Speciation Reading: Chap. 26 I. Introduction I. Intro A. Motivating question A. Motivating Question: B. What is a species? 1. Biological Darwin’s finches 2. Morphospecies 3. Phylogenetic II. Modes of speciation A. Allopatric speciation B. Sympatric speciation C. Contact between diverging populations

Know: mechanisms for genetic shifts within populations

Q: How do these genetic shifts (adaptations) lead to new species? Q: How do these genetic shifts lead to formation of major new taxa (genus, family, order, class, etc.)?

C&R Fig. 1.17 Galapagos finches

Macroevolution IB. What is a “Species”? The evolution of species and larger taxa Evolutionary theory must also explain macroevolution Latin meaning “kind” or “appearance” Speciation is the keystone process in the origination of diversity of higher taxa. Traditionally distinguished by morphological differences Today distinguished in addition by differences in body function, biochemistry, behavior, and genetic makeup

Galapagos tortoise

1 1. Biological species concept How are biological species isolated? - Reproductive isolation between Horse Donkey species. - Individuals within a species can Mule potentially interbreed to produce viable, fertile offspring.

Eastern Meadowlark Western Meadowlark

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C&R Fig. 24.2a Similar morphology, C&R Fig. 24.2b Diversity within species 1. Prezygotic barrier: 2. Postzygotic barrier: but hybrids infertile. behavioral isolation reduced hybrid fertility

How are biological species isolated? How are biological species isolated? 1. Prezygotic barriers – impede mating 1. Prezygotic barriers – impede mating and fertilization: and fertilization: a. Impede coupling of different species b. If mating, impede fertilization: habitat, behavioral, and temporal isolation mechanical and gametic isolation b. If mating, impede fertilization

Seed beetle, male genitalia C&R Fig. 24.5

C&R Fig. 24.5 http://www.cosmosmagazine.com/node/1380

How are biological species isolated? Limitations of the biological species concept

Impractical or impossible to assess: Fossils Asexual species (bacteria, fungi, protists) Many living sexual species (e.g., plants)

2. Postzygotic barriers – prevent A - California black oak (Q. kellogii) development B - Interior live oak - reduced hybrid viability (Q. wislizenii var. frutescens) C - Oracle Oak (Q. x morehus) - reduced hybrid fertility

- hybrid breakdown C&R Fig. 24.5 http://waynesword.palomar.edu/hybrids1.htm

2 2. Morphospecies 3. Phylogenetic Species Smallest monophyletic group in a tree that compares populations. Distinguishing physical characteristics. Advantages: Widely applicable – sexual, asexual, - logical fossil species - broadly applicable, at least theoretically Disadvantage: Disadvantage: which traits, and how - data not widely available much difference is enough? - more species?

Not monophyletic = polyphyletic http://waynesword.palomar.edu/hybrids1.htm

Case study: Seaside Dusky Sparrow Seaside sparrow phylogeny conservation

Only 6 males left – taken for captive breeding

Geographically closest population

Speciation: Types of Speciation Cladogenesis

Anagenesis: Transformation of Creation of one or more one species into another new species from a “parent” species Promotes biological diversity by increasing the number of species

C&R Fig. 24.1a C&R Fig. 24.1b

3 Key point: II. Modes of Speciation Gene flow among populations is key to possibility of A. Allopatric speciation - speciation. geographic separation restricts gene flow - high gene flow: populations remain homogenous in terms of allelic composition B. Sympatric speciation - biological factors - low gene flow: populations may diverge due to mutation, selection, & drift, but may not become reduce gene flow reproductively isolated. C&R Fig. 24.6 - No gene flow: populations free to diverge.

1. Dispersal and colonization: A. Allopatric speciation – geographic isolation Island Radiations The evolution of many diversely- adapted species from a common ancestor.

C&R Fig. 24.11

Seen in some island chains: C&R Fig. 1.17 (Hawai’i, Galapagos)

Cool Hawai’ian examples 2. Ring species Honeycreepers Euphorbia’s - arborescence Drosophila

http://www.hawaiiecoregionplan.info/FBC.htm

Fig. 24.9 Ensatina eschscholtzii salamanders C&R Fig. 22.16 Emphasizes gradient in gene flow.

4 B. Sympatric speciation 3. Vicariance In animals, sympatric speciation may result from gene- based shifts in habitat or mate preference Cichlid fishes in Lake Victoria, East Africa Ratites: giant, flightless birds Ostrich - Africa Emu - Australia Rheas – S. America Kiwis, moas (extinct) – N.Z. Cassowaries – Australia, New Guinea Elephant bird (extinct) - Madagascar males females

C&R Fig. 24.16

Example 1: different selective pressures, but continued gene flow.

Water snakes: Reproductive barriers must evolve between selection for unbanded on sympatric populations islands, banded on mainland (substrate color).

But, gene flow keep population intact.

Example 3: Reproductive isolation first - Polyploidy In plants, sympatric speciation often results from polyploidy 2 steps: Example 2: disruptive selection, 1. Mistake in mitosis or meiosis habitat isolation in soapberry bugs. Æ chromosome doubling 2. Polyploid individual can’t Speciation happening cross with 2n individuals. (Fig. 26.8)

5 How do plants become polyploid? 2. Allopolyploidy – generated Species 1 Species 2 1. Autopolyploidy – self-generated by “other” species

Meiosis - May Occur after Two Species Hybridize Haploid gametes

Fertilization

These chromosomes do not synapse and separate normally

Error in meiosis or mitosis

Allopolyploid cell—now each chromosome has a homolog

Meiosis Diploid gametes Maidenhair fern (can fuse to form a tetraploid individual)

Hybrid Zones

C. What Happens When Isolated Populations Come into Contact?

Motivating Question: Darwin’s finches New Species through Hybridization

6 KEY CONCEPTS KEY CONCEPTS

Populations can be recognized as distinct Speciation occurs when populations of the species if they are reproductively isolated same species become genetically isolated by from each other, if they have distinct lack of gene flow and then diverge from morphological characteristics, or if they each other due to selection, genetic drift, or form independent branches on a mutation. phylogenetic tree.

KEY CONCEPTS KEY CONCEPTS

Populations can become genetically isolated When populations that have diverged come from each other if they occupy different back into contact, several outcomes are geographic areas, if they use different possible: habitats within the same area, or if one Reinforcement of evolved differences population is polyploid and cannot breed Hybrid zones with the other. New species from hybrids

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