Lecture 5A

Lecture 5A - Origin of Species Overview: The Mystery of...

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Unformatted text preview: Origin of Species Overview: The Mystery of Mysteries Darwin explored the Galpagos Islands And discovered plants and animals found nowhere else on Earth Figure 24.1 The origin of new species, or speciation Is at the focal point of evolutionary theory, because the appearance of new species is the source of biological diversity Evolutionary theory Must explain how new species originate in addition to how populations evolve Macroevolution Refers to evolutionary change above the species level Two basic patterns of evolutionary change can be distinguished Anagenesis Cladogenesis Figure 24.2 (b) Cladogenesis (a) Anagenesis The biological species concept emphasizes reproductive isolation Species Is a Latin word meaning kind or appearance The Biological Species Concept The biological species concept Defines a species as a population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring but are unable to produce viable fertile offspring with members of other populations Similarity between different species. The eastern meadowlark ( Sturnella magna, left) and the western meadowlark ( Sturnella neglecta, right) have similar body shapes and colorations. Nevertheless, they are distinct biological species because their songs and other behaviors are different enough to prevent interbreeding should they meet in the wild. (a) Diversity within a species. As diverse as we may be in appearance, all humans belong to a single biological species ( Homo sapiens ), defined by our capacity to interbreed. (b) Figure 24.3 A, B Reproductive Isolation Reproductive isolation Is the existence of biological factors that impede members of two species from producing viable, fertile hybrids Is a combination of various reproductive barriers Prezygotic barriers Impede mating between species or hinder the fertilization of ova if members of different species attempt to mate Postzygotic barriers Often prevent the hybrid zygote from developing into a viable, fertile adult Prezygotic and postzygotic barriers Figure 24.4 Prezygotic barriers impede mating or hinder fertilization if mating does occur Individuals of different species Mating attempt Habitat isolation Temporal isolation Behavioral isolation Mechanical isolation HABITAT ISOLATION TEMPORAL ISOLATION BEHAVIORAL ISOLATION MECHANICAL ISOLATION (b) (a) (c) (d) (e) (f) (g) Viable fertile offspring Reduce hybrid viability Reduce hybrid fertility Hybrid breakdown Fertilization Gametic isolation GAMETIC ISOLATION REDUCED HYBRID VIABILITY REDUCED HYBRID FERTILITY HYBRID BREAKDOWN (h) (i) (j) (k) (l) (m) Limitations of the Biological Species Concept The biological species concept cannot be applied to Asexual organisms Fossils Organisms about which little is known regarding their reproduction Other Definitions of Species The morphological species concept...
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Lecture 5A - Origin of Species Overview: The Mystery of...

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