Chapter 22: Origin of Species

How do species originate from an existing species?

Overtime, populations of a single species connected by gene flow can diverge genetically, giving rise to a new species

Speciation

Evolutionary process in which one species splits into two or more species. Darwins mystery of mysteries

Resulting species of speciation

Share many characteristics inherited from their common ancestor

Speciation forms:

a bridge between microevolution and macroevolution

Macroevolution

Broad pattern of evolution above the species level, can result in change in origin of new groups of organisms

Microevolution

Change in allele frequencies in a population overtime

Species is latin for

Kind or Appearance

How to determine if organisms are divided into species

Compare morphology, physiology, biochemistry, and DNA sequences

Biological species concept

Defines species as a group of populations whose members have potential to interbreed and reproduce, but NOT produce offspring with members of other groups

Members of a biological species

United by being reproductively compatible

Reproductive isolation

Biological factors impede members of two different species from interbreeding and producing viable offspring

Biological barriers

Break gene flow between species and limit hybrid formation

Hybrid

Offspring that result from an interspecific mating

Mechanisms of speciation

prezygotic barriers and postzygotic barriers

Prezygotic barriers

Barriers that impede mating or hinder fertilization

Postzygotic barriers

Barriers that prevent the hybrid zygote from becoming a fertile adult

Habitat isolation

Prezygotic barrier, two species occupying different habitats within the same area

Temporal isolation

Prezygotic barrier, when different species breed during different times, seasons, or years

Behavioral isolation

Prezygotic barrier, Species have different mating rituals

Mechanical isolation

Prezygotic barrier, mating is attempted buy morphological differences prevent success

Gametic isolation

Prezygotic barrier, sperm of one species cannot fertilize egg of another species

Reduced hybrid viability

Postzygotic barrier, genes of different parent species impair hybrid development

Reduced hybrid fertility

Postzygotic barrier, hybrid may survive, but can be sterile

Hybrid breakdown

Postzygotic barrier, first generation hybrid is viable and fertile, but next generation is not

Morphological species concept

Defines a species by structural features, applies to sexual and asexual species, and relies on subjective criteria.

Ecological species concept

Defines a species in terms of its ecological niche, applies to sexual and asexual species, and emphasizes the role of disruptive selection

Niche

Sum of how members of the species interact with living and non-living parts of their environment

Allopatric speciation

Speciation occurs in populations that are geographically isolated, gene flow is interrupted into subpopulations

Sympatric speciation

Speciation occurs in populations that live in the same geographic area.

Sympatric speciation can occur through:

Polyploidy, habitat differentiation, sexual selection

Polyploidy

Accident in cell division that results in extra sets of chromosomes. More common in plants.

Autoploidy

A fertile individual that has more than two chromosome sets, due to two different species interbreeding and combining their chromosomes

Habitat differentiation

Subpopulation exploits a habitat or resource not used by the parent population

Sexual selection

Favored selection of mates based on appearances

Sym-

Together or with

Allo-

Other or different

-patric

Native homeland or place

Hybrid zone

A region in which members of different species meet, mate, and produce offspring of mixed ancestry.

Hybrid zone location

Located where the habitats of the interbreeding species meet. Can move due to environmental conditions altering habitats

Outcomes of hybrid zones

Reinforcement of barriers, fusion of species, stability,

Reinforcement of barriers

Natural selection should strengthen prezygotic barriers, if this occurs then barriers should be stronger in sympatric populations.

Fusion of species

Gene flow may weaken reproductive barriers, causing gene pools of two species to be increasingly alike. This causes speciation to reverse, making two hybrid species fuse into one.

Stability

Hybrid zones are stable in the sense of hybrids continuing to be produced, due to their ability to survive and reproduce better than the parent.

Time course for speciation

Determined by broad patterns in the fossil record, morphological data, or molecular data.

Punctuated equilibrium

Periods of apparent stasis in which species undergo little or no change through the fossil record.

Punctuated model

New species change most as they branch from parent species and change little

Gradual model

Species diverge more slowly and steadily over time