Speciation Flashcards
Speciation
one species becoming two or more species Bridges gap between microevolution and macroevolution Rise of new groups of organisms Speciation results in differences in morphology (structure of organisms) Physiology Biochemistry (chemical processes) DNA sequences
Species
Characterized based on differences in body shape and other anatomical structures
Categorized by ecological niche: sum of interactions between a species and the abiotic factors (nonliving) of the environment
Smallest group of organisms (individuals) with a common ancestor
Focuses on reproductive barriers
Process of speciation
Isolation of gene pools or two or more populations of a species
Preventing gene flow
Inability to interbreed even if mating is attempted, and if offspring is produced, they are not fertile
Pre-zygotic Barrier
if for some reason a sperm from one species does fertilize an egg of another species, get a hybrid
Post-zygotic Barrier
result in reproductive isolation of the hybrid
Habitat isolation
impedes mating, get reproductive isolation and over time speciation
Temporal Isolation
Results in speciation Breeding at different times of the day Breeding during different seasons Breeding during different years Crickets: G. Firmus (left) Matures later G. Pennylvanicus Matures earlier
Blue-footed Boobies
Female will not mate with the male unless he does a high-stepping dance that impresses her
Female is looking for mate that will increase her offsprings survival and chance of success
Prevents breeding between different species
Once the male has attracted the female, she has to do the pointing display
Mechanical Isolation
genitals of male and female have to fit like a lock and key; if they don’t, sexual activity will not occur. Cannot get passing of sperm to the egg
Gametic Isolation
Mating occurs but the gametes do not fuse
Sponges release their egg and sperm into the water, can have many species. Receptor site on the surface of the egg must match the sperm. Only sperm from the same species is going to fertilize the egg
Postzygotic Barriers: reduced hybrid viability
Result in reproductive isolation
This occurs after a hybrid is formed
Hybrid = offspring of 2 sub species (closely related species )
Prevent the hybrid from developing into a viable fertile adult
Salamander - genus ensatina, sometimes inbreed, usually hybrid embryo does not complete development
If it does, they don’t last long - decreased viability
Post zygotic Barriers: reduced hybrid fertility
Horse has 32 chromosomes per gamete
Donkey has 31 chromosomes per gamete
Not much difference in # of genes that are donated by each parent
Why the hybrid (mule or hinny) is viable, live to be old, but are infertile
Post zygotic Barriers: hybrid breakdown
First generation hybrid is viable and fertile due to hybrid breakdown
Mating between hybrids or between hybrid and one of the parents results in hybrid that is weak and infertile
Different strains have accumulated recessive mutant alleles as they have evolved from a common ancestor
Hybrids are plants of the next generation
Have too many recessive mutant alleles
Allopatric Speciation
Population is decided by physical barriers into sub-populations
Snapping shrimp
Large population until isthmus of panama formed
Prevented gene flow
Different species on either side of the isthmus
Geographical separation
Can also occur when individuals of a population colonize remote areas
Happened with flightless cormorant
Ancestor was a flying species
Some colonized in Galápagos Islands - no gene flow between colonists and original population - leads to reproductive isolation due to genetic divergence and results in speciation
Sympatric Speciation
Speciation can also occur while individuals of a population are in the same location.
Need to have a decrease in gene flow
Sympathetic Speciation: polyploidy
More than 1 complete set of chromosomes
Chromosome # is greater than 2n
Reproductively isolated from diploid individuals
4n x 2n = 3n
Can produce fertile offspring
If mate with another tetraploid..produce tetraploid offspring that is fertile
Tetraploid is a new biological species
Allopolyploidy
Two different species interbreed to produce hybrid
Produce very few egg and sperm, don’t have any homologous chromosomes
During meiosis to produce egg and sperm, homologous pairs cannot form
Gametes without correct # of chromosomes or the correct combination of chromosomes
Mechanisms that can change a sterile hybrid into a fertile allopolyploidy in subsequent generations
Fertile when mating with each other, new biological species
Habitat Differentiation
Occurs when genetic factors allow a sub population to exploit a habitat or resources that are not used by the parent population
N. American maggot fly
Colonized the Hawthorne tree originally
Apple tree was introduced to US 200 years ago-a subpopulation of maggot fly colonized apple tree
Fruit of hawthorn is produced one month later than the fruit of the apple tree
Offset of life cycle - prevents gene flow
Not yet separate species
Sexual Selection
Lake Victoria, Africa - 600 species of cichlids
Species originated 100,000 years ago from a few species
1. Sub groups - exploit different food sources led to genetic divergence resulting in reproductive isolation and speciation
2. Sexual selection is another factor - females choose their mate based on male breeding color
Main reproductive barrier, led to decrease is gene flow
How long does it take for a new species to form?
Gradualism Model: small constant evolutionary changes that occur over hundreds of thousands of years, leads to speciation
Diagram on left
Punctuated Equilibrium Model: hundreds of thousands of years of no evolutionary change. Followed by rapid evolutionary change
Occurs over a few thousand years
What is the total time between speciation events?
Can be as little as 4,000 years or as long as 40 million years
Lots of variability in time frame
How much genetic change must occur to give rise to a new species?
Evolution of reproductive isolation can be the result of a single gene change Japanese land snail (on left) 1 gene change reversed the direction of the spiral in the shell When the spiral is in different directions, the genitalia of the snails are not properly oriented for mating Mechanical isolation Hybrid Sunflower (on right) Took at least 26 chromosomal changes for reproductive isolation and speciation to occur It can take very few changes in genetic code
From speciation to macroevolution
Genetic changes accumulate resulting in speciation occurring over and over again results in differences in organisms that accumulate
Leads to formation of new groups of organisms - dramatically different than their ancestors
Increase in population size
Other groups decrease in size or become extinct
These events lead to large scale of evolutionary change — macroevolution
