True or False 1. Speciation can be observed only over millions of years. 2. Some features (such as the human eye) are too complex to evolve by natural selection.

Imagine this scenario. A few birds are blown from the mainland to a remote volcanic island. There is limited vegetation on the island. The few plants have very large seeds. The birds establish a small, viable population on the island. Select all correct statements. a. The birds will evolve larger bills in order to eat the large seeds. b. Birds with large bills will have greater evolutionary fitness than birds with small bills. c. The bill size of all birds will gradually increase in the population. d. Alleles for large bills will arise by mutation because of selection for large bills. e. Birds with large bills will come to make up a larger percentage of the population.

Biological Species Concept 1. A group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring – but do not produce viable, fertile offspring with members of other such groups

Alternative concept of species (emphasizes unity within a species) 1. Morphological – can be applied to sexual and asexual species/subjective/used most often 2. Ecological – in terms of niche/emphasizes role of disruptive natural selection/can be applied to sexual and asexual species 3. Phylogenetic – smallest group of individuals that share a common ancestor/compare morphology or molecular sequences to other organisms/degree of differences required????

For the following questions, consider 2 populations of birds: the original one on the mainland and the small population on the volcanic island. Consider each species concept in turn: biological, morphological, ecological, and phylogenetic. 1. Which information is most relevant to the biological species concept? a. The physical appearance of the birds in the two populations. b. The percentage of viable, fertile hybrid offspring, formed if the two populations encounter each other. c. The degree of genetic difference between the two populations. d. The range of foods eaten by members of the two populations.

Which information is most relevant to the morphological species concept? a. The physical appearance of the birds in the two populations. b. The percentage of viable, fertile hybrid offspring formed if the two populations encounter each other. c. The degree of genetic difference between the two populations. d. The range of foods eaten by members of the two populations.

Which information is most relevant to the ecological species concept? a. The physical appearance of the birds in the two populations. b. The percentage of hybrid offspring formed if the two populations encounter each other. c. The degree of genetic differences between the two populations. d. The range of foods eaten by members of the two populations.

Which information is most relevant to the phylogenetic species concept? a. The physical appearance of the birds in the two populations. b. The percentage of hybrid offspring formed if the two populations encounter each other. c. The degree of genetic difference between the two populations. d. The range of foods eaten by members of the two populations.

24.2 – Speciation can take place with or without geographical separation 1. Allopatric speciation – geographic separation restricts gene flow(depends on ability of organism to move about) Ex) mountain ranges, glaciers, land bridges, splintering of lakes 2. Sympatric speciation – geographically overlapping populations/gene flow restricted by chromosomal changes, nonrandom mating

Allopatric speciation Mechanisms by which gene pools may begin to diverge: a. Different mutation rates b. Different selective pressures c. Genetic drift alters allele frequencies

Fruit fly experiment – Diane Dodd

Sympatric speciation - new species arise within the range of the parent population - Gene flow may be reduced by such factors as: polyploidy, habitat differentiation, and sexual selection

Autopolyploidy - an individual with more than 2 sets of chromosomes all derived from a single species - Reproductive isolation in a single generation

Allopolyploidy - more common - When 2 different species mate to produce offspring - Hybrids usually sterile - Propagate asexually - If fertile, can mate with each other

Sympatric speciation in animals Ex) North American maggot fly – hawthorne tree vs apple tree n_id=114129

24.3 Hybrid Zones An opportunity to study factors that cause reproductive isolation Possible outcome if allopatric populations come back into contact with one another

Patterns within hybrid zones Fig p. 498 – What’s causing the pattern here? What is the obstacle to gene flow? Other hybrid zones  ground crickets of the Appalachian mountains  hybrid fitness varies from year to year

Hybrid zones over time Fig p. 499 – 3 possible outcomes 1. Reinforcement – hybrids gradually cease to be formed 2. Fusion – the two species fuse 3. Stability – continued production of hybrid individuals

Reinforcement - Barriers to hybridization should be stronger for sympatric populations than allopatric populations - Ex) pied flycatcher vs collared flycatcher - Allopatric populations  male flycatchers of the two species resemble one another - How about in sympatric populations?

Fusion Barriers to reproduction are weak, speciation process reverses Ex) cichlids of Lake Victoria – fig female mate choice Question: What is responsible for the decline in the number of cichlid species? ws/090301_cichlidspeciation ws/090301_cichlidspeciation

Stability Bombina hybrid zone – Why isn’t reinforcement occuring? May be due to the narrowness of the hybrid zone and the extensive gene flow from outside the zone Allonemobius hybrid zone – some hybrids more fit than parent species/hybrids mate with each other and with both parent species  gene pools of parent species would fuse

Why aren’t we seeing more hybrid species? Because locations where hybrids form may appear and disappear rapidly, hybrids remain uncommon and fusion of gene pools do not occur