Chapter 17 Processes of Evolution (Sections 17.11 - 17.14)

www.cengage.com/biology/starr

Albia Dugger • Miami Dade College

Cecie StarrChristine EversLisa Starr

Chapter 17Processes of Evolution

(Sections 17.11 - 17.14)

http://www.cengage.com/biology/Starr/Concepts8e

http://www.cengage.com/biology/Starr/Concepts8e

17.11 Allopatric Speciation

• In allopatric speciation, a geographic barrier arises and ends 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

Barriers to Reproduction

• Whether a geographic barrier can block gene flow depends on whether and how an organism travels (e.g. by swimming, walking, or flying), and how it reproduces (e.g. by internal fertilization or by pollen dispersal)

• Example:• When the Isthmus of Panama formed, it cut off gene flow

among populations of aquatic organisms in the Pacific and Atlantic oceans

Allopatric Speciation in Snapping Shrimp

Fig. 17.20, p. 272

Isthmus of Panama

Alpheus millsae (Pacific)

Alpheus nuttingi (Atlantic)


Fig. 17.20a, p. 272

Isthmus of Panama

Columbia

Atlantic Ocean

Mexico

Pacific Ocean


Fig. 17.20b, p. 272

Alpheus nuttingi (Atlantic)


Fig. 17.20b, p. 272

Alpheus millsae (Pacific)


Speciation in Archipelagos

• Archipelagos are isolated island chains formed by volcanoes, such as the Hawaiian and Galápagos Islands

• Archipelagos were populated by a few individuals of mainland species whose descendants diverged over time

• Selection pressures within and between the islands can foster even more divergences

The Hawaiian Islands

Hawaiian Honeycreepers

• The first birds to colonize the Hawaiian Islands found a near absence of competitors and predators and an abundance of rich and vacant habitats, which encouraged rapid speciation

• The many species of honeycreepers, unique to the Hawaiian Islands, have specialized bills and behaviors adapted to feed on certain insects, seeds, fruits, nectar, or other foods

Honeycreeper Diversity

Fig. 17.21a, p. 273

Akepa (Loxops coccineus)

Insects, spiders, nectar; high mountain rain forest


Fig. 17.21b, p. 273

Akekee (Loxops caeruleirostris)

Insects, spiders, nectar; high mountain rain forest


Fig. 17.21c, p. 273

Nihoa finch (Telespiza ultima)

Insects, buds, seeds, flowers, seabird eggs; rocky or shrubby slopes


Fig. 17.21d, p. 273

Palila Maui (Loxioides bailleui)

Mamane seeds, buds, flowers, berries, insects; high mountain dry forests


Fig. 17.21e, p. 273

Maui parrotbill (Pseudonestor xanthophrys)

Insect larvae, pupae, caterpillars; mountain forests, dense underbrush


Fig. 17.21f, p. 273

Apapane(Himatione sanguinea)

Nectar, caterpillars and other insects, spiders; high mountain forests


Fig. 17.21g, p. 273

Poouli (Melamprosops phaeosoma)

Tree snails, insects in understory; last one died in 2004


Fig. 17.21h, p. 273

Maui Alauahio(Paroreomyza montana)

Bark or leaf insects, high mountain rain forest


Fig. 17.21i, p. 273

Kauai Amakihi (Hemignathus kauaiensis)

Bark-picker; insects, spiders, nectar; high mountain rain forest


Fig. 17.21j, p. 273

Akiapolaau(Hemignathus munroi)

Probes, digs insects from big trees; high mountain rain forest


Fig. 17.21k, p. 273

Akohekohe (Palmeria dolei)

Mostly nectar from flowering trees, some insects, pollen; high mountain rain forest


Fig. 17.21l, p. 273

Iiwi (Vestiaria coccinea)

Mostly nectar (ohia flowers, some nectar; lobelias, mints), some insects; high mountain rain forest


ANIMATION: Allopatric speciation on an archipelago

To play movie you must be in Slide Show ModePC Users: Please wait for content to load, then click to play

Mac Users: CLICK HERE

ANIMATION: Models of speciation



17.12 Sympatric and Parapatric Speciation

• Populations sometimes speciate even without a physical barrier that bars gene flow between them

• In sympatric speciation, populations in physical contact speciate

• With parapatric speciation, populations in contact along a common border speciate

Sympatric Speciation

• Sympatric speciation can occur instantly with a change in chromosome number – many plants are polyploid (e.g. wheat)

• Sympatric speciation can also occur with no change in chromosome number (e.g. mechanically isolated sage plants)

• sympatric speciation • Pattern in which populations inhabiting the same

geographic region speciate in the absence of a physical barrier between them

Sympatric Speciation in Wheat

Fig. 17.22, p. 274

C Emmer probably hybridized with a wild goatgrass having a diploid chromosome number of 14 (two sets of 7 DD). The resulting common bread wheat has six sets of 7 chromosomes (42 AABBDD).

B About 8,000 years ago, the chromo-some number of an AB hybrid plant spontaneouslydoubled. The resulting species, emmer, is tetraploid: it has two sets of 14 chromosomes (28 AABB).

A Einkorn has a diploid chromosome number of 14 (two sets of 7, shown here as 14 AA). Wild einkorn probably hybridized with another wild species having the same chromosome number (14 BB) about 11,000 years ago. The resulting hybrid was diploid (14 AB).

Triticum mono-

coccum (einkorn)

Unknown species of Triticum

spontaneous chromosome doubling T. turgidum

(emmer)T. tauschii (goatgrass)

T. aestivum (common

bread wheat)

42 AABBDD28 AABB14 BB14 AA 14 DD X14 ABX

Sympatric Speciation in Wheat

Examples of Sympatric Speciation

• Lake Victoria cichlids (sexual selection)• In the same lake, female cichlids of different species

visually select and mate with brightly colored males of their own species

• Warblers around the Tibetan plateau (behavioral isolation)• Two populations overlap in range, but don’t interbreed

because they don’t recognize one another’s songs

Male Cichlids of Lake Victoria

Parapatric Speciation

• Parapatric speciation may occur when one population extends across a broad region with diverse habitats

• Example: Two species of velvet walking worm with overlapping habitats in Tasmania: Where they interbreed, their hybrids are sterile

• parapatric speciation • Speciation model in which different selection pressures

lead to divergences within a single population

Comparing Speciation Models

Key Concepts

• How Species Arise• Speciation varies in its details, but it always involves the

end of gene flow between populations• Microevolutionary events that occur independently lead to

genetic divergences, which are reinforced by reproductive isolation

ANIMATION: Sympatric Speciation in Wheat



17.13 Macroevolution

• A central theme of macroevolution is that major evolutionary novelties often stem from the adaptation of an existing structure for a completely different purpose (exaptation)

• exaptation • Adaptation of an existing structure for a completely

different purpose; a major evolutionary novelty

Patterns of Macroevolution

• Macroevolution includes patterns of evolution above the species level, such as one species giving rise to multiple species, origin of major groups, and major extinction events

• Four patterns of macroevolution:• Stasis• Adaptive radiation• Coevolution• Extinction

Stasis

• With the simplest macroevolutionary pattern, stasis, a lineage persists for millions of years with little or no change

• Example: Coelacanths

• stasis • Evolutionary pattern in which a lineage persists with little

or no change over evolutionary time

Coelacanth: Fossil and Living

Mass Extinctions

• More than 99% of all species that ever lived are now extinct

• There have been more than twenty mass extinctions, which are simultaneous losses of many lineages, including five catastrophic events in which the majority of species on Earth disappeared

• extinct • Refers to a species that has been permanently lost

Adaptive Radiation

• In adaptive radiation, a lineage rapidly diversifies into several new species

• Adaptive radiation can occur after individuals colonize a new environment that has a variety of different habitats with few or no competitors (e.g. Hawaiian honeycreepers)

• adaptive radiation • A burst of genetic divergences from a lineage gives rise to

many new species

An Example of Adaptive Radiation

• This evolutionary tree diagram shows how one ancestral species gave rise to the Hawaiian honeycreepers

• Only 41 of many hundreds of species are represented here (orange are extinct)

Adaptive Radiation (cont.)

• Adaptive radiations also occur after geologic or climatic events eliminate some species from a habitat

• Example: Mammals were able to undergo an adaptive radiation after the dinosaurs disappeared

Adaptive Radiation (cont.)

• A key innovation can result in an adaptive radiation, or rapid diversification into new species

• Example: evolution of lungs opened the way for an adaptive radiation of vertebrates on land

• key innovation • An evolutionary adaptation that gives its bearer the

opportunity to exploit a particular environment more efficiently or in a new way

Coevolution

• In coevolution, close ecological interactions between two species cause them to evolve jointly

• Over evolutionary time, two species may become so interdependent that they can no longer survive without one another (e.g. the large blue butterfly (Maculinea arion) and red ant (Myrmica sabuleti))

• coevolution • Joint evolution of two closely interacting species• Each species is a selective agent for traits of the other• Each adapts to changes in the other

Coevolved Species

• The ant eats honey exuded by the butterfly larva and carries it to its nest

• The caterpillar lives in the ant nest and eats ant larvae until it pupates

Evolutionary Theory

• Many biologists disagree about how macroevolution occurs

• Dramatic jumps in morphology may be the result of mutations in homeotic or other regulatory genes

• Macroevolution may be an accumulation of many microevolutionary events, or it may be an entirely different process

Key Concepts

• Macroevolution• Patterns of genetic change that involve more than one

species are called macroevolution• Recurring patterns of macroevolution include the origin of

major groups, one species giving rise to many, and mass extinction

ANIMATION: Adaptation to What?



ANIMATION: Animal evolution in Phyla



ANIMATION: Evolution of Horses



17.14 Phylogeny

• Instead of trying to divide the diversity of living organisms into a series of taxonomic ranks, most biologists are now focusing on evolutionary connections

• Cladistics allows us to reconstruct evolutionary history (phylogeny) by grouping species on the basis of their shared characters

Key Terms

• phylogeny• Evolutionary history of a species or group of species

• cladistics • Method of determining evolutionary relationships by

grouping species into clades based on shared characters

• character • Quantifiable, heritable characteristic—any physical,

behavioral, physiological, or molecular trait of a species

Examples of Characters

Ranking Versus Grouping

• The result of a cladistic analysis is a cladogram, a type of evolutionary tree used to visualize evolutionary patterns

• Each line represents a lineage, which may branch into two sister groups at a node, which represents a shared ancestor

• Every branch ends with a clade, a species or group based on a set of shares characters

• Ideally, each clade is a monophyletic group that comprises an ancestor and all of its descendants

Key Terms

• evolutionary tree • Type of diagram that summarizes evolutionary

relationships among a group of species

• cladogram• Evolutionary tree that shows a network of evolutionary

relationships among clades

• clade • A species or group of species that share a set of

characters

Key Terms

• sister groups • The two lineages that emerge from a node on a cladogram

• monophyletic group• An ancestor and all of its descendants

Cladograms

Fig. 17.27, p. 278

earthworm

multicellular with a backbone, legs, and fur or hair

multicellular with a backbone and legs

multicellular with a backbone

multicellular

A human

mouse

lizard

tuna

B

earthworm

human

mouse

lizard

tuna

Cladograms

ANIMATION: Interpreting a cladogram



How We Use Evolutionary Biology

• Hawaiian honeycreepers illustrate how evolution works:• Isolation that spurred honeycreepers’ adaptive radiations

also ensured they had no built-in defenses against predators or diseases from the mainland

• Specializations became hindrances when habitats suddenly changed or disappeared

• At least 43 species of honeycreeper that thrived on the islands before humans arrived were extinct by 1778 -- today, 32 of the remaining 71 species are endangered, and 26 are extinct

Going, Going, and Gone

• Destruction of food sources and avian malaria decimated the palila and akekee

• The poouli is probably now extinct

Key Concepts

• Cladistics• Evolutionary tree diagrams are based on the premise that

all species interconnect through shared ancestors• Grouping species by shared ancestry better reflects

evolutionary history than do traditional ranking systems

Rise of the Super Rats (revisited)

• The allele that makes rats resistant to warfarin is adaptive when warfarin is present, and maladaptive when it is not

• Periodic exposure to warfarin maintains a balanced polymorphism of the resistance gene in rat populations

Chapter 17 Processes of Evolution (Sections 17.11 - 17.14)

Documents

Transcript of Chapter 17 Processes of Evolution (Sections 17.11 - 17.14)