23 terms

AP Biology Chapter 24

The Origin of Species

Terms in this set (...)

df: process by which one species splits into 2+ species
-resulting species share many characteristics b/c descended from common ancestor
changes over time in allele frequencies in a population
broad pattern of evolution over time
group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring BUT do not produce viable, fertile offspring w/ members of other such groups
Reproductive Isolation
existence of biological factors (barriers) that impede members of 2 species from producing viable offspring
offspring that result form interspecific mating
Prezygotic Barriers
df: block fertilization from occurring (before the zygote)
1. impede members of different species from attempting to mate
2. prevent attempted mating from being completed successfully
3. hinder fertilization if mating completed successfully

ex. habitat isolation, temporal isolation, behavioral isolation, mechanical isolation, gametic isolation
Postzygotic Barriers
df: contribute to reproductive isolation AFTER zygote formed

ex. reduced hybrid fertility, reduced hybrid viability, hybrid breakdown
Morphological Species Concept
df: characterizes species by body shape and other structural features
-applies to asexual and sexual organisms
-relies on subjective criteria
Ecological Species Concept
df: views species in terms of ecological niche - sum of how members of species interact w/ living and nonliving parts of environment
-accommodate asexual and sexual species
-emphasizes rate of disruptive natural selection as organisms adapt to different environmental conditions
Phylogenetic Species Concept
df: defines species as smallest group of individuals that share a common ancestor, forming one branch on the tree of life
-trace phylogenetic history of species by comparing characteristics like morphology or molecular sequences
-difficult to determine degree of difference to indicate separate species
Allopatric Speciation
df: gene flow interrupted when population divided into geographically isolated subpopulations (allopatric = other country)
-allows separated gene pools to diverge
-likely with gene pools of highly isolated populations b/c very little gene flow
Sympatric Speciation
df: speciation that occurs in populations that live in same geographic area (sympatric = same country)
-occurs if gene flow reduced by polyploidy, habitat differentiation, and sexual selection
df: extra set of chromosomes from accident in cell division
-can originate new species
df: individual w/ 2+ chromosome sets all derived from single species
-can generate reproductive isolation w/o geographic separation
1. failure of cell division after chromosome duplication could double cell's chromosome number from diploid (2n) to tetraploid (4n) [or other number ___n]
2. tetraploid is reproductively isolated from diploids of original population b/c triploid (3n) offspring of such unions have reduced fertility
3. tetraploid plants can produce fertile tetraploids by self-pollinating or by mating w/ other tetraploids
df: when 2 different species interbreed and produce hybrid offspring which are usually sterile b/c set of chromosomes from one species can't pair during meiosis w/ set of chromosomes from other species -> some infertile hybrids can asexually reproduce - change from sterile hybrid to fertile polyploid
-fertile when mating w/ each other but cannot interbreed w/ either parent speices
Habitat Differentiation
genetic factors enable subpopulation to exploit a habitat or resource not used by parent population
Sexual Selection
mate choice based on male breeding (coloration, pattern, mating call, etc...) is main reproductive barrier that normally keeps gene pools of 2 species from separating
Hybrid Zone
df: region in which members of different species meet and mate -> offspring of mixed ancestry
1. 4 populations of species connected by gene flow
2. barrier to gene flow established
3. population begins to diverge from other 3 populations
4. speciation nearly complete
5. gene flow reestablished in hybrid zone
df: natural selection strengthens prezygotic barriers to reproduction -> reduce formation of unfit hybrids -> reinforce reproductive barriers
-barriers to reproduction between species should be stronger for sympatric species than for allopatric species
-reproductive barriers strengthen, hybrids gradually cease to be formed
df: 2 species contact one another in a hybrid zone but barriers of reproduction not strong -> barriers weaken further b/c gene flow -> gene pools of 2 species become very alike -> speciation reverses -> 2 species fuse into
-ability of females to distinguish males decreases
df: hybrids continue to be produced
-extensive gene flow from outside hybrid zone -> continued production of hybrids, overwhelms selection for increased reproductive isolation in hybrid zone
-less likely to occur if hybrid zone
-as hybrids mated w/ each other and w/ parent species, gene pools of parents could fuse, reversing speciation
Punctuated Equilibrium
periods of apparent stasis punctuated by sudden change