Exam Four Nonrandom mating 11 18 2013 Mating within a population is almost never random o Inbreeding can occur because related individuals reside in the same area o Sexual selection o Individuals can prefer a certain look Any time an allele provides a little superiority natural selection favors the individuals Key points about evolution Natural selection acts on variation that is already present Natural selection acts on individuals nut causes change in the genetic traits of a population Evolution is the change in allele frequencies of a population o Fitness the reproductive success of an organism Evolution doesn t make organisms better How does natural selection work Improved survival improved reproduction Natural Selection acts on the phenotype of an individual However evolution is defined as the changes in the genotype of a population The selection of phenotypes by natural selection influences a populations genotypes driving evolution Some phenotypes reproduce more successfully than others Adaptations characteristics that help and individuals survive and Abiotic Nonliving factors availability of water and resources such reproduce as minerals Biotic living factors other living organisms Agents of natural selection o Competition for resources o Predator and prey o Sexual selection Agents for natural selection Competition Competition with other organisms for scarce resources o Most intense among members of the same species Predator and prey Coevolution when two species interact extensively each can exert a strong selective pressure on the other o Other found in predator prey relationships Wolves and deer o Wolves select against slow or careless deer o Swift alert deer select against slow clumsy wolves Sexual selection Can be driven by female preference or by sexual competition between males o Female guppies prefer brightly colored males o Male bighorn sheep compete for the right to mate o Females often prefer males with the most extravagant characteristics Why o The ability to survive with the burden of extravagant characteristics could indicate a strong healthy individual Bright colored male guppies must be faster to escape predators Peacocks with large heavy tails must be stronger and healthier to deal with carrying the weight of the feathers Types of natural selection Directional selection o Favors individuals with an extreme trait and selects against both average individuals and individuals with the other extreme o Favors average individuals In other words selecting against Stabilizing selection any extremes Disruptive selection o May occur when a population inhabits an area with more than one useful resource Selection that selects against the average or intermediate organisms of a population o Ex Food source Chapter 16 Origin of Species 11 18 2013 Species the basic unit of taxonomic classification A population that evolves independently of other populations The biological species concept groups of interbreeding natural populations which are reproductively isolated from other such groups Kingdom phylum class order family genus species Biological species concept Based on the observation that reproductive isolation ensures evolutionary independence Defining a species can be confusing Appearance can be misleading o Some organisms look very similar but are different species o Some organisms look very different but are the same species Isolating mechanisms traits that maintain reproductive isolation Premating isolating mechanisms o Traits or mechanisms that prevent mating between species Postmating isolating mechanisms o Mechanisms that prevent the formation of vigorous fertile hybrids between species Premating isolating mechanisms Geographic Isolation o Interbreeding is prevented because species live in different areas o Does not necessarily mean they cannot interbreed o So geographic isolation is usually considered more of a mechanism that allows new species to form Kaibab squirrel lives only on the north rim of the grand Abert squirrel lives only on the south rim of the grand canon canyon Geographically isolated but are they separate species Ecological Isolation o Different species may occupy different habitats within the same general area White crowned sparrow inhabits fields and meadows White throated sparrow inhabits dense thickets Temporal Isolation o Different species may breed at different time Bishop pine releases pollen in the summer Monterey pine releases pollen in early spring Behavioral Isolation o Different species may have different courtship signals and behaviors Colors mating calls etc Mechanical Isolation o Differing sexual organ may foil mating attempts Postmating isolating mechanisms Serve to limit hybrid offspring o Gametic incompatibility sperm from one species may not be able to fertilize eggs of another o Hybrid inviability hybrids either abort early in development due to genetic differences or have difficulties performing tasks like carrying nest material Hybrid infertility Most common because due to inability of chromosomes to pair up properly during meiosis so gametes fail to develop Speciation the process by which new species form Speciation depends on two factors o Isolation o Genetic divergence Isolation followed by genetic divergence can occur in several different ways There are two broad categories of pathways to speciation o Allopatric speciation When two populations are geographically separated from one another Organisms may colonize isolated habitats Landscape changes Rising sea levels formation of mountain ranges etc may isolate populations Genetic differences between two isolated populations may become sufficient to prevent interbreeding When two populations share the same geographic area Can occur in an area with two distinct types of habitats Biologists are watching such an event right now in a species of fruit fly R pomonella is a fruit fly that lives in hawthorn trees o Sympatric speciation Lay eggis in the fruit Maggots hatch and eat the fruit About 150 yeard ago scientist notices that R pomonella had started to infest apple trees o Today it appears that R pomonella 11 18 2013 Chapter 17 Earth is 4 5 billion years old and electrical storms Early earth was thought to be very hot with a lot of volcanic activity The earths early atmosphere was thought to be low in oxygen Life began during the Precambrian Era The oldest fossil organisms found so far are about 3 5 billion years old The first cells were presumably anaerobic prokaryotes Some
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