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Processes of Evolution Chapter 12 Part 2 12.4 Factors That Affect Variation in Traits Interactions within species, and among genes and the environment, also influence natural selection • • • • Sexual selection Balanced polymorphism Genetic drift Gene flow Sexual Selection Sexual selection leads to forms of traits that enhance reproductive success Sexual dimorphism is one outcome Sexual selection • Some individuals of a population outreproduce others because they are better at securing mates Examples of Sexual Selection Balanced Polymorphism In balanced polymorphism, nonidentical alleles for a trait are maintained in a population Balanced polymorphism • Maintenance of two or more alleles for a trait in some populations • Occurs when environmental conditions favor heterozygotes over homozygotes Balanced Polymorphism and Sickle Cell Trait Genetic Drift Genetic drift can lead to the loss of genetic diversity (fixation) Genetic drift • Random change in allele frequencies in a population over time, due to chance alone Fixed • Refers to an allele for which all members of a population are homozygous Genetic Drift in Flour Beetles Fig. 12-12a, p. 225 Fig. 12-12b, p. 225 Animation: Simulation of genetic drift Genetic Drift and Bottlenecks Genetic drift is pronounced in small or inbreeding populations, such as those that occur after an evolutionary bottleneck Bottleneck • Reduction in population size so severe that it reduces genetic diversity Inbreeding • Nonrandom mating among close relatives Genetic Drift and the Founder Effect A bottleneck can lead to the founder effect Founder effect • Change in allele frequencies that occurs after a small number of individuals establish a population The Founder Effect in Old Order Amish Populations of Old Order Amish in Pennsylvania are moderately inbred – 1 in 200 is homozygous for the recessive allele that causes Ellis vanCreveld syndrome Gene Flow Gene flow counters the effects of mutation, natural selection, and genetic drift in a population Gene flow • The physical movement of alleles into and out of a population, as by individuals that immigrate or emigrate Animation: Distribution of sickle-cell trait Animation: Life cycle of Plasmodium Animation: Morphological differences within a species 12.5 Speciation Individuals of sexually reproducing species can interbreed successfully under natural conditions, produce fertile offspring, and are reproductively isolated from other species Speciation • Process by which new species arise from existing species Four Butterflies, Two Species Reproductive Isolation Reproductive isolation typically occurs after gene flow stops Divergences then lead to speciation Reproductive isolation • Absence of gene flow between populations Reproductive Isolating Mechanisms Different species form and . . . Prezygotic mechanisms Individuals reproduce at different times (temporal isolation). Physical incompatibilities prevent individuals from interbreeding (mechanical isolation). Individuals live in different places so they never meet up (ecological isolation). Individuals ignore or do not get the required cues for sex (behavioral isolation). Mating occurs and . . . No fertilization occurs (gamete incompatibility). Zygotes form and . . . Postzygotic mechanisms Hybrid embryos die early, or new individuals die before they can reproduce (hybrid inviability). Hybrid individuals or their offspring do not make functional gametes (hybrid sterility). Interbreeding is successful Fig. 12-15, p. 227 Different species form and . . . Prezygotic mechanisms Individuals reproduce at different times (temporal isolation). Physical incompatibilities prevent individuals from interbreeding (mechanical isolation). Individuals live in different places so they never meet up (ecological isolation). Individuals ignore or do not get the required cues for sex (behavioral isolation). Mating occurs and . . . No fertilization occurs (gamete incompatibility). Zygotes form and . . . Postzygotic mechanisms Hybrid embryos die early, or new individuals die before they can reproduce (hybrid inviability). Hybrid individuals or their offspring do not make functional gametes (hybrid sterility). Interbreeding is successful Stepped Art Fig. 12-15, p. 227 Animation: Reproductive isolating mechanisms Mechanical Isolation Behavioral Isolation Animation: Albatross courtship Allopatric Speciation In allopatric speciation, a geographic barrier interrupts gene flow between populations Genetic divergences then give rise to new species Allopatric speciation • Speciation pattern in which a physical barrier that separates members of a population ends gene flow between them Allopatric Speciation in Snapping Shrimp Sympatric Speciation With sympatric speciation, populations in physical contact speciate(???) Polyploid species of many plants (and a few animals) originated by chromosome doublings and hybridizations Sympatric speciation • Pattern in which speciation occurs in the absence of a physical barrier Sympatric Speciation in Wheat 2 Triticum monococcum (einkorn) 14AA 1 × Unknown spontaneous species of chromosome T. turgidum (emmer) doubling Triticum 14BB 14AB 28AABB 3 × T. tauschii (goatgrass) 14DD T. aestivum (common bread wheat) 42AABBDD Fig. 12-19, p. 229 Animation: Sympatric speciation in wheat Sympatric Speciation in Cichlids Different Speciation Models Animation: Models of speciation Animation: Temporal isolation among cicadas 12.6 Macroevolution Macroevolution refers to large-scale patterns of evolutionary change such as adaptive radiations, the origin of major groups, and loss through extinction Macroevolution • Patterns of evolution that occur above the species level Stasis With stasis, a lineage changes very little over evolutionary time Stasis • Macroevolutionary pattern in which a lineage persists with little or no change over evolutionary time Stasis: The Coelacanth Coevolution Coevolution occurs when two species act as agents of selection upon one another Coevolution • The joint evolution of two closely interacting species; each species is a selective agent that shifts the range of variation in the other • Examples: predator and prey, host and parasite, pollinator and flower Coevolved Species Madagascar orchid and its pollinator Exaptation In exaptation, a lineage uses a structure for a different purpose than its ancestor did Exaptation • Adaptation of an existing structure for a completely different purpose; a major evolutionary novelty Extinction Permanent loss of a species is extinction Extinct • A species that has been permanently lost Mass extinction • Simultaneous extinction of many lineages Adaptive Radiation An adaptive radiation is a rapid diversification into new species that occupy novel niches Adaptive radiation • A burst of genetic divergences from a lineage gives rise to many new species Key innovation • An evolutionary adaptation that gives its bearer the opportunity to exploit a particular environment more efficiently or in a new way Adaptive Radiation of Hawaiian Honeycreepers Fig. 12-23 (right), p. 232 Fig. 12-23a, p. 232 Fig. 12-23b, p. 232 Fig. 12-23c, p. 232 Fig. 12-23d, p. 232 Fig. 12-23e, p. 232 Fig. 12-23f, p. 232 Fig. 12-23g, p. 232 Fig. 12-23h, p. 232 Fig. 12-23i, p. 232 Fig. 12-23j, p. 232 Fig. 12-23k, p. 232 Evolutionary Theory Many biologists disagree about how macroevolution occurs Dramatic jumps in morphology may result from mutations in homeotic or other regulatory genes Macroevolution may be an accumulation of many microevolutionary events, or an entirely different process Animation: Allopatric speciation on an archipelago 12.7 Organizing Information About Species Taxonomy • Science of naming and classifying species • In traditional taxonomy, species are organized into a series of ranks (taxa) based on their traits • Such systems do not necessarily reflect evolutionary relationships Taxon (taxa) • A grouping of organisms Linnaean Classification System DOMAIN KINGDOM PHYLUM CLASS ORDER FAMILY GENUS SPECIES COMMON NAME Eukarya Plantae Magnoliophyta Magnoliopsida Apiales Apiaceae Daucus carota carrot Eukarya Plantae Magnoliophyta Magnoliopsida Rosales Cannabaceae Cannabis sativa marijuana Eukarya Plantae Magnoliophyta Magnoliopsida Rosales Rosaceae Malus domesticus apple Eukarya Plantae Magnoliophyta Magnoliopsida Rosales Rosaceae Rosa acicularis arctic rose Eukarya Plantae Magnoliophyta Magnoliopsida Rosales Rosaceae Rosa canina dog rose Fig. 12-24, p. 233 Ranking Versus Grouping Cladistics is a set of methods that allow us to reconstruct evolutionary history (phylogeny) Phylogeny • Evolutionary history of a species or group of species Cladistics • Method of determining evolutionary relationships by grouping species into clades Cladistics Cladistics groups species into clades on the basis of shared characters Character • Quantifiable, heritable characteristic or trait Clade • A group of species that share a set of characters Cladistic Analysis The result of a cladistic analysis is an evolutionary tree diagram in which a line represents a lineage Evolutionary tree • Type of diagram that summarizes evolutionary relationships among a group of species Cladograms In evolutionary trees called cladograms, a line (lineage) can branch into two sister groups at a node, which represents a shared ancestor Cladogram • Evolutionary tree diagram that shows a network of evolutionary relationships among clades Sister groups • Two lineages that emerge from a node on a cladogram Clades Every branch of a cladogram ends in a clade Ideally, each clade is a monophyletic group Monophyletic group • An ancestor and all of its descendants Cladograms hagfishes lampreys cartilaginous fishes ray-finned fishes lobe-finned fishes lungfishes amphibians amniotes (reptiles, birds, and mammals) Fig. 12-25a, p. 234 hagfishes animals with a skull lampreys cartilaginous fishes ray-finned fishes lobe-finned fishes lungfishes amphibians amniotes (reptiles, birds, and mammals) animals with a backbone and a skull animals with a swim bladder or lungs, a backbone, and a skull animals with four limbs,* a swim bladder or lungs, a backbone, and a skull animals with four membranes around their eggs, four limbs,* a swim bladder or lungs, a backbone, and a skull *Snakes are included in these clades because their ancestors had four legs. Fig. 12-25b, p. 234 Classification Systems Evolutionary trees are revised as new information is gathered Two different ways to organize life’s diversity • Six-kingdom classification system • Three-domain classification system Two Major Classification Systems Bacteria Archaea Protists Plants Fungi Animals A. This tree represents all life classified into six kingdoms. We have discovered that the kingdom of protists is not monophyletic, so some biologists now divide it up into a number of new kingdoms. Fig. 12-26a, p. 235 Bacteria Archaea Eukarya B. This tree represents all life classified into three domains. The kingdoms protists, plants, fungi, and animals are subsumed into domain Eukarya. Fig. 12-26b, p. 235 Animation: Classification systems Animation: Constructing a cladogram Animation: Current evolutionary tree Animation: Evolutionary tree diagrams Animation: Interpreting a cladogram 12.8 Impacts/Issues Revisited The allele that confers resistance to warfarin in rats also causes vitamin K deficiency • The trait is polymorphic – adaptive when warfarin is present, maladaptive when it is not Digging Into Data: Resistance to Rodenticides in Wild Rat Populations not resistant to warfarin or bromadiolone 21% 58% 21% resistant to warfarin resistant to warfarin and bromadiolone Olfen 5% 8% Germany 87% Stadtlohn 5% 5% 56% 100% 44% Dorsten Ludwigshafen 90% Drensteinfurt Fig. 12-27, p. 237