6_Speciation 2009-1

6_Speciation 2009-1 - Chapter 24 The Origin of...

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Chapter 24 The Origin of Species/Speciation 2 Species = fundamental unit of organization in nature (unit of classification and rank) • Ornithologist Ernst Mayr identified 137 birds in Papua New Guinea • Native Papuans already had names for 136 species 3 Concept 24.1: The biological species concept • The biological species concept states that a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with other populations • Gene flow between populations holds the phenotype of a population together (emphasizes reproductive isolation) 4 Species Concepts • Morphological : defines a species by structural features (different species look different from each other) • Paleontological : focuses on morphologically discrete species known only from the fossil record • Ecological : (habitat) views a species in terms of its ecological niche • Phylogenetic : defines a species as a set of organisms with a unique genetic history • Biological : actually or potentially capable of interbreeding (e.g. all dogs, all pigeons, etc) • Physicological/biochemical : organisms groups by physiological role (e.g. early microbiology)
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5 No species concept works in all situations • Many species have few distinguishing morphological characters • Often have too little information to apply ecological or phylogenetic concepts • Fossils rarely distinguish taxa down to the species level…. 6 Fig. 24-2a (a) Similarity between different species 7 Fig. 24-2b (b) Diversity within a species 8 Speciation , the origin of new species, is at the focal point of evolutionary theory • Evolutionary theory must explain how new species originate and how populations evolve Microevolution consists of adaptations that evolve within a population, confined to one gene pool Macroevolution refers to evolutionary change above the species level
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9 Two basic patterns of speciation – Anagenesis (phyletic or vertical evolution) transforms one species into another –C ladogene s i s (branching evolution) is the splitting of a gene pool, giving rise to one or more new species Anagenesis Cladogenesis 10 Biological species concept is most popular, but does not work in all situations • Fossils • Asexual taxa • Taxa not amenable to breeding studies 11 Concept 24.2: Speciation can take place with or without geographic separation • Speciation can occur in two ways: – Allopatric speciation – Sympatric speciation 12 Modes of speciation • Allopatric (allos = other, patra = homeland) •S ym p a t r i c (sym = same, patra = homeland) Allopatric speciation Sympatric speciation
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13 Allopatric speciation • Gene flow impeded by physical or geographic barrier • Selection and drift lead to reproductive isolation Mainland gray fox Island fox Initial population of fruit flies (Drosophila pseudoobscura) Mating experiments after several generations Some flies raised on maltose medium Some flies raised on starch medium Allopatric speciation in the lab
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6_Speciation 2009-1 - Chapter 24 The Origin of...

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