24 Flashcards
speciation
the origin of new species, is at the focal point of evolutionary theory
• Evolutionary theory must explain how new species originate AND how populations evolve
microevolution
consists of adaptations that evolve within a population, confined to one gene pool
macroevolution
refers to evolutionary change above the species level
morphological species concept
“They look the same”
+ widely applicable (sexual and asexual organisms)
- Subjective (which structural features distinguish a species?)
genetic species concept
“They have the same DNA”
- DNA sequences may not be available
- How similar is enough to be the same?
ecological species concept
• “They have the same role”
• Criterion: A species is a set of organisms utilizing a single niche
- Many organisms may be adapted to the same niche
biological species concept
“They can mate”
• Criterion: Organisms are classified in the same species if members have the potential to interbreed in nature and produce viable, fertile offspring.
– Note: gene flow between populations holds a species together genetically
• Members of a biological species are united by being reproductively compatible, at least potentially.
reproductive isolation
is the existence of biological factors (barriers) that impede two species from producing viable, fertile offspring. Reproductive isolation can be classified by whether factors act before or after fertilization
Prezygotic barriers
“before the zygote”
• may prevent members of different species from attempting to mate
• may prevent an attempted mating from being completed successfully
• may hinder fertilization if mating is completed successfully
Postzygotic barriers
“after the zygote”
• contribute to reproductive isolation after the zygote is formed
• reduced hybrid viability, reduced hybrid fertility, hybrid breakdown
allopatric speciation
gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations
sympatric speciation
sympatric = “of the same country”
• The key to sympatric speciation is that populations of a single species don’t need to be separated geographically in order to become reproductively isolated from one another.
polyploidy
the presence of extra sets of chromosomes due to accidents during cell division
– Polyploidy is much more common in plants than in animals
hybrid zone
is a region in which members of different species mate and produce hybrids
– it can occur in a single band where adjacent species meet
reinforcement
strengthening reproductive barriers
– reinforcement of barriers occurs when hybrids are less fit than the parent species
fusion
weakening reproductive barriers
stability
continued formation of hybrid individuals
Punctuated equilibria
used to describe these periods of apparent spurts punctuated by sudden change
In punctuated equilibrium, change comes in spurts. There is a period of very little change, and then one or a few huge changes occur, often through mutations in the genes of a few individuals.
graduated
s selection and variation that happens more gradually. Over a short period of time it is hard to notice.
The largest unit within which gene flow can readily occur is a
species
Males of different species of the fruit fly Drosophila that live in the same parts of the Hawaiian Islands have different elaborate courtship rituals. These rituals involve fighting other males and making stylized movements that attract females. What type of reproductive isolation does this represent?
behavioral isolation
According to the punctuated equilibria model,
most new species accumulate their unique features relatively rapidly as they come into existence, then change little for the rest of their duration as a species.
Bird guides once listed the myrtle warbler and Audubon’s warbler as distinct species. Recently, these birds have been classified as eastern and western forms of a single species, the yellow-rumped warbler. Which of the following pieces of evidence, if true, would be cause for this reclassification?
The two forms interbreed often in nature, and their offspring have good survival and reproduction.
Which of the following factors would not contribute to al-lopatric speciation?
Gene flow between the two populations is extensive.
Plant species A has a diploid number of 12. Plant species B has a diploid number of 16. A new species, C, arises as an allopolyploid from A and B. The diploid number for species C would probably be
28
Suppose that a group of male pied flycatchers migrated from a region where there were no collared flycatchers to a region where both species were present (see Figure 24.15). Assuming events like this are very rare, which of the following scenarios is least likely?
The frequency of hybrid offspring would decrease.
whats a limitation for biological species concept?
Hybrids pose a problem for BSC. Different species are able to mate to make a hybrid
deceased or fossilized species can’t mate
BSC is based on _____ rather than physical similarity
reproductive compatibility
what are prezygotic barriers?
- habitat isolation
- temporal isolation
- behavioral isolation
- mechanical isolation
- gametic isolation
habitat isolation
Two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers
example: water dwelling vs terrestrial
temporal isolation
Species that breed at different times of the day, different seasons, or different years cannot mix their gametes
behavioral isolation
Courtship rituals and other behaviors unique to a species are effective barriers
mechanical isolation
Morphological differences can prevent successful mating
example: Bradybaena with shells spiraling in opposite directions
gametic isolation
Sperm of one species may not be able to fertilize eggs of another species
example: difficult for gametes of different species (red and purple sea urchins) to fuse because of the proteins on the surface of eggs and sperm bind very poorly to each other
what are post zygotic barriers?
- reduced hybrid viability
- reduced hybrid fertility
- hybrid breakdown
reduced hybrid viability
Genes of the different parent species may interact and impair the hybrid’s development
example: A leopon (lioness and leopard) or a lipard (lion and leopardess) is sterile and has a very short lifespan. None have grown to maturity
reduced hybrid fertility
Even if hybrids are vigorous, they may be sterile
ex. mules are sterile
hybrid breakdown
Some first-generation hybrids are fertile, but when they mate with another species or with either parent species, offspring of the next generation are feeble or sterile
true or false.
Speciation can take place with or without geographic separation
true
how is gene flow reduced for sympatric speciation?
gene flow is reduced by polyploidy, habitat differentiation, or sexual selection
habitat differentiation
occurs when a subpopulation exploits a habitat or resource not used by the parent population
There are two different types of Rhagoletis pomonella fruit flies: apple flies and haw flies- with each variety courting, mating, and laying eggs almost exclusively on its own type of tree.
this is a prezygotic barrier.
sexual selection
mate choice by females may be a reproductive barrier that keeps gene pools separate
What happens when isolated populations come into contact?
Option 1: Prezygotic isolation exists, mating between populations is rare, gene flow is minimal, populations continue to diverges
- Option 2: Prezygotic isolation does not exist, populations begin interbreeding
- Formation of hybrid zones • Reinforcement
- Populations fuse over time • Stability
hybrid zone
a region in which members of different species mate and produce hybrids
Hybrids often have ______ compared with parent species
reduced fitness
how are hybrid zones affected over time?
- reinforcement
- fusion
- stability
reinforcement
strengthening reproductive barriers
– reinforcement of barriers occurs when hybrids are less fit than the parent species
– Over time, the rate of hybridization decreases
fusion
weakening reproductive barriers
– If hybrids are as fit as parents, there can be substantial gene flow between species
– If gene flow is great enough, the parent species can fuse into a single species
stability
continued formation of hybrid individuals
– Extensive gene flow from outside the hybrid zone can overwhelm selection for increased reproductive isolation inside the hybrid zone
true or false.
Speciation can occur rapidly or slowly and can result from changes in few or many genes
true
what is the tempo of speciation?
The punctuated pattern in the fossil record and evidence from lab studies suggest that speciation can be rapid
How many genes change when a new species forms?
Depending on the species in question, speciation might require the change of only a single allele or many alleles
what are the two models of tempo for speciation?
- punctuated- new species change most as they branch from parent and then have little change
- gradual - species diverge more slowly and steadily
Is it possible for a mutation in one gene to result in reproductive isolation? Why or why not? Provide an example to justify your answer.
yes.
A mutation in a gene affecting flower color may have caused a shift in pollinator preferences, reproductively isolating some individuals in the population. One mutation might have caused a population to diverge into two species!
Mechanical isolation
Hummingbirds – one gene coding for color of flower- shift in pollinators being attracted to flower
Depending on the species in question, speciation might require the change of only a single allele or many alleles
