Download Part 3 - glenbrook s hs

• Species - a population(s) whose
members have the potential to
interbreed with one another in
nature to produce fertile offspring,
and cannot with members of other
species.
• Ex: (Left) These birds look
similar, but cannot interbreed with
one another. Q: Are they two
different species?
• Yes.
• Ex: Breeds of dogs look different
from one another, but all can
interbreed. Q: Are they all
different species?
• No. They are all the same species.
• Ex: These humans may live in
different geographical areas,
and may never get together.
But if they did, could they
interbreed? Are they the same
species?
• Yes, all humans belong to the
same species.
• Q: Are humans and
chimpanzees the same species?
• A: No
• Q: What about dogs and
wolves?
• A: No.
Q: What prevents two species from reproducing with each other?
A: Reproductive Barriers!
Courtship rituals of Blue-footed
boobies in Galapagos Islands.
Male does “high-step,”showing
bright blue feet.
• 2 types of Reproductive Barriers:
• I. Pre-zygotic barriers - impedes
mating or hinders fertilization of eggs.
•
A. Temporal isolation - time based.
Ex: Western spotted skunks breed in the
fall, but eastern species breed in late
winter.
•
B. Habitat isolation - spatially
segregated. Ex: one species of garter
snake lives in water, and a closely
related species lives on land.
•
C. Behavioral isolation - courtship
rituals. Ex: in bird species, courtship is
so elaborate that individuals are unlikely
to mistake a bird of a different species as
one of their kind.
•
D. Mechanical isolation male and female sex organs
of different species are
anatomically incompatible.
Ex: 2 insects’ copulatory
organs may not fit together
correctly; no sperm is
transferred.
•
E. Gametic isolation individuals may copulate,
but their gametes are
incompatible and
fertilization does not occur.
Ex: mammal sperm may not
survive in female of a
different species.
II. Post-zygotic barriers - if mating actually occurs between different species
and a zygote is formed, these mechanisms affect the hybrid offspring. (baby)
A. Hybrid inviability - the hybrid offspring die before reaching reproductive
maturity. Ex: certain frogs
B. Hybrid sterility - the hybrid offspring may become vigorous adults,
but are infertile. Ex: see below
Horse
+
Donkey
=
Mule
(but is sterile)