8.2 - Speciation Flashcards
Speciation
Formation of new species
Species
All members of a population that can interbreed under natural conditions
Allopatric speciation
Formation of new species from geographic separation. These species eventually become less and less genetically related as evolution goes on.
Ex. Pacific wrasse and caribbean wrasse cannot interbreed due to a thin strip of land called the Isthmus of Panama dividing the wrasse species 2 million years ago.
Sympatric speciation
Formation of new species within the same geographic area. Can occur due to competition for resources or mutations. Disruptive selection can lead to this speciation.
Ex. Hawthorn flies laying eggs on both hawthorns & apples after apple trees were brought over to North America.
Reproductive isolating mechanism
Any behavioural/structural/biochemical trait that prevents individuals of different species from reproducing successfully together
Prezygotic mechanism
Prevents interspecies mating & fertilization (formation of zygotes)
Postzygotic mechanism
Prevents maturation & reproduction in offspring from interspecies reproduction (prevents zygote from becoming a viable & reproducing adult)
Behavioural isolation
Pre/Post?
Desc.?
Ex.?
Prezygotic mechanism
Different species use different courtship and other mating cues to find and attract a mate.
Ex. Male frogs of different species have unique calls that attract only females of their own species.
Hybrid infertility
Pre/Post?
Desc.?
Ex.?
Postzygotic mechanism
Hybrid offspring remain healthy and viable, but are sterile.
Ex. Mules are the sterile hybrid offspring of a horse-donkey cross.
Mechanical isolation
Pre/Post?
Desc.?
Ex.?
Prezygotic mechanism
Differences in morphological features may make two species incompatible.
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.
Zygotic mortality
Pre/Post?
Desc.?
Ex.?
Postzygotic mechanism
Mating & fertilization are possible, but genetic differences result in a zygote that is unable to develop properly.
Some species of the sheep and goat are able to mate, but the zygote is not viable.
Temporal isolation
Pre/Post?
Desc.?
Ex.?
Prezygotic mechanism
Different species breed at different times of the year.
Pussy willow produce flowers in the early spring. They are reproductively isolated from plant species that produce flowers at a different time of the year.
Hybrid inviability
Pre/Post?
Desc.?
Ex.?
Postzygotic mechanism
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.
Ecological isolation
Pre/Post?
Desc.?
Ex.?
Prezygotic mechanism
Very similar species may occupy different habitats within a region.
The mountain bluebird lives at high elevations, while the eastern bluebird prefers lower elevations and does not encounter the mountain species.
Gametic isolation
Pre/Post?
Desc.?
Ex.?
Prezygotic mechanism
Male gametes may not be able to recognize and fertilize an egg of a different species.
Many marine animals including corals, clams, and sea cucumbers release their sperm and eggs into open water. The sperm recognizes eggs of their own species through chemical markers on the surface of the eggs.
Adaptive radiation
When a single species rapidly evolves into many different species, filling formerly empty ecological niches. Ex. Finches
Divergent evolution
Large-scale evolution of a group of organisms into many different species, filling specialized ecological niches. Ex. Rodents in Ontario; deer mouse, flying squirrel, beaver
Convergent evolution
Evolution of similar traits in distantly related species (analogous features). Ex. Cacti in South America & Africa
Co-evolution
Process where one species evolves in response to the evolution of another species. Ex. Hawkmoth & star orchid
