Lecture 8 Evolution III Flashcards
what is the biological species concept?
- a species consists of a group of actually or potentially interbreeding individuals that are reproductively isolated from other groups
- based on potential to interbreed rather than on physical similarity
- problems: can’t be applied to fossils, asexual species, emphasizes absence of gene flow - but gene flow can occur between distinct species
what is the morphological species concept?
- defines a species by structural features
- applies to sexual and asexual species but relies on subjective criteria
what is the biological species concept?
- species is a set of organisms adapted to a particular set of resources, called a niche, in the environment
- based on ecological niche
- applies to sexual and asexual species
- emphasizes the role of disruptive selective
what is the phylogenic species concept?
- defines species as the smallest group of individuals on a phylogenic tree
- based on evolutionary history
- applies to both sexual and asexual characteristics
- can be difficult to determine degree of difference required for separate species
what is reproductive isolation?
- existence of biological factors/barriers that impede two species from producing viable, fertile offspring (hybrids)
what are hybrids?
- OFFSPRING of crosses between different species
what are the two types of reproductive isolation?
- prezygotic
- postzygotic
what are the five prezygotic isolation mechanisms?
- habitat/ecological isolation: 2 species encounter each other rarely/not at all bc they occupy different habitats, even though not isolated by physical barrier
- temporal isolation: breed at different times of day/season/years
- behavioural isolation: courtship patterns and other behaviours unique to a species are barriers
- mechanical isolation: morphological differences can prevent successful mating - anatomically impossible
- gametic isolation: sperm of one species may not be able to fertilize eggs of another species
what is prezygotic isolation?
block fertilization by
- impeding different species from attempting to mate
- preventing the successful completion of mating
- hindering fertilization if mating is successful
what is postzygotic isolation?
prevent the hybrid zygote from developing into a viable, fertile adult
what are 3 postzygotic isolation?
- reduced hybrid viability: genes impair hybrid’s development - DEATH
- reduced hybrid fertility: even if hybrids are vigorous, they are sterile
- hybrid breakdown: some 1st gen hybrids are fertile, but next gen are feeble/sterile
what are the two types of speciation?
- allopatric
- sympatric
what is allopatric speciation?
- gene flow interrupted when pop’n is divided into geographically isolated subpopulations
- regions with more barriers typically have more species
- ex: ensantina salamanders
what is sympatric speciation?
- speciation takes place in geographically overlapping populations
- NO geographic separation
how does sympatric speciation occur?
- habit differentiation, sexual selection, polyploidy
what is habitat differentiation?
sympatric speciation
- appearance of new ecological niches
- ex NA fly can live on native hawthorn trees as well as recently introduced apple trees
what is an example of sexual selection re: sympatric speciation?
- mates of different colour - cichlid fish in L. Victoria
what is polypoidy?
- presence of extra chromosomes sets due to accidents during cell division
- more common in plants than in animals
what is autopolyploid?
- individual with more than 2 chromosome sets derived from one species
- failure of cell division leads to doubles, triples, etc
- plants may be self-compatible but isolated from parents
what is allopolyploid?
- species with multiple sets of chromosomes derived from different species
- ex: wheat
what are hybrids?
result of mating between species with incomplete reproductive barriers
what is a hybrid zone?
region in which members of different species mate and produce hybrids - often have reduced fitness compared w parents
what are 3 hybrid zone outcomes?
reinforcement
stability
fusion
what is reinforcement?
HZ
- hybrids less fit than parents
- over time hybridization decreases
- NS favours genes that cause individuals to avoid mating with hybrids
- reproductive barriers should be stronger for sympatric than allopatric species
what is stability?
HZ
- continued formation of hybrid individuals
- extensive gene flow from outside hybrid zone can overwhelm selection for increased reproductive isolation inside the hybrid zone
what is fusion?
HZ
- weakening reproductive barriers
- if hybrids are as fit as parents there can be substantial gene flow between species
- potential for parent species can fuse into a single speceis ex: coywolf
what are the two models of speciation?
- punctuated equilibrium
- gradualism
what is punctuated equilibrium?
- speciation happens rapidly, followed by relatively long periods of stasis (no change)
what is gradualism?
- slow differentiation by NS over many generations
