Chapter 24 Flashcards
Species
Kind or appearance
Morphological Species Concept
- defined by anatomical features
- practical for extant and fossil species
- difficult to apply - what is different enough
- does not explain speciation as a process
Ecological Species Concept
- species can be defined by their niche
- hard to test in nature
- BUT can accommodate sexual and asexual reproduction
Phylogenetic Species Concept
- the smallest group of individuals that share a common ancestor
- species are monophyletic groups
- how much difference defines a species?
Biological Species Concept
- defined by reproductive isolation
- members of all populations with potential to interbreed and produce viable and fertile offspring in the wild
- sometimes difficult to apply (asexual species and fossils/extinct species)
- potential to interbreed in wild is difficult to assess
- provides insights on how species become, and remain, distinct
Reproductive Isolation
- Biological factors (barriers) that impede two species from producing viable, fertile offspring
- usually more than one barrier involved
- barriers isolate species, so evolution of barriers is key to speciation
- founder population often in a different niche from parent
- founder population usually small = susceptible to genetic drift
- two populations diverge, eventually are not reproductively compatible
Prezygotic Barriers (5)
Classified by timing:
- Habitat Isolation
- Temporal Isolation
- Behavioural Isolation
- Mechanical Isolation
- Gametic Isolation
Habitat Isolation
-the snakes may look alike, but one is aquatic and the other is terrestrial (water vs. dessert)
Temporal Isolation
-species may mate at different times of day or during different seasons
Behavioural Isolation
-species may have differences in the context of mating rituals and signals
Mechanical Isolation
-ex: snails shells may wind different ways so genitals don’t line up for mating
Gametic Isolation
-gametes don’t fuse therefor a zygote can’t fertilize
Prezygotic vs. Postzygotic
Pre: Before fertilization
Post: After fertilization
Postzygotic Barriers (3)
- Reduced Hybrid Viability
- Reduced Hybrid Fertility
- Hybrid Breakdown
Reduced Hybrid Viability
-Refers to lower potential to survive for organisms whose parents have incompatible genetics
Reduced Hybrid Fertility
-A viable hybrid individual is sterile often due to the inability to produce normal gametes in meiosis
Hybrid Breakdown
-Reproductive failure that appears after F2 generation of crosses between incompatible species
Hybrid Zones
-Biological barriers not always complete-hybrids produced
-Stable hybrid populations may be established between two species - hybrid zones
-3 Outcomes Possible:
~reinforcement
~fusion
~stability
ex: two toads are isolated by habitat, but when two habitats come together, 2 species can hybridize and mix. HOWEVER MIXED TOADS WILL DEVELOP MENTAL ISSUES/BARRIERS
Speciation
Two geographical Modes:
- Allopatry
- Sympatry
Allopatry
Geographic barriers isolate population.
- geological processes
- emigration
- extinction is likely
- if they survive, they are likely to evolve relative to parent population
Sympatry
Subpopulations isolated in the midst of the of the parental population.
- reduction in gene flow
- sexual selection
- habitat differentiation
- polyploidy
Polyploidy
Accidents of cell division that result in reproductive isolation in a single generation
Adaptive Radiation
Common ancestor spreading into many new environments over a short period of time
