Chapter 5 - Origin of Species Flashcards
Speciation
the process by which one species splits into two or more species
Microevolution
changes in allele frequency in a population over time
Macroevolution
refers to broad patterns of evolutionary change above the species level
How do we define a species?
- a group of similar living things that ranks below the genus in scientific classification and is made up of individuals able to produce offspring with one another
- Used to be based just on physical similarity (morphology).
- Now use morphology, physiology, DNA, ecology.
Biological Species Concept
states that a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with members of other such groups
i.e., they are reproductively isolated from other species.
Reproductive barriers (isolating mechanisms)
Pre-zygotic Barriers
Post-zygotic Barriers
Pre-zygotic Barriers
Habitat isolation
Temporal isolation
Behavioral isolation
Mechanical isolation
Gametic Isolation
Post-zygotic Barriers
- Reduced Hybrid Viability
- Reduced Hybrid Fertility
- Hybrid breakdown
Habitat isolation
populations live in different habitats and do not meet
Temporal isolation
different breeding times, seasons
Behavioral isolation
courtship or mating behaviors
Mechanical isolation
sex organs are mechanically incompatible
Gametic Isolation
gametes (egg and sperm) are incompatible
Reduced Hybrid Viability
Genes of the different parent species may interact and impair the hybrid’s development or survival in its environment
Reduced Hybrid Fertility
a common feature of reproductive barriers separating recently diverged species
Hybrid breakdown
Some first-generation hybrids are fertile, but when they mate with each other or with either parent species, offspring of the next generation are feeble or sterile
Limitations of the Biological Species Concept
- Cannot be applied to fossils or asexual organisms
- Hybridization sometimes observed in nature
Morphological species concept
defines a species by structural features
- It applies to both sexual and asexual species but relies on subjective criteria
Ecological species concept
defines a species in terms of its ecological niche
How Does Speciation Occur?
Speciation will occur if environmental conditions are different, and populations are separated for long periods and developed their own unique characteristics.
Speciation can occur in two ways:
- Allopatric speciation
- Sympatric speciation
Allopatric speciation
geologic barrier divides a population, leaving each group to follow its own evolutionary path.
Sympatric speciation
more common in plants, no geographic barrier. Isolation is due to accidents during cell division resulting in polyploid offspring.
The Process of Allopatric Speciation
Geographical barrier arises
Separated populations may evolve independently through mutation, natural selection, and genetic drift
- Causes genetic divergence
Reproductive isolation may arise as a by-product of genetic divergence
- E.g., geographically isolated populations of mosquitofish have become reproductively isolated as a result of selection under different levels of predation
Sympatric Speciation
Can occur if gene flow is reduced by factors including:
- Polyploidy
- Sexual selection
- Habitat differentiation
Polyploidy
involves a spontaneous doubling of chromosomes, also means random
is a condition of having more than 2 complete sets of chromosomes
the presence of extra sets of chromosomes due to accidents during cell division
much more common in plants than in animals
can produce new biological species in sympatry within a single generation
Autopolyploid
individual has more than two sets of chromosomes that came from same parent of species
Allopolyploid
individual that has more than 2 copies, but these copies come from different type of species.
Sexual selection
members of one sex choose mates of the other sex to mate with and compete with members of the same sex for access to members of the opposite sex.
Sexual selection for mates of different colors has likely contributed to speciation in cichlid fish in Lake Victoria
Habitat differentiation
more types of habitat in the same quantity in geographical zones
Sympatric speciation can also result from the appearance of new ecological niches
E.g., North American maggot fly (Rhagoletis pomonella) can live on native hawthorn trees, as well as more recently introduced apple trees
Hybrid Zones
where ranges overlap, and mating occurs
Hybrid Zones
Three possibilities:
Reinforcement
Fusion
Stability
Reinforcement
strengthens reproductive barriers if hybrids have reduced fitness
Fusion
members of the two lineages mate together forming hybrids
Stability
each lineage keeps its own range apart of each other save for some areas of overlap.
Punctuated Equilibrium
is a theory that proposes that once a species appears in the fossil record, the population will become stable, showing little evolutionary change for most of its geological history
Gradualism
is a hypothesis, a theory, or a tenet assuming that change comes about gradually or that variation is gradual in nature and happens over time as opposed to in large steps
