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LEQ: How do new species form?

LEQ: How do new species form?. 14.1 to 14.3. The Biological Species Concept.

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LEQ: How do new species form?

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  1. LEQ: How do new species form? 14.1 to 14.3

  2. 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

  3. Fig. 24-2 (a) Similarity between different species (b) Diversity within a species

  4. Reproductive Isolation • Reproductive isolation is the existence of biological factors (barriers) that impede two species from producing viable, fertile offspring • Reproductive isolation can be classified by whether factors act before or after fertilization

  5. Prezygotic barriers block fertilization from occurring by: • Impeding different species from attempting to mate – courtship rituals, timing, and/or habitat • Preventing the successful completion of mating - Morphological differences can prevent successful mating • Hindering fertilization if mating is successful - Sperm of one species may not be able to fertilize eggs of another species

  6. Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult: • Reduced hybrid viability - Genes of the different parent species may interact and impair the hybrid’s development • Reduced hybrid fertility - Even if hybrids are vigorous, they may be sterile • Hybrid breakdown - Some first-generation hybrids are fertile, but when they mate with another species or with either parent species, offspring of the next generation are feeble or sterile

  7. Fig. 24-4a Prezygotic barriers Mechanical Isolation Habitat Isolation Temporal Isolation Behavioral Isolation Individuals of different species Mating attempt (e) (f) (a) (c) (d) (b)

  8. Fig. 24-4i Prezygotic barriers Postzygotic barriers Reduced Hybrid Viability Reduced Hybrid Fertility Hybrid Breakdown Gametic Isolation Viable, fertile offspring Fertilization (h) (g) (l) (i) (j) (k)

  9. Speciation • Reproductive barriers may lead to speciation. • Speciation, the origin of new species, is at the focal point of evolutionary theory

  10. Limitations of the Biological Species Concept • The biological species concept cannot be applied to fossils or asexual organisms (including all prokaryotes)

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