Transcript Chapter 15 – The Origin of Species

Chapter 14 –
The Origin of Species
Honors Biology
Mr. Martino
Introduction
• 1960’s studies of sexual
repro habits showed
Western and Eastern
spotted skunks are two
separate species
Western Spotted Skunk
• No opportunity for gene
flow between populations
• Mating occurs at different
times of year
Eastern Spotted Skunk
14.1 What is a species?
• Taxonomy: naming and
classifying organisms
• Carolus Linnaeus developed
binomial nomenclature (two
name system)
• Phenotype alone is not
enough to classify organisms
• Biological species:
population or group of
organisms which have
potential to interbreed and
produce fertile offspring
• Failure of sexual
reproduction prevents
gene flow
• Sometimes different
populations of a species may
look different…but still
interbreed….so they are
technically still the same
species…..
Ring Salamander – Ensatina eschscholtzii
Happyface Spiders – Theridion grallator
14.2
Reproductive
Barriers
• Reproductive Barrier:
biological feature that
prevents populations of
closely related individuals
from interbreeding
• 2 types:
• Prezygotic
• Postzygotic
Prezygotic Barriers
• Prevent mating or
fertilization
• 5 types of isolation:
• 1. Temporal: breed at
different times
−Ex. Spotted skunks
• 2. Habitat: live in
same area, but not
same types of places
−Ex. Garter snake –
water/land
Temporal Isolation of Frogs
• Behavioral: little or no sexual attraction
• Ex. Different species of fireflies
• Ex. Courtship dances, rituals,
pheromones
Mechanical
Isolation
• Mechanical:
female and
male sex
organs are not
compatible
• Ex. Certain
insect and
flowers
• Ex.
Hummingbird
beak length
and specific
flowers
Gametic Isolation
• If two different
species copulate –
a zygote will not
form
• Molecular
recognition
• Ex. Sea urchins,
flower pollen,
etc.
Postzygotic Barriers
• Prevent development of fertile adults
• 5 types:
• 1. Gamete Mortality: cannot survive
under the given conditions
• Ex. Sonoran topminnow and nematodes
• 2. Zygotic Mortality: zygotes
cannot survive under given
conditions
• Ex. Goat x sheep and some
leopard frogs
• 3. Hybrid Inviability: hybrid
zygotes fail to develop or
reach sexual maturity
• 4. Hybrid Sterility:
hybrids fail to produce
functional gametes
• ex. Mules, camas, and many
other cross species matings…
• Liger: result of cross between
male lion and female tiger
• Tigon: hybrid between male
tiger and female lion
• 5. Hybrid breakdown:
offspring of hybrids are
weak and infertile
• Ex: cotton and sunflowers
14.3 Geographic Isolation
Can Lead to Speciation
• Key event in speciation is often
separation of population
• Allopatric speciation: block of gene pool
due to geographic barrier
• Speciation may not occur even if gene pool in
population changes as result of local
environment
• Speciation occurs when reproductive barriers
develop between new population and parental
population
Geographic Isolation
Geographic Isolation
14.4 Islands and
Speciation
• On many islands,
species arrive
frequently and fill
available niches
• On remote
islands, rate of
arrival is so low –
niches are filled
by species
evolving:
adaptive radiation
Adaptive Radiation
• ADAPTIVE
RADIATION:
evolutionary
diversification of
single lineage into
variety of species
with different
adaptive traits
• Two classic examples:
• Galapagos finches
• Hawaiian
honeycreepers
Origin of Galapagos Finches
• About 10 mya
original species
arrived from S.A.
• Found an isolated
location relatively
predator-free
• Absence of
competition
permitted adaptive
radiation
• Produces wide range
of species occupying
a variety of niches
Variety
• Diversity of beak
structure and feeding
habits is remarkable
• Some eat seeds,
insects, ticks from
tortoises, leaves,
flowers, blood from
seabirds, & use twigs
to extract insect larvae
from dead tree
branches!
• 13 species fill niches of
7 different families of
South American
mainland birds
• Intriguing to
biologists - how
the different
species evolved
• Genetic analysis
suggests all 13
species evolved
from a flock of
about 30
• Probably arriving
millions of years
ago
Darwin Collected These
Finches
• 13 species of small,
plain (usually) birds
• Show continued
significance in
development of
evolutionary theory
• Referred to as
“Darwin’s Finches” –
although he didn’t
name them this
Importance of Darwin’s
Finches
• All 13 species
probably descended
one species
• Darwin had no idea
even that some of
the finches were
not same species but referred to it as
a “Transmutation of
Species”
Hawaiian Islands
• Volcanic islands
• Species arrived by
air and sea from
America and Asia
• Degree of genetic
differentiation
suggests founders
arrived 3.5 – 8 mya
Hawaiian Honeycreepers
• Probably descended from
finch-like, seed-eating
ancestor
• Some have finch-like
beaks for eating seeds,
insect and fruit
• Some have long thin
beaks for sucking nectar
• Others are intermediate
Honeycreeper
Species
• 29-33 species
• 14 sub-species
• Most
extinctions
followed
arrival of
Polynesians
Conservation Nightmare?
• Island endemics
present serious
problems:
• Found nowhere else –
once extinct are gone
forever
• Island populations are
relatively small and
vulnerable
• Human pressure on
space and habitat are
particularly high
Video: Biological Invaders
14.5 New Species May
Arise Near Parents
• Sympatric Speciation:
development of new
species without
geographic barriers
• Polyploids: more than
two complete sets of
chromosomes
14.6 Polyploid
Plants
• 25-50% of all plants are
polyploids
• Hybridization (cross
between two species)
accounts for most
• Many of our food plants
• Bread wheat – our most
important wheat species is
polyploid with 42 chromos.
• Probably arose naturally
• Scientists use chemicals
to induce meiotic and
mitotic errors
• Used to create new species
with special qualities
Normal Sexual Reproduction
Plants can self-fertilize
Autopolyploidy (meiosis fails)
Why is it a new species?
Parapatric Speciation
• Neighboring
populations become
distinct species
while maintaining
contact along a
common border
• Hybrid Zone: where
individuals interbreed
individuals along this
common border
Hybrids
14.8 Speciation Tempos
• Evidence comes mainly
from the fossil record
• 2 models of evol. patterns
• 1. Gradualism: gradual
evolution of differences as
they become adapted to
environment
• Fits Darwin’s view
• Most fossil species appear
suddenly
• Punctuated Equilibrium:
evolution comes in spurts
• Mutation of just a few genes
can result in radical changes