Chapter 16
The Origin of Species
“Species” Definitions:
• Pre-Darwin:
– _______________ of organisms (based on
appearance)
• Biological species concept:
– Species are groups of actually or potentially
___________________________, which are
reproductively isolated from other such
groups.
– Appearance Can Be Misleading
Appearance Can Be Misleading
• Same species?
– Cordilleran flycatcher and Pacific slope
flycatcher
– They __________
Appearance Can Be Misleading
• Same species?
– The myrtle warbler and Audubon’s warbler
used to be classified as different species
– __________ where their ranges overlap
Species
• Limitations of species definition
– _________reproducing organisms or ______
– Often _______ to observe whether members
of two different groups interbreed
Speciation
• Process by which new species form. It
depends on 2 factors:
– A. __________
– B. __________ __________
• When populations are isolated, gene flow
between them is __________
• Isolated populations subsequently _____
genetic differences large enough to
prevent interbreeding
– Differences arise by _______ (genetic drift) or
through __________ __________
Hypothetical mechanisms of speciation:
• __________ speciation
occurs when two populations
of a species become
separated by a __________
barrier
– Colonization of remote ______
by mainland organisms
– __________________ such
as volcanism, earthquakes,
continental drift, and rivers
changing course
– speciation occurs when
isolated populations diverge
__________
Allopatric Speciation
• Is believed to be the ___________ type of
speciation, especially among animals
• Two allopatric populations, the Kaibab
squirrel and Abert’s squirrel, may be
evolving into two separate species
Hypothetical mechanisms of speciation:
• __________
speciation occurs
when
– Two populations of a
species living in the
same geographical
area become _______
to different _________
– Isolated populations
__________
Sympatric Speciation
• Two sympatric populations of fruit flies
(Rhagoletis pomonella) may be
evolving into two separate species.
– One population lays its eggs in _______
fruit, while the other prefers __________
– The two populations experience very
little interbreeding
– Males and females prefer the same type
of fruit in which they developed
– Apples mature two or three weeks ____
than hawthorn fruit (flies mature and
mate at different times)
New Species
• Mechanisms of speciation and reproductive
isolation lead to _______ branches in the
__________ _____ of life, as one species
splits into two
Adaptive Radiation
• Adaptive radiation is the rise of _____
__________ over a relatively _____ period
of time
Adaptive Radiation
• Occurs when
populations of one
species invade a
variety of __________
– Cichlid fish
colonization of Lake
Malawi
– __________ in the
Galapagos Islands
Adaptive Radiation
– Tarweed plant colonization of the Hawaiian
Islands
Maintenance of Reproductive
Isolation Between Species
• __________ isolating mechanisms
(prevents the mating between 2
organisms)
– __________ isolation
– __________ isolation
– __________ isolation.
– __________ isolation
– __________ incompatibility
Premating Isolating Mechanisms
• __________ isolation occurs when populations
cannot mate because of physical barriers
– In nature, lions do not mate with tigers
• Lions live in __________ Savanna
• Tigers live in __________ lands.
Premating Isolating Mechanisms
• …Geographical isolation Kaibab and Abert
squirrels; in different areas of the Grand
Canyon. Very similar, but have they diverged?
Premating Isolating Mechanisms
• __________ isolation occurs when
species might live in the _____ area, but
use different __________ of the habitat:
– White-crowned sparrows inhabit fields and
meadows, while white-throated sparrows
inhabit __________
Premating Isolating Mechanisms
• …Ecological isolation
– Each species of fig wasp breeds in the fruits
of a particular species of fig
Premating Isolating Mechanisms
• _________ isolation occurs when species
can’t mate because they _____ at ______
__________
• In nature, Bishop pines and Monterey
pines do not interbreed
– Bishop pine pollination occurs in
summer
– Monterey pine pollination occurs in early
spring
Premating Isolating Mechanisms
• __________ isolation occurs when species
can’t mate because they have different
courtship and mating rituals
• ____ and ________
of male songbirds
are species specific
– Attract females of
the same species
– Females of other
species are
unresponsive
Premating Isolating Mechanisms
• …Behavioral isolation
• Male frogs embrace ___ female regardless
of species
– Female frogs encountering males of a
different species utter the “_______ call”
Premating Isolating Mechanisms
• Mechanical
incompatibility. In plants
or animals: Size or
________ of reproductive
organs __________ .
– e.g., snails of species
whose shells have lefthanded spirals may be
unable to successfully
copulate with snails whose
shells have right-handed
spirals
Maintenance of Reproductive
Isolation Between Species
• __________ isolating mechanisms
(prevents the production of vigorous
and fertile offspring)
– __________ incompatibility
– Hybrid __________
– Hybrid __________
Postmating Isolating Mechanisms
• __________ incompatibility occurs when
sperm from one species __________
eggs of another
– In animals, fluids of the female reproductive
tract my ________ or __________ of another
species
– In plants, ______ from one species may ____
to __________ when it lands on the stigma of
another species
Postmating Isolating Mechanisms
• Hybrid __________ occurs when hybrid
offspring ________________ to maturity
• Hybrid may _______ early in development
• Hybrid may be unable to reproduce
because it display behaviors that are
__________ of the two parental types
– Lovebird hybrids have great difficulty
learning to carry nest materials during
flight
Postmating Isolating Mechanisms
• Hybrid __________ occurs when hybrid
offspring are ______ or have reduced _____
• Horse + donkey  sterile __________
• Lion + tiger  sterile __________
• Infertility is caused by the failure of
chromosomes to _____ properly during
_______, so eggs and sperm never develop
R.M.L. Lulu born 06-19-04. Very active Bay with
black legs, mane and tail. Molly Mule Foal. Very
good conformation. Mother is dark brown/black
quarter horse mare, 15-1 hands. Sire is Knute's
Centinela Gomez Black Catalonian Mammoth Jack,
14.2 Hands. $1,650.00
Ligers
Ecological isolation: liger only in captivity
Extinction
• Extinction is the ______________
__________ ______
• At least ____% of all species that ever
existed are now extinct
• Factors that can cause extinction:
– __________ Distribution
– __________
– Competition for __________ __________
– ________ __________ (living and non-living)
Localized Distribution
• Species inhabiting extremely limited
ranges may become extinct if the area is
__________
– Devil’s Hole pupfish is found in only one
spring-fed water hole in the Nevada desert
Overspecialization
• Species that develop __________ that
favor survival in a _________ __________
are at risk of becoming extinct
– The Karner blue
butterfly feeds ___ on
the blue lupine plant
– Lupine’s habitat is
now reduced.
– Loss of the lupine will
lead to extinction of
the Karner blue
butterfly
Competition Among Species
• Species that are __________ to exploit
__________ more efficiently and
effectively than their competitors may
become extinct
• After formation of land bridge between
North and South America 2.5 million years
ago, many species in South America were
displaced and became extinct.
Habitat Destruction
• Habitat destruction is the single _______________ of
extinction
• ______ activities are the primary cause of present-day
habitat destruction
– Clearing of tropical rainforests could lead to loss of up to half
of all current species over the next ___years
The Ethiopian wolf - the most endangered
canid in the world - faces a variety of threats
due to conflict with Ethiopia's ever-expanding
human population. The EWCP works with local
herders and communities to reduce conflict
with livestock, protect wolves from hunting,
and to reduce disease transfer from, and
inbreeding with, local domestic dogs. With only
an estimated 400-500 Ethiopian wolves left in
a few isolated populations throughout the
country, research and community involvement
are crucial to the survival of this unique wolf.
Other notes on speciation
• 1. Polyploidy in plants can lead to
speciation
Case 1: Selffertilization
meiosis
fertilization
Case 2: Breeds with
normal diploid parent
Speciation by
polyploidy
meiosis
viable, diploid gametes
meiosis fails;
no viable gametes