Speciation #4: BIO 1A

Speciation

Emergence of new species from existing species

• responsible for biodiversity

Reproductive isolation

cuts of gene flow— allows populations to diverge (become different from each other

Taxonomy

scientific study of naming, defineing, and classifying groups of organisms

taxon

refers to taxnomic group of any rank, such as species, family, class, etc.
taxa: eukaryoes, animals, mammals, carnivals, canids, red fox

binomial nomenclature

system developed of genius and species, e.g homo sapiens
developed by carn von linne, classifying organisms

Black bear - ursus americanus

genus: ursus, specific epithet: americanus
ursus americanus or Ursus americanus

how does speciation happen?

barrier to sexual reproduction between wo populations, preventing gene flow

gene flow depends on sexual reproduction

Causes of reproductive isolation

reproductive barrier:

• prezygotic barriers

• postzygotic barriers

Reproductive barrier

biological features of species that prevents it from interbreeding with other species, even when populations of the two species live in the same area

prezygotic barrier (reproductive barrier)

biological feature of species that prevents from interbreeding with other species, preventing formation of zygote

postzygotic barriers (reproductive barrier)

a reproductive barrier that prevents hybrid zygotes produced by two different species from developing into viable, fertile adults

types of prezygotic barriers to reproduction

• habitat isolation (popln, inhabit diff. habitats and don’t meet)

• behavioral isolation (diff, in mating behavior, prevents mating)

• temporal isolation (diff, in time of reproduction, prevents mating)

• mechanical isolation (mating unsuccessful b/c genitals are incompatible)

habitat isolation

populations inhabit different habitats and don’t meet

behavioral isolation

differences in mating behavior prevent mating

temporal isolation

differences in time of reproduction prevent mating

mechanical isolation

mating is unsuccessful b/x genitals are incompatible

• ‘Lock-&-Key’ model; genitals of males fit genitals of females of same species but not other species

Postzygotic barriers to reproduction

1 reduced viability - hybrid offspring doesn’t survive

reduced fertility - hybrid offspring are sterile

reduced viability

hybrid offspring do not survive

reduced fertility

hybrid offspring are sterile (hybrid sterility)

ex. mule: hybrid offspring of horse and donkey

horses: 64 chromosomes

donkeys: 62 chromosomes

mules: 63 chromosomes → sterile

hybrid inviability

(postzygotic barrier) hybrid embryos produced by crossing of sheep and goat don’t survive

Which of the links below relate to prezygotic barriers and which relate to postzygotic barriers?

prezygotic: contact, mate choice

postzygotic: mating and gamete transfer, survival and successful reproduction

• reproductive barriers can break any of the links in this cycle, if any link is broken, 2 popln. are reproductively isolated

Allopatric speciation

allopatry = geographic isolation

• if populations are allopatric there is no gene flow

• geographic range of species splits resulting in geographically isolated populations

• cuts off gene flow→allows popls. to diverge (evolved differences), doesn’t cause speciation

Pleistocene glaciations

(approx. 2.5 mya - 12,000 ya) a fragmented forest habitat in North America— created isolated popls. of numerous organisms

Can reproductive barriers evolved as by-products of adaption of populations to different environments? (fruit fly experiment)

(allopatric speciation experiment) fruit flies (Drosophila) from single populations split into 2 separate populations in lab- each fed different food

• prezygotic barrier has begun to evolve btwn two popls.

• og fly popls splits into 2, both fed different foods for many generation → when combined members of each popls prefer to mate with flies raised w/ same food type → development of prezygotic barrier

Biological Species Concept (BSC)

species are groups of interbreeding natural populations that are reproductively isolated form other such groups