Speciation Flashcards
what is a species
- multiple definitions
- smallest evolutionarily independent unit
- interbreeding populations that evolve independently of other populations
- a group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding
what are the three species concepts
- morphological species concept
- phylogenetic species concept
- biological species concept
morphological species concept - criterion for identifying species
phenotypic similarities and differences
morphological species concept - strength
works for everything (extinct, asexual)
morphological species concept - weakness
- cryptic species
- groups that were or are actually independent of one another appear to be members of the same species based on morphological similarity
Phylogenetic species concepts - criterion for identifying species
- monophyly (Lineage has all descendants and a common ancestor)
- if it cannot be distinguished phylogenetically, it will be considered a single species
Phylogenetic species concepts - strength
Powerful and works for anything with DNA and is testable
Phylogenetic species concepts - weakness
- Need good DNA and understanding of it
- Different inputs used to build the tree results in differing phylogenies and conflicting species designations
- would double the number of named species and might create confusion
biological species concept - criterion for identifying a species
- Emphasizes reproductive isolation and barriers
- Members are interbreeding and producing viable offspring and do not breed with other species
- it is the legal definition of a species under the endangered species act
biological species concept - strength
Reproductive isolation is a meaningful criterion for identifying species bc is confirms lacks of gene flow
biological species concept - weakness
Cannot use for asexual organisms, fossils, organisms about which little is known about their reproduction
why should we care about species concepts?
- human health (algal blooms)
- conservation
why should we care about species concepts? - human health
- red tides: can kill fishes and people
- different species of dinoflagellates cause this
- but some species do not cause human health issues
- need to identify which do and do not
why should we care about species concepts? - conservation
- endangered species act uses the biological species concepts
- but different concept can determine which species are on the act
- mammals and birds are overrepresented (invertebrates)
biological species concept - what are the reproductive barriers
- prezygotic barriers
- postzygotic barriers
reproductive barriers - prezygotic barriers
- impede mating between species
- no fertilization in the first plce
reproductive barriers - postzygotic barriers
- fertilization occurs
- produces a hybrid
- prevents hybrid zygote from developing into a viable and fertile adult
types of prezygotic barriers
- no mating attempted:
1. habitat isolation
2. temporal isolation
3. behavioral isolation - mating attempt:
1. mechanic isolation - copulation has occurred:
1. gametic isolation
prezygotic barriers - habitat isolation and example
- 2 species in diff habitat and do not encounter each other
- no interaction
- ex: apple maggot fly mates and feeds on red apples, hawthorn fly mates and feeds on grapes
prezygotic barriers - temporal isolation and example
- species breed during different times
- example: western spotted skink and eastern spotted skunk. habitat overlaps but one breeds in winter and the other in summer
prezygotic barriers - behavioral isolation and example
- courtship rituals that attract mates and other behaviors cause species to only mates with their own
- example: blue footed boobies pick up their feet and stomp. this reveals blue feet to females
prezygotic barriers - mechanical isolation and example
- mating is attempted
- not successful bc morphological differences prevent copulation
- example: snails cannot get their genitalia to touch if their shells do not spin in the same direction
prezygotic barriers - gametic isolation and examples (2 here)
- copulation has occurred
- but sperm and egg are not compatible
- example (1): red and purple sea urchins release eggs into water but the gametes will not fuse if its red an purple bc of proteins on the egg
- example (2): species that has internal fertilization, the sperm may not survive in reproductive tract of female
types of postzygotic barriers
- fertilization has occurred:
1. reduced hybrid viability
2. reduced hybrid fertility
3. hybrid breakdown
post zygotic barriers - reduced hybrid viability
- genes may interact in ways that impar hybrid’s development or survival
- hybrids are more likely to die
post zygotic barriers - reduced hybrid fertility
hybrids survive to adulthood but are not fertile (sterile)
post zygotic barriers - hybrid breakdown
- hybrids are produced and the hybrid can produce offspring
- but 2nd generation of offspring is sterile
explain the classic model of speciation
- isolation of population (reduced gene flow)
- divergence of traits
- speciation (evolution of reproductive isolation)
classic model of speciation - isolation of population (reduced gene flow)
- can be done in 2 ways:
1. allopatric speciation
2. sympatric speciation
isolation of population (reduced gene flow) - allopatric speciation
- a population forms a new species while geographically isolated from its parent population
- ex: mountain or river
isolation of population (reduced gene flow) - sympatric speciation
a subset of a population forms a new species without geographic separation
isolation of population (reduced gene flow): allopatric speciation model - explain the 2 ways of geographical isolation
- dispersal allopatry
- vicariance allopatry
the allopatric model - dispersal allopatry
- movement of individuals results in physical isolation
- can happen when there is not much gene flow
the allopatric model - dispersal allopatry example
- Drosophila fly
- each time they colonize a new island, they become a new species
- pattern of relatedness matches the geography of the island
the allopatric model - vicariance allopatry
geological events result in isolation of population
the allopatric model - vicariance allopatry example
- Isthmus of Panama divided the Atlantic and Pacific Ocean
- 15 species of snapping shrimp on each side
- all look really similar but when comparing morphological and phylogenetic species concepts the sister species are divided by the two sides (they are different species)
divergence of traits - what processes cause trait divergence?
- All mechanisms of evolution can contribute to trait divergence between populations (the forces from Hardy-Weinberg)
- but selection makes the strongest contribution
divergence of traits - how can selection cause divergence
- natural: when one of the populations occupies a novel environment or uses a novel resource
- sexual: assertive matting
divergence of traits - natural selection example
- monkey flower faces different pressures in the coast vs inland
- led to distinct phenotypic and genetic differences
divergence of traits - natural + sexual selection example: Cichlid fish
- the fish have diff colors
- Light is filtered through water – only blue goes really far down and it affects visual system of fishes
divergence of traits: natural + sexual selection example: Cichlid fish - how does natural selection and sexual selection play a role?
- Natural – drives diff in tuning of female eyes
- Sexual – females can only see blue and mates with blue male
divergence of traits: natural + sexual selection example: Cichlid fish - what did researchers find?
- tested what filtered light (muddy water) does to the tuning of eyes and mating preferences
- When water is clear – females see well, and mating (sexual selection) was stronger
speciation (evolution of reproductive isolation) - define secondary contact
- gene flow is re-established in a hybrid zone (after speciation)
- species come into contact again via migration or geographic changes
speciation (evolution of reproductive isolation): secondary contact - when the two populations meet again, can they breed?
- multiple options:
1. no hybrids reproduced
2. unfit hybrids
3. equal or better fitness in hybrids
secondary contact - no hybrids reproduced
Suggests that reproductive isolation has evolved, and speciation has occurred
secondary contact - unfit hybrids
- Reinforcement selection – postzygotic barrier and selection is reinforcing the barrier
- hybrids are formed but should see a decrease in hybrids overtime
secondary contact - equal or better fitness in hybrids
- 3 options:
1. fusion
2. stable hybrid zone
3. hybrid speciation
secondary contact: equal or better fitness in hybrids - fusion
- Recently diverged species will fuse back into one
- reversal speciation effect
secondary contact: equal or better fitness in hybrids - stable hybrid zone
Continued production of hybrids but still maintain 2 distinct species
secondary contact: equal or better fitness in hybrids - hybrid speciation
- hybrid becomes its own species
- 3 species instead of 2
