Lecture 5 - Speciation Flashcards
species
a kind or appearance
list examples of species concepts
- > morphological
- > biological
- > phylogenetic
- > ecological
… there are well over 20 speci
Morphological species concept
- > a way of defining species by anatomical features
- > distinguishing different types of organisms by their phenotypes
- > practical for extant and fossil species
- > difficult to apply (what is different enought)
- > does not explain speciation as a process
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
- fossils and extinct species
- > potential to interbreed in wild is difficult to asses
- . provides insights on how species become, and remain, distinct
reproductive isolation and the different types of isolation
- > Reproductive isolation between species works as a mechanism for maintenance of separation and individuality of different gene pools that are incompatible and/or adapted to different environments
1. geographical isolation
2. behavioural isolation
3. temporal isolation
Characteristics of reproductive isolation
- > can also include biological factors (barriers) that impede two species from producing a 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
- > two populations diverge/separate, eventually are not compatible (why there are so many species of robins)
clasiffication of reproductive isolation (time)
1. Perzygotic (before fertilation)
2. Postzygotic (after fertilization)
two geographic modes of speciation
1. Allopatry (geographic barriers isolate populations)
- > geological processes
- > emigration
2. Sympatry (subpopulations isolated in the midst of the parental population)
- > reduction in gene flow
adaptive radiation
common ancestor spreading into many new environments over short period of time
allopatric speciation
– Geographic isolation restricts gene flow between populations
– Reproductive isolation may then arise by natural selection, genetic drift, or sexual selection in the isolated populations (evolve independently)
– Even if contact is restored between populations, interbreeding is prevented
sympatric speciation
– A reproductive barrier isolates a subset of a population without geographic separation from the parent species
- reduction in gene flow
– Sympatric speciation can result from polyploidy, natural selection, or sexual selection
polyploidy vs autopolyploidy vs allopolyploidy
Polyploidy
- > accidents of cell division that result in reproductive isolation in a single generation
Autopolyploidy
- > Autopolyploidy appears when an individual has more than two sets of chromosomes, both of which from the same parental species.
Allopolyploidy
- > Allopolyploidy, on the other hand, occurs when the individual has more than two copies but these copies, come from different species
hybrid zones
- > Hybrid zones are areas where the hybrid offspring of two divergent taxa (species, subspecies or genetic “forms”) are prevalent and there is a cline in the genetic composition of populations from one taxon to the other.
- > stable hybrid populations may be established between two species (hybrid zones)
possible outcomes of hybrid zones
- Reinforcement
- > strengthening reproductive barriers and reduces gene flow, eventually no more hybrids - Fusion
- > reproductive barriers weaken untill the two species become one - Stability
- > continual production of both parent and hybrid species
Prezygotic vs Postzygotic barriers
Prezygotic
- > mechanisms that prevent fertilization i.e. failure of zygote fusion
Postzygotic
- > prevents zygote from functioning (i.e. hybrids are sterile or don’t survive)
