Biology Final Review > Chapter 24 - The Origin of Species > Flashcards
Chapter 24 - The Origin of Species Flashcards
allo
other
metron
measure
ana
up
genesis
origin, birth
auto
self
poly
many
clado
branch
hetero
different
macro
large
paedo
child
post
after
sym
together
patri
father or country
Allopatric speciation
A mode of speciation induced when an ancestral population becomes segregated by a geographic barrier or is itself divided into two or more geographically isolated subpopulations.
Biological species concept
Definition of a species as a population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but are not able to produce viable, fertile offspring with members of other populations.
Ecological species concept
Defining species in terms of ecological roles (niches).
Macroevolution
Evolutionary change above the species level, including the appearance of major evolutionary developments, such as flight, that we use to define higher taxa.
Microevolution
Evolutionary change below the species level; change in the genetic makeup of a population from generation to generation.
Morphological species concept
Defining species by measurable anatomical criteria.
Phylogenetic species concept
Definition of a species as a set of organisms with a unique genetic history—that is, as one branch on the tree of life.
Polyploidy
A chromosomal alteration in which the organism possesses more than two complete chromosome sets.
Postzygotic barrier
Any of several species-isolating mechanisms that prevent hybrids produced by two different species from developing into viable, fertile adults.
Prezygotic barrier
A reproductive barrier that impedes mating between species or hinders fertilization of ova if interspecific mating is attempted.
Punctuated equilibrium
In evolutionary theory, long periods of apparent stasis (no change) interrupted by relatively brief periods of sudden change.
Speciation
The origin of new species in evolution.
Species
A group whose members possess similar anatomical characteristics and have the ability to interbreed.
Sympatric speciation
A mode of speciation occurring as a result of a change in the genome of a subpopulation, reproductively isolating the subpopulation from the parent population.
New species arise through
speciation events driven by various selection pressure
One of the most common ways to define a species is using the biological species concept which maintains members of a species must naturally reproduce and produce viable, fertile offspring
o There are limitations to the biological species concept so other methods to define species exist
Hybrids, in terms of speciation
refers to offspring of 2 different species
Reproductive isolation between species can be maintained at many levels
o Prezygotic barriers such habitat isolation, timing of mating, mating behavior differences contributing to sexual selection, incompatible mating appendages and gametes that can not combine for chemical or physical reasons
o Postzygotic barriers assume a zygote is formed by it may have reduced viability so it does not survive or if it does, it is sterile or subsequent hybrid offspring have reduced viability
Speciation can occur with
physical, geographical barriers which keeps gene pools separate (allopatric) or by other means even when species are not isolated (sympatric)
In sympatric speciation, species may exploit smaller areas of their habitats called ecological niches which can drive differences between populations eventually to the point of speciation or sexual selection may subdivide populations so that eventually this behavioral isolation leads to other reproductive barriers
o In plants, duplication of entire sets of chromosomes can lead to polyploidism in which new species have stable, new chromosome numbers compared to original species
Hybrid zones exist in the middle ground between where
2 separate species overlap so that mating can take place
Different scenarios can develop from hybrid zones
o Reinforcement: Original species are selected for and hybrids do not do very well so that the original species continue to diverge
o Fusion: Hybrids are very fit and the 2 original species may eventually become one single species
o Stability: Original species stay separate but occasional hybrids continue to form in the hybrid zone but don’t increase or decrease in number
The length of time it takes for a new species to evolve is very variable with some speciation events being very quick if certain selection factors favor speciation
o Species that appear quickly in a geological time frame in the fossil record are said to follow the punctuated equilibrium pattern of speciation while others form very gradually over much longer periods of time
What is the difference between microevolution and macroevolution?
Microevolution refers to changes in the gene pool of a population over time which result in relatively small changes to the organisms in the population — changes which would not result in the newer organisms being considered as different species. Examples of such microevolutionary changes would include a change in a species’ coloring or size and overall adaptations to its environment.
Macroevolution, in contrast, refers to changes in organisms which are significant enough that, over time, the newer organisms would be considered an entirely new species. In other words, the new organisms would be unable to mate with their ancestors, assuming we were able to bring them together.
What is the relationship between the biological species concept and reproduction? What are some other ways to define a species?
In the biological species concept, a species is defined as a group of individuals who are able to breed with one another and produce viable (living), fertile (able to reproduce themselves) offspring. This implies a continuation of a genome from one generation to the next. For reproduction to be successful, many conditions must be met.
There are other ways to define species other than by just reproductive success, important in deducing species information for fossilized organisms or asexually producing organisms such as the prokaryotes.
Some other methods include the morphological concept which relies on anatomical structures and appearances to group related organisms, the ecological concept which involves the study of where and how organisms live and how they interact with the environment and the phylogenetic concept which used the evolutionary tree and common ancestry to separate species.
Describe some prezygotic and postzygotic barriers to successful reproduction.
One prezygotic barrier to reproduction is habitat isolation in which different species occupy different locations in the habitat such as some being aquatic organisms and some being terrestrial.
- Temporal isolation refers to organisms that live in the same area but reproduce during different times of the year so that they avoid reproducing together.
- Behavioral isolation can mean different species have evolved elaborate mating rituals and behaviors that vary so much that different species are not attracted to each other.
- Mechanical isolation refers to physical differences that impede successful implantation of sperm between species.
- Gametic isolation involves differences in reproductive tracts which make it difficult for gametes to successfully meet.
Postzygotic barriers typically involve the reduced viability and/or survival of hybrids. Some hybrids themselves are viable but have reduced fertility or are sterile due to chromosomal differences typically. Some hybrids are able to reproduce but their offspring are less robust and fail to thrive or reproduce due to too many genetic differences between the parental species.
Compare and contract allopatric and sympatric speciation.
Both allopatric and sympatric speciation will lead to the reproductive isolation of individuals due to separation of gene pools that will eventually cause the creation of a new species.
In allopatric speciation, geographic isolation will prevent populations from mixing their gene pools and once separate, each population is subject to potential differences in mutations, genetic drift and possibly different selection pressures that will cause microevolution in each population. After enough microevolution, the 2 populations could be reproductively isolated enough to speciate.
In sympatric isolation, you don’t need complete geographic isolation but changes in chromosome numbers due to mistakes in meiosis may create polyploidy which can lead to new species even in the same geographic locations.
Some other factors can cause sympatric speciation such as exploiting different zones within the same geographic area (habitat differentiation) or sexual selection (variety of behaviors or mate choice factors that can isolate some members of a population).
Whatever the cause of the separation, eventual speciation can occur.
What is a hybrid zone and what possible long term outcomes of a hybrid zone?
A hybrid zone is an area between the geographic distributions of two species that are similar enough to allow reproduction (reproductive barriers are not complete) so that offspring are created that are a mixture of each parental species.
Depending on factors such as hybrid viability, different outcomes can occur.
If the hybrids are ultimately less fit than either parent species, reinforcement will occur which will select against hybrids so, over time, there are fewer hybrids.
If there continues to be the creation of new hybrids and their fitness levels are similar to the parental species’, fusion may occur where the two species become one single species.
Finally, stability may occur if enough hybrids survive compared to the parental populations as to overwhelm any potential selection against the hybrids. In this case, the hybrids will still continue to form in the hybrid zone area.
How does punctuated equilibrium contrast with a more gradual speciation model?
Sometimes the fossil record shows the existence of species that seem to suddenly appear, remain unchanged for a period of time and then just as suddenly disappear. This contrasts with a fossil record that shows a slow change in certain species with many small differences noted along the way.
The important point in punctuated equilibrium is that what appears to be “sudden” changes can still be a considerably long time. A time period of 50,000 years is relatively short in geologic time so that a species forming in a shorter time span (due to increased speciation events such as geographic isolation or intense environmental selection), might appear to just come “out of nowhere” as opposed to those species that took longer to evolve.
