Speciation Flashcards
Species
Group of organisms whose members can breed and produce viable and fertile offspring typically by sexual reproduction
Species (biological species concept)
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
If individuals from different species interbreed the offspring will not be viable or fertile
Species (morphological species concept)
Most species can be classifies based on similarities with respect to measurable physical traits
Species (ecological species concept)
Defining species as groups or populations that share the exact same ecological niche-or functional role it plays within an ecosystem
Species (genetic species concept)
Define species with respect to similarities solely on basis of molecular data
Anagenesis
-Phyletic Evolution (non-branching evolution)
-accumulation of changes that gradually transform a given entire species into a species with different characteristics (evolution within a lineage)
-no net increase in species diversity
Cladogenesis
-branching evolution (diversifying evolution)
-one or more species arising from one original species (evolution that results in the splitting of a lineage)
-net increase in species diversity
Gradualism
example
-gradual speciation model
- species diverge gradually over time in small steps
ex. small variations over time in a population of wolves- larger ears, longer teeth and a heightened sense of smell
ex. a species of butterfly is yellow and black in color, however a butterfly is born that happens to be orange and yellow in color making it difficult to see. over time the yellow and black die out
Punctuated Equilibrium
example
A new species undergoes changes quickly from the parent species, and then remains largely unchanged for long periods of time afterward
ex. species of birds exist in stasis for many thousands of years, suddenly bacteria cause their primary tree of sheltering choice to die.
ex. cheetah species has no spots, due to a gene mutation a cheetah cub is born with spots
Biological Species Concept
Based on the potential to interbreed rather than on physical similarity
- similarity between different species - the eastern meadowlark and the western meadowlark have similar body shapes and colorations, they are distinct, their songs and other behaviors are different enough to prevent interbreeding should they meet in the wild
- diversity within a species - as diverse as we may all appear humans belong to a single biological species
Why we cannot apply the biological species concept to all situations
-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)
Prezygotic Barrier
Which barriers prevent mating attempt and which prevent fertilization following mating
Impede mating between species or hinder the fertilization of ova if members of different species attempt to mate
-prevent mating attempt - habitat, temporal, behavioral
-prevent fertilization attempt - mechanical, gametic
Postzygotic Barrier
Prevent zygote from developing into a viable and fertile adult
Types of Prezygotic Barriers
Habitat, Temporal, Behavioral, Mechanical, Gametic Isolation
Temporal Isolation
example
Species breed at different times (different times of day or different seasons or even years)
ex. western spotted skunk and the eastern spotted skunk overlap in distribution, even though they are very similar, western breed in late summer, eastern in late winter
Habitat Isolation
example
Species found in different habitats but in same area that rarely come across each other even though there are no obvious physical barriers
ex. two species of garter snake live in the same area, but one species lives mainly in water, other is mainly terrestrial
Behavioral Isolation
example
Every species has its own mating/courting rituals and behaviors and because of this, different species will not attract each other with prevents them from mating
ex. male fireflies have different light flashing patterns and only female of same species recognizes the pattern as being courtship behavior
Mechanical Isolation
example
When male and female sex organs are not compatible which means fertilization cannot occur
ex. 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
Gametic Isolation
example
Gametes do not unite to form a zygote (so egg and sperm cells are incompatible)
ex. many marine species broadcast their egg and sperm in the water. the gametes or more than one species can encounter each other, but they generally will not fuse
ex. sea urchins, bindin allows sperm cells to penetrate eggs
Types of Postzygotic Barriers
Hybrid inviability, hybrid sterility, hybrid breakdown
Reduced Hybrid Viability
zygote forms but dies after a few series of cell divisions (genetic information from a male and female parent were insufficient to carry the organism through morphogenesis)
most often the hybrid embryo dies before birth, sometimes the offspring develops fully with mixed traits from each parent, forming a frail, often infertile adult
ex. species of frog
Reduced Hybrid Fertility
When the offspring of two parents cannot reproduce (offspring are sterile)
ex. male horse mates with female donkey to produce a hinny that is sterile
ex. male donkey mates with female horse to produce mule- sterile
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
ex. different rice species can produce fertile hybrid offspring but in the next generation the hybrids offspring die as seeds or grow into weak defective plants
Five General Modes of Speciation
Allopatric, Peripatric, Parapatric, Sympatric, Artificial speciation
