chapter 24 species & speciation. slide 2 of 25 chapter 24 in a nutshell microevolution v....
TRANSCRIPT
Chapter 24
Species & Speciation
Slide 2 of 25
Chapter 24 in a nutshell
Microevolution v. Macroevolution
Speciation Prezygotic Postzygotic
Gradualism v. Punctuated equilibrium
Slide 3 of 25
Species
Morphological species concept Divisions of organisms into discrete units called species If two organisms look different enough, then they are
considered different species
Biological species concept Population or group of populations whose members have
the potential to interbreed in nature and produce viable, fertile offspring
This population is unable to produce viable, fertile offspring with members of another population
Slide 4 of 25
Micro- vs. Macro- Evolutions
Microevolution Change in the genetic makeup of a population over
generations Changes (adaptations) confined to a particular gene pool
or population
Macroevolution Changes (evolution) above the species level Changes used to define higher taxa
Slide 5 of 25
Speciation
The process that produces a new species
May be the result of microevolution OR macroevolution
How could microevolution lead to speciation?
How could a new species arise from macroevolution?
Slide 6 of 25
Slide 7 of 25
Reproductive Isolation
Biological barriers that impede members of 2 species from producing viable, fertile offspring
There are 2 types of barriers that lead to reproductive isolation Prezygotic
Pre-mating Post-mating
Postzygotic
Slide 8 of 25
Prezygotic Barriers
Pre-Mating Habitat isolation Temporal isolation Behavioral isolation
Post-Mating Mechanical isolation Gametic isolation
Slide 9 of 25
Prezygotic Barriers (Page 1)
Pre-Mating Habitat isolation
2 species occupy different habitats in the geographic area Tree-dwelling species, Bush-dwelling species
Temporal isolation Temporal = time Species breed at different times
Different time of day, different seasons, or different years Behavioral isolation
Certain signals or types of behavior are integral to courtship, and these signals/behaviors are unique to the species
Other species do not respond to these signals or behaviors
Slide 10 of 25
Different habitats – water or terrestrial
Different mating season – late winter or late summer
Boobies!! (blue-footed)
Slide 11 of 25
Prezygotic Barriers (Post-Mating)
Mechanical isolation Anatomical incompatibility Insect copulatory organs are elaborated for a particular
species
Gametic isolation Even if gametes meet, they are unable to fuse Sperm may not be able to survive in the reproductive
tract of females from another species Purple + Red sea urchins cannot mate b/c gametes
cannot fuse
Slide 12 of 25
Postzygotic Barriers
Reduced hybrid vitality
Reduced hybrid fertility
Hybrid Breakdown
Slide 13 of 25
Postzygotic Barriers
Reduced Hybrid vitality Although zygote forms, genetic incompatibility causes
developmental cessation In some salamanders, hybrids form but do not complete
development
Reduced Hybrid fertility Sterile hybrids Donkey + Horse = mule (Sterile)
Hybrid breakdown Although first-generation hybrids survive & reproduce,
their offspring are feeble or sterile
Slide 14 of 25
Slide 15 of 25
Geographic Barrier No Geographic Barrier
Slide 16 of 25
Allopatric Speciation
Causes Geologic events or processes that fragment the
population Emergence of a mountain range Formation of a land bridge Evaporation of a large lake into multiple smaller lakes
Leads to a significant alteration of a gene pool
Slide 17 of 25
Slide 18 of 25
Sympatric Speciation
Sympatric = sym (same) + patr (fatherland) Same country
Geographically overlapping populations
Major mechanism of sympatric speciation is Polyploidy Autopolyploidy Allopolyploidy
Preferential Habitation
Slide 19 of 25
Polyploidy Extra set(s) of chromosomes
Autopolyploidy > 2n Typically, nondisjunction (Meiosis) in Plants All chromosomes from the same species
Example Tetraploid (4n) + diploid (2n) Produce triploid (3n) offspring which are sterile But plant tetraploids can self fertilize or mate with other
tetraploids = viable, fertile polyploid offspring Tetraploids are reproductively isolated from the diploid
population
Slide 20 of 25
Polyploidy (Page 2)
Allopolyploidy Plants 2 different species interbreed = hybrid Hybrids cannot breed with either original species But hybrids can successfully mate with each other Self-pollination successfully occurs as well
Slide 21 of 25
Polyploidy (Page 3)
Can happen in animals but not common
In animals, sympatric speciation is usually due to part of the population switching to a new habitat, food source, or other resource
Slide 22 of 25
Adaptive Radiation
Many new species arise from a common ancestor given new environmental opportunities or challenges
Think Darwin’s finches & Galapagos islands As the finches moved from South America to the
Galapagos, different environments and food sources were encountered
Hawaiian Plants As the plants spread to Hawaiian islands, different
environments on different islands = evolution into several distinct forms
Slide 23 of 25
Slide 24 of 25
Hawaiian Plants that had a common ancestor
Arose from Adaptive Radiation
Slide 25 of 25
Gradualism vs. Punctuated Equilibrium
Gradualism – species descended from a common ancestor and gradually diverge in morphology (acquiring unique adaptations) until they are reproductively isolated
Punctuated Equilibrium – long periods of apparent stasis punctuated by brief periods of sudden and rapid change Fossil record confirms the punctuated equilibrium model Also eliminates the necessity of finding “missing links”