Speciation Flashcards
selection doesn’t favor traits that are good for the population or the specie as a whole….
it only favors traits that are good for individuals
favorable traits
increase the fitness of an individual in a given environment
true or false:
individuals don’t evolve, populations do!
true
speciation
formation of new and distinct species
population
an interactive group of individuals of a single specie that occupies the same area at the same time
birds common on campus
- house sparrow (passer domesticus)
- black phoebe (savoriness nigricans)
- house finch (carpodaccus maxicanus)
species
kind
how does speciation (the process by which one species give rise to another or several new species) happen?
- morphological species concept
- phylogenetic species concept
- biological species concept
Morphological Species concept
groups of organisms with a similar phenotype (look alike) are members of same species
details on morphological species concept
- many species look similar over large geographic ranges
- blackbirds in upstate NY look similar those across north america - sometimes not all members of same species don’t look alike (males and females may look different from each other)
- sometimes they look different from they fulfill different ecological roles ( ants- major and minor workers)
cryptic species
- 2 or more distinct species are mostly morphologically indistinguishable
- dna barcodes identify cryptic species and determine their geographical rages
Phylogenetic species concept
smallest group of organisms that shares a common ancestor is a distinct species
- ex. phylogeny of fruit flies
- not useful for understanding how species form
biological specie concept
species are groups of actually or potentially interbreeding natural populations that can mate and produce fertile offspring
actually
live in the same place and actually interbreed
potentially
don’t live in same place, but could interbreed
- blackbirds in NY and BC aren’t likely to encounter but are still able to interbreed
details of biological species concept
- most widely used and most mechanistic of the species concepts
- new species are formed when populations whose members can potentially exchange genes become reproductively isolated from eachother
reproductive barriers
- prezygotic reproductive barrier
- postzygotic reproductive barrier
prezygotic reproductive barrier
-act before fertilization to prevent it
postzygotic reproductive barrier
act after fertilization to prevent development of viable and or fertile offspring
habitat isolation
- individuals of one population evolve preferences for one habitat, and individuals of another for a different habitat
- species live and mate in their preferred habitats and may never com into contact during mating season
temporal isolation
individuals of population evolve to mate during one season and individuals of another to mate during a different season
-ex. 3 species of co-occuring leopard frogs reproductive seasons don’t overlap
behavioral isolation
when individuals reject or fail to recognize potential mating partners because of their behaviors
- bredding calls of male gray tree frogs differ among related species
- calls of sister species differ in frequency
- females ignore calls made by males of their sister species
mechanical isolation
when differences in shapes, positions, or sizes of reproductive structures prevents cross-fertilization
- conspecific snails
- reproductive parts both on right side of head easy to line up and mate
- heterospecific snails
- reproductive parts of one individual on left side and other on right which makes hard to fuck
gametic isolation
when sperm and eggs in a species-specific manner
-if protein doesn’t bind, then the sperm can’t fertilize the egg
reduced hybrid viability/fertility
hybrid offspring may have problems developing, surviving, and or reproducing
- goat and sheep
- mule
- both are sterile
are hybrids ever fertile?
yes but many suffer from:
-hybrid breackdown
hybrid breakdown
when 2 hybrids mate or when hybrids mate with the parent species, the next generation may not survive/ reproduce
- rice
- 1st gen was fine
- 2nd gen are stunted and sterile
allopatric
new species form a single species due to geographic isolation
sympatric
new species evolve from a single species while inhabiting the same geographic region
details on allopatric
- common mode of speciation
- speciation occurs when a geographic barrier isolates populations into 2 or more groups
geographic barriers
mountains, rivers, pond, rising sea level
stages of how allopatric speciation proceeds
- 2 populations become geographically separated (barrier gene flow)
- accumulated genetic differences isolate them reproductively
secondary contact
occurs when isolated reestablish contact with elimination of a geographic barrier
what happens after secondary contact?
- if each population’s gene pool didn’t differentiate enough to be reproductively isolated, the populations will interbreed and may merge
- if they have differentiated, then they have become separate species
sympatric isolation details
- less common mode of speciation
- speciation and reproduction occurs without a geographical isolation
sympatric speciation occurs due to:
- habitat preferences (food, light) which may lead to mating in that preferred habitat
- sexual selection
- ex. apple maggot fly
- over time, genetic differences between subpopulations accumulated, leading to speciation without isolation
hybridization
- reproductive barriers are often not perfect
- if separated populations reunited before they are fully reproductively isolated, interbreeding can occur
hybrid zone
regions where hybrids are produced
3 possible outcomes of hybridization
- stability
- fusion
- reinforcement
stability
hybrid zones may last for many generations if hybrids continue to be produced
- ex. hybrid toads are much less fit but zone persists because toads keep on going at it.
- weak reproductive barriers and lots of gene flow stabilizes production of hybrids
fusion
2 species may fuse to one species
-with weakened reproductive barriers and continued gene flow, distinct cichlid species are fusing into one
reinforcement
hybrids are much less fit (lower survival) than members of both parent species
-natural selection reinforces reproductive barriers
-reducing formation of unfit hybrids
favoring breeding within a specie
-in time hybrids are no longer formed and 2 species have completely diverged
-reinforcement occurs only if population is sympatric
-leopard frogs
how rapidly does speciation occur in geological time?
- punctuated equilibrium
- gradualism
punctuated equilibrium
speciation occurs in short bursts, new species appearing suddenly and remaining the same for years (cladogenesis)
gradualism
speciation proceeds uniformly and by steady, gradual transformation of whole lineages into new species (anagenesis)
why do rates of speciation vary?
- usually higher in groups with poor dispersal abilities; in such organisms, even “small” geographic barriers can lead to allopatry
- rates higher in groups with specialized diets
- rates higher in animal-pollinated than wind-palliated plants
- rates are higher in groups that undergo strong sexual selection
fusion
2 species may fuse to one species
- some distinct cichlids species in East Africa lakes are fusing
- pollution makes water murky, hampers female ability to identify males, so hybrids are regularly formed
- with weakened reproductive barriers and continued gene flow, distinct cichlid species are fusing into one
why do rates of speciation vary?
- usually higher in groups with poor dispersal abilities; in such organisms, even “small” geographic barriers can lead to allopatry
- rates higher in groups with specialized diets
- rates higher in animal-pollinated than wind-palliated plants
- rates are higher in groups that undergo strong sexual selection
