What keeps a species from subdividing into other species? What causes a species to branch into two new species?

 Finish Chapter 22  We will lecture Today and Tomorrow  Friday we will begin the H-W Modeling Lab  2-3 days  Quiz on CH 22 and 21 Next week

Speciation is the process by which one species splits into two or more species

 Microevolution consists of changes in allele frequency in a population over time  Macroevolution refers to broad patterns of evolutionary change above the species level

 Biological Species Concept

 Morphological – Species based on shape, size, color, etc.  Ecological – based on niche  Phylogenetic – based on evolutionary relationships (smallest group of individuals that come from a common ancestor)

 Biological – asexual  Ecological – gene flow  Phyolgenetic – genetically subjective  Morphological – subjective bridge

 Allopatric speciation  Sympatric speciation  Polyploidy  Habitat Differentiation  Sexual Selection

Prezygotic barriersPostzygotic barriers Habitat isolation Temporal isolation Behavioral isolation Mechanical isolation Gametic isolation Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown MATING ATTEMPT FERTILI- ZATION VIABLE, FERTILE OFF- SPRING (a)(c)(e)(f)(g)(h)(i)(l) (j) (k) (d) (b)

 A physical barrier separates (splits) the original population  As time passes, the environment may selects for different traits and the 2 populations become genetically different AND can’t reproduce  Barriers: Rivers, mountains, bodies of water

- The Kaibab squirrel (Sciurus aberti kaibabensis) became geographically isolated from the common ancestor about 10,000 years ago. - Its closest relative is the Abert squirrel (Sciurus aberti aberti) - They live in opposite sides of the Grand Canyon KaibabAbert

Example: Emus, ostriches, rheas, Cassowaries,  Common ancestor lived in the continent of Gondwana (all southern continents together)  When Gondwana broke up, the populations separated and changed over time. All these birds are closely related but live far apart.

 Groups of individuals reproduce at different times. The genes of the 2 groups do not mix.  It is happening now with some of the migratory birds that decide not to migrate.  The birds that do not migrate start mating before the migratory ones come back.  Eventually they might become different enough that they may not recognize each other.

Experiment Mating experiments after 40 generations Some flies raised on starch medium Results Some flies raised on maltose medium Initial population of fruit flies (Drosophila pseudoobscura) Female StarchMaltose Starch population 1 Starch population Male Maltose Starch population 1 Starch population 2 Number of matings in experimental group Number of matings in control group

Experiment Mating experiments after 40 generations Some flies raised on starch medium Some flies raised on maltose medium Initial population of fruit flies (Drosophila pseudoobscura)

Results Female StarchMaltose Starch population 1 Starch population Male Maltose Starch population 1 Starch population 2 Number of matings in experimental group Number of matings in control group

 Polyploidy is the presence of extra sets of chromosomes due to accidents during cell division  Polyploidy is much more common in plants than in animals  An autopolyploid is an individual with more than two chromosome sets, derived from one species  The offspring of matings between autopolyploids and diploids have reduced fertility

Cell division error Tetraploid cell 4n  12 New species (4n) 2n  6 2n2n Gametes produced by tetraploids

 An allopolyploid is a species with multiple sets of chromosomes derived from different species  Allopolyploids cannot interbreed with either parent species

Species A 2n  6 Species B 2n  4 Normal gamete n  3 Unreduced gamete with 4 chromosomes Meiotic error; chromosome number not reduced from 2n to n

Species A 2n  6 Species B 2n  4 Normal gamete n  3 Hybrid with 7 chromosomes Unreduced gamete with 4 chromosomes Meiotic error; chromosome number not reduced from 2n to n

Species A 2n  6 Species B 2n  4 Normal gamete n  3 Normal gamete n  3 Hybrid with 7 chromosomes Unreduced gamete with 7 chromosomes Unreduced gamete with 4 chromosomes Meiotic error; chromosome number not reduced from 2n to n

Species A 2n  6 Species B 2n  4 Normal gamete n  3 Normal gamete n  3 Hybrid with 7 chromosomes Unreduced gamete with 7 chromosomes Unreduced gamete with 4 chromosomes New species: viable fertile hybrid (allopolyploid) 2n  10 Meiotic error; chromosome number not reduced from 2n to n

 Many important crops (oats, cotton, potatoes, tobacco, and wheat) are polyploids

 NA maggot fly can live on native hawthorn trees as well as more recently introduced apple trees

Normal light Monochromatic orange light Experiment P. pundamilia P. nyererei

Under low predation: body shape that favors long, steady swimming (b)Under high predation: body shape that enables rapid bursts of speed (a)

 Hyrbid Zone - region in which members of different species mate and produce hybrids

Fire-bellied toad range Fire-bellied toad, Bombina bombina Yellow-bellied toad range Hybrid zone Hybrid zone Fire-bellied toad range Yellow-bellied toad range Distance from hybrid zone center (km) Frequency of B. variegata-specific allele Yellow-bellied toad, Bombina variegata 0.5

Hybrid zone Fire-bellied toad range Yellow-bellied toad range Distance from hybrid zone center (km) Frequency of B. variegata-specific allele 0.5

Isolated population diverges. Hybrid zone Hybrid individual Barrier to gene flow Gene flow Population

Isolated population diverges. Possible outcomes: Reinforcement Fusion Stability Hybrid zone Hybrid individual Barrier to gene flow Gene flow Population

 Reinforcement – hybrids less fit than the parent species  Natural selection reinforces reproductive barriers, and, over time, the rate of hybridization decreases  Where reinforcement occurs, reproductive barriers should be stronger for sympatric than for allopatric species

 Fusion of the parent species into a single species may occur if hybrids are as fit as parents, allowing substantial gene flow between species  For example, researchers think that pollution in Lake Victoria has reduced the ability of female cichlids to distinguish males of different species  This might be causing the fusion of many species

Pundamilia nyerereiPundamilia pundamilia Pundamilia “turbid water,” hybrid offspring from a location with turbid water Fusion

Rates of Speciation

Gradualism Punctuated Equilibrium

 Organisms go through gradual and continuous change

 Organisms go through fast periods of change, followed by long periods of no change (according to fossil record)

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 Repeated Speciation and Macroevolution

 Maintaining Variety  Diploidy, heterozygote advantage, Frequency dependant Selection  Sympatric Speciation - Polyploidy  Vestigial Structures