Lecture 4 origin of species Flashcards
What two phenomenas does the concept of a species must account for?
The distinctiveness of species that occur together at a single locality and the connection that exists among different populations belonging to the same species.
What is the morphological species concept?
- All individuals of a species share measurable anatomical traits that distinguish them from individuals of other species.
When can relying exclusively on morphology present problems?
when there is much variability within a single species or when two species are nearly identical in appearance.
What is the biological species concept?
species are composed of populations whose members mater with each other and produce fertile offspring.
What is reproductive isolation?
they do not mate with each other or do not produce fertile offspring.
What are prezygotic isolating mechanisms?
mechanisms that prevent formation of a zygote
What are postzygotic isolating mechanisms?
mechanisms that prevent proper functioning of zygote after they form
What does the biological species concept focus on?
the ability to exchange genes
What are some prezygotic isolating mechanisms?
ecological isolation, behavioral isolation, temporal isolation, mechanical isolation, and prevention of gamete fusion
What are some postzygotic isolating mechanisms?
hybrid inviability or infertility
What is ecological isolation (PIS)
species occur in the same area, but occupy different habitats and rarely encounter each other
What is behavioral isolation (PIS)
species differ in their mating rituals
what is temporal isolation? (PIS)
species reproduce in different seasons ar at different times of the day
what is mechanical isolation?
Structural differences between species prevent mating
what is prevention of gamete fusion (PIS)?
gametes of one species function poorly with the gametes of another species or within the reproductive tract of another species.
What is hybrid or infertility (PIS)?
hybrid embryos do not develop properly, or do not survive in nature, or are sterile
With behavioral isolation what are some differences that keep sympatric species from mating with each other?
visual signals, sound protection, chemical signals (pheromones), and electrical signals (electroreception)
With hybrids what are some defects?
They may have abnormal sex organs, or fail to form gametes and chromosomes may not be able to pair properly in meiosis
What can lead to speciation?
Adaptation
How does adaption lead to speciation?
as populations of species adapt to different circumstances, they likely accumulate many differences that may lead to reproductive isolation
What are some criticisms of the biological species concept?
- reproductive isolation may not be the only force maintain species integrity
- interspecific hybridization
- difficult to apply the concept to populations that geographically separated
- many organisms are asexual
- many species that do not hybridize in the wild do in captivity
- it is possible that different processes maintain species identity in different organisms
What are some benefits of the ecological species concept?
1.Each species adapted to its environment
2.distinctions among species are maintained by natural selection
3.stabilizing selection maintains the species’ adaptions
4. hybrids are quickly eliminated from gene pool
What is the phylogenetic species concept?
A species is defined as a cluster of populations that share a recent evolutionary history as shown on the evolutionary tree
What is to used to reconstruct an organism’s evolutionary tree?
morphological and genetic sequence data
Why can’t the phylogenetic species concept not be applied to all forms of life?
Because evolutionary histories have been described for relatively few groups
What is the two step process of speciation?
- initially identical populations must diverge
- reproductive isolation must evolve to maintain these differences
What effect of gene flow erases differences?
Homogenizing effect
Where is speciation more likely to occur?
in geographically isolated populations
What is allopatric speciation?
It takes place when a physical barrier subdivides a large population, or when a small population becomes separated from a species’ main geographical distribution
What are the two stages of allopatric speciation?
- two populations become geographically separated (preventing gene flow)
- accumulated genetic differences isolate them reproductively
What is sympatric speciation?
one species splits into two at a single locality, without the new species ever having been geographically separated
how does sympatric speciation occur as a result of polyploidy?
Because individuals have more than two sets of chromosomes
What is autoploidy?
all chromosomes arise from a single species and an error occurs in cell division which produces tetraploids which cannnot produce fertile offspring
How can sympatric speciation occur by disruptive selection?
It can cause a population to contain individuals exhibiting two different phenotypes
what is allopolyploidy?
two species hybridize, resulting in offspring having one copy of chromosomes of each species,
What is polymorphism?
a discontinuous genetic variation which results in one species having several different phenotypes
What is adaptive radiation?
closely related species that have recently evolved from a common ancestor by adapting to different parts of the environment (the bats and pollen)
What is key innovation?
New traits evolves within a species allowing it to use resources that were previously inaccessible
What is character displacement?
Two reproductively isolated but ecologically similar species come into contact, and natural selection in each species favors those individuals that use resources not used by the other species
What is are some results of character displacement?
greater fitness
2. trait differences in resources use will increase in frequency over time
3. species will diverge
With pace of evolution, what is gradualism?
accumulation of small changes over time
What is punctuated equilibrium?
Long periods of stasis followed by rapid changes
What has greatly increased over the last 600 million years?
Biological diversity
Define mass extinction
sharp decline of species divirsity
How many mass extinctions have occured?
5 mass extinctions
What is the cause of the 6th ongoing mass extinction?
human activity
What are the names of the five mass extinctions?
- ordovician
- devonian
- permian
- triassic
- cretaceous
What is another word for the cretaceous extinction?
K-T extinction
What is the K-T or cretaceous extinction, and when did it happen?
It is the extinction of nonavian dinosaurs and it happed 66 MYA because of a meteor impact
