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BIO152H5 Chapter Notes - Chapter all: Mate Choice, Punctuated Equilibrium, Ibm 7090

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Maria Arts

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Speciation the process by which one species splits into two or more species
o Responsible for tremendous diversity of life, creates new species that are different from the
current ones (they have similarities between them)
o When speciation occurs, the species share many common similarities because they have one
common ancestor
o For example, Flightless cormorant is related to flying cormorant
Microevolution changes overtime in allele frequencies
o Mutations, natural selection, genetic drift, and gene flow
Macroevolution pattern of evolution above species level
o For example, changes in the origin of groups of organisms, such as mammals or flowering plants
Concept 24.1- The biological species concept emphasizes reproduction isolation:
The ord speies is Lati for kid or appearae
Biologist compare morphology (body form) of different groups of organisms, physiology, biochemistry,
and DNA sequence
o Biological species concept
o Morphospecies concept
o Ecological species concept
o Phylogenetic species concept
These results confirm that morphologically distinct species are indeed discrete groups
Species is a group of populations whose members have potential to interbreed in nature and produce
viable, fertile offspring
o But do not produce viable, fertile offspring with members of other groups
These species are united by the reproductive compatibility (potentially)
What holds gene flow of a species together, causing them to resemble each other than they resemble
other species?
o Gene flow occurs between different populations of a species
o Ongoing exchange of alleles tends to hold the population together genetically
o ABSENCE of gene flow plays a key role in formation of new species
Keeping them apart once their potential to interbreed has reduced
Reproductive isolation:
Formation of new species hinges on reproductive isolation
Reproductive Isolation existence of biological factors (barriers) that impede members and producing
viable and fertile offspring
These barriers block gene flow between species and limit the formation of hybrids
Hybrid offspring that results from interspecific mating
Single barrier may not prevent all gene flow combination of several barriers can effective isolate a
species gene pool
There are barriers between closely related species which are not so obvious
Prezygotic barriers (before the zygote) block fertilization from occurring
o Impeding members of different species from mating
o Preventing an attempted mating from being completed successfully
o By hindering fertilization if mating is completed successfully
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Postzygotic barriers (after zygote) contribute to reproductive isolation after hybrid zygote is formed
o Developmental errors may reduce survival among hybrid embryos
o Problems after birth may cause hybrid to be infertile or may decrease chances of surviving long
enough to reproduce
Limitations of the Biological Species Concept
This concept applies to a limited # of species
There is no way to evaluate the reproductive isolation of fossils
Does not apply to organisms that reproduce asexually all or most of the time (i.e. prokaryotes)
Species are designated by absence of gene flow
Many pairs of species that are morphologically and ecologically distinct yet gene flow occurs between
o I.e. grizzy bear and polar bear
Natural selection can cause species to remain distinct even though some gene flow occurs between them
BSC may overemphasize gene flow and downplay role of natural selection
Morphological species concept characterizes a species by body shape and other structures
o Can be applied to asexual and sexual organisms
o Useful even without info on extent of gene flow
o Disadvantage: relies on subjective criteria researches have to disagree on which structural
features distinguish a species
Ecological species conceptviews species in terms of ecological niche the sum of how members of
the species interact with nonliving and living parts of their environment
o Two species of salamanders might be similar in appearance but differ in the foods they eat or
ability to tolerate dry conditions
o Accommodates asexual as well as sexual species
o Emphasizes the role of environmental conditions
as organisms adapt to different environmental conditions
favors traits that benefit organisms in exploiting resources in their environment
Phylogenetic species concept species as smallest group of individuals that share a common ancestor
forming one branch of tree of life
Compare characteristics (i.e. morphology or molecular sequences with those of other organisms)
Distinguish groups of individuals that are sufficiently different to be considered separate species
Difficulty with species concept determining the degree of differences required to separate species
Concept 24.2- Speciation can take place with or without geographic separation
Allopatric speciation (Greek; allos other and patra homeland)
gene flow is interrupted when a population is divided into geographically isolated subpopulations
o i.e. water level in lake may subside result in 2 or more smaller lakes that are now home to
separate populations
o river change course and divide population of animals that cannot cross it
allopatric speciation can also occur without geological remodelling
o individuals colonize remote area and descendants become geographically isolated from parent
Process of Allopatric Speciation:
How formidable must a geographic barrier be to promote allopatric speciation?
o Depends on the ability of organisms to move about
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Birds, mountain lions, and coyotes can cross rivers and canyons
Windblown pollen of pine trees and seeds of many flowering plants
Small rodents may find a wide river or deep canyon a formidable barrier
Once geographical separation occurs, separated pools diverge
Different mutatuons arise
Natural selection and genetic drift may alter allele frequencies
Reproductive isolation may arise as a by-product of selection of drift having the populations diverge
o i.e. Andros Island (Bahamas) populations of mosquitofish colonized a series of ponds that later
isolated from one another
o genetic analyses indicates that there was little or no gene flow currently occurs between the
o environments of these ponds are similar except that some contain many predatory fishes while
others do not
o In high predation selection has favoured the evolution of a mosquitofish body that enables
rapid burst of speed
o In ponds that lack predation, selection has favored a different body shape improves ability to
swim for long periods
o How have these different selective pressures affected the evolution of reproductive barriers?
o Researchers mated the mosquitofish from both bonds
Female mosquitofish prefer to mate with males whose body shape is similar to their own
Establishes barrier to reproduction between mosquitofish from ponds with and without
By-product of selection for avoiding predators reproductive barriers have started to
form in there allopatric populations
Evidence of Allopatric Speciation:
Speciation can occur in allopatric populations
o i.e. 30 species of snapping shrimp in genus Alpheus that live off the Isthmus of Panama
o 15 of the species live on the Atlantic side of the isthmus, while the rest live on the Pacific side
o Before the isthmus, gene flow could occur between the Atlantic and Pacific populations of
snapping shrimp
o Did the species on different sides of the isthmus originate by allopatric speciation?
o Morphological and genetic data group these shrimp into 15 pairs of sibling species (pair of whose
eer speies are eah other’s losest relatie
o Each of these 15 pairs one of the sibling species lives on the Atlantic while other lives on Pacific
o This is due to geographic separation
Importance of allopatric speciation is also suggested by the fact that regions that are isolated or highly
subdivided by barriers typically have more species than do otherwise similar regions that lack such
o i.e. many unique plants and animals are found on the geographically located Hawaiian Islands
o Similarly, unusually high numbers of butterfly species are found in SA regions that are subdivided
by many rivers
Lab and field tests also provide evidence that reproductive isolation between 2 populations generally
increase as the distance between them increase
o Study with dusky salamanders
o Biologist brought individuals from different populations into lab and tested their ability to
produce viable and fertile offspring
o researchers observed that little reproduction isolation from neighbouring populations
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