Week 9 - Speciation Flashcards
What is speciation?
Speciation means that different populations undergo independent divergence maintaining separate identities, evolutionary tendencies and fates
Can speciation be studied in the fossil record?
No - speciation is too fast to be documented in the fossil record but too slow for us to study as it occurs
–> Thus, the study of speciation is largely based on inferences from living species
Why do we define species?
Species can be defined in a way that:
- Enables us to classify organisms systematically
- Corresponds to discrete groups of similar organisms
- Helps us to understand how discrete clusters of organisms arise in nature
- Represents products of evolutionary history
What is the ‘Phylogenetic Species Concept’ and what is a cline?
“A species is a set of organisms that are sufficiently similar to one another, and sufficiently different from members of other species’
ISSUE: variation between and within populations
Cline: A gradual change in character (or in allele frequencies) over a geographical distance
What is the ‘Biological Species Concept’
“A species is a group of individuals fully fertile, but barred from interbreeding with other similar groups by its physiological properties”
can breed but are reproductively isolated from other such groups
What prevents gene flow?
-> Isolating mechanisms
-> Isolating barriers
-> Barriers to gene flow
Outline what are pre-zygotic barriers
Pre-Zygotic: Prevent transfer of gametes to members of another species
- Ecological: geographic - populations on different sides of a mountains
- Behavioural: not recognising different mating calls
- Post-Mating: gametes don’t successfully fuse
Outline what are post-zygotic barriers
Post-Zygotic: consist of reduced survival/reproductive rates of hybrid zygotes
- Hybrid unviability (embryo is formed but doesn’t reach full term)
- Hybrid sterility
Pre-Zygotic: What is ecological isolation? What are isolating behaviours?
Ecological Isolation
- Seasonal: one population reproducing at different times to others in the year
- Habitat: feeding/mating on different plants, segregating populations
Isolating Behaviours
- Mate recognition systems consist of displays and response to signal from potential maters
Post-Zygotic: Genital variability? Conspecific sperm precedence?
Genital Variability - if the male genitalia doesn’t fit then reproduction won’t happen
Conspecific Sperm Precedence - female choice after mating with multiple males
Gamete Isolation - gametes of different species fail to unite (eg. due to cell surface proteins)
Why do hybrids not always work?
UNVIABLE
- Lower survival rates than “full species”
- Mortality is often intrinsic during embryogenesis
STERILE
- Survival to maturity but unable to produce viable gametes, and are hence infertile
What are the four types of speciation?
- Allopatric
- Peripatric
- Parapatric
- Sympatric
What is allopatric speciation?
Geographical speciation - populations of the species become isolated and hence form into new species
What is peripatric speciation?
Closely related species in an isolated, nearby but UNCONNECTED area
–> Population buds off (geographically) and becomes reproductively isolated, maintains that isolation when the population is much smaller than the other
–> One population is much smaller than the other
What is parapatric speciation?
Adjacent ranges with a narrow contact zone so species form in a new area (no geographical barrier)
