Speciation Flashcards
speciation preserves
differences because specialized populations no longer interbreed
environment determines local conditions which influences
adaptive evolution and degree of isolation
environment cahnges over space and time so that
populations may experience different selection pressures (which change) and population isolation (which may change)
population isolation leads to
population divergence
population divergence leads to
speciation
within a collection of populations each population is influenced by
local conditions
populations can diverge, but what overcomes small differences between populations
gene flow
what happens if populations become isolated
gene flow stops (genetic isolation), divergence of populations, and speciation - genetically independent
allopatric speciation
speciation that begins with geographic isolation
two types of allopatric speciation
dispersal or vicariance
dispersal
Founder effect - members of population colonize a new space, which may change allele frequencies and course of natural selection
vicariance
a physical barrier divides the original population into two separated populations
speciation of shrimp - Isthmus of Panama
Caribbean shrimp more closely related to sister species in Pacific than to other species in Caribbean due to common ancestor from population before the separation
sympatric speciation
speciation that occurs even though species live in same geographic region
two modes of sympatric speciation
disruptive selection and polyploidy
disruptive selection
leads to reproductive isolation, resulting in divergence and speciation
apple hawthorne fly case study
related, but have genetically based different scent receptors - hybrids aren’t attracted well to either fruit resulting in reduced fitness of hybrids
speciation can lead to
speciation
example of speciation leading to speciation
speciation of apple/hawthorne flies lead to speciation of parasitic wasps that feed on larvae
how do plants protect against herbivory by caterpillars
in response to leaf wounds and caterpillar regurgitate, signal pathway leads to release of chemical that recruits parasitic wasps
two main mecahnisms of reproductive isolation
prezygotic and postzygotic
pre-zygotic mechanisms fo reproductive isolation
temporal, habitat, behavioral, gametic barrier, mechanical barrier
temporal reproductive isolation
populations isolated because they breed at different times
habitat reproductive isolation
populations isolated because they breed in different habitats
behavioral reproductive isolation
populations do not interbreed because courtship displays differ
gametic barrier reproductive isolation
matings fail because egg and sperm incompatible
mechanical barrier reproductive isolation
matings fail because male and female reproductive structures incompatible
post-zygotic reproductive isolation
hybrid viability and hybrid sterility
hybrid viability
hybrid offspring do not develop normally and die as embryos
hybrid sterility
hybrid offspring mature but are sterile as adults
frog mating calls in allopatry
two species calls are closer in pitch and have a wider pitch range for each species
frog mating calls in sympatry
two species calls are more distinct in pitch and have a smaller pitch range for each species
frog mating call disctinctiveness in sympatry example of
behavioral isolation
mimicry of plants orchids
reproductive isolation - only males of specific species of insect will pollinate the flower, prevents pollination by other species or orchids
possible outcomes of bringing two isolated populations together
interbreeding, independence, hybrid zones, new species
interbreeding when isolated populations come together
interbreeding allows sufficient gene flow to re-distribute genetic variability - become one population
independence when isolated populations come together
if sufficient reproductive isolation has developed, populations continue to diverge into separate species
hybrid zone
geographic area where two species interbreed and hybrid offspring are common
over time hybrid zones can
shift or stabilize
how can hybrid zones stabilize over time
hybrids half as fit as non-hybrids - hybrid zone narrows - hybrid zone still exists as pure species continue to move into space and interbreed to produce more hybrids
how might hybrids develop a new species
hybrids may have adaptive trait
allopolyploidy
two species hybridize and the hybrid offspring undergo genetic doubling (one species is n=3 one species is n=2 so that hybrid is n=5)
allopolyploidy hybrids are sterile unless
chromosome doubling occurs (n=5 fails during meiosis, doubling has 2n=10 so meiosis can happen)
autoployploidy
one species has genetic doubling that results in new species
autopolyploidy occurs when nondisjunction results in
diploid egg and diploid sperm that self fertilize to produce tetraploid offspring that is new species
biological species concept
species is members of populations that actually or potentially interbreed in nature
pros of biological species concept
works with sexually reproducing organisms
cons of biological species concept
doesnt apply to asexual reproduction or fossils; grey area with “potentially” interbreeding
morphological species concept
species are defined by size, shape, or other morphological features
pros of morphological species concept
works with fossil and living species
cons of morphological species concept
misidentifies polymorphs as diff. species; identitifes cryptic species as same species; morphology is subjective
phylogenetic species concept
species defined by evolutionary history
pros of phylogenetic species concept
widely applicable
cons of phylogenetic species concept
not many well-estimated phylogenies are available
diet speciation
populations with more specialized diets are more likely to diverge than populations with general diet (diet specilization leads to isolation)
pollination affects speciation rates
speciation rates faster in animal pollinated cs. wind pollinated
speciation rates correllated with pollinator _____
specialization
dispersal affects speciation rates
decreased dispersal leads to isolation leads to increased speciation
sexual selection affects speciation rates
organisms with increased sexual dimorphism have higher rates of speciation
