punctuated equilibria?
In the fossil record, long periods of apparent stasis, in which a species undergoes little or no morphological change, interrupted by relatively brief periods of sudden change.
In contrast to punctuated equilibria, what is typically expected over long periods of times for speciation?
It is expected that species will gradually change over long periods of time rather than a sudden change followed by little change for a long period of time.
What does punctuated pattern termed from punctuated equilibria suggest in terms of the speed of speciation?
What else does it indicate in terms of apparences of new species and a "speciation clock"?
It suggests that once the process begins, speciation can be completed relatively rapidly.
This indicates that there may be a long period of relatively no to little change before the appearance of a new species and that there is no "speciation clock" within species for speciation to occur.
(T/F) The evolution of reproductive isolation is always due to large number alleles in genes.
It some cases, the allele of a single gene may induce a reproductive barrier. For instance, in a snail, the allele of the gene that controls the spiraling of the shell induces mechanical isolation.
Speciation can occur rapidly between diverging populations, yet the length of time between speciation events is often more than a million years. Explain this apparent contradiction.
The time between speciation events includes:
- a) The length of time that it takes for populations of a newly formed species to begin diverging reproductively from one another
- b) The time it takes for speciation to be complete once this divergence begins.
Although speciation can occur rapidly once populations have begun to diverge from one another, it may take millions of years for that divergence to begin.
(T/F) Due to repeated events, small differences between organisms can accumulate, leading to the formation of new groups of organisms.
This leads from speciation to macroevolution.
The largest unit within which gene flow can readily occur is a
Gene flow is the transfer of alleles into or out of a population due to the movement of fertiel individuals or their gametes. While gene flow is typically applied to populations, the gene flow is still possible within a species as per the definition of a species.
Bird guides once listed the myrtle warbler and the Audubon's warbler as distinct species. Recently, these birds have been classified as eastern and western forms of a single species, the yellow-rumped warbler. Which of the following pieces of evidence, if true, would be cause for this reclassification?
a) The two forms interbreed often in nature, and their offspring have good survival and reproduction
b) The two forms live in similar habitats
c) The two forms have many genes in common
d) The two forms have similar food requirements
e) The two forms are very similar in coloration
Going back to the definition of a species, a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring - but do not produce viable, fertile offspring with members of other such groups.
Males of different species of the fruit fly Drosophila that live in the same parts of the Hawaiian Islands have different elaborate courtship rituals that involve fighting other males and stylized movements that attract females. What type of reproductive isolation does this represent?
a) habitat isolation
b) temporal isolation
c) behavioral isolation
d) gametic isolation
e) postzygotic barriers
The mating rituals exhibited by the fruit flies are behavioral barriers between species.
Which of the following factors would not contribute to allopatric speciation?
a) A population becomes geographically isolated from the parent population
b) The separated population is small, and genetic drift occurs
c) The isolated population is exposed to different selection pressures than the ancestral population
d) Different mutations begin to distinguish the gene pools of the separated populations
e) Gene flow between the two populations is extensive
Extensive gene flow is not possible in allopatric speciation as the two populations are separated by a geographical barrier.
Plant species A has a diploid number of 12. Plant species B has a diploid number of 16. A new species, C, arises as an allopolyploid from A and B. The diploid number for species C would probably be
This is the sum of both - allopolyploid
According to the punctuated equilibria model,
a) natural selection is unimportant as a mechanism of evolution.
b) given enough time, most existing species will branch gradually into new species.
c) most new species accumulate their unique features relatively rapidly as they come into existence, then change little for the rest of their duration as a species.
d) most evolution occurs in sympatric populations
e) speciation is uaully due to a single mutation.