CAMPBELL TENTH BIOLOGY EDITION Reece • Urry • Cain • Wasserman • Minorsky • Jackson 24 The Origin of Species Lecture Presentation by Nicole Tunbridge and Kathleen Fitzpatrick © 2014 Pearson Education, Inc. Figure 24.2a What is a species Eastern meadowlark (Sturnella magna) and western meadowlark (Sturnella neglecta) © 2014 Pearson Education, Inc. That “Mystery of Mysteries” first appearance of creatures on EARTH . In the Galápagos Islands Darwin discovered plants and animals found nowhere else on Earth . Volcanic islands – relatively new – therefore species relatively new !! © 2014 Pearson Education, Inc. Figure 24.1 Flightless bird Endemic species Galápagos giant tortoise, another species unique to the islands © 2014 Pearson Education, Inc. 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 changes in allele frequency in a population over time . Macroevolution refers to broad patterns of evolutionary change above the species level © 2014 Pearson Education, Inc. Concept 24.1: The biological species concept emphasizes reproductive isolation . Species is a Latin word meaning “kind” or “appearance” . Biologists compare morphology, physiology, biochemistry, and DNA sequences when grouping organisms © 2014 Pearson Education, Inc. 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 members of other populations . Gene flow between populations holds a species together genetically © 2014 Pearson Education, Inc. Figure 24.2 (a) Similarity between different species (b) Diversity within a species © 2014 Pearson Education, Inc. Reproductive Isolation . Reproductive isolation is the existence of biological factors (barriers) that impede two species from producing viable, fertile offspring . Hybrids are the offspring of crosses between different species . Reproductive isolation can be classified by whether factors act before or after fertilization © 2014 Pearson Education, Inc. Figure 24.3 Prezygotic barriers Postzygotic barriers Habitat Temporal Behavioral Mechanical Gametic Reduced Reduced Hybrid isolation isolation isolation isolation isolation hybrid hybrid breakdown viability fertility Indivi- VIABLE, duals of MATING FERTILI- FERTILE different ATTEMP ZATION OFF- species T SPRING (a) (c) (e) (f) (g) (h) (i) (l) (d) (j) (b) (k) © 2014 Pearson Education, Inc. Prezygotic barriers block fertilization from occurring by . Impeding different species from attempting to mate . Preventing the successful completion of mating . Hindering fertilization if mating is successful © 2014 Pearson Education, Inc. Figure 24.3a Prezygotic barriers Habitat Temporal Behavioral isolation isolation isolation Indivi- duals of MATING different ATTEMPT species (a) (c) (e) (d) (b) © 2014 Pearson Education, Inc. Habitat isolation: Two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers © 2014 Pearson Education, Inc. Temporal isolation: Species that breed at different times of the day, different seasons, or different years cannot mix their gametes © 2014 Pearson Education, Inc. Figure 24.3ae Behavioral isolation: Courtship rituals and other behaviors unique to a species are effective barriers to mating (e) https://www.youtube.com/watch ?v=oYmzdvMoUUA © 2014 Pearson Education, Inc. Video: Blue-footed Boobies Courtship Ritual © 2014 Pearson Education, Inc. Figure 24.3b Prezygotic barriers Mechanical Gametic isolation isolation MATING FERTILI- ATTEMPT ZATION (f) (g) © 2014 Pearson Education, Inc. Mechanical isolation: Morphological differences can prevent successful completion of mating © 2014 Pearson Education, Inc. Gametic Isolation: Sperm of one species may not be able to fertilize eggs of another species © 2014 Pearson Education, Inc. Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult . Reduced hybrid viability . Reduced hybrid fertility . Hybrid breakdown © 2014 Pearson Education, Inc. Figure 24.3c Postzygotic barriers Reduced Reduced Hybrid hybrid hybrid breakdown viability fertility VIABLE, FERTILI- FERTILE ZATION OFF- SPRING (h) (i) (l) (j) (k) © 2014 Pearson Education, Inc. Reduced hybrid viability: Genes of the different parent species may interact and impair the hybrid’s development or survival in its environment © 2014 Pearson Education, Inc. Reduced hybrid fertility: Even if hybrids are vigorous, they may be sterile © 2014 Pearson Education, Inc. Hybrid breakdown: Some first-generation hybrids are fertile, but when they mate with each other or with either parent species, offspring of the next generation are feeble or sterile © 2014 Pearson Education, Inc. Limitations of the Biological Species Concept . The biological species concept cannot be applied to fossils or asexual organisms (including all prokaryotes) . The biological species concept emphasizes absence of gene flow . However, gene flow can occur between distinct species . For example, grizzly bears and polar bears can mate to produce “grolar bears” © 2014 Pearson Education, Inc. Figure 24.4 ▶ Grizzly bear (U. arctos) ▶ Polar bear (U. maritimus) ▶ Hybrid “grolar bear” © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. Liger = male lion, female tiger Liliger = male lion, female Liger Tigon = male tiger, female lion Titigon = male tiger, female tigon © 2014 Pearson Education, Inc. Other Definitions of Species . Other species concepts emphasize the unity within a species rather than the separateness of different species . The morphological species concept defines a species by structural features . It applies to sexual and asexual species but relies on subjective criteria © 2014 Pearson Education, Inc. 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 © 2014 Pearson Education, Inc. Ecological species concept A species is a set of organisms exploiting a single niche. The key aspects of this definition are the resources exploited and the habitat occupied by the members of a species. niche = the position or function of an organism in a community of plants and animals. 31 © 2014 Pearson Education, Inc. 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 © 2014 Pearson Education, Inc. Phylogenetic species concept A species may be defined by its unique genetic history as a tip of a phylogenetic tree. Species are defined by their unique derived features and shared ancestry. 33 © 2014 Pearson Education, Inc..