Speciation

• There are two main types of speciation: allopatric (geographic) and sympatric (non-geographic).
• Allopatric speciation occurs when populations become geographically isolated from one another due to physical barriers or changes in the environment.
• micro evolution= still same species
• Macro evolution: large changes that lead to new species
• speciation: one species splits into 2 or more species
• There are three species concepts: morphological, ecological, and biological
• morphological species concepts : body shape and other structural features
• ecological species concept: how a species interacts with non living and living environment
• Biological species concept: Species is a group of organisms that can interbreed to produce fertile offspring, share a common gene pool and do not exchange genes with different species
• Reproductive isolation: prevents gene flow in different species
• pre-zygotic barriers: happen before zygote is formed, preventing fertilization from taking place
• Three types of pre-zygotic barriers: habitat, temporal, and behavioral isolation to prevent mating attempts
• Habitat Isolation: two species are living in same geographic area but live and breed in different habitats in that area
• Temporal Isolation: Breed at different times (day, season, year)
• Behavioral isolation: behaviors unique to species that enable recognition of mates, like courtship rituals
• Two types of prezygotic barriers that are used to prevent fertilization if mating is attempted: mechanical and gametic isolation
• Mechanical Isolation: shape compatible only with female of same species
• Gametic Isolation: molecular and chemical difference between species, egg and sperm not compatible, sperm can not survive in female repro tract
• Postzygotic barriers: occur after zygote is formed and prevent hybrid zygote from developing into a viable fertile adult
• There are three types of post zygotic barriers: reduced hybrid viability, reduced hybrid fertility, and hybrid breakdown
• Reduced hybrid viability: genetic incompatibility, embryo dies in early development
• Reduced hybrid fertility: hybrids produced but are sterile or not very fertile
• Hybrid Breakdown: 1st generation hybrids are viable and fertile but then when hybrid mates their offspring are frail or infertile
• Allopatric speciation: when a population splits into two or more species due to geographic separation and gene flow is interrupted
• allopatric speciation evolves by natural selection or genetic drift
• allopatric speciation can occur due to geographic barriers or migration
• once allopatric speciation occurs separate gene pools diverge and can not breed with original species even if the population comes back
• Sympatric isolation: new species arise within the range of parent population, reproductive isolation without geographic isolation
• Two possible mechanisms of polyploidy: autopolyploidy and allopolyploidy
• autopolyploidy (4n): doubling of chromosome number before meiosis, they cannot interbreed with 2n
• allopolypolidy: two different species interbreed and produce hybrid offspring
• Punctuated equilibrium: little or no evolutionary change, punctuated by rapid bursts of speciation
• Gradual model: slow and constant accumulation of adaptive change over time.