Review from last lecture Genetic drift 1 of 5 mechanisms of evolution Bottleneck effect o Example Cheetah went through two bottlenecks famine and hunting and disease Greatly reduced the genetic diversity in modern cheetahs Only mutation can increase genetic diversity in this example they lost the ability to respond to new selective pressures Mechanisms of Evolution Microevolution Changes in population allele frequency 1 Mutation 2 Gene flow 3 Nonrandom Mating 4 Genetic Drift 5 Selection Multiple mechanisms of evolution can be acting on a single population at any given time Macroevolution speciation 1 Changes over time of one species into another species 2 Split ancestral species into 2 or more descendant species Both still depend on microevolution What is a species Historically species were defined based upon morphology Problems Males and females look different Sexual Dimorphism Cryptic Species Look identical but cannot breed Biological Species Concept Ernst Mayr o A species is defined as groups of actually or potentially interbreeding natural populations that are reproductively isolated form other such groups What does reproductive isolation mean o Reproduction is defined as the union of sperm and egg o Pre zygotic Isolation happens before fertilization o Post zygotic Isolation happens after fertilization Pre zygotic Isolation Mating can t happen Mechanical Isolation Physically impossible for mating to occur Body Mismatch o Can t match up reproductive structures Lock and Key o Even if reproductive structures could match up the male reproductive structure can t fit appropriately into the female reproductive structure Example Carabidae Have copulatory pieces specific to a female s opening So different male species will never fit with a female of a different species Pre zygotic all isolations from this point on will be pre zygotic until noted otherwise Mating could happen but it doesn t Geographical Isolation Barriers to organismal movement or reproductive particle movement No movement of individual genetic material Shuts down gene flow Barriers o Geological mountain ranges bodies of water o Environmental Factors high temperature o Human Influences roads cities Example Desert Pupfish Death Valley 10 Species of fish Very closely related Likely shared a common ancestor Isolated each species has its own pool stream Death valley had a lot of water 22 000 years ago Ecological Isolation preferences Anoles use chin flaps to attract females o Anolis homolechis lives on ground o Anolis sagrei lives in trees o These two species never meet or breed Organisms living in same general area but some environmental factor isolates them habitat Behavioral Isolation Some aspect of organismal interaction behavior that differs between groups and prevents mating between those groups o Song call o Ritualized Courtship dancing flying Example Jumping Spiders rub body parts together to make sounds that attract females
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