Chapter 17 Processes of Evolution

Chapter 17 Processes of Evolution
(Sections ) 1

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

Alpheus nuttingi (Atlantic) Isthmus of Panama Figure Allopatric speciation in snapping shrimp. The Isthmus of Panama (above) cut off gene flow among populations of these aquatic shrimp when it formed 4 million years ago. Today, individuals from opposite sides of the isthmus are so similar that they might interbreed, but they are behaviorally isolated: Instead of mating when they are brought together, they snap their claws at one another aggressively. The photos on the right show two of the many closely related species that live on opposite sides of the isthmus. Alpheus millsae (Pacific) Fig , p. 272

Atlantic Ocean Mexico Pacific Ocean Figure Allopatric speciation in snapping shrimp. The Isthmus of Panama (above) cut off gene flow among populations of these aquatic shrimp when it formed 4 million years ago. Today, individuals from opposite sides of the isthmus are so similar that they might interbreed, but they are behaviorally isolated: Instead of mating when they are brought together, they snap their claws at one another aggressively. The photos on the right show two of the many closely related species that live on opposite sides of the isthmus. Isthmus of Panama Columbia Fig a, p. 272

Figure Allopatric speciation in snapping shrimp. The Isthmus of Panama (above) cut off gene flow among populations of these aquatic shrimp when it formed 4 million years ago. Today, individuals from opposite sides of the isthmus are so similar that they might interbreed, but they are behaviorally isolated: Instead of mating when they are brought together, they snap their claws at one another aggressively. The photos on the right show two of the many closely related species that live on opposite sides of the isthmus. Alpheus nuttingi (Atlantic) Fig b, p. 272

Figure Allopatric speciation in snapping shrimp. The Isthmus of Panama (above) cut off gene flow among populations of these aquatic shrimp when it formed 4 million years ago. Today, individuals from opposite sides of the isthmus are so similar that they might interbreed, but they are behaviorally isolated: Instead of mating when they are brought together, they snap their claws at one another aggressively. The photos on the right show two of the many closely related species that live on opposite sides of the isthmus. Alpheus millsae (Pacific) Fig b, p. 272

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 Figure Allopatric speciation on an archipelago. Archipelagos such as the Hawaiian Islands (right) are separated from mainland continents by thousands of miles of open ocean—a geographic barrier that pre- honeycreepers to feed on certain insects, seeds, fruits, nectar, or other foods. DNA sequence comparisons suggest that the ancestor of all Hawaiian honeycreep vents gene flow between any island colonizers and mainland populations. Further divergences occur as colonizers spread to the other islands in the chain. A few of the known species of Hawaiian honeycreepers, with some of their dietary and habitat preferences. Specialized bills and behaviors adapt the honeycreepers to feed on certain insects, seeds, fruits, nectar, or other foods. DNA sequence comparisons suggest that the ancestor of all Hawaiian honeycreepers resembled the housefinch (Carpodacus) at left.

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

Akepa (Loxops coccineus) Insects, spiders, nectar; high mountain rain forest Figure Allopatric speciation on an archipelago. Archipelagos such as the Hawaiian Islands (right) are separated from mainland continents by thousands of miles of open ocean—a geographic barrier that pre- honeycreepers to feed on certain insects, seeds, fruits, nectar, or other foods. DNA sequence comparisons suggest that the ancestor of all Hawaiian honeycreep vents gene flow between any island colonizers and mainland populations. Further divergences occur as colonizers spread to the other islands in the chain. A few of the known species of Hawaiian honeycreepers, with some of their dietary and habitat preferences. Specialized bills and behaviors adapt the honeycreepers to feed on certain insects, seeds, fruits, nectar, or other foods. DNA sequence comparisons suggest that the ancestor of all Hawaiian honeycreepers resembled the housefinch (Carpodacus) at left. Fig a, p. 273

Akekee (Loxops caeruleirostris) Insects, spiders, nectar; high mountain rain forest Figure Allopatric speciation on an archipelago. Archipelagos such as the Hawaiian Islands (right) are separated from mainland continents by thousands of miles of open ocean—a geographic barrier that pre- honeycreepers to feed on certain insects, seeds, fruits, nectar, or other foods. DNA sequence comparisons suggest that the ancestor of all Hawaiian honeycreep vents gene flow between any island colonizers and mainland populations. Further divergences occur as colonizers spread to the other islands in the chain. A few of the known species of Hawaiian honeycreepers, with some of their dietary and habitat preferences. Specialized bills and behaviors adapt the honeycreepers to feed on certain insects, seeds, fruits, nectar, or other foods. DNA sequence comparisons suggest that the ancestor of all Hawaiian honeycreepers resembled the housefinch (Carpodacus) at left. Fig b, p. 273

Nihoa finch (Telespiza ultima) Insects, buds, seeds, flowers, seabird eggs; rocky or shrubby slopes Figure Allopatric speciation on an archipelago. Archipelagos such as the Hawaiian Islands (right) are separated from mainland continents by thousands of miles of open ocean—a geographic barrier that pre- honeycreepers to feed on certain insects, seeds, fruits, nectar, or other foods. DNA sequence comparisons suggest that the ancestor of all Hawaiian honeycreep vents gene flow between any island colonizers and mainland populations. Further divergences occur as colonizers spread to the other islands in the chain. A few of the known species of Hawaiian honeycreepers, with some of their dietary and habitat preferences. Specialized bills and behaviors adapt the honeycreepers to feed on certain insects, seeds, fruits, nectar, or other foods. DNA sequence comparisons suggest that the ancestor of all Hawaiian honeycreepers resembled the housefinch (Carpodacus) at left. Fig c, p. 273

Palila Maui (Loxioides bailleui) Mamane seeds, buds, flowers, berries, insects; high mountain dry forests Figure Allopatric speciation on an archipelago. Archipelagos such as the Hawaiian Islands (right) are separated from mainland continents by thousands of miles of open ocean—a geographic barrier that pre- honeycreepers to feed on certain insects, seeds, fruits, nectar, or other foods. DNA sequence comparisons suggest that the ancestor of all Hawaiian honeycreep vents gene flow between any island colonizers and mainland populations. Further divergences occur as colonizers spread to the other islands in the chain. A few of the known species of Hawaiian honeycreepers, with some of their dietary and habitat preferences. Specialized bills and behaviors adapt the honeycreepers to feed on certain insects, seeds, fruits, nectar, or other foods. DNA sequence comparisons suggest that the ancestor of all Hawaiian honeycreepers resembled the housefinch (Carpodacus) at left. Fig d, p. 273

Maui parrotbill (Pseudonestor xanthophrys) Insect larvae, pupae, caterpillars; mountain forests, dense underbrush Figure Allopatric speciation on an archipelago. Archipelagos such as the Hawaiian Islands (right) are separated from mainland continents by thousands of miles of open ocean—a geographic barrier that pre- honeycreepers to feed on certain insects, seeds, fruits, nectar, or other foods. DNA sequence comparisons suggest that the ancestor of all Hawaiian honeycreep vents gene flow between any island colonizers and mainland populations. Further divergences occur as colonizers spread to the other islands in the chain. A few of the known species of Hawaiian honeycreepers, with some of their dietary and habitat preferences. Specialized bills and behaviors adapt the honeycreepers to feed on certain insects, seeds, fruits, nectar, or other foods. DNA sequence comparisons suggest that the ancestor of all Hawaiian honeycreepers resembled the housefinch (Carpodacus) at left. Fig e, p. 273

Apapane (Himatione sanguinea) Nectar, caterpillars and other insects, spiders; high mountain forests Figure Allopatric speciation on an archipelago. Archipelagos such as the Hawaiian Islands (right) are separated from mainland continents by thousands of miles of open ocean—a geographic barrier that pre- honeycreepers to feed on certain insects, seeds, fruits, nectar, or other foods. DNA sequence comparisons suggest that the ancestor of all Hawaiian honeycreep vents gene flow between any island colonizers and mainland populations. Further divergences occur as colonizers spread to the other islands in the chain. A few of the known species of Hawaiian honeycreepers, with some of their dietary and habitat preferences. Specialized bills and behaviors adapt the honeycreepers to feed on certain insects, seeds, fruits, nectar, or other foods. DNA sequence comparisons suggest that the ancestor of all Hawaiian honeycreepers resembled the housefinch (Carpodacus) at left. Fig f, p. 273

Poouli (Melamprosops phaeosoma) Tree snails, insects in understory; last one died in 2004 Figure Allopatric speciation on an archipelago. Archipelagos such as the Hawaiian Islands (right) are separated from mainland continents by thousands of miles of open ocean—a geographic barrier that pre- honeycreepers to feed on certain insects, seeds, fruits, nectar, or other foods. DNA sequence comparisons suggest that the ancestor of all Hawaiian honeycreep vents gene flow between any island colonizers and mainland populations. Further divergences occur as colonizers spread to the other islands in the chain. A few of the known species of Hawaiian honeycreepers, with some of their dietary and habitat preferences. Specialized bills and behaviors adapt the honeycreepers to feed on certain insects, seeds, fruits, nectar, or other foods. DNA sequence comparisons suggest that the ancestor of all Hawaiian honeycreepers resembled the housefinch (Carpodacus) at left. Fig g, p. 273

Maui Alauahio (Paroreomyza montana) Bark or leaf insects, high mountain rain forest Figure Allopatric speciation on an archipelago. Archipelagos such as the Hawaiian Islands (right) are separated from mainland continents by thousands of miles of open ocean—a geographic barrier that pre- honeycreepers to feed on certain insects, seeds, fruits, nectar, or other foods. DNA sequence comparisons suggest that the ancestor of all Hawaiian honeycreep vents gene flow between any island colonizers and mainland populations. Further divergences occur as colonizers spread to the other islands in the chain. A few of the known species of Hawaiian honeycreepers, with some of their dietary and habitat preferences. Specialized bills and behaviors adapt the honeycreepers to feed on certain insects, seeds, fruits, nectar, or other foods. DNA sequence comparisons suggest that the ancestor of all Hawaiian honeycreepers resembled the housefinch (Carpodacus) at left. Fig h, p. 273

Kauai Amakihi (Hemignathus kauaiensis) Bark-picker; insects, spiders, nectar; high mountain rain forest Figure Allopatric speciation on an archipelago. Archipelagos such as the Hawaiian Islands (right) are separated from mainland continents by thousands of miles of open ocean—a geographic barrier that pre- honeycreepers to feed on certain insects, seeds, fruits, nectar, or other foods. DNA sequence comparisons suggest that the ancestor of all Hawaiian honeycreep vents gene flow between any island colonizers and mainland populations. Further divergences occur as colonizers spread to the other islands in the chain. A few of the known species of Hawaiian honeycreepers, with some of their dietary and habitat preferences. Specialized bills and behaviors adapt the honeycreepers to feed on certain insects, seeds, fruits, nectar, or other foods. DNA sequence comparisons suggest that the ancestor of all Hawaiian honeycreepers resembled the housefinch (Carpodacus) at left. Fig i, p. 273

Akiapolaau (Hemignathus munroi) Probes, digs insects from big trees; high mountain rain forest Figure Allopatric speciation on an archipelago. Archipelagos such as the Hawaiian Islands (right) are separated from mainland continents by thousands of miles of open ocean—a geographic barrier that pre- honeycreepers to feed on certain insects, seeds, fruits, nectar, or other foods. DNA sequence comparisons suggest that the ancestor of all Hawaiian honeycreep vents gene flow between any island colonizers and mainland populations. Further divergences occur as colonizers spread to the other islands in the chain. A few of the known species of Hawaiian honeycreepers, with some of their dietary and habitat preferences. Specialized bills and behaviors adapt the honeycreepers to feed on certain insects, seeds, fruits, nectar, or other foods. DNA sequence comparisons suggest that the ancestor of all Hawaiian honeycreepers resembled the housefinch (Carpodacus) at left. Fig j, p. 273

Akohekohe (Palmeria dolei) Mostly nectar from flowering trees, some insects, pollen; high mountain rain forest Figure Allopatric speciation on an archipelago. Archipelagos such as the Hawaiian Islands (right) are separated from mainland continents by thousands of miles of open ocean—a geographic barrier that pre- honeycreepers to feed on certain insects, seeds, fruits, nectar, or other foods. DNA sequence comparisons suggest that the ancestor of all Hawaiian honeycreep vents gene flow between any island colonizers and mainland populations. Further divergences occur as colonizers spread to the other islands in the chain. A few of the known species of Hawaiian honeycreepers, with some of their dietary and habitat preferences. Specialized bills and behaviors adapt the honeycreepers to feed on certain insects, seeds, fruits, nectar, or other foods. DNA sequence comparisons suggest that the ancestor of all Hawaiian honeycreepers resembled the housefinch (Carpodacus) at left. Fig k, p. 273

Iiwi (Vestiaria coccinea) Mostly nectar (ohia flowers, some nectar; lobelias, mints), some insects; high mountain rain forest Figure Allopatric speciation on an archipelago. Archipelagos such as the Hawaiian Islands (right) are separated from mainland continents by thousands of miles of open ocean—a geographic barrier that pre- honeycreepers to feed on certain insects, seeds, fruits, nectar, or other foods. DNA sequence comparisons suggest that the ancestor of all Hawaiian honeycreep vents gene flow between any island colonizers and mainland populations. Further divergences occur as colonizers spread to the other islands in the chain. A few of the known species of Hawaiian honeycreepers, with some of their dietary and habitat preferences. Specialized bills and behaviors adapt the honeycreepers to feed on certain insects, seeds, fruits, nectar, or other foods. DNA sequence comparisons suggest that the ancestor of all Hawaiian honeycreepers resembled the housefinch (Carpodacus) at left. Fig l, p. 273

ANIMATION: Allopatric speciation on an archipelago
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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

Sympatric Speciation in Wheat
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). B About 8,000 years ago, the chromo-some number of an AB hybrid plant spontaneously doubled. The resulting species, emmer, is tetraploid: it has two sets of 14 chromosomes (28 AABB). 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). spontaneous chromosome doubling Triticum mono-coccum (einkorn) T. aestivum (common bread wheat) Unknown species of Triticum T. turgidum (emmer) T. tauschii (goatgrass) Figure Sympatric speciation in wheat. 14 AA X 14 BB 14 AB 28 AABB X 14 DD 42 AABBDD Fig , p. 274

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
Figure Red fish, blue fish: Males of four closely related species of cichlid native to Lake Victoria, Africa. Hundreds of cichlids speciated in sympatry in this lake. Mutations in genes that affect females’ perception of the color of ambient light in deeper or shallower regions of the lake also affect their choice of mates. Female cichlids prefer to mate with brightly colored males of their own species.

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
Figure An example of stasis. Top, 320-million-year-old coelacanth fossil found in Montana. Bottom, a live coelacanth (Latimeria chalumnae) caught off the waters of Sulawesi in The coelacanth lineage has changed very little over evolutionary time.

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) Figure An example of adaptive radiation. This evolutionary tree diagram shows how one ancestral species gave rise to the Hawaiian honeycreepers. Of many hundreds of honeycreeper species, only 41 are represented here. Those in orange type are now 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 Figure An example of coevolved species. A The large blue butterfly (Maculinea arion) parasitizes a species of red ant, Myrmica sabuleti. B To an ant, a honey-exuding, hunched-up Maculinea arion caterpillar appears to be an ant larva. This deceived ant is preparing to carry the caterpillar back to its nest, where the caterpillar will eat ant larvae for the next 10 months 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

Cladograms earthworm earthworm multicellular tuna tuna
multicellular with a backbone lizard lizard multicellular with a backbone and legs mouse multicellular with a backbone, legs, and fur or hair mouse A human human Figure Cladograms. A This example is based on the set of characters chosen in Table B We can visualize the same cladogram as ‘sets within sets’ of characters. B Fig , p. 278

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 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 Figure Three honeycreeper species: going, going, and gone. A The palila has an adaptation that allows it to feed on mamane seeds, which are toxic to most other birds. The one remaining palila population is declining because mamane plants are being trampled by cows and gnawed to death by goats and sheep. Only about 2,640 palila remained in B Avian malaria carried by mosquitoes to higher altitudes is decimating the last population of the akekee. Between 2000 and 2007, the number of akekee plummeted from 7,839 birds to 3,536. C This male poouli—rare, old, and missing an eye—died in 2004 from avian malaria. There were two other poouli alive at the time, but neither has been seen since then.

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

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