Processes of Evolution. Chapter 18 Part 2

Transcription

1 Processes of Evolution Chapter 18 Part 2

2 18.6 Maintaining Variation Natural selection theory helps explain diverse aspects of nature, including differences between males and females, and the relationship between sickle-cell anemia and malaria

3 Sexual Selection With sexual selection, some version of a trait gives an individual an advantage over others in attracting mates Distinct male and female phenotypes (sexual dimorphism) is one outcome of sexual selection

4 Sexual Selection

5 Balanced Polymorphism Balanced polymorphism A state in which natural selection maintains two or more alleles at relatively high frequencies Occurs when environmental conditions favor heterozygotes Example: Sickle cell anemia and malaria Hb A /Hb S heterozygotes survive malaria more often than people who make only normal hemoglobin

6 Sickle Cell Anemia and Malaria

7 Fig a, p. 287

8 Fig b, p. 287

9 Fig c, p. 287

10 18.7 Genetic Drift The Chance Changes Genetic drift A random change in allele frequencies over time Can lead to a loss of genetic diversity, especially in small populations Fixation has occurred when all individuals in a population are homozygous for one allele

11 Genetic Drift and Population Size

12 Genetic Drift and Population Size

13 Bottlenecks Bottleneck A drastic reduction in population size brought about by severe pressure After a bottleneck, genetic drift is pronounced when a few individuals rebuild a population Example: Northern elephant seals

14 The Founder Effect Founder effect Genetic drift is pronounced when a few individuals start a new population Inbreeding Breeding or mating between close relatives who share a large number of alleles Example: Old Order Amish in Lancaster County, Pennsylvania (Ellis-van Creveld syndrome)

15 Key Concepts Patterns of Natural Selection Natural selection is a microevolutionary process Depending on the population and its environment, natural selection can shift or maintain the range of variation in heritable traits

16 18.8 Gene Flow Gene flow Physical movement of alleles caused by individuals moving into and away from populations Tends to counter the evolutionary effects of mutation, natural selection, and genetic drift on a population Example: Movement of acorns by blue jays

17 Gene Flow Between Oak Populations

18 Key Concepts Other Microevolutionary Processes With genetic drift, change can occur in a line of descent by chance alone Gene flow counters the evolutionary effects of mutation, natural selection, and genetic drift

19 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

20 Four Butterflies, Two Species

21 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

22 Prezygotic Isolating Mechanisms Temporal isolation Mechanical isolation Behavioral isolation Ecological isolation Gamete incompatibility

23 Mechanical Isolation

24 Behavioral Isolation

25 Animation: Albatross courtship

26 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

27 Reproductive Isolating Mechanisms

28 Different species! They interbreed anyway. Prezygotic isolating mechanisms Temporal isolation: Individuals of different species reproduce at different times. Mechanical isolation: Individuals cannot mate or pollinate because of physical incompatibilities. Behavioral isolation: Individuals of different species ignore or do not get the required cues for sex. Ecological isolation: Individuals of different species live in different places and never do meet up. Gamete incompatibility: Reproductive cells meet up, but no fertilization occurs. Zygotes form, but... Postzygotic isolating mechanisms Hybrid inviability: Hybrid embryos die early, or new individuals die before they can reproduce. Hybrid sterility: Hybrid individuals or their offspring do not make functional gametes. No offspring, sterile offspring, or weak offspring that die before reproducing Fig , p. 290

29 Animation: Reproductive isolating mechanisms

30 18.10 Allopatric Speciation Allopatric speciation A physical barrier arises and ends gene flow between populations Genetic divergence results in speciation Example: llamas, vicunas, and camels

31 Allopatric Speciation

32 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

33 Allopatric Speciation on an Isolated Archipelago

34 A A few individuals of a mainland species reach isolated island 1. In the new habitat, populations of their descendants diverge, and speciation occurs. B Later, a few individuals of a new species colonize nearby island 2. Speciation follows genetic divergence in the new habitat. C Genetically different descendants of the ancestral species may colonize islands 3 and 4 or even invade island 1. Genetic divergence and speciation may follow. Fig a, p. 293

35 Akepa (Loxops coccineus) Insects, spiders from buds twisted apart by bill, some nectar; high mountain rain forest Akekee (L. caeruleirostris) Insects, spiders, some nectar; high mountain rain forest Nihoa finch (Telespiza ultima) Insects, buds, seeds, flowers, seabird eggs; rocky or shrubby slopes Palila(Loxioides bailleui) Mamane seeds ripped from pods; buds, flowers, some berries, insects; high mountain dry forests Maui parrotbill (Pseudonestor xanthophrys) Rips dry branches for insect larvae, pupae, caterpillars; mountain forest with open canopy, dense underbrush Apapane (Himatione sanguinea) Nectar, especially of ohialehua flowers; caterpillars and other insects; spiders; high mountain forests Fig b, p. 293

36 Poouli (Melamprosops phaeosoma) Tree snails, insects in understory; last known male died in 2004 Maui Alauahio (Paroreomyza montana) Bark or leaf insects, some nectar; high mountain rain forest Kauai Amakihi (Hemignathus kauaiensis) Bark-picker; insects, spiders, nectar; high mountain rain forest Akiapolaau (Hemignathus munroi) Probes, digs insects from big trees; high mountain rain forest Akohekohe (Palmeria dolei) Mostly nectar from flowering trees, some insects, pollen; high mountain rain forest Iiwi (Vestiaria coccinea) Mostly nectar (ohia flowers, lobelias, mints), some insects; high mountain rain forest Fig c, p. 293

37 Animation: Allopatric speciation on an archipelago

38 18.11 Other Speciation Models Populations sometimes speciate even without a physical barrier that blocks gene flow Sympatric speciation Parapatric speciation

39 Sympatric Speciation In sympatric speciation, new species form within a home range of an existing species, in the absence of a physical barrier A change in chromosome number (polyploidy) can cause instant speciation On Lord Howe Island, species of palms are reproductively isolated

40 Sympatric Speciation in Wheat

41 Triticum monococcum (einkorn) Unknown species of Triticum spontaneous chromosome doubling T. turgidum (wild emmer) T. tauschii (a wild relative) T. aestivum (one of the common bread wheats) 14AA X 14BB 14AB 28AABB X 14DD 42AABBDD A By 11,000 years ago, humans were cultivating wild wheats. Einkorn has a diploid chromosome number of 14 (two sets of 7). It probably hybridized with another wild wheat species having the same number of chromosomes. B About 8,000 years ago, the allopolyploid wild emmer originated from an AB hybrid wheat plant in which the chromosome number doubled. Wild emmer is tetraploid, or AABB; it has two sets of 14 chromosomes. There is recently renewed culinary interest in emmer, also called farro. C AABB emmer probably hybridized with T. tauschii, a wild relative of wheat. Its diploid chromosome number s 14 (two sets of 7 DD). Common bread wheats have a chromosome number of 42 (six sets of 7 AABBDD). Fig , p. 294

42 Animation: Sympatric speciation in wheat

43 Sympatric Speciation in Palms

44 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

45 Parapatric Speciation

46 T. barretti hybrid zone T. anophthalmus Fig c, p. 295

47 Different Speciation Models

48 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

49 18.12 Macroevolution Macroevolution Large-scale patterns of evolutioary change Includes patterns of change such as one species giving rise to multiple species, the origin of major groups, and major extinction events

50 Coevolution Two species in close ecological contact act as agents of selection on each other (coevolution) Predator and prey Host and parasite Pollinator and flower Over time, the two species may come to depend on each other

51 Coevolution

52 proboscis nectar tube 10 cm Fig , p. 296

53 Stasis and Exaptation Stasis A lineage exists for millions of years with little or no change (e.g. coelacanth) Exaptation (preadaptation) Some complex traits in modern species held different adaptive value in ancestral lineages (e.g. feathers in birds and dinosaurs)

54 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

55 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

56 Adaptive Radiation of Mammals Following the K-T Extinction

57 Eomaia scansoria platypus, other monotremes kangaroos, other marsupials elephants, other proboscideans manatees anteaters armadillos shrews, other insectivores; bats carnivores whales, dolphins deer, other artiodactyls horses, other perissodactyls primates rodents rabbits Cenozoic Mesozoic Fig a, p. 297

58 Evolutionary Theory Evolutionary biologists try to explain how all species are related by descent from common ancestors Genetic change is the basis of evolution, but many biologists disagree about how it occurs

59 18.12 Key Concepts Macroevolutionary Patterns Patterns of genetic change that involve more than one species are called macroevolution Recurring patterns of macroevolution include exaptation, adaptive radiation, and extinction

60 Animation: Models of speciation

61 Animation: Morphological differences within a species

62 Animation: Simulation of genetic drift

63 Animation: Temporal isolation among cicadas

64 Video: Rise of the super rats

65 Video: Humpback whales

66 Video: Salamander gills