Speciation 2025 PDF

The Origin of Species Reading: Chapter 24 Dynamic Study Module: Chapter 24  Quiz 1 (L2-3) Due tonight! Wednesday, January 15th midnight  Key Concepts What are species and species concepts? Reproductive isolation is central to speciation Biological barriers p...

The Origin of Species Reading: Chapter 24 Dynamic Study Module: Chapter 24  Quiz 1 (L2-3) Due tonight! Wednesday, January 15th midnight  Key Concepts What are species and species concepts? Reproductive isolation is central to speciation Biological barriers prevent gene flow resulting in reproductive isolation Isolated populations evolve independently - eventually becoming distinct species Speciation episodes occur in two geographic modes Hybridization can occur if barriers are incomplete  Speciation Speciation is the process by which one species splits into two species over time Microevolution consists of changes in allele frequency in a population over time Macroevolution refers to broad patterns of evolutionary change above the species level Speciation forms a conceptual bridge between microevolution and macroevolution  The Origin of Species THINK-PAIR-SHARE How do you define a species? What information do you need to classify species?  Species Concepts Morphological Biological Phylogenetic Ecological … there are well over 20 species concepts  Species Species: kind or appearance Morphological Species Concept Defined by anatomical features Practical for extant & fossil species Difficult to apply – what is different enough? Does not explain speciation as a process Exposed Intermediate Sheltered Dilsea pygmaea Dilsea californica How many species? Now how many species?  Other Definitions of Species The ecological species concept views a species in terms of its ecological niche – It applies to sexual and asexual species and emphasizes the role of disruptive selection  Other Definitions of Species The phylogenetic species concept defines a species as the smallest group of individuals on a phylogenetic tree – It applies to sexual and asexual species, but it can be difficult to determine the degree of difference required for separate species  Species (cont’d) Biological Species Concept Defined by reproductive isolation Members of all populations with potential to interbreed & produce viable & fertile offspring in the wild Sometimes difficult to apply – Asexual species – Fossils & extinct species Potential to interbreed in wild is difficult to assess Provides insights on how species become, and remain, distinct  Reproductive Isolation Biological factors (barriers) that impede two species from producing viable, fertile offspring Usually more than one barrier involved Barriers isolate species, so evolution of barriers is key to speciation  Reproductive Isolation (cont’d) Founder population often in a different niche from parent Different selective pressures Founder population usually small = susceptible to genetic drift Two populations diverge, eventually are not reproductively compatible  Reproductive Isolation (cont’d) Classified by timing: 1. 2. 3. 4. 5. Prezygotic = before fertilization Figure 24.3  Reproductive Isolation (cont’d) 6. 7. 8. Postzygotic = after fertilization Figure 24.3  Speciation Two Geographic modes: Allopatry - geographic barriers isolate populations – Geological processes – Emigration Sympatry – subpopulations isolated in the midst of the Figure 24.5 parental population – Reduction in gene flow  Speciation (cont’d) Allopatric Speciation Small splinter groups important – Extinction likely – If survive, likely to evolve relative to parent population Genetic drift - Founder effect Natural selection may be different in new environment Adaptive radiation: common ancestor spreading into many new environments over short period of time  Allopatric Speciation in Snapping Shrimp (Alpheus) Figure 24.8 Allopatric speciation in snapping shrimp (Alpheus). Copyright © 2025 Pearson Canada, Inc. 24 - 20  Speciation (cont’d) Sympatric Speciation Reduction in gene flow – Sexual selection – Habitat differentiation – Polyploidy - accidents of cell division that result in reproductive isolation in a single generation Autopolyploidy  Polyploidy Polyploidy is the presence of Figure 24.9 Sympatric extra chromosome sets due to speciation by autopolyploidy. accidents during cell division Polyploidy is more common in plants than in animals, and can produce new biological species in sympatry within a single generation An autopolyploid is an individual with more than two chromosome sets that are all derived from a single species  One Mechanism for Allopolyploid Speciation in Plants An allopolyploid is a species with multiple sets of chromosomes derived from different species Figure 24.10 One mechanism for allopolyploid speciation in plants.  Hybrid Zones Biological barriers not always complete - hybrids produced Stable hybrid populations may be established between two species – hybrid zones Figure 24.4  Hybrid Zones (cont’d) 3 possible outcomes: Figure 24.14  Hybrid Zones (cont’d) Hybrid zones reveal potential barriers 4000 km long, 10 km wide Figure 24.13  FOR NEXT CLASS PRE-READING D2L Orca Species Concepts