Speciation Flashcards
What causes speciation?
Various evolutionary processes and geographical circumstances
What provides a population’s genetic variance?
Gene pool
What constitutes a population’s gene pool?
All the alleles of all genes of each individual in that population
Define microevolution
The change in percentages, or frequencies, of alleles within populations. These are the small events that lead to evolution within a population
What five processes can cause allele frequencies to change and microevolution to occur?
Mutation, gene flow (migration), non-random mating, genetic drift, natural selection
What is the most significant factor in the formation of new species?
Natural selection
Give an example of mutation causing selective advantage
Norway’s rats are resistant to poison warfarin
Give an example of speciation
The Galápagos Islands iguana can swim
What is notable about people with blue eyes?
All people originate from a common ancestor. This is neither a positive nor negative mutation
Describe gene flow
The net movement of alleles from one population to another as a result of migration
Give an example of gene flow
Grey wolves travel great distances to find a neighbouring pack and mate with an individual in that pack. This introduces new alleles into the distant pack
Describe non-random mating
Mating among individuals on the basis of a particular phenotype or due to inbreeding. In animals, individuals may choose mates based on their physical or behavioural characteristics, affecting the alleles in the gene pool of the next generation
How does inbreeding occur?
When closely related individuals breed, either naturally or by human-led breeding programs
Give an example of non-random mating and its consequence
The Chinese shar-pei dog has an inherited genetic mutation, enhanced by inbreeding, that increases the production of hyaluronic acid, contributing to a skin disorder called mucinosis
Give an example of non-random mating and it’s benefit
The pea flower can self-fertilize which helps if the plant is not able to reproduce sexually via pollination from an insect
Describe genetic drift
The change in frequencies of alleles due to random events in a small breeding population. The smaller the population, the less likely it is that the parent gene pool will be reflected in the next generation
What intensifies the effects of genetic drift?
The failure of a few individuals to reproduce
Which famous person suffered from non-random mating and how?
King Charles II of Spain became severely disabled (Hapsburg jaw)
Describe the founder effect
Often new populations in areas like islands are formed by only a few individuals. They carry some of the alleles from the original population’s gene pool. Inevitably, the gene pool is reduced
Give an example of the founder effect
Polydactylism in Amish communities in Philadelphia
Describe the bottleneck effect
If a population is quickly reduced by starvation, disease, or a natural catastrophe, the surviving population likely only has a fraction of the alleles that were present before the population declined. The gene pool will have lost its diversity and allele frequencies will have changed
What types of natural selection change allele frequency?
Stabilizing selection, directional selection, disruptive selection
Describe stabilizing selection
Favours an intermediate phenotype and acts against extreme variants of it. This improves adaptation of the population to aspects of the environment that remain fairly constant
Describe directional selection
Favours the phenotypes at one extreme over the other. This type of selection is common during times of environmental change or when a population migrates to a new habitat
Describe disruptive selection
Favours two extremes of a population. As a result, intermediate phenotypes can be eliminated from a population
Describe sexual selection
Involves the competition between males through combat or visual displays. It also includes choices females make in mates
What term is used for males and females of a species that look markedly different?
Sexual dimorphism
What is another word for speciation?
Macroevolution
Define speciation
The formation of new species from existing species. Two populations become reproductively isolated over time if there is little or no gene flow between them. Without gene flow, the populations may become different species
What prevents gene flow in a population?
Reproductive isolating mechanisms
What are the two types of reproductive isolating mechanisms?
Pre-zygotic and post-zygotic
What are the main branches of pre-zygotic reproductive isolating mechanisms?
Prevention of mating, prevention of fertilization
Give factors relating to the prevention of mating
Behavioural isolation, temporal isolation, ecological/habitat isolation
What type of post-zygotic reproductive isolating mechanism is there?
Prevention of hybrids
Give factors relating to the prevention of hybrids FIX THIS!!
Zygotic mortality, hybrid inviability, hybrid infertility
Describe pre-zygotic isolating mechanisms
Mechanisms which either impede mating between species or prevent fertilization of the eggs of individuals from different species to mate
Describe behavioural isolating mechanisms
Any special signals or behaviours that are species-specific to prevent interbreeding with closely related species
Give an example of a behavioural isolating mechanism
Eastern meadowlark and Western meadowlark have similar habits but differences in songs and thus, do not mate
Describe temporal isolating mechanisms
Two species may occupy the same habitat and have timing barriers
Give an example of a temporal isolating mechanism
Tropical orchids live in the same area but flower on different days. This prevents fertilization among the orchid types
Describe habitat isolating mechanisms
Two species may live in the same general region but in different habitats, so they may rarely encounter each other
Describe mechanical isolating mechanisms
Two closely related species may attempt to mate but are unsuccessful due to anatomical incompatibility
Give an example of a mechanical isolating mechanism
The genitals of some insects operate in a kind of lock and key system, they are so distinctive that they prevent successful fertilization of other species
Describe gametic isolating mechanisms
Gametes from two different species may meet but do not fuse to form a zygote
Give an example of gametic isolating mechanisms
The sperm of one species may not be able to survive in the environment of the female reproductive tract of another species
Describe post-zygotic isolating mechanisms
In rare cases, the sperm and egg of different species produce a zygote. They prevent such hybrids from developing into viable, fertile individuals. Thus, the original two parental species are proven to be separate species
Describe zygotic mortality
Genetic incompatibility of the interbred species may stop development of the hybrid zygote
Give an example of zygotic mortality
Embryos from these species die in early development due to dysfunctional mitosis
Describe hybrid inviability
The original two-species cross produces viable and fertile hybrid offspring. However, the mating hybrids cannot produce viable and fertile offspring
What is another word for hybrid sterility?
Infertility
Describe hybrid infertility
The hybrid offspring is sterile, representing a reproductive barrier
Give an example of hybrid sterility
Female horses and make donkeys produce mules that are sterile due to dysfunctional mitosis
What are the types of speciation?
Sympatric speciation, allopatric speciation
Describe sympatric speciation
More common in plants than animals, chromosomal changes in plants or non-random mating in animals alters gene flow. The result is reproductive incompatibility without geographical isolation
Give an example of sympatric speciation
An error in cell division of polyploidy plants results in an extra set of chromosomes in the offspring. How reproductively and genetically isolated, the plant may self-fertilize to survive
Describe allopatric speciation
Speciation occurs when a population is split into two or more isolated groups by a geographical barrier. Eventually, the gene pool of the split population becomes so distinct due to natural selection, mutations, and gene flow that the two groups are unable to interbreed when reintroduced
Give an example of allopatric speciation
Finches may have been blown to an island that was uninhabited. They adapted to an unoccupied ecological niche and over time, evolve into a new species
Define adaptive radiation
When the common ancestral species diversifies into a variety of differently adapted species
Give an example of adaptive radiation
Different-sized red crossbill birds have different beaks that can open different- sized cones
Where is adaptive radiation seen most readily?
Island chains
Describe divergent evolution
A pattern of evolution in which species that were once similar to ancestral species become increasingly distinct
Describe convergent evolution
A pattern of evolution in which similar traits arise because different species have independently adapted to similar environmental conditions
Give an example of convergent evolution
Wings on birds and bats. Natural selection favoured flight among these species, but they do not share a common ancestor. Their wings thus evolved differently from different structures
What are the models proposed to explain the speed at which evolution occurs?
Gradualism and punctuated equilibrium
Describe gradualism
Views evolutionary change as slow and steady, before and after a divergence. Big changes occur by the accumulation of small changes. This has been supported since Darwin’s time
Describe punctuated equilibrium
Views evolutionary history as long periods of stasis that are interrupted by periods of divergence. Proposed by Eldredge and Jay Gould in 1972
Which model of evolutionary change is accepted?
Both gradualism and punctuated equilibrium
Give examples of human-made barriers that result in allopatric speciation
Conversion of wilderness into cropland, development of areas for tourism, building urban subdivisions and roads
What are the outcomes of human activities with regards to wildlife
Speciation through: adaptive radiation after geographical isolation, genetic drift after bottleneck affect; species endangerment due to insufficient genetic diversity from population isolation
Give an example of insufficient genetic diversity from population isolation leading to endangerment
Giant panda
Describe mass extinctions
A decrease in the number of species. This allows for adaptive radiation of surviving species that may evolve. Thus, the general trend is an increase in species over time
