What keeps a species from subdividing into other

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

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

THE ORIGIN OF SPECIES Speciation is the process by which one species splits into two or more species

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

WHAT IS A SPECIES? � Biological Species Concept

OTHER SPECIES CONCEPTS � 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)

WEAKNESSES � Biological – asexual � Ecological – gene flow � Phyolgenetic – genetically subjective � Morphological – subjective bridge

WHAT HOLDS A SPECIES TOGETHER?

WHAT CAUSES SPECIATION? � Allopatric speciation � Sympatric speciation � Polyploidy � Habitat Differentiation � Sexual Selection

FIGURE 22. 3 Prezygotic barriers Habitat isolation Temporal isolation Behavioral isolation Mechanical isolation Postzygotic barriers Gametic isolation MATING ATTEMPT (a) (c) (d) (e) (f) Reduced hybrid viability Reduced Hybrid hybrid breakdown fertility VIABLE, FERTILE OFFSPRING FERTILIZATION (g) (h) (i) (j) (b) (k) (l)

1. GEOGRAPHIC ISOLATION �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

KAIBAB AND ABERT SQUIRRELS Kaibab Abert - 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) - They live in opposite sides of the Grand Canyon

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.

WRASSES: ORIGINAL POPULATION SPLIT UP WHEN THE ISTHMUS OF PANAMA WAS FORMED - 2 SPECIES NOW, ONE ON EACH SIDE OF CENTRAL AMERICA

2. TEMPORAL ISOLATION (TIME OF REPRODUCTION) � 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.

ROBINS USUALLY MIGRATE SOUTH TO WARMER CLIMATES. SOME ARE NOT MIGRATING. THEY REPRODUCE BEFORE THE MIGRATING INDIVIDUALS RETURN. TEMPORAL ISOLATION

Experiment Initial population of fruit flies (Drosophila pseudoobscura) Some flies raised on starch medium Some flies raised on maltose medium Mating experiments after 40 generations Results 22 9 8 20 Number of matings in experimental group Starch population 2 population 1 Maltose Starch population 1 population 2 Male Starch Female Maltose Female Male FIGURE 22. 8 18 15 12 15 Number of matings in control group

FIGURE 22. 8 A Experiment Initial population of fruit flies (Drosophila pseudoobscura) Some flies raised on starch medium Some flies raised on maltose medium Mating experiments after 40 generations

FIGURE 22. 8 B Results Female Maltose 22 9 8 20 Number of matings in experimental group Starch population 2 population 1 Starch population 1 population 2 Male Starch Maltose Female 18 15 12 15 Number of matings in control group

POLYPLOIDY � 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

FIGURE 22. UN 01 Cell division error 2 n 6 2 n Gametes produced by tetraploids Tetraploid cell 4 n 12 New species (4 n)

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

FIGURE 22. 9 -1 Species A 2 n 6 Species B 2 n 4 Meiotic error; chromosome number not reduced from 2 n to n Normal gamete n 3 Unreduced gamete with 4 chromosomes

FIGURE 22. 9 -2 Species A 2 n 6 Species B 2 n 4 Meiotic error; chromosome number not reduced from 2 n to n Normal gamete n 3 Unreduced gamete with 4 chromosomes Hybrid with 7 chromosomes

FIGURE 22. 9 -3 Species A 2 n 6 Species B 2 n 4 Meiotic error; chromosome number not reduced from 2 n to n Normal gamete n 3 Unreduced gamete with 4 chromosomes Hybrid with 7 chromosomes Normal gamete n 3 Unreduced gamete with 7 chromosomes

FIGURE 22. 9 -4 Species A 2 n 6 Species B 2 n 4 Meiotic error; chromosome number not reduced from 2 n to n Normal gamete n 3 Unreduced gamete with 4 chromosomes Hybrid with 7 chromosomes Normal gamete n 3 Unreduced gamete with 7 chromosomes New species: viable fertile hybrid (allopolyploid) 2 n 10

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

HABITAT DIFFERENTIATION � NA maggot fly can live on native hawthorn trees as well as more recently introduced apple trees

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

FIGURE 22. 6 SYMPATRIC SPECIATION SEXUAL SELECTION (a) Under high predation: (b) Under low predation: body shape that enables body shape that favors rapid bursts of speed long, steady swimming

WHAT HYBRIDS TELL US ABOUT SPECIATION � Hyrbid Zone - region in which members of different species mate and produce hybrids

FIGURE 22. 11 Fire-bellied toad range Hybrid zone Fire-bellied toad, Bombina bombina Yellow-bellied toad, Bombina variegata Frequency of B. variegata-specific allele Yellow-bellied toad range 0. 99 Hybrid zone 0. 9 Yellow-bellied toad range 0. 5 Fire-bellied toad range 0. 1 0. 01 40 30 20 10 20 Distance from hybrid zone center (km)

Frequency of B. variegata-specific allele FIGURE 22. 11 B 0. 99 Hybrid zone 0. 9 Yellow-bellied toad range 0. 5 Fire-bellied toad range 0. 1 0. 01 40 30 20 10 20 Distance from hybrid zone center (km)

FIGURE 22. 12 -3 Isolated population diverges. Gene flow Population Barrier to gene flow Hybrid zone Hybrid individual

FIGURE 22. 12 -4 Isolated population diverges. Hybrid zone Possible outcomes: Reinforcement Gene flow Population Barrier to gene flow Fusion Hybrid individual Stability

�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

FIGURE 22. 13 Pundamilia nyererei Pundamilia pundamilia Fusion Pundamilia “turbid water, ” hybrid offspring from a location with turbid water

Rates of Speciation HOW FAST DO SPECIES FORM?

HOW FAST IS EVOLUTION? HOW FAST DO ORGANISMS CHANGE? Gradualism Punctuated Equilibrium

GRADUALISM � Organisms go through gradual and continuous change

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

PUNCTUATED EQUILIBRIUM PROPOSED BY STEPHEN JAY GOULD (1941 -2002)

http: //www. youtube. com/watch? v=8 Xgg. WL pupp 4

GRADUALISM PUNCTUATED EQUILIBRIUM

� Repeated Speciation and Macroevolution

THINGS WE’VE MISSED � Maintaining Variety � Diploidy, heterozygote advantage, Frequency dependant Selection � Sympatric Speciation - Polyploidy � Vestigial Structures