Biology 102 Fall 2016 Lecture 2 (Speciation) Lecture Notes PDF

General Biology 2 BSB 102 http://hydrodictyon.eeb.uconn.edu/courses/EEB210/evolution.jpg T. Michael Dodson  Theory of Evolution descent with modification natural selection Genetic variation is th...

General Biology 2 BSB 102 http://hydrodictyon.eeb.uconn.edu/courses/EEB210/evolution.jpg T. Michael Dodson  Theory of Evolution descent with modification natural selection Genetic variation is the substrate of natural selection. mutation sexual recombination Tracking alleles and genotypes from one generation to the next. (Mendelian genetics) Hardy-Weinberg Equilibrium Genetic divergence leads to speciation. species concepts THE ORIGIN OF SPECIES – In the 150 years since the publication of Darwin’s book On the Origin of Species by Means of Natural Selection, new discoveries and technological advances have given scientists a wealth of new information about the evolution of life. – The diversity of life evolved through speciation, the process in which one species splits into two or more species. © 2013 Pearson Education, Inc.  What Is a Species? – Species is a Latin word meaning “kind” or “appearance.” – The biological species concept defines a species as “A group of populations whose members have the potential to interbreed with one another in nature to produce fertile offspring.” © 2013 Pearson Education, Inc. Figure 14.2 Similarity between different species Diversity within one species How do we declare a population a new, or different, species? Ernst Mayr 1904-2005 evolutionary biologist Harvard University professor The Biological Species Concept Proposed by Ernst Mayr in 1942 A biological species is a group of interbreeding natural populations that are reproductively isolated from other such groups. The Biological Species Concept cannot be applied to all situations…... species that reproduce asexually extinct organisms (fossils only) limited gene flow between populations 18.9 Reproductive Isolation  Speciation Evolutionary process by which new species form Reproductive isolating mechanisms are always part of the process  Reproductive isolation The end of gene exchange between populations Beginning of speciation Reproductive Isolating Mechanisms  Reproductive isolating mechanisms prevent interbreeding among species Heritable aspects of body form, function, or behavior that arise as populations diverge Prezygotic isolating mechanisms prevent pollination or mating Postzygotic isolating mechanisms result in weak or infertile hybrids Figure 14.3 INDIVIDUALS OF DIFFERENT SPECIES Prezygotic Barriers Temporal isolation Habitat isolation Behavioral isolation MATING ATTEMPT Mechanical isolation Gametic isolation FERTILIZATION (ZYGOTE FORMS) Postzygotic Barriers Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown VIABLE, FERTILE OFFSPRING No Barriers Prezygotic Isolating Mechanisms  Temporal isolation-cicadas  Behavioral isolation – bird songs and dances  Ecological (habitat) isolation-tigers and lions  Mechanical isolation – flower parts  Gamete incompatibility – any cross between two very different gametes Figure 14.4a Temporal Isolation Skunk species that mate at different times Behavioral Isolation Mechanical Isolation Figure 14.4d Mechanical Isolation Snail species whose genital openings cannot align Figure 14.4b Habitat Isolation Garter snake species from different habitats Figure 14.4e Gametic Isolation Sea urchin species whose gametes cannot fuse Postzygotic Isolation Mechanisms  Reduced hybrid viability (ligers, tigons) Extra or missing genes  Reduced hybrid fertility (mules) Robust but sterile offspring  Hybrid breakdown Lower fitness with successive generations http://www.dwm.ks.edu.tw/bio/activelearner/19/images/ch19c3.jpg 64 63 62 http://members.tripod.com/~lion_roar/MoreTigers.html http://www.shelktone.com/2008/01/11/cat-porn/ Figure 14.5c Hybrid Breakdown Sterile next-generation rice hybrid Mechanisms of Speciation A key event in the potential origin of a species occurs when a population is somehow cut off from other populations of the parent species. Species can form by – allopatric speciation, due to geographic isolation, or – sympatric speciation, without geographic isolation. © 2013 Pearson Education, Inc. Figure 14.6 Allopatric speciation Sympatric speciation Figure 14.7 Ammospermophilus Ammospermophilus harrisii leucurus Allopatric Speciation Speciation occurs with the evolution of reproductive barriers between – the isolated population and – its parent population. Even if the two populations should come back into contact at some later time, the reproductive barriers will keep them as separate species. © 2013 Pearson Education, Inc. Figure 14.8 Populations Populations become become allopatric sympatric Populations interbreed Gene pools merge: No speciation Geographic Populations barrier cannot interbreed Reproductive isolation: Speciation has occurred Time Allopatric Speciation The Inviting Archipelagos  Winds or ocean currents carry a few individuals of mainland species to remote, isolated islands chains (archipelagos) such as Hawaii  Habitats and selection pressures that differ within and between the islands foster divergences that result in allopatric speciation Allopatric Speciation on an Isolated Archipelago A A few individuals of a B Later, a few C Genetically different mainland species reach individuals of a new descendants of the isolated island 1. In the new species colonize ancestral species may habitat, populations of their nearby island 2. colonize islands 3 and 4 descendants diverge, and Speciation follows or even invade island 1. speciation occurs. genetic divergence Genetic divergence and in the new habitat. speciation may follow. Fig. 18-21a, p. 293 18.11 Other Speciation Models  Populations sometimes speciate even without a physical barrier that blocks gene flow Sympatric speciation Parapatric speciation  Sympatric Speciation – Sympatric speciation occurs in populations that live in the same geographic area. – An accident during cell division that results in an extra set of chromosomes is a common route to sympatric speciation in plants. – Many polyploid species arise from the hybridization of two parent species. © 2013 Pearson Education, Inc. Sympatric Speciation – Many domesticated plants are the result of sympatric speciation, including oats, potatoes, bananas, peanuts, apples, coffee, and wheat. © 2013 Pearson Education, Inc. Figure 14.9-1 Domesticated AA BB Wild Triticum Triticum monococcum (14 chromosomes) (14 chromosomes) 1 AB Sterile hybrid (14 chromosomes) Figure 14.9-2 Domesticated AA BB Wild Triticum Triticum monococcum (14 chromosomes) (14 chromosomes) 1 AB Sterile hybrid (14 chromosomes) 2 T. turgidum Emmer wheat AA BB (28 chromosomes) Figure 14.9-3 Domesticated AA BB Wild Triticum Triticum monococcum (14 chromosomes) (14 chromosomes) 1 AB Sterile hybrid (14 chromosomes) 2 T. turgidum Wild Emmer wheat AA BB DD T. tauschii (28 chromosomes) (14 chromosomes) 3 ABD Sterile hybrid (21 chromosomes) Figure 14.9-4 Domesticated AA BB Wild Triticum Triticum monococcum (14 chromosomes) (14 chromosomes) 1 AB Sterile hybrid (14 chromosomes) 2 T. turgidum Wild Emmer wheat AA BB DD T. tauschii (28 chromosomes) (14 chromosomes) 3 ABD Sterile hybrid (21 chromosomes) 4 T. aestivum Bread wheat AA BB DD (42 chromosomes) Parapatric Speciation  In parapatric speciation, populations in contact along a common border evolve into distinct species  Hybrids in the contact zone are less fit than individuals on either side Parapatric Speciation Different Speciation Models 18.9-18.11 Key Concepts How Species Arise  Speciation varies in its details, but it typically starts after gene flow ends  Microevolutionary events that occur independently lead to genetic divergences, which are reinforced as reproductive isolation mechanisms evolve Adaptive Radiation  Adaptive radiation A burst of speciation that occurs when a lineage encounters a new set of niches  Key innovation A structural or functional adaptation that allows individuals to exploit their habitat in a new way Extinction  Extinction The irrevocable loss of a species from Earth  Mass extinctions Extinctions of many lineages, followed by adaptive radiations Five catastrophic events in which the majority of species on Earth disappeared Extinction is a natural process, but the pace of extinction is increasing due to human activities.