Lecture 20 Flashcards
What is a species?
- Biological species concept
- Morphological traits species concept
- Common ancestor: phylogenetic species concept
Reproductive isolation? and its limitations
Reproductive isolation: is the existence of biological factors (barriers) that impede 2 species from producing viable, fertile offspring
- Reproductive isolation restricts gene flow b/w 2 species.
Limits to this definition:
Can’t be used for species that reproduce asexually or that are extinct.
To know if reproductive isolation exists, need to know all the breeding partners of the species in question, but can’t know for sure who breeds with who in nature. (see bear example)
Gene flow can sometimes occur between distinct species (see hybrids)
Prezygotic & postzygotic barriers lead to reproductive isolation definition?
Barriers prevent interbreeding b/w 2 different species whose living ranges overlap.
If living ranges don’t overlap, no need for a barrier.
Prezygotic barriers
Prevent fertilization ie formation of a zygote
postzygotic barriers
Reduce viability or fertility of the hybrid
what are Prezygotic barriers?
- Habitat isolation
- Temporal isolation
- Behavioral (sexual) isolation (Distinctive courtship behaviors prevent mating between species)
- Mechanical isolation (Structural differences in the reproductive organs of similar species) In animals Often reproductive organs “don’t fit”
- gametic isolation (Gametes from different species are incompatible: sperm of 1 species can’t fertilize eggs of another species)
what are some POSTzygotic barriers ?
- Hybrid inviability
- Hybrid sterility
- Hybrid breakdown
Hybrid inviability?
Death of interspecific embryos during development.
Ex If artificially fertilize bullfrog eggs with leopard frog sperm: almost all hybrids die in embryonic stage
Hybrid sterility?
Hybrids can’t reproduce successfully
Can’t do meiosis so can’t make gametes: sterile
why are mules sterile?
no homologous chromosomes
Hybrid breakdown?
Offspring of hybrids do reproduce, but only for a few generations
Morphological species concept?
A species is a group of organisms with similar structure (morphology) & behavior.
Phylogenetic species concept
The smallest group of individuals that share a unique common ancestor and who all possess a unique set of morphological or genetic traits.
Patterns of Speciation, how do new species rise?
- New species arise by evolution of ancestor species
- New species arise by hybridization of 2 different species
Allopatric speciation VS Sympatric speciation
Allopatric speciation: Start with 2 separate populations of the same species → evolve into 2 separate species
Sympatric speciation: Start with 1 population (same species) → evolve into 2 separate species
Allopatric speciation
- Habitat isolation occurs : pre-zygotic reproductive barrier b/w groups
- Each population exposed to different selective pressures, genetic drift, +/or mutation that cause micro-evolution
- Eventually, 1 or both populations undergo enough genetic changes that results in the formation of permanent reproductive barrier
sympatric speciation
In sympatric speciation, speciation takes place in geographically overlapping populations
Sympatric speciation can occur if gene flow is reduced by factors including:
Mutations
Habitat differentiation
Polyploidy
Paedomorphosis
juvenile characteristics are kept in the adult
Causes big changes in the behavior
Polyploidy?
the presence of extra chromosome sets due to errors during cell division (mitosis or meiosis)
many sets of chromosomes
__% of all plants are polyploids
25-50
__% of flowering plants are polyploid
80
How do polyploids arise?
NON-DISJUNCTION
allopolyploidy ?
a polyploid individual or strain having a chromosome set composed of two or more chromosome sets derived more or less complete from different species.
Hybridization: Species A + B =
species C
3 possible outcomes of a new species In same environment as “parent species”
- New species may not survive if not well adapted: becomes extinct
- New species coexists with parent species
- New species survives better than 1 or both parents: may even replace the parent species
Possible outcomes as a species diverges:
- reinforcement: Hybrids stop forming. Two separate species
- fusion: Two “species” fuse into one
- stability: Hybrids keep forming
species may be identified by the __& __aspects
Biological Morphological
Biological species concept based on __ caused by __ and __
Reproductive isolation
prezygotic barriers and postzygotic barriers
Morphological species concept based on __
distinct body structures.
Species may originate by __ and __ in which __
Allopatric speciation and Sympatric speciation
gene flow is interrupted
gene flow interrupted in allopatric speciation between _
geographically isolated populations
gene flow interrupted in Sympatric speciation by _
Mutations- sexual selections
Habitat differentiation
Polyploidy
species may interbreed in __ which may result in __, __ and ___.
hybrid zones
fusion of species, stable hybrid zone, reinforcement (reproductive barriers.)
which concept of speciation is most commonly used
BSC Biological species concept
where can speciation occur
Can occur in different environments (allopatric), or in a shared environment (sympatric)
Speciation Can be due to ?
Can be due to changes in genomes of a single ancestor or can be due to hybridization.
10 reproductive barriers
Prezygotic barriers Postzygotic barriers Habitat isolation Temporal isolation Behavioral (sexual) isolation Mechanical isolation gametic isolation Hybrid inviability Hybrid sterility Hybrid breakdown
