11. Speciation Flashcards
What is a Species?
group of organisms whose members can breed and produce viable and fertile offspring typically by sexual reproduction
What is Anagenesis?
- Also called phyletic evolution (nonbranching evolution)
- Accumulation of changes that gradually transform a given ENTIRE species into a species with different characteristics (evolution within a lineage) – so NO net increase in species diversity
What is Cladogenesis?
- Also called branching evolution (diversifying evolution)
- One or more species arising from one original species (an evolution that results in the splitting of a lineage) – so net increase in species diversity
- Cladogenesis, unlike anagenesis, is a process of evolution in which a small subset of an existing species evolves, but NOT the entire species (this leaves the original species more or less intact, allowing for both the older species and the new species to co-exist)
What is the Gradual Speciation Model?
In the gradual speciation model, species diverge gradually over time in small steps
Examples:
- Small variations occur over time in a population of wolves — larger ears, longer teeth and a heightened sense of smell. Wolves with these helpful traits tend to survive better than those without; as time progresses slowly, the traits gradually become the norm among the population.
- A species of butterfly is yellow and black in colour. However, a butterfly is born that happens to be orange and yellow in color making it difficult to see. Over a long period of time, the yellow and black butterflies die out, because the orange and yellow color combination makes the butterflies less visible to predators.
What is the Punctuated Equilibrium Model?
In the punctuated equilibrium model, a new species undergoes changes quickly from the parent species, and then remains largely unchanged for long periods of time afterward
Examples:
- A species of birds exist in stasis for many thousands of years. Suddenly, bacteria cause their primary tree of sheltering choice to die. The birds must adapt within the environment to trees that are much higher, requiring more wing strength. Some birds die. The remaining birds’ bodies adapt longer, stronger wings to survive. The strong birds survive meaning more are born until the others die out. The species returns to a state of stasis.
- A cheetah species has no spots. However, due to a gene mutation, a cheetah cub is born with spots. Because this adaptation helps the cheetah to hide and survive, more cheetahs are born with spots. This continues until the spotless cheetahs are all replaced by spotted cheetahs. The species stays that way for many years.
What is the Biological Species Concept?
The biological species concept defines species as:
– A group of individuals that can potentially interbreed in nature and produce viable, fertile offspring
- Individuals of different species are REPRODUCTIVELY ISOLATED from each other
Why can’t we apply the biological species concept to all situations? (2)
– Does not apply to organisms that reproduce asexually all or most of the time, such as prokaryotes
– No way to evaluate the reproductive isolation of fossils (obviously they cannot mate any longer, although we still have to classify them)
What is the Morphological Species Concept?
For example, most species can be classified based on similarities with respect to measurable physical traits (morphological species concept)
What is the Ecological Species Concept?
Another approach is defining species as groups or populations that share the exact same ecological niche – or the functional role it plays within an ecosystem (ecological species concept)
What is the Genetic Species Concept?
Also, one can define species with respect to similarities solely on the basis of molecular data (genetic species concept)
What are Prezygotic Barriers?
Impede mating between species or hinder the fertilization of ova if members of different species attempt to mate
- before zygote is formed
What are Postzygotic barriers?
Prevent zygote from developing into a viable and fertile adult
What is Temporal Isolation?
– Species breed at different times (this means different times of day or different seasons or even different years!)
– Example: The western spotted skunk and the eastern spotted skunk overlap in distribution. Even though these species are very similar, the western spotted skunk breeds in late summer and the eastern in late winter.
What is Habitat Isolation?
– Species found in different habitats but in same area that rarely comes across each other even though there are no obvious physical barriers
– Example: Two species of garter snake live in the same area, but one species lives mainly in water, and the other is mainly terrestrial.
What is Behavioral Isolation?
– Every species has its own mating/courtship rituals and behaviors and because of this, different species will not attract each other which prevents them from mating
– Example: Male fireflies have different light flashing patterns, and only females of same species recognizes the pattern as being courtship behavior.
What is Mechanical Isolation?
– When male and female sex organs are not compatible which means fertilization cannot occur
– Example: An example of this is the direction a snail’s shell spirals. If it spirals in the direction opposite from another snail, they will not be able to mate since their reproductive organs will not align.
- Example: Bush Babies, a group of small nocturnal primates are divided into several species based on mechanical isolation. Each species has distinctly shaped genitalia that, like locks and keys, only fit with the genitalia of its own species.
What is Gametic Isolation?
– Gametes do not unite to form a zygote (so egg and sperm cells are incompatible)
– Example: Many marine species broadcast their eggs and sperm in the water. The gametes of more than one species can encounter each other, but they generally will not fuse.
– Example: In sea urchins, a protein called bindin allows sperm cells to penetrate eggs. Differences in the amino acid sequence of binding can cause the failure of fertilization to occur between closely related populations.
What is Hybrid Inviability?
– Zygote forms, but dies after a few series of cell divisions (genetic information from male and female parents were insufficient to carry the organism through morphogenesis)
– Most often, the hybrid embryo dies before birth…however, sometimes, the offspring develops fully with mixed traits from each parent, forming a frail, often infertile adult
– Example: Species of frogs (genus Rana) overlap in habitat use and sometimes hybridize. Their offspring usually die during development. A few frail offspring sometimes survive development but die shortly after they hatch into tadpoles.
What is Hybrid Sterility?
– When the offspring of two parents cannot reproduce (offspring are sterile)
– Example: Male horse mates with a female donkey to produce a hinny that is sterile…or male donkey mates with female horse to produce a mule that is sterile
What is Hybrid Breakdown?
– Some first-generation hybrids are viable and fertile, but when they mate with one another or with either parent species, offspring of the next generation are feeble or sterile
– Example: Different rice species can produce fertile hybrid offspring, but in the next generation, the hybrid’s offspring die as seeds or grow into weak defective plants
What is Incipient Species?
The key to speciation is the evolution of genetic differences between the incipient species (a group of organisms that is about to become a separate species from other, related individuals)
For a lineage to split once and for all, the two incipient species must have genetic differences that are expressed in some way
that causes matings between them to either not happen or to be unsuccessful
What are the Five general modes of speciation?
- Allopatric speciation
- Peripatric speciation
- Parapatric speciation
- Sympatric speciation
- Artificial speciation
What is Allopatric Speciation?
- One large population is split into two populations that are separated by a physical barrier
* A population can colonize a new habitat (dispersal and colonization)
* A new physical barrier can split a widespread population into two or more isolated groups (a vicariance event) - The two populations diverge from each other due to genetic drift, natural selection, and mutation
- END RESULT: The two populations become so different that they can no longer reproduce with each other due to pre- or post-zygotic barriers à they are separate species
What is Peripatric speciation?
When small groups of individuals break off from the larger group and form a new species, this is called peripatric speciation
– As in allopatric speciation, physical barriers make it impossible for members of the groups to interbreed with one another
– The main difference between allopatric speciation and peripatric speciation is that in peripatric speciation, one group is much smaller than the other