How Biological Diversity Evolves © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Postzygotic barriers •Mechanisms that operates should interspecies mating

Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Lectures by Chris C. Romero

PowerPoint® Lectures for

Essential Biology, Third Edition

– Neil Campbell, Jane Reece, and Eric Simon

Essential Biology with Physiology, Second Edition

– Neil Campbell, Jane Reece, and Eric Simon

CHAPTER 14

How Biological Diversity

Evolves





MACROEVOLUTION AND THE DIVERSITY OF LIFE

• Macroevolution

• Evolutionary Theory

• Generates biological diversity (Origin of new

species)


WHAT IS A SPECIES?

•The biological species concept defines a species

as a population or group of populations whose

members have the potential to interbreed with

one another in nature to produce fertile offspring.


•Speciation

Is the formation of new species; occurs when one or

more new species branch from a parent species,

which may continue to exist.


• Nonbranching

evolution

• Evolution that can

transform a population

significantly but does

not create a new

species.


Branching evolution splits a lineage into

two or more species, thereby increasing

the total number of species. New

formations are called speciation.


REPRODUCTIVE BARRIERS BETWEEN SPECIES

•Prezygotic barriers prevent mating between species.

•Postzygotic barriers are mechanisms that operate

should interspecies occur and form hybrid zygotes.

•Geographic ranges overlap yet they maintain a

species boundary

Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin CummingsFigure 14.4

Reproductive Barriers

Gene pools:

• Prezygotic

• Postzygotic

(Depends when they

block interbreeding -

before or after

formation of zygotes)


Prezygotic barriers include:

• Temporal isolation - species breed in different seasons

• Habitat isolation - species live in same region, different habitats

• Behavioral isolation - recognizable traits for reproduction

Albatross, Giraffe, and Blue-Footed Boobies

Courtship Ritual

• Mechanical isolation - male/female sex organs anatomically

incompatible

• Gametic isolation - copulation but incompatible gametes; no

reproduction



Behavioral isolation

• Traits that enable individuals to

recognize potential mates, such as

odor, coloration, or courtship ritual,

can also function as reproductive

barriers.

• In many bird species, for example,

courtship behavior is so elaborate that

individuals are unlikely to mistake a

bird of a different species as one of

their kind.

Ex: Courtship ritual - These blue-footed boobies, inhabitants of

the Galápagos Islands, will mate only after a specific ritual of

courtship displays. Part of the “script” calls for the male to high-

step, a dance that advertises the bright blue feet characteristic of

the species.



Postzygotic barriers

• Mechanisms that operates should interspecies mating actually

occur and form hybrid zygotes.

• Hybrid Inviability - offspring die before reaching reproductive

maturity

• Hybrid Sterility - offspring fail to develop normally because of

genetic incompatibilities between the two species or infertile

• Hybrid Breakdown - first generation hybrids are viable and

fertile, when these hybrids mate with one another or with either

parent species, the offspring is sterile and less likely to survive

Ex: Hybrid sterility - Horses and donkeys remain separate species because their hybrid

offspring, mules, are sterile.



MECHANISMS OF SPECIATION

•A key event in the potential origin of a species occurs

when a population is somehow severed from other

populations of the parent species.


• The two modes of speciation are

• Sympatric speciation

• Process where new species evolve from a

single ancestral species while in the same

region.

• Allopatric speciation (geographic speciation)

• Occurs when biological population of the

same species get isolated from each other

preventing interchange.



ALLOPATRIC SPECIATION

Geologic processes

Continuous action, series in a definite manner

affecting a specific region. Can be physical or human

caused

Examples include:

Grand Canyon

Galápagos Islands Overview



• (example in next slide)

• In the both example there is an allopatric scenario

but then the top becomes different because it

doesn‟t go though speciation but creates

interbreed species.

• In the bottom example there is speciation which in

time would not create interbreed species



SYMPATRIC SPECIATION

When a species is developed or created

without any natural/physical barriers, but still

within the same population and area

Examples include most shrubs, trees and

fungi, and some insects

E.G. -A fruit fly may lay eggs on a mango, but

another variation of fruit fly may lay eggs in

oranges causing behavioral differences down

the line


Classifying the Diversity of Life

• Systematics

The study of the diversity and relationships of

organisms, both past and present

Taxonomy

The identification, naming and classification of

species


SOME BASICS OF TAXONOMY

•Carolus Linnaeus

A Swedish Physician and Botanist. Her system has

two main characteristics, a two-part name for each

species and a hierarchical classification of species

into broader and broader groups of organisms.


NAMING SPECIES

This system assigns each species a two part

latinized name, or binomial. The first part of the

binomial is the genus (plural, general) to which

species belong. The second part of a binomial refers

to one particular species within the genus.


HIERARCHICAL CLASSIFICATION

1st step of hierarchical classification is built into the

binomial. We group the species that are closely

related into the same genus. Hierarchical

Classification also puts species into broader

categories of classification; family into orders, orders

into classes, classes into phyla, and phyla into

kingdoms and kingdoms into domains.


Hierarchical Classification

Kingdom:

Animalia

Plantae

Fungi

Protista

Archaea

Bacteria

Domain Highest/ largest

classification

Eukarya

Kingdom Kingdom is put into

Domain

Animalia

Phylum Phylum is put into

kingdom

Chordata

Class Class is put into phylum Mammalia

Order Order is put into class Carnivora

Family Family is put into order Felidae

Genus Genus is put into family Felis

Species Name of species Felis catus

Domain:

Bacteria

Archaea

Eukarya



CLASSIFICATION AND PHYLOGENY

Phylogeny: the evolutionary history of a species.

How an organism is named and classified should

reflect its place within the evolutionary trees of life

The final product takes place on the branching

pattern of a phytogenetic tree.



SORTING HOMOLOGY FROM ANALOGY

•Homologous structures

• Homologous structures is a source of information about

phylogenetic relationships. Homologous structures may

look different and function very differently in different

species, but they exhibit fundamental similarities

because they evolved from the same structure that

existed in a common ancestor. The greater the number

of homologous structures between two species, the more

closely the species are related.

• An example is, the whale limb is adapted for steering in

the water; the bat wing is adapted for flight. There are

many basic similarities in the bones supporting these

two structures.


• Convergent evolution: Species from different

evolutionary branches may have certain

structures that are superficially similar if natural

selection has shaped analogous adaptations

• Analogy: similarity due to convergence


MOLECULAR BIOLOGY AS A TOOL IN SYSTEMATICS

•Molecular systematics

• Comparing the genes and proteins of organisms to

find their evolutionary relationships. The more

recently two species have branched from a similar

ancestor, the more similar their DNA and amino

acid sequences will be.

• Molecular systematics provides a new way to test

hypotheses about the phylogeny of species


This slide shows an example of molecular systematics. The strongest support for

any such hypothesis is agreement between molecular data and other means of

tracing phylogeny, such as evaluating anatomical homology and analyzing the

fossil record. Some fossils are preserved in a way that it is possible to extract DNA

fragments for comparison with modern organisms


•Scientific search for „Clades‟

–Consists of ancestral

species and all of its

descendants; a distinctive

branch in the tree of life.

•Derived from Greek word

“Branch”

•Focuses on evolutionary

relationships between

organisms rather than

Taxonomic

Cladistics


The Cladistic Revolution

• Cladistics: A scientific search for clades or specific

branches on the tree of life, with ancestrial species

and all their descendants. This search involves

finding homologies, which connect species into

smaller groups.


-This is an example of

cladistics. -In the picture the 3

mammals are compared to

the turtle.

-The primitive and derived

characters are separated,

with the primitive characters

being those contained by all

animals because of common

ancestry and derived

characters being those

developed through evolution.

-The chart shows each point

which changes along the way

to evolution, creating new

species.


• Cladistics is the process of hypothesizing

relationships (branches) between species

• Members share common ancestors

• Can classify species into a specific genus

• All organisms can be connected to one tree, but

they are separated into


All forms of genus share one common ancestor from eons ago, but many species

have developed new traits that can put them in these different genera ranging from

fish or mammals


Genera can be classified by specific traits that they have, like jaws or thumbs. For example,

a shark and a dolphin may look similar in shape (pectoral and dorsal fins, tails) but they also

have defining characteristics, like a sharks cartilage and a dolphin’s blowhole.

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How Biological Diversity Evolves © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Postzygotic barriers •Mechanisms that operates should interspecies mating