New species arise through the process of…
speciation.
- an ancestral species splits into two or more descendant species that are genetically different from one another, and can no longer interbreed.
What is macroevolution?
broad patterns of evolutionary change above the species level.
- evolutionary changes occurring on geological time scales.
What is the difference between microevolution and macroevolution?
nothing!
they are fundamentally identical processes on different time scales.
What is a species under the Biological Species Concept (BSC)?
a group of actually (or potentially) interbreeding individuals that produce viable, fertile offspring and are reproductively isolated from other species.
What are some limitations of the BSC?
- cannot be applied to fossils or asexual organisms
- emphasizes the absence of gene flow
What is the morphological species concept?
defines a species by structural features
- applies to sexual and asexual species
What is the ecological species concept?
defines a species as a set of organisms adapted to a particular set of resources called a niche, in the environment
- applies to sexual and asexual species.
What is the phylogenetic species concept?
defines a species as the smallest group of individuals on a phylogenetic tree.
- applies to sexual and asexual species.
BSC emphasizes…
reproductive isolation.
What is reproductive isolation caused by?
caused by biological factors (barriers) that impede two species from interbreeding and producing viable, fertile offspring (hybrids)
What are hybrids?
offspring of crosses between different species
what are prezygotic barriers?
block fertilization from occurring.
Prezygotic Reproductive Barriers
What is habitat isolation?
when two species encounter each other rarely, or not at all because they occupy different habitats
- not isolated by physical barriers
Prezygotic reproductive barriers
What is temporal isolation?
A species that breed at different times of the day or different seasons and cannot mix their gametes.
- occupy the same habitat
Prezygotic reproductive barriers
What is behavioral isolation?
courtship rituals and other behaviors unique to a species are effective barriers
Prezygotic reproductive barriers
What is mechanical isolation?
morphological differences can prevent successful mating
(anatomically incompatible)
Prezygotic reproductive barriers
what is gametic isolation?
gametes (ex: sperm) of one species may not be able to fertilize the eggs of another species
What are postzygotic barriers?
prevent a hybrid zygote from developing into a viable, fertile adult
Postzygotic reproductive barriers
what is reduced hybrid viability?
genes of the different parent species may interact to impair the hybrid’s development or survival
- often results in zygote death.
postzygotic reproductive barriers
what is reduced hybrid fertility?
even if the hybrids are vigorous, they may be sterile.
Postzygotic reproductive barriers
what is hybrid breakdown?
some first generation hybrids are vigorous and fertile, but when these hybrids mate with one another, or with either parent species, offspring of subsequent generations are feeble and sterile.
What is allopatric speciation?
The evolution of a new species following the geographic isolation of two or more subpopulations of an ancestral species.
- separated subpopulations may evolve independently through natural selection, mutation, and genetic drift
What is sympatric speciation?
the evolution of a new species from an ancestral species while both continue to inhabit the same geographic region
- speciation without geographic separation
- when individuals in a sub group of the population stop gene flow with individuals of the larger population, they may eventually become a new species
What is polyploid speciation?
occurs when changes in the number of chromosome sets (polyploidy) create genetically distinct descendants that are reproductively isolated from parental forms.
