BSC 305 exam 2 Flashcards
Negative frequency dependent selection
rare phenotype has the highest fitness. Maintains the genetic variation
Ex: Mouth shape in scale-eating fish. Fish that parasitize larger fish, bite their sides. They can only attack prey from one side because of their mouth shape. SO…the rarer mouth shape has an advantage because they take prey by surprise
Positive frequency dependent selection
most common phenotype has the highest fitness. Lowers the genetic variation
Ex: The butterflies Heliconius melpomene and H. erato each show extraordinary geographical variation in coloration, and their colors vary in parallel. Both species gain a fitness advantage by resembling the other because birds are more likely to associate their coloration with distastefulness and so avoid attacking them. The birds learn to avoid a color pattern more quickly when it is common.
Vicariance
when a barrier appears and divides a population that was dividing a larger region
Ex: The snapping shrimps Alpheus nuttingi, found on the Atlantic side of the Isthmus of Panama, and A. millsae, found on the Pacific side, are sister species that evolved from a common ancestor that became divided into two populations as the isthmus formed.
Dispersal
When individuals from one population colonize another region. Speciation by dispersal has happened innumerable times when oceanic islands have been colonized from continental populations.
Ex: Several wild coffee trees speciated via dispersion on the islands of Hawaii
Florida Panthers
brought over 8 new panthers from texas to florida in order to increase the genetic diversity of the florida panthers bc of the dwindling population size. they mate and create a heterozygous gene and that has the highest fitness.
Sympatric Speciation
When a population splits into two species without geographic isolation. Sympatric speciation is less likely than allopatric because recombination breaks down genetic combinations that might form new species
Ex: Two ‘races’ of North American Hawthorn fly (R. pomonella), one parasitizing hawthorns and one apple trees. Ancestors laid eggs only in hawthorns. In the late nineteenth century, the fly started to infest apple trees in the same areas as the normal host. There was a temporal reproductive shift due to the different fruiting times of plants, 4-6% reduced gene flow per year.
Why switch? Apples have larger fruits and switching provided an escape from parasitoid wasps in hawthorn trees.
Allopatric Speciation
Allopatric speciation is the evolution of genetic barriers between populations that are geographically separated by a physical barrier (for example, a mountain range). The most common way for speciation to begin.
genetic drift
Genetic change between generations happens even when selection is not at work. We have already seen that mutation changes allele frequencies. Evolution also results from chance events of survival, reproduction, and inheritance. The evolutionary process that results is called genetic drift.
Definition- Random changes in the frequencies of two or more alleles or genotypes within a population
four criteria for natural selection
Criteria 1- There must be phenotypic variation among individuals of a species
Criteria 2- the phenotypic variation must be due to genetic differences
Criteria 3- more individuals are born in the population than will survive and reproduce (opportunity for selection)
Criteria 4- individuals show more success (greater survivorship or reproduction) due to new trait
Ecological Speciation
1a- Usually occurs via selection for traits associated with adaptation to different environmental conditions. Reproductive isolation can result when natural selection acts differently on two populations.
1b- BIologists ran an experiment in which laboratory populations of Drosophila melanogaster were selected for adaptation to two different environments. In only about 20 generations, the divergently selected subpopulations became substantially reproductively isolated.
