4/4/2017. Extrinsic Isolating Barriers. 1. Biological species concept: 2. Phylogenetic species concept:

Transcription

1 Chapter 13 The origin of species 13.1 What Is a Species? p. 414 Ways to identify species 1. Biological species concept: 1. There are many different concepts of species 2. Species are important taxonomic units 3. Species are independently evolving lineages 1 2. Phylogenetic species concept: 3. General Lineage Species Concept A. Species are metapopulations B. A metapopulation consists of a group of spatially separated populations which interact at some level Two patterns of 1. Anagensis (Box 14.1, p. 461) A. transformation of one species into another 2. Cladogenesis A. branching evolution B. cladogenesis promotes biologic diversity by increasing the number of species 13.2 Barriers to Gene Flow: Keeping Species Apart p Isolating barriers reduce or impede gene flow. 3 4 Extrinsic Isolating Barriers 1. Extrinsic properties of the environment in which an organism lives A. Physically separate populations B. Geographic barriers [p. 477] 1. Elk and red deer: two species? (Fig. 13.3) A. Geographically isolated (allopatric). B. Are they reproductively isolated? C. Allopatry D. Allopatric 1

2 Prezygotic Reproductive Barriers: P. 418 Prezygotic Reproductive Barriers: P reduce the likelihood that that individuals mate and form a zygote A. timing of reproduction a. Corals release gametes into the water (13.4) A. mismatched morphology B. pollinator isolation (13.5) B. Behavioral Isolation C. Habitat Isolation 8 Postmating-prezygotic barriers p Sperm can fail to reach eggs after mating, 2. Gametic incompatibility: 9 Reproductive Barriers: After Fertilization p Postzygotic Reproductive Barriers A. fertilized zygotes do not successfully develop and/or reproduce B. Genetic incompatibilities a. hybrid offspring are sterile or have low fitness. Extrinsic» Ecological inviability» Behavioral sterility Intrinsic» Hybrid inviability» Hybrid sterility 10 Bateson-Dobzhansky-Muller incompatibilties (B-D-M Two loci associated with hybrid male sterility (Hms1, Hms2). Hybrid individuals inheriting M. guttatus alleles at the Hms1 locus produce viable pollen if they also have at least one M. guttatus allele at the Hms2 locus The Origin of Isolating Barriers: How New Species Form p Geographic Isolation p Allopatric 3. Reinforcement 4. An example of a vicariance event separating populations A. Isthmus of Panama land bridge between North and South America developed some 3 million years ago 12 2

3 Phylogenetic signature of allopatric (Fig. 13.9) 1. Panamanian isthmus and snapping shrimp 2. There are 7 pairs of closely related species, with one member of each pair found on either side of the isthmus, 3. Pairs do not interbreed Sympatric in Rhagoletis Ecological : The evolution of reproductive barriers between populations by adaptation to different environment or ecological niches. Islands provide opportunity for allopatric Colonization leads to 1. Geographic Isolation through Dispersal and Colonization 2. Geological history of the Hawaiian Islands [Fig ]. 1. Evidence for and dispersal events 2. Crickets on the Hawaiian Islands 13.5 The Speed of Speciation p. 436 The speed of 1. Animal populations may take hundreds of thousands of years to diverge into clearly delineated species. 2. Plants can take far less time. 17 3

4 Allopolyploidy 1. Polyploidy (more than two paired chromosomes) resulting from interspecific hybridization. 2. (If polyploidy arises within a species, it's called autopolyploidy). Allopolyploidy can lead to extremely rapid 19 Key Concepts 1. The speed of depends on genetic architecture of organisms A. Genome duplication common in plants 13.6 Uncovering Hidden Species p Cryptic species A. Very similar-looking organisms sometimes turn out to be previously unknown species B. Groups of organisms that are genetically distinct and do not interbreed, but are morphologically almost indistinguishable 22 Cryptic diversity in skipper butterflies 13.7 The Puzzle of Microbial Species p Bacteria and other microbes do not fit the biological species concept. 2. Their species may be defined by ecological separation 24 4

5 Horizontal gene transfer in E. coli Bacterial species often defined by specific adaptations Core genome includes 993 genes Pan-genome includes 15,741 genes Some scientists criticize this method Horizontal gene transfer makes classification difficult Horizontal gene transfer is common Key Concepts 1. Ultimately, species concepts are human artifacts A. Methods for recognizing species continue to improve 5