speciation Flashcards
Species
includes all the members of a population that can interbreed under natural conditions.
Microevolution
changes in gene (allele) frequencies and phenotypic traits within a population and species.
speciation
the formation of new species
New species can evolve under a variety of circumstances, however, this process always includes the evolution of distinct features that isolate the new species reproductively, therefore genetically, from other species.
Reproductive isolating mechanism
A Reproductive isolating mechanism is any biological factor that prevents the two populations from interbreeding when living in the same region. There are 2 types:
prezygotic mechanism
a reproductive isolating mechanism that prevents interspecies mating and fertilization.
Postzygotic mechanism
a reproductive isolating mechanism that prevents maturation and reproduction in offspring from interspecies reproduction.
Prezygotic Mechanisms
behavioural Isolation- different species use different courtship and other mating clues to find and attract a mate. Ex) Frogs
temporal Isolation- different species breed at different times of the year. Ex) Pussy Willows
ecological Isolation- very similar species may occupy different habitats within a region. Ex) Bluebirds
mechanical Isolation- differences in morphological features may may two species incompatible. Ex) Damselflies
gametic Isolation- male gametes may not be able to recognize and fertilize an egg of a different species. Ex) Corals
Postzygotic Mechanisms
zygotic mortality - mating and fertilization are possible, but genetic differences result in a zygote that is unable to develop properly. Ex) Sheep and Goats
hybrid inviability- a hybrid individual develops but either dies before birth or, if born alive, cannot survive to maturity. Ex) Tigers x Leopards
hybrid infertility - hybrid offspring remain healthy and viable but are sterile. Ex) Mules
Types of Speciation
Allopatric speciation
Sympatric speciation
Allopatric speciation
the formation of a new species as a result of evolutionary changes following a period of geographic isolation.
Sympatric speciation
the evolution of populations within the same geographic area into separate species.
Allopatric Speciation
Once populations are physically separated, they can no longer exchange genetic information.
Over many generations, the populations will gradually become less alike.
Any mutations or differences in the environments are not shared between the two populations and will lead to different forms of natural selection.
Changes that result from may also cause the population to become increasingly different.
Once enough time has passed, there is a good chance that the two populations will have evolved some sort of reproductive isolating mechanism.
Sympatric Speciation
This form of isolation can occur gradually or suddenly.
Gradual Ex) Hawthorn Fly- laid eggs in the fruit of hawthorn trees until apple trees were introduced to North America. Some then began to lay eggs in apples. Today the population consists of two populations, one now called apple maggot flies and the other feeds only on hawthorns.
Sudden Ex) Even a single mutation can render an individual unable to reproduce with other members of the population. If two individuals share this mutation then from the reproductively isolated population a new species may result. Occurs frequently in plants.
Polyploidy & Hybrid Species
Mutations causing polyploidy (double the number of chromosomes) can result in sympatric speciation.
Polyploids produce fertile offspring when mated with each other but produce sterile offspring when mated with the original species. The evolution of 30% to 70% of all flowering plant species has involved polyploidy.
When two polyploids mate the hybrid becomes diploid with a mix of chromosomes from two original species. The hybrid can now form a new species that will not produce fertile offspring when crossed with either of the two parent species.
Human Influence on Speciation
Many human activities such as agricultural expansion and the construction of roads, are causing once large habitats to be fragmented into smaller areas that effectively isolate populations.
These create low genetic diversity within the populations and increase their risk of being threatened by disease or changing environmental conditions.
To help counter this, fragmented habitats should have some way of being connected. For example, animal corridors under or over highways.
Adaptive Radiation
is the relatively rapid evolution of a single species into many new species, filling a variety of formerly empty ecological niches.
Adaptive Radiation
is the relatively rapid evolution of a single species into many new species, filling a variety of formerly empty ecological niches.
This process usually occurs when a variety of new resources become available, resources that are not being used by other species.
Divergent Evolution
Divergent evolution- the large-scale evolution of a group into many different forms.
All natural ecosystems, have a number of ecological roles (producers, decomposers, consumers & scavengers).
These major roles are never filled by a single species.
Divergent evolution leads to 2 predictable outcomes:
Competition between species is minimized as new species diverge to fill specialized ecological niches.
New species continue to evolve until most available resources are used.
Convergent Evolution
the evolution of similar traits in distantly related species.
Ex) Sharks & Dolphins- both have evolved very similar streamlined bodies well suited for their high-speed carnivorous behaviour. Natural selection favoured the same body shapes in two very distantly related species.
Two outcomes:
Natural selection will favour the evolution of similar traits in similar environments.
Some traits will converge in form or function, each species will retain other features that provide evidence of their distinct evolutionary past.
Co-Evolution
a process in which one species evolved in response to the evolution of another species.
Ex) certain plants have evolved hard protective shells to protect their seeds, whole some seed-eating mammals have evolved powerful jaws and teeth for chewing through hard shells.
Sometimes referred to as the “evolutionary arms race”
As species coevolve, one or both species may become increasingly dependent on the other. A threat to one may become a threat to the other.
