BSC2010-evolution-8-2023 (1).ppt

Macroevolution 1: Origin of Species Global Call Direct BSC2010, Fall 2023 Microevolution Change in the frequencies of genotypes in a population Macroevolution The formation of species Outline • What is a species? • Reproductive barriers • How do new species form? • Allopatric speciation • S...

Macroevolution 1: Origin of Species Global Call Direct BSC2010, Fall 2023 Microevolution Change in the frequencies of genotypes in a population Macroevolution The formation of species Outline • What is a species? • Reproductive barriers • How do new species form? • Allopatric speciation • Sympatric speciation • Adaptive radiation • Coevolution • Red Queen Hypothesis Human Meadowlark Which one is a species? A species is... a group of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups -Ernst Mayr 1942 Problems with definition of species ? • Does not apply to asexual organisms • Can not be applied to fossils • “potentially interbreeding” is ill-defined, particularly in the case of hybrids Reproductive barriers between species • Prezygotic barriers • barriers that prevent mating • Postzygotic barriers • barriers that operate after mating occurs Prezygotic barriers • • • • • Habitat isolation Temporal isolation Behavioral isolation Mechanical isolation Gametic isolation What type of prezygotic barrier is this? Behavioral Isolation Postzygotic barriers • Reduced hybrid survivorship • Reduced hybrid fertility What type of barrier is this? Once a barrier to gene flow is established... Can species interbreed if they get back together? Pizzly Bear Species of European and American sycamores have been separated for 20 million years, yet they can still interbreed How do new species form? 1. Allopatric speciation 2. Sympatric speciation 1. Allopatric speciation • Literally “other country” • Geographic barrier divides population or Part of population crosses barrier and “founds” new population • Most prevalent form of speciation Allopatric speciation • Geographic barrier divides population • Gene flow is cut off • Microevolution takes over • Populations differentiate Hawaiian Drosophila: Allopatric speciation Antelope squirrels: Allopatric speciation How do species become reproductive isolated? The Dobzhansky–Muller model: • A subdivided population evolves independently. • In each lineage, new alleles become fixed at different loci, but they are incompatible.over Dobzhansky-Muller Model Speciation by Centric Fusion Reproductive Isolation and Genetic Divergence 2. Sympatric speciation • Literally “same country” • Species arise from a connected population • Common in plants, occasional in animals • Generally two types: polyploidy, behavioral change Sympatric speciation by polyploidy (plants) • Mistake during cell division • New individual is viable but genetically isolated • In plants, individual with new ploidy-level can often self-fertilize Sympatric speciation by polyploidy (plants) Autopolyploidy—chromosome duplication in a single species Allopolyploidy—combining chromosomes of two different species Tetraploids are reproductively isolated Sympatric speciation by polyploidy in Animals Sympatric speciation by behavioral change (animals) • Parents separate into new subpopulations in same region • Young return to new place to mate • No gene flow with original population Sympatric Speciation: The Apple Maggot Fly Adaptive Radiation • The evolution of many new, diverse species from a common ancestor under new environmental conditions Hawaiian silverswords Coevolution • mutual evolutionary influence between two species occurring in the same environment “the red queen hypothesis”