3: Species & Speciation

Biological Species Concept

a species is group of freely interbreeding population reproductively isolated from other groups

-most accepted species concept

limitations of Biological Species Concept

1) does not apply to asexual organisms

2) reproductive isolation is usually inferred

Evolutionary Species Concept

-limitation?

species is a single lineage of ancestral dependent population different from other lineages

-applies to asexual organisms

-limitation: evolutionary tendency is difficult to evaluate

Phylogenetic Species Concept

-limitations

Species is diagnosable by unique combination of character states (pattern-based)

-limitations: applies to non-living entities & variable traits difficult to evaluate

Applying Phylogenetic Species Concept, how many species of humans would there be?

many human species

allopatric vs. sympatric distribution

allopatric→geographically separated

sympatric→existing in same geographical area (can hybridize)

parapatric distribution

what is a contact zone?

meets only along borders

contact zone: narrow zone of overlap between 2 parapatrically distributed taxa

hybridization

-how is this recognized?

interbreeding of morphologically distinct populations

-recognized by increased intermediacy & variability within a contact zone

Sibling species (allospecies)

recently split species that are close relatives & similar in appearance

superspecies

formed by 2 or more sibling species

subspecies

geographically separated species

-can interbreed where ranges meet

cline

ex?

gradual morphological changes across an environmental gradient

ex// plant heights decrease as they go up in altitude

prezygotic isolating mechanism

prevents fertilization from occurring

mechanical isolation

-common in?

gamete shapes differ so cannot fertilize

-common in insects

postzygotic isolating mechanisms

fertilization takes place but reproductive failure occurs

hybrid inviability
hybrid sterility
hybrid breakdown

hybrid inviability→offspring dies
hybrid sterility→offspring is sterile (e.g. mule)
hybrid breakdown→hybrid can reproduce but offspring cannot

what happens when isolating mechanisms between 2 taxa are incomplete?

hybridization occurs

What 2 types of allopatric speciation?

1) vicariance→formation of geographical barrier splits population into 2
2) dispersal→few individuals cross an existing barrier to form 2 population

what can occur after secondary contact?

1) two populations changed too much so will not breed
2) two populations can interbreed

what is the most common form of speciation?

allopatric speciation

_____ selection & _____mating occurs in sympatric speciation

disruptive; assortative

in what type of environment is sympatric speciation most likely to occur?

heterogenous or patchy environment

examples of sympatric speciations

1) Apple Maggot Fly→some feed on apples and others on hawthorns

2) polyploidy of flowers

what explains rapid appearance of flowering plants and their diversity?

polyploidy

gene inversion vs. gene translocation

gene inversion→ within the same chromosome

gene translocation→to another chromosome

Polyploid has which 3 fates...

1) extinction
2) coexistence
3) replacement

if humans mate assortively, would there be more than 1 species?

no bc of human culture

parapatric speciation

two populations evolve into distinct species along environmental gradient

-abrupt environmental change reduces gene flow

in what kind of organisms is parapatric most likely to occur in?

ex?

those w/ low mobility, less gene flow between populations

ex// plants in uncontaminated and contaminated soil

peripatric speciation

divergence occurs in small, peripheral populations next to main distribution