What does “species” mean to
you?

Consider:

2 tree frogs are identical, are they the same
species?
What does “species” mean to
you?

Consider:

2 dogs are not identical but can mate and
reproduce, are they the same species?
What does “species” mean to
you?
Hyla versicolor
Hyla chrysoscelis
Although they look similar, these are 2
different species of tree frogs.
 They can be differentiated by their mating
calls.

What does “species” mean to
you?
All domestic dogs belong
to the species:

Canis lupus familiaris

(Over history, breeders have used artificial
selection to create the different breeds of
dogs we have today.)
Reproductive
Isolating
Mechanisms
What is a species?
 Members
of groups or
populations that can
reproduce with each other
and produce fertile offspring
(that can reproduce)
Differentiating species

Use reproductive isolating
mechanisms to distinguish between
species:

Behavioural, structural, or biochemical
traits that prevent individuals from
reproducing successfully together
Reproductive Barriers
Between Species

1.
There are 2 types:
Prezygotic Barriers

2.
prevent species from mating and
fertilization
Postzygotic Barriers

prevent maturation and
reproduction of offspring (hybrids)
1. Prezygotic Barriers
a) Behavioural isolation

Behavioral
isolation


distinct mating rituals isolate
different species
Ex: Blue-footed booby vs. redfooted booby
•
•
Blue-footed booby shows feet during mating dance
Red-footed booby squawks and displays throat
1. Prezygotic Barriers


Behavioral
isolation
Habitat
isolation
b) Habitat (ecological) isolation

species in separate habitats or niches
do not encounter one another to
reproduce


Ex: Marmot (type of squirrel)
Different species of marmot occupy
different mountainous regions

Hoary marmot (NW North
America)

Vancouver Island marmot
1. Prezygotic Barriers



Behavioral
isolation
Habitat
isolation
Temporal
isolation
c) Temporal isolation


species are compatible, but their
reproductive cycles occur at different
times
Ex: Day-blooming cactus vs nightblooming cactus
1. Prezygotic Barriers




Behavioral
isolation
Habitat
isolation
Temporal
isolation
Mechanical
isolation
d) Mechanical isolation


structural differences prevent copulation
between similar species
Ex: Shells of different snail species
spiral in different directions, genitals do
not align
1. Prezygotic Barriers





Behavioral
isolation
Habitat
isolation
Temporal
isolation
Mechanical
isolation
Gametic
isolation
e) Gametic isolation



prevents fertilization at molecular level
gametes have markers that do not
recognize each other
Ex: red and purple sea urchin gametes
are unable to bind
2. Postzygotic Barriers

Hybrid
inviability
a) Hybrid inviability

after fertilization, the zygote/embryo fails
to develop properly
does not develop to birth
due to genetic incompatibility

Ex: Sheep-goat zygotes do not survive


2. Postzygotic Barriers


Hybrid
inviability
Hybrid
sterility
b) Hybrid sterility




offspring (hybrid) of 2 species is unable
to reproduce
Ex: Mule, etc.
Ex: Wholphin (whale + dolphin)
Ex: Loganberry (raspberry + blackberry)
2. Postzygotic Barriers



Hybrid
inviability
Hybrid
sterility
Hybrid
breakdown
c) Hybrid breakdown




1st generation hybrids are fertile, but
their offspring are weak or sterile
Ex: Beefalo (cow + bison), fertile
Ex: Grolar bear, rare offspring reported
Ex: Liger can reproduce with tigers and
lions
Beefalo (cow + bison)
Grolar bear (grizzly + polar bear)
REVIEW
PREZYGOTIC BARRIERS
TYPE
MATCH THE DESCRIPTION WITH THE TYPE
a) Behavioral
isolation
1) Different irises bloom in different seasons (some in spring, some
in summer), this prevents them from mating.
C
b) Habitat
isolation
2) Pollen tubes in plants prevent male gametes from surviving
E
inside the female (they are not recognized).
c) Temporal
isolation
3) The northwest garter snake prefers open areas (meadows), and
the common garter snake is found near water, this prevents them
B
from mating.
d) Mechanical
isolation
4) The eastern and western meadowlark are very similar but are
different species since they have different songs. A
e) Gametic
isolation
5) Different flower structures prevent them from being pollinated by
certain bees.
D
REVIEW
POSTZYGOTIC BARRIERS
TYPE
MATCH THE DESCRIPTION WITH THE TYPE
a) Hybrid
inviability
1) The “cama” (camel + llama) can reproduce, but their offspring are
unknown to be successful or fit.
C
b) Hybrid
sterility
2) Rumours say that there have been attempts to create a
“humanzee” (human + chimp), but none have ever survived.
A
c) Hybrid
breakdown
3) When 2 different species successfully mate, they produce strong
and viable offspring that are unable to reproduce.
B