Chapter 18: Macroevolution Flashcards
1
Q
microevolutionary processes will
A
alter the pattern and extent of genetic and phenotypic variation within populations
- when these processes differ between populations, the populations will diverge genetically, and they may eventually become so different that they become different and distinct species
2
Q
speciation
A
smallest evolutionary independent unit
the process of species formation
- independence occurs when mutation, selection, gene flow, and drift operate on populations seperately
- evolution=changes in allele frequencies
- species form a boundary for the spread of alleles
WOULDN’T REPRODUCE W/ ANOTHER SPECIES
- genetics are too different it would create a nonviable offspring
- if they can interbreed fine then they aren’t different species
3
Q
Morphological definition of a species
A
- all individuals of a species share measurable traits that distinguish them from individuals of other species
- concept dates to Linnaeus’ classification system
PRO: works for extinct (fossils) or living species
i.e. field guides for plants/birds use this information
4
Q
macroevolution
A
occurs at or above the species level
5
Q
Mutation, NS, migration, and drift causes populations to diverge and form new species…. these can only be beneficial if
A
isolated
6
Q
different species follow
A
different evolutionary trajectories
speciation has never been DIRECTLY observed in nature or a lab, but there are many examples of where populations become so divergent that they can no longer exchange genetic material and become distinct species
example: stickleback (isolated in freshwater)
7
Q
a lack of gene flow
A
can also be described as speciation
8
Q
Disadvantages for morphological definition
A
- individuals in a single species look very different in size and coloration (mallards)
morphology does not help distinguish some closely related species that are nearly identical in appearance
- tells us little about evolutionary processes that produce new species
{MALARD}
male = green
female = beige
(we initially thought they were 2 different species)
- individuals may look different subtle ways
- can vary by sex, geography, which makes them look different
- could have subtle differences that WE must generalize
9
Q
Diagnostic Characters
A
Warblers:
these birds can look very similar but they actually have subtle differences
= diagnostic character
= experts can see these
- distinguished species via feather colour on throat and rump
10
Q
Biological Species Concept
A
- groups of interbreeding natural populations that are reproductively isolated from (don’t produce fertile offspring with) other such groups
- legal definition for endangered species acts
advantage:
- meaningful criteria for identifying species because it confirms lack of gene flow
- lack of gene flow is the key test of evolutionary independence (sexually reproducing spp)
- hard to apply in many situations (hard to force organisms to mate = you kinda have to SEE if they breed together)
- if populations don’t overlap, its hard to tell (“is this whale in SA = whale in NA?”, if they have a geographic barrier how will they mate?)
11
Q
Disadvantages for biological species concept
A
- problems with biological species (cannot be used for the following)
*asexual organisms = some insects
*extinct organisms = dinosaurs
12
Q
Phylogenetic Species definition
A
- using both morphological and genetic sequence data you have to first reconstruct the evolutionary tree for the organism of interest
- then define a phylogenetic species as a cluster [B1;B2;B3] of populations that emerge from the same branch
= is the species in the same cluster, if yes, then they’re the same species - thus, phylogenetic species comprises populations that share a recent evolutionary history
PRO:
- can be applied to any group of organisms including extinct ones (if u have morphological {fossils} or genetic data)
- works for asexually reproducing species
13
Q
Disadvantages of Phylogenetic Species
A
- detailed phylogenies not available for all organisms, and thus, not able to apply phylogenetic criterion to all species
= if you don’t have a strong data set you probably cant compare them to a lot of things
14
Q
Geographical Variation
A
- species can exhibit geographic variation
(i.e. birds from Canada vs birds from Mexico= gain subtle differences) - populations can differ genetically and phenotypically due to geographical separation
- neighbouring popns share characteristics because they’re in the same environments, exchange individuals and experience comparable NS
- very different in populations that are far away
15
Q
Gene Flow and Geographical variation
(populations living far away)
A
- gene flow is less likely to occur between distant populations, their gene pools and phenotypes will be different
- widely separated populations live in diff conditions and experience diff patterns of selection
- geographically separated populations of a species have dramatic phenotypic variation, we identify them as different subspecies [local variants of a species]
16
Q
Individuals from different subspecies will
A
interbreed where their distribution meets
- offspring will usually exhibit intermediate phenotypes
- 5 subspecies of rat snakes in eastern N.A. and they differ in colour and presence of stripes
17
Q
What is geographical variation
2 versions
A
patterns of geographic and studies that examine how the variation related to climatic or habitat variation provide insights into the speciation process
Two of the best studied patterns are:
- ring species [salamander case study]
- clinal variation [house sparrow case study]
how does climate and habitat provide insight into speciation
18
Q
Ring species
A
- ring shaped geographic distribution that surrounds uninhabitable areas
- adjacent populations exchange genetic material
- BUT gene flow btwn distant populations occur only through intermediate populations
(further apart the animals get the less genes are shared) - i.e. lungless salamander
a) SOUTHERN SUBSPECIES: since they still have the ability to exchange genetic information through intervening populations that form the ring they are of the same species - in the intermediate stage of species formation
b) but in general, the populations are so divergent they’re separate species
19
Q
Salamanders and being Ring species
A
- widely distributed in coastal mountains and Sierra Nevada, BUT, cannot survive in hot dry central valley
- 7 subspecies differ in a variety of traits (e.g. colour, size, ecology, etc.)
- adjacent subspecies interbreed where they overlap in geography (intermediate phenotypes are common)
- southern end of Central Valley adjacent subspecies rarely interbreed (differentiated so much, no longer exchange genetics)
20
Q
What would happen if one of the salamander species came back to the ring
A
- after a long period of separation, they won’t recognize each other
- but they’ll still produce the same fertile babies
21
Q
clinical variation
A
- when species distributed over large, environmentally diverse area, some traits exhibit a cline
CLINE= pattern of smooth variation in a trait along a geographic gradient (continuous connection amongst all populations)
- e.g. clinal variation in body size
- northern species have larger bodies and shorter appendages (conserve body heat)
22
Q
clinial variation is due to
A
- oftentimes, due to gene flow between adjacent populations that are adapted to slightly different conditions
- at opposite ends of clines (separated by large distances) may have little gene flow via reproduction
- thus, over big enough cline, distant populations are genetically and morphologically distinct
23
Q
mechanisms of genetic isolation
A
*how do species form?
1) initial step isolates the population
2) next step results in divergence in traits such as mating system or habitat use
3) final step produces reproductive isolation
- isolation and divergence steps take place over time and to occur while populations were located in and adapting to different geographic regions
24
Q
final phase:
A
- occurs when the diverged populations came back into physical contact (secondary contact)
{test to see if two individuals, one that has been separated can still be fertile}
*isolation/divergence/secondary contact model provides framework to work with (too simple)
25
physical isolation as a barrier to gene flow
- allopatric model (Mayr 1942)
- physical isolation creates an effective barrier to gene flow (i.e. mountain ranges)
- geographic isolation is important for second stage of speciation (genetic and ecological divergence)
- isolation comes about due to dispersal [moving away/they isolate themselves] or through vicariance events [geography isolates them]
[mountain ranges comes up]
26
does a river work as physical isolation for a bird
No, because it can just fly over it
27
dispersal diagram
large island A
small island B
- seperated from each other
1) before: everyone is on A
2) during: some individuals migrate to B
3) the B individuals are isolated population and will become new birds asap
= physical isolation as a barrier to gene flow
28
vicariance diagram
large land C
1)before: everyone is on C
2) a Geographic barrier (i.e. mountain range) cuts off land that animals cant move through
3) the isolated land of C diverges carrying individuals with it
= physical isolation as a barrier to gene flow
29
geographic isolation via dispersal and colonization: fruit flies
- Hawaiian fruit flies
- 1000 species are known w/ high ecological diversity
HOW:
- geographical isolation: some were cut off from the mainland and developed a separate, large species with their own niches
- Hawaiian finches are endemic (Single Island), only in Hawaii and particular to a single island, only in one place in the world
= if small populations, or one pregnant female, disperse to new islands then they are physically cut off from the ancestral species
30
Fruit Fly Hawaiian Islands
Oldest Island: Nihau
Youngest: Hawaii, we use carbon dating to find this out
- five species of drosophila re closely related
- older to younger sequence of branches on phylogeny correspond to age of islands
- some of speciation was a result of island hopping
31
2 predictions of dispersal and conditions
| islands
1) Closely related species should almost always be found on adjacent islands
2) some sequences of branching events [oldest island] should correspond to the sequence in which islands were formed
32
Case Study: Bonocum et al. 2005
- used sequence data differences in mitochondrial and nuclear genes to estimate phylogeny of closely related Hawaiian flies
- found patterns supportive of dispersal and colonization hypothesis
- evidence that dispersal to new habitats triggered speciation
= dispersal + colonization: increased chance of speciation
CONCLUSION: some of speciation was a result of island hopping
33
the closer the branches on the cladogram
the more related the species are
34
Similar studies to Bonocum reveal the same pattern in
- Hawaiian crickets (Mendelson and Shaw 2005)
- Galapagos Turtles (Beheregaray et al. 2004)
NOTE:
- its not just islands but other habitats too (islands are good because we can determine their age and the population is cut off from mainland)
35
sessile organism meaning
cant move; idle
36
Vicariance can eventually
lead to dispersal
vicariance-splitting of a populations former range into 2+ isolated patches
37
how did Ernest Mayr define biological species
"groups of interbreeding natural populations that are reproductively isolated from (Don't produce fertile offspring with other such groups)
- thus, we can think of them as a large gene pool that can be subdivided into local populations
38
what's the catch to members of 2 populations interbreeding and producing fertile offspring
it has to be under natural conditions
39
what does the biological species concept help explain
why individuals of a species generally look alike
- members of the same gene pool share genetic traits that determine their appearance
*despite its limitations it currently provides the best evolutionary definition of a sexually reproducing species*
40
species that reproduce asexually have to use what speciation criteria
morphological or biochemical criteria
41
what would a cluster be on the evolutionary tree
the twigs
42
what is a subspecies
local variants of a species
43
Clinal Variation
- when a species is distributed over a large environmentally diverse area, some traits can exhibit a CLINE
CLINE=. a sooth pattern of variation across a geographic gradient
*usually results from gene flow between adjacent populations that are adapting to slightly different conditions, but if populations at opposite ends of a cline are separated by great distance they may exchange little genetic material via reproduction
= when a cline extends over a large geographical gradient, distant populations may become genetically and morphologically distinct
44
populations in colder environments will have
larger bodies and shorter appendages
- pattern that is usually interpreted as a mechanism to conserve body heat
45
Reproductive Isolating Mechanism
- prevent individuals of different species from mating and producing successful offspring (progeny)
- by reducing the chances of interspecific mating and the production of hybrid offspring these isolating mechanisms prevent the gene pools of distinct species from mixing
46
Reproductive isolating mechanisms operate at different times during the reproductive process
| prezygotic vs postzygotic
PREZYGOTIC
- exert their effects before fertilization and the production of a zygote
POSTZYGOTIC
- operate after fertilization and zygote formation
= isolating mechanisms are not mutually exclusive and two or more of them can affect the outcome of a between species interaction
47
Prezygotic Isolating Mechanisms
- prevent production of hybrid offspring:
- blocks interspecific fertilization
1) ecological: live in diff habitats
*tigers and lions were common in India until extreme hunting, but even still they lived in different environments (lions-grasslands, and tigers-forests) and didn't interbreed
2) temporal: breed at diff times
- fruit flies (pesimilis and psuedoobscura) overlap in their geographical distributions but persimilis mates in the morning and psudoobscura in the afternoon
- pine in california, where pines radiata release pollen in February and pinus muricate release pollen in April
3) behavioural: can't communicate
- animals rely on specific signals that differ between species, used to identify potential mates
- female birds rely on the song, colour and display of males to identify members of their own species
- female fireflies identify mates by their flashing patterns
{COURTSHIP DISPLAYS}
4) mechanical: can't mate
- for plants, many have anatomical features only allowing certain pollinators
- flowers and nectar of 2 Californian plants (purple-monkey flower and scarlet monkey-flower), the purple-monkey is pollinated by bees and gives it a landing platform, has bright yellow streaks as a nectar guide to the short nectar tube located among the petals
the scarlet one is for hummingbirds (its red and bees cant see it, but hummingbirds are attracted to red) the reproductive extend above the petals and the nectar is more dilute and produced in greater quantity making it easy for hummingbirds to ingest
5) gametic: non-matching
receptors on genes (incompatability between sperm of one species and the eggs of another may prevent fertilization)
- many marine invertebrates release gametes into the envrironment for external fertilization, the sperm and eggs recognize each others complementary surface proteins but if they're diff species it won't match
- for animals with internal fertilization, the sperm of one species may not survive and function within the reproductive tract of another
- interspecific mating amongst fruit flies induces a reaction in the female reproductive part that blocks foreign sperm
- physiological incompatibilities btwn pollen tube and stigma prevent interspecific fertilization in some plants
48
Postzygotic Isolating Mechanisms reduce the success of hybrid individuals
- if prezygotic isolating mechanisms between 2 closely related species are incomplete or ineffective, sperm from 1 species sometimes fertilizes an egg of the other
- 2 species will be reproductively isolated if their offspring (interspecific hybrids) have lower fitness than the offspring of intraspecific mating
49
Three post zygotic Isolating Mechnaism
Hybrid Inviability:
- hybrid organisms frequently die as embryos or at an early age
i.e. domestic sheep and goats can mate and fertilize one another's ova, but the hybrid embryos always die before coming to term because the developmental programs are incompatible
Hybrid Sterility:
- the parent species differ in the number of structure of their chromosomes, which cannot pair properly during meiosis
- hybrids have 0 futness because they leave no descendants
- most familiar exmaple= MULE, product of matching a female horse and male donkey {ZEBROIDS} producing usually sterile offspring
Hybrid Breakdown
- Some F1 are healthy + fertile, they can breed with other hybrids and with both parental species
- second generation produced by matings btwn F1 hybrids or btwn F1 hybrids and either parental species may exhibit reduced survival or fertility
- experimental crosses btwn fruit flies can produce high rates of chromosomal abnormalities and harmful types of genetic recombinations
= reduces fitness of hybrid individuals
**hybrid individuals have 2 sets of developmental instructions, one from each parent species that may not interact properly for embryonic development**
50
allopatric speciation occurs between geographically separated populations
ALLOPATRIC SPECIATION
- may take place when a place when a physical barrier subdivides a large population or when a small populations becomes separated from a species main geographical distribution
- allopatric speciation occurs in 2 stages:
1) populations become geographically separated, preventing gene flow btwn them, then as the populations experience distinct mutations and different pattern of NS and genetic drift, they may accumulate genetic differences that isolate them reproductively
2) Genetic divergence
The isolated populations evolve genetic differences due to mutations, natural selection, and genetic drift.
= MOST COMMON MODE OF SPECIATION IN LARGE ANIMALS
51
Geographical Seperation
- can sometimes occur when a barrier divides a large population into 2+ units
- i.e. hurricane can create new channels that divide the low coastal islands and the populations inhabiting them
PANAMA EXAMPLE
- movements of earths crust 5 mill years ago, separate a shallow sea into tropical Pacific Ocean leading to marine animal populations to be subdivided
- experienced patterns of mutation, NS, and genetic drift different from those experienced by populations in the tropical pacific ocean
- populations diverged genetically, and pairs of closely related but distinct species that now live on either side of the divide
52
small populations may become isolated at the edge of a species' geographical distribution
- peripheral populations like these can differ genetically from the central population because they're adapted to somewhat different environments
*founder effects and small population size can promote genetic drift, and NS can favour the evolution of distinctive traits
= if they experience limited gene flow from the parent population, these agents of evolution will foster genetic differentiation between them
*accumulated differences=reproductive isolation*
EXAMPLE
- populations established by colonization of oceanic islands where the founder effect makes the populations genetically distinct
53
founder populations of a species may colonize an island multiple times and the process can be repeated leading to
the evolution of a SPECIES cluster
- a group of closely related species recently descended from a common ancestors
- can evolve relatively quickly
54
secondary contact provides a test of whether allopatric speciation has occurred
- may reestablish contact when a geographical barrier is eliminated or breached
- test of whether genes have diverged enough to make them Reproductively isolated
SECONDARY CONTACT: contact after a period of geographical isolation
55
what happens if the gene pools of two populations didn't differentiate much during geographical separation
-the populations will interbreed and merge into one, a phenomenon described as SPECIES FUSION
- IF THEY DID THOUGH, they'd be reproductively isolated and be separate species
56
Early stages of secondary contact + prezygotic rep. isolation
| where could populations mate
- may be weak or incomplete
- members of each population may mate with others from a diff population to produce fertile offspring in HYBRID ZONES
(generally narrow + geographical factors maintain the separation of their gene pools)
57
Hybrid Zones and Breeding Ranges of Bullock's Oriole and Baltimore Oriole
- overlap in midwest NA
- 2011 study of Carling et. al from Cornell showed a narrow hybrid zone with only 2 environments
(BULLOCK=HOTTER AND DRIER CLIMATES
BALTIMORE=COOLER AND MOISTER CLIMATE)
they hypothesized that although hybrids may survive and reproduce in mixed habitat, they're probably not well adapted to either extreme environment
- therefore, if NS eliminates hybrids outside narrow hybrid zone (the middle), the two species will remain reproductively isolated
58
Postzygotic isolating mechanisms cause
hybrids to have lower fitness than either parent species
- NS will favour individuals that choose mates of their own species, thus promoting the evolution of prezygotic isolating mechanisms
59
phenomenon of evolution of prezygotic barriers to reproduction after post zygotic barriers
REINFORCEMENT
- bc the prezygotic mechanisms REINFORCE those post zygotic barriers
60
Sympatric Speciation
(occurs within one continuous distributed pop)
- here, reproductive isolation evolves btwn distinct subgroups that arise within 1 population
- models of sympatric speciation don't require that the population is geographically or environmentally separated as gene pools diverge
EXAMPLES;
- insects that feed on just 1 OR 2 plant species are likely to evolve by sympatric speciation
- they will carry out important life cycle activities on or near host plants (mating, laying eggs, feeding, etc) the plant they chose is usually genetically determined/based on the plant they ate as larvae
## Footnote
specices from ancestal in same habitat
61
could a genetic mutation change the insects' choice of a host plant
- mutant individuals would shift their life cycle activities to the new host = ecological isolation
- they'd form a separate subpopulation = HOST RACE
*reproductive isolation could evolve between different host races if the individuals are more likely to mate with each other than outsiders
BUT THIS IS CONTROVERSIAL
- assumes that genes controlling host plant choice and mating preferences change simultaneously
62
what's a host race
- a lineage of a parasite species that inherits phenotypic traits adapted for a specific type of host
OR
- arises from mutations favouring genetically distinct host of parasite
| sub population
63
Host plant choice is controlled by
several gene loci in insect species or past experience in others
- apple maggot example
natural choice: hawthorn (N.A)
- 2 host species have appeared in the last 150 years
- reside on apples and cherries
- controlled by a few genes
1st host race: feeding on apples
2nd host race: feeding on cherries
Andrew Michel of Notre Dame:
- variations at a few gene loci can change their feeding preferences
- other genetic differences can cause the host races to mate at different times but they don't show preference for their own members of their own host race
*no behavioural isolation*
DIVERGENCE LARGELY DRIVEN BY DISRUPTIVE SELECTION: diversifying form of natural selection
64
sympatric speciation and polyploidy
- often occurs in plants through polyploidy (where individual has 1+ copies of entire haploid complement of chromosomes)
- polyploidy can lead to speciation because these large-scale genetic changes may prevent polyploid individuals from breeding with individuals of the parent species
- nearly half of all flowering plant species are polyploid
## Footnote
Sympatric speciation is when a new species forms in the same area as the original one, without physical separation,
65
3 genetic mechanisms that can lead to reproductive isolation
genetic divergence between allopathic populations, polyploidy in sympatric populations, and chromosome alterations that occur independently the geographical distributions of populations
66
Without gene flow...
- geographically separated populations inevitably accumulate genetic differences through mutation, drift, and NS
67
With post zygotic reproductive isolation, mutations in a few gene loci can establish
reproductive isolation
- for example 2 common aquarium fishes, swordtails and platys mate and 2 genes induce the development of lethal tumours in their hybrid offspring
- when hybrid sterility is the primary cause of reproductive isolation amongst fruit flies, at least 5 gene loci are responsible
- 55 gene loci contribute to post zygotic reproductive isolation btwn fire-bellied toad and yellow-bellied toad
68
For prezygotic reproductive isolation,,, some mechanism have
a simple genetic basis
i.e. a single mutation reverses the direction of coiling in the shells of some snails
- some clockwise some counterclockwise and they can't mate with each other
69
T/F: many traits that are now prezygotic isolating mechanisms are from sexual selection
T
- exaggerates showy structures and courtship in males
- prevent interspecific mating
- closely related duck species exhibit dramatic variation in the appearance of males, but they also hybridize in captivity w/ viable offspring
70
reproductive isolation and speciation in ducks
- likely result of geographical isolation and sexual selection on just a few morphological and behavioural characteristics that influence mating behaviour
- doesn't require much genetic change, rather sexual selection helps
71
sexually dimorphic
sexes of the same species exhibit different morphological characteristics
- include more species than non-dimorphic ones
72
Autopolypolidy VS Allopolyploidy
chromosome duplications in a single species (autopolyploidy)
hybridization of diff species (allopolypoloidy)
73
AUTOPOLYPLOIDY
- 2n producing 4n offspring
- caused by error in mitosis or meiosis (spontaneously receive same number of chromosomes as somatic cell)= UNREDUCED GAMETES)
- diploid pollen can fertilize diploid ovules of self-fertilizing or another plant with unreduced gametes
- the resulting 4n can reproduce by itself or by intercrossing breeding but cant produce fertile offspring by hybridizing with its diploid parents
= REPRODUCTIVELY ISOLATED FROM OG 2N POPULATION
74
fusion of diploid with normal haploid
3n
- triploid
- usually sterile because its an odd number of chromosomes can't segregate properly during meiosis
75
ALLOPOLYPLOIDY
- two closely related species hybridize and form polyploid offspring, hybrid offspring are sterile if 2 parents have diverged where chromosomes don't pair properly
- if hybrids chromosome number is x2, then chromosome complement is also x2
= PRODUCING HOMOLOGUS CHROMOSOMES THAT CAN PAIR DURING MEIOSIS
- they can produce polyploid gametes and through self/cross fertilization can establish a polyploid population (can happen fast without geographical isolation)
76
T/F: even when sterile, polyploids are often robust, growing larger than either parent species
T
- thus, autopolyploids and all-polyploids (coffee, cotton, etc)
are important to agriculture
i.e. bread wheat for at least 30% of the world arose through hybridization
77
Bread wheat
- genome includes three diploid sub genomes (AA,BB,DD)
* divergence from ancestor produced AA na dBB
* hybridization between decedents produced DD
- all 3 genomes are diploid (2 sets of 7 chromosomes, 2n=14)
* then AA hybridized with BB to form tetraploid (2n=28, AABB)
* then this hybridized with DD to form hexaploid (2n=48, AABBDD)
= each of the 3 ancestor contributed 2 sets of 7 chromosomes
at the end= hexaploid with 42 chromosomes
78
plant breeders and allopolyploid
- increase probability (bc they grow so big) with chemicals that foster nondisjunction during mitosis
Experiment 1:
scientific crossed radish and cabbage hoping to develop a plant with edible roots and leaves but they actually got a cabbage like root and radish like leaves (opposite)
Experiment 2:
- allopolyploid grain= has disease resistance of rye parent and high productivity of wheat parent
79
Chromosome Alterations can foster speciation
- closely related species have a substantial number of chromosome differences between them (inversions, translocation, deletion, and duplication)
= foster postzygotic isolation which we can compare with banding patterns in stained chromosomes
*if bands are similar from related species then its comparable portions of genome, so we can use this to identify chromosome segments and compare positions*
80
Banding positions amongst the great apes
- reveals that whole sections of chromosomes have been rearranged over evolutionary time
HUMANS: diploid complement of 46 chromosomes
CHIMP/GORILLA/ORANG: 48 chromosomes
* difference is due to fusion of two ancestral chromosomes into chromosome 2 of humans; the ancestral chromosomes are separate in the other apes *
BANDING PATTERNS SHOW:
- humans centromere position in chromosome 2 closely matches that of a centromere in chimpanzee chromosomes, reflecting their close evolutionary relationship
- this falls within an inverted region of the chromosome in gorillas and orangutans; showing evolutionary diverge from chimps and humans
81
Navarro study
- from University in Spain
- compared the rates of evolution in protein-coding genes that lie in rearranged chromosome segments of humans and chimps to those in genes outside rearranged segments
WHAT THEY SAW:
- proteins evolved more than twice as fast in rearranged segment
- reasoning that: rearrangements inhibit chromosome pairing and recombination during meiosis, new genetic variation favoured by NS would be conserved in these rearranged segments
= VARIATIONS WOULD ACCUMULATE OVER TIME AND CONTRIBUTE TO GENETIC DIVERGENCE BTWN POPULATIONS WITH THE REARRANGEMENT AND THOSE W/O IT
= CHROMOSOME REARRANGEMENTS CAN BE A TRIGGER FOR SPECIATION: once a chromosome rearrangement becomes established within a population, that population will diverge quicker
- genetic divergence eventually causes reproductive isolation
| CHROMOSOME REARRANGEMENT=LOW RECOMBINATION
## Footnote
low recombination actually helps preserve genetic differences.
Here’s why:
Normally, recombination shuffles genes, which can blend traits and slow divergence.
In low-recombination regions, genes stay linked together longer, preventing mixing.
This allows natural selection to act more effectively on beneficial mutations in these regions, reinforcing differences between species.
So, instead of slowing divergence, lower recombination actually protected key genetic changes, helping humans and chimps evolve separately!
82
the steps of allopatric speciation
1) pops become geographically separated, preventing gene flow btwn them
2) as populations experiences mutations and diff patterns of NS and genetic drift, they may accumulate genetic diff that isolate them reproductively
83
if during secondary contact, species breed and produce babies what is it called
species fusion
84
geographical separation case study: isthmus of Panama
- 5 mya uplift
- separated once continuous shallow sea into eastern tropical Pacific Ocean and wester tropical Atlantic ocean
- mutation, NS, and drift differed on each side
- populations diverged genetically and pairs of closely related species live on either side
**cortez rainbow wrasse and blue-headed wrasse are genetically diff w/ a common ancestor**
85
species cluster is
a group of closely related species recently descended from a common ancestor
86
when can allopatric populations reestablish contact
- when the barrier is eliminated or breached
87
secondary contact
- contact after a period of geographical isolation
- provides a test of whether the genes in a population have diverged enough to make them reproductively isolated
88
if the species are not very different, they'll interbreed and merge into one....
species fusion
89
hybrid zones are
geographic areas where the hybrid offspring of two divergent species are common
90
reinforcement
evolution of prezygotic barriers to reproduction after post zygotic barriers exist
91
polyploidy
species have multiple sets of chromosomes (plants), cant breed with parent species
92
chromosome alterations can
foster speciation
93
genetic divergence in allopatric populations can lead to
speciation
94
polyploidy is a common mechanism of
sympatric speciation in plants
95
polyploidy is a
common mechanism of sympatric speciation in plants
96
genetic divergence in allopatric popns.
can lead to speciation
97
chromosome alterations can
foster speciation
