Lesson 5: Types of Evolution Flashcards
what is speciation
when an evolution leads to the evolution of an entirely new species
- if evolution evolves so much to a point where a new species is formed, then its called speciation
- evolution itself is advancements of a species, not a changed or new species
modes of speciation: reproductive isolation - what is it and how does it work
for a new species to form, individuals from the original species must evolve to become reproductively isolated from the remainder of the population
- the individuals in the species are no longer reproducing with one another
- becoming reproductively isolated with each other can lead to speciation
what is a reproductive isolating mechanism
any factor that prevents two populations from interbreeding while in the same region
what are the reproductive isolating mechanisms
prezygotic and postzygotic
prezygotic- what is it and how does it work + examples
these are mechanisms that prevent fertilization and zygote formation
- examples: differences in breeding season, physical or behavioural traits, habitat preferences, or incompatibility of gametes
postzygotic- what is it and how does it work + examples
these are mechanisms that prevent a fertilized egg from growing into a viable adult
- examples: zygote mortality, hybrid individual inviability, or hybrid infertility
prezygotic examples: behavioural isolation
different species use different courtship and other mating clues to find and attract a mate
(the presence and absence of specific behavioural mating calls to find a mate)
- male frogs of different species have unique calls that attract only females of their own species
prezygotic examples: temporal isolation
different species breed at different times of the year
(prevents species from breeding because they breed at different times)
- pussy willows produce flowers in the early spring; they are reproductively isolated from plant species that produces flowers at a different time of year
prezygotic examples: ecological isolation
very similar species may occupy different habitats within a region
(two species cant interbreed due to living in different environments/areas)
- the mountain bluebird lives at high elevations, while the eastern bluebird prefers lower elevations and does not encounter the mountain species
prezygotic examples: mechanical isolation
differences in morphological features may make two species incompatible
(physical differences in reproductive systems and gentilia make it impossible to breed)
- male damselflies transfer sperm during an unusual mating flight; the male and female genitalia of each species are uniquely shaped and are physically incompatible with other species
prezygotic examples: gametic isolation
male gametes may not be able to recognize and fertilize an egg of a different species
(gametes aka reproductive cells are not compatible and are unable to achieve fertilization)
- many marine animals including corals, clams, and sea cucumbers release their sperm and eggs into open water; the sperm recognize eggs of their own species through chemical markers on the surface of the eggs
postzygotic examples: zygotic mortality
mating and fertilization are possible, but genetic differences result in a zygote that is unable to develop properly
- some species of sheep and goat are able to mate, but the zygote is not viable
postzyotic examples: hybrid inviability
a hybrid individual develops but either dies before birth or, if born alive, cannot survive to maturity
- when tigers and leopards are crossed, the zygote begins to develop but the pregnancy ends in a miscarriage or stillborn offspring
postzygotic examples: hybrid infertility
hybrid offspring remain healthy and viable but are sterile
- mules are the sterile hybrid offpsring of a horse-donkey cross
modes of speciation: allopatric speciation
most new species form when a single species is seperating into two geographically isolated populations
- once populations are physically seperated, they cannot exchange genetic information so are reproductively isolated
- they will respond to their environment and will become less and less similar over time
modes of speciation: sympatric speciation
a new species can also evolve from within a large population
- no geographic isolation is necessary
- this can happen gradually as a response to a change in the environment, or suddenly through a random mutation
- both species will inhabit the same geographic area but are genetically incompatible
natural selection leads to what predictable outcomes? (according to the patterns of evolution)
- closely related species share many homologous/same features, even if they do not serve the same function
- species may have vestigal structures that once served as a function in their ancestors
- remote islands are inhabited by unique species that are descended from a few individuals who were able to reach the island
types of evolution: adaptive radiation
this occurs when a single species evolves into a number of distinct but closely related species (each new species fills a different niche)
- this process most commonly occurs when a variety of new resources become available that are not being used by other species
- EX: darwins finches is a good example of this
types of evolution: divergent evolution
this is when a group/closely related groups that share a common ancestor are placed under selective pressures and therefore evolve to occupy unique niches (due to the development of differences over time)
what has divergent evolution allowed us to do?
it allowed us to develop such great biodiversity of life
- this is because all natural ecosystems require a number of species each with unique ecological roles
- EX: we need producers, consumers, decomposers, and scavengers to maintain balance with the ecosystem
- EX: rodents in ontario forests- all species (chipmunks, squirrels, beavers, etc) evolved from a single common ancestor but now show unique characteristrics and fill various niches in the ecosystem
types of evolution: convergent evolution
this occurs when two different species or taxa evolve to occupy similar ecological niches
- similar adaptations may be favoured in very different geographic regions that have very similar selection pressures
- EX: sharks and dolphins have evolved streamlined bodies even though they are very distantly related
- KEY: similar features have evolved in very distantly related organisms which has allowed for them to occupy similar niches (unlike what we looked at in divergent evolution)
types of evolution: coevolution
when a species evolutionary success is closely linked to that of another species
- EX: certain plants have evolved hard protective shells to protect their seeds while birds developed stronger jaws and teeth for chewing through those same hard shells
- symbiotic relationships are good examples of coevolution
what extreme cases can occur in coevolution?
species can become so closely dependent that the extinction of one species could lead to the extinction of the other
RECAP: divergent evolution
two or more species diverge from a common ancestor
- they share a common ancestor but evolved into two different species
RECAP: convergent evolution
two or more distinct species share traits NOT due to a common ancestors
- EX: birds, butterflies, and bats- they all have wings that allows them to fly but they don’t share a common ancestor with wings, so each one evolved to have wings independently; evolution converged on a similar trait in vastly different species
RECAP: reproductive isolation
meaning two populations of the same species can no longer mate together successfully
RECAP: prezygotic
type of isolation that happened between groups of the same species before an egg even got fertilized
- Behavioral isolation: when species can have different behaviors, even very slight differences, that can isolate them; EX= birds having different songs
- Temporal isolation: species could breed at different seasons, years, even different times of the day- they may look very similar, but if they don’t have the same breeding season, then you’re going to have an isolation
- Habitat isolation: you can have two species living in the general same area but if one prefers an aquatic environment and one prefers a terrestrial environment, that will be a habitat isolation
RECAP: allopatric speciation
when one species diverges into two new species because of geographic isolation
- there is a geographic barrier that separates the populations; while natural selection is acting on these populations, there is also some geographical barrier- like a river, or mountain that keeps them from being able to interbreed and share the same gene pool
RECAP: sympatric speciation
the speciation that happens in the same area
RECAP: postzygotic
sometimes offspring that are produced between two different species are very weak and do not survive long
- Sometimes if species interbreed, the offspring is NOT able to develop in even very early embryonic stages because there is a genetic incompatibility
