Outstanding Origin of Outstanding Origin of SpeciesSpecies

Ch 24Ch 24

VocabularyVocabulary

1. Macroevolution – origin of new 1. Macroevolution – origin of new taxonomic groups (new species, taxonomic groups (new species, genera, families etc)genera, families etc)

2. Speciation – origin of new species 2. Speciation – origin of new species – key process in macroevolution– key process in macroevolution

3. Biological species concept- a species is 3. Biological species concept- a species is a population or group of populations a population or group of populations whose members have the potential to whose members have the potential to interbreed with one another in nature to interbreed with one another in nature to produce viable, fertile offspring but cannot produce viable, fertile offspring but cannot produce viable, fertile offspring with produce viable, fertile offspring with members of another species. members of another species.

*Hinges on *Hinges on reproductive isolationreproductive isolation – each – each species is isolated by barriers that prevent species is isolated by barriers that prevent interbreedinginterbreeding

Same or different?Same or different?

Same or Different?Same or Different?

Pre-zygotic Barriers to reproduction Pre-zygotic Barriers to reproduction

impede mating or hinder fertilization impede mating or hinder fertilization of the eggof the egg

1. Habitat Isolation – two species 1. Habitat Isolation – two species that live in different that live in different habitats within habitats within the same area may encounter each the same area may encounter each other rarely, if at all. (i.e. parasite on other rarely, if at all. (i.e. parasite on different host or garter snake – one different host or garter snake – one lives in water, other on land)lives in water, other on land)

Pre-zygotic Barriers to reproductionPre-zygotic Barriers to reproduction

2. Behavioral Isolation – sexual 2. Behavioral Isolation – sexual signals that attract mates and signals that attract mates and elaborate behavior unique to a elaborate behavior unique to a species (songs, mating dances etc. species (songs, mating dances etc. specific to a species)specific to a species)

3. Temporal Isolation – two species 3. Temporal Isolation – two species that breed during different times of that breed during different times of day, different seasons or different day, different seasons or different years can’t mate togetheryears can’t mate together

Pre-zygotic Barriers to reproductionPre-zygotic Barriers to reproduction

4. Mechanical Isolation – anatomical 4. Mechanical Isolation – anatomical differences might prevent closely differences might prevent closely related species from matingrelated species from mating

5. Gametic Isolation – even if 5. Gametic Isolation – even if gametes from different species meet, gametes from different species meet, they rarely fuse to make a zygotethey rarely fuse to make a zygote

(i.e. sperm of different species can’t (i.e. sperm of different species can’t survive internal conditions of female)survive internal conditions of female)

Post-zygotic BarriersPost-zygotic Barriers

occur when a sperm from a different occur when a sperm from a different species does fertilize the eggspecies does fertilize the egg

1. Reduced hybrid viability – genetic 1. Reduced hybrid viability – genetic incompatibility may incompatibility may abort abort development of hybrid during development of hybrid during embryonic embryonic developmentdevelopment

Post-zygotic BarriersPost-zygotic Barriers

2. Reduced hybrid fertility – if two 2. Reduced hybrid fertility – if two different species do mate and produce a different species do mate and produce a hybrid, many hybrids are sterile and hybrid, many hybrids are sterile and cannot produce offspring (mule)cannot produce offspring (mule)

3. Hybrid Breakdown – occasionally, first 3. Hybrid Breakdown – occasionally, first generation hybrids are viable and fertile, generation hybrids are viable and fertile, but when hybrids mate the next but when hybrids mate the next generation is often feeble or generation is often feeble or

sterilesterile

Other concepts of speciesOther concepts of species

Biological species concept doesn’t work in Biological species concept doesn’t work in all situations. Here are some alternative all situations. Here are some alternative concepts (like for fossils/prokaryotes)concepts (like for fossils/prokaryotes)

*Ecological species concept – species is *Ecological species concept – species is defined in terms of their niche (role in defined in terms of their niche (role in environment)environment)

*Phylogenetic Species concept- species is *Phylogenetic Species concept- species is the smallest group of individuals that the smallest group of individuals that share a common ancestor, forming one share a common ancestor, forming one branch in the tree of lifebranch in the tree of life

*Morphological species concept – *Morphological species concept – relies on structural features to relies on structural features to distinguish speciesdistinguish species– i.e. body shape and other structural i.e. body shape and other structural

features (problem – can be subjective)features (problem – can be subjective)

Modes of SpeciationModes of Speciation

1. Allopatric Speciation – speciation 1. Allopatric Speciation – speciation takes place in populations with takes place in populations with geographically separate ranges. As geographically separate ranges. As the isolated population’s gene pool the isolated population’s gene pool changes, reproductive isolation can changes, reproductive isolation can result.result.

Allopatric SpeciationAllopatric Speciation *geologic processes can fragment a population *geologic processes can fragment a population

(i.e. mountain emerges, land bridge forms (i.e. mountain emerges, land bridge forms separating marine life etc)separating marine life etc)

*amount that geography separates organisms *amount that geography separates organisms depends on their ability to move (fly, swim etc)depends on their ability to move (fly, swim etc)

*allopatric speciation increases when population *allopatric speciation increases when population becomes small and isolated from others. These becomes small and isolated from others. These populations are more likely to have gene pool populations are more likely to have gene pool changed dramatically.changed dramatically.

Allopatric SpeciationAllopatric Speciation

*Adaptive radiation – evolution of *Adaptive radiation – evolution of many diversely many diversely adapted species adapted species from a common ancestor (i.e. finches from a common ancestor (i.e. finches

on Galapagos islands, many on Galapagos islands, many indigenous species on Hawaiian indigenous species on Hawaiian islands islands ))

How do reproductive barriers How do reproductive barriers evolve?evolve?

*must be intrinsic to organism and *must be intrinsic to organism and prevent interbreeding even when prevent interbreeding even when species are brought back togetherspecies are brought back together

*most likely coincidental – not that *most likely coincidental – not that organism is trying to make a barrier organism is trying to make a barrier to reproductionto reproduction

*Fruit fly experiment shows *Fruit fly experiment shows formation of pre-zygotic barrier due formation of pre-zygotic barrier due to different mating ritualto different mating ritual

How do reproductive barriers How do reproductive barriers evolve?evolve?

*When trying to mate same plant *When trying to mate same plant from different areas of U.S., those from different areas of U.S., those that were close together that were close together (Wisconsin/Michigan) could (Wisconsin/Michigan) could interbreed while farther apart interbreed while farther apart (Wisconsin/Texas) were unable to (Wisconsin/Texas) were unable to interbreed (post-zygotic barrier due interbreed (post-zygotic barrier due to hybrid breakdown)to hybrid breakdown)

2. Sympatric Speciation 2. Sympatric Speciation

speciation takes place in speciation takes place in geographically overlapping geographically overlapping populations. Biological factors such populations. Biological factors such as chromosomal changes and non-as chromosomal changes and non-random mating reduce gene flow.random mating reduce gene flow.

2. Sympatric Speciation2. Sympatric Speciation

*In Plants – *In Plants – polyploidypolyploidy – cell division that – cell division that results in extra sets of chromosomesresults in extra sets of chromosomes

-autopolyploid – individual that has more -autopolyploid – individual that has more than two sets of chromosomes derived than two sets of chromosomes derived from a single speciesfrom a single species

*could be tetraploid instead of diploid if *could be tetraploid instead of diploid if meiosis meiosis does not occur. Tetraploid can does not occur. Tetraploid can self fertilize or mate with other tetraploids, self fertilize or mate with other tetraploids, but can not mate with diploid plants (new but can not mate with diploid plants (new species formed)species formed)

Sympatric SpeciationSympatric Speciation

-allopolyploid – two different species -allopolyploid – two different species interbreed, combine chromosomes interbreed, combine chromosomes and produce a hybrid. Hybrid can and produce a hybrid. Hybrid can only mate with other hybridsonly mate with other hybrids

Ex. – oats, cotton, potatoes, tobacco, Ex. – oats, cotton, potatoes, tobacco, wheatwheat

Sympatric SpeciationSympatric Speciation

*In animals -can become *In animals -can become reproductively isolated within the reproductively isolated within the same geographic region (wasps – dif same geographic region (wasps – dif species pollinate dif fig plant)species pollinate dif fig plant)

3. Punctuated Equilibrium 3. Punctuated Equilibrium

Species diverge in spurts of relatively Species diverge in spurts of relatively rapid change (thousands of years) rapid change (thousands of years) followed by long periods of stasis followed by long periods of stasis (unchanging) – based on fossil (unchanging) – based on fossil evidenceevidence

Speciation RatesSpeciation Rates

In general, once speciation begins, it In general, once speciation begins, it can be a relatively rapid process (in can be a relatively rapid process (in geologic time)geologic time)

It varies from species to species – It varies from species to species – can take anywhere from 4000 years can take anywhere from 4000 years to 40 million years – avg about 6.5 to 40 million years – avg about 6.5 million yearsmillion years

From Speciation to MacroevolutionFrom Speciation to Macroevolution

*Most evolutionary novelties (like human eye) are *Most evolutionary novelties (like human eye) are modified versions of older structures that have modified versions of older structures that have evolved in many stages.evolved in many stages.

*genes that control rate of development play a *genes that control rate of development play a major role in evolution. Mutations in these genes major role in evolution. Mutations in these genes can cause macro-evolutionary changes.can cause macro-evolutionary changes.

*Long-term evolutionary trends may be a result of *Long-term evolutionary trends may be a result of adaptations to surrounding environment or may adaptations to surrounding environment or may results when species with certain characteristics results when species with certain characteristics endure longer and speciate more often than endure longer and speciate more often than those with other characteristics.those with other characteristics.