chapter 24: Orgin of Species

Anagenesis

The transformation of an unbranched lineage of organisms, sometimes to a state different enough to become new species

Cladogenesis

The budding of one or more new species from a parent species that continues to exist.

Macroevolution

Refers to broad patterns of evolutionary change above the species level.

The biological species concept

States that a species (multicellular reproducing animals) is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring.

Prezygotic barriers

Block fertilization by:

• Impending diff species from attempting to mate

• preventing successful completion of mating

• Hindering fertilization if mating is successful

Reproductive Isolation

The existence of biological factors (barriers) that impede 2 species from producing viable, fertile offspring.

Habitat isolation

2 species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers.

Temporal Isolation

Species that breed at different times of the day, different seasons, or different years cannot mix their gametes.

Behavioral Isolation

Courtship rituals and other behaviors unique to a species are effective barriers to mating

Mechanical Isolation

Morphological differences can prevent successful completion of mating.

Gametes Isolation

Sperms of one species may not be able to fertilize eggs of another species

Postzygotic barriers

Prevent the hybrid zygote from developing into viable, fertile adult by

• Reduced hybrid viability

• reduced hybrid fertility

• Hybrid breakdown

Allopatric Speciation

Genetic flow is interrupted or reduce when a population is divided into geographically isolated sub populations.

Sympatric Speciation

Occurs in populations that live in the same geographic area

Autopolyploid

An organism that results from a single species that doubles its chromosome number ie. Diploid to tetraploid

Allopolyploid

A polyploid hybrid resulting from contributions of two different species

Gradualism

An accumulation of small changes over a long period of time resulting in significant change

Punctuated Equilibrium

Sees Speciation taking place in rapid periods of change filled by long periods of genetic stability