Transcript In This Lesson

In This Lesson:
Speciation
(Lesson 3 of 3)
Today is Friday (!),
th
September 16 , 2016
Pre-Class:
How would you define a
species?
Today’s Agenda
• The Origin of Species
– Well, not Darwin’s work. Just his work.
• Where is this in my book?
– Chapter 24.
By the end of this lesson…
• You should be able to identify the point at which
evolution has created a new species.
• You should be able to distinguish between
microevolution and macroevolution.
• You should be able to distinguish between
homologous structures and analogous structures.
• You should be able to tell me why this is wrong:
http://si.wsj.net/public/resources/images/PT-AO773_EVOLUT_F_20100521192057.jpg
Macro- and Microevolution
• So far we’ve actually discussed both of these.
• Microevolution is the small, short-term
changes in a population.
• Macroevolution is the long-term change in a
population leading to the development of a
new species, which is called speciation.
– (we’ll define species later)
• What’s the difference?
– Time and scale.
Macroevolution/Microevolution
Case in Point
• Archaeopteryx – the first bird:
• The development of the feathers was
microevolution; the rise of birds was
macroevolution.
http://4.bp.blogspot.com/-zTFRKQESx9w/UQEoSRCnKnI/AAAAAAAANnI/U2c3Y8R1ES0/s400/archaeopterix1.jpg
http://en.wikipedia.org/wiki/Archaeopteryx#mediaviewer/File:Archaeopteryx_lithographica_%28Berlin_specimen%29.jpg
Evolutionary Time
• Speciation occurs either
by…
– …cladogenesis, when one
species splits into two or
more species.
– …anagenesis, wherein one
species simply evolves on
its own into a distinct new
species.
Tree of Life
• Darwin had the idea of
speciation in his earliest
notes.
• The trunk of the “tree” is the
distantly related common
ancestor to all other branches.
• The closer the branches, the
more recently they diverged.
Tree of Life
• Any branch that
doesn’t make it all
the way to the top
represents an
extinction.
• You can also trace
the path back to the
common ancestor.
Tree of Life
• More modern cladograms (tree of life-like
diagrams) look like this:
cow
Egg-Layers
Less
Cowish
Mammals
More
Cowish
Species
• Ernst Mayr proposed the most concrete
species definition in 1942:
– A population whose individuals can interbreed
AND produce fertile offspring.
• This is called the biological species concept.
• There are some issues with this, but it works
pretty well for currently-living creatures.
• We’ll outline those issues later.
Mule
• Horse + Donkey
http://cloud.equinenow.com/140171_1/mare_mule_horse.jpg
Liger
• ♂ Lion, ♀ Tiger
http://2.bp.blogspot.com/__jinAaXs1i4/TGzaZyBwtmI/AAAAAAAAAI8/bMYSAFod7bw/s640/Liger4.jpg
Tiglon
• ♂ Tiger, ♀ Lion
http://www.metrolic.com/wp-content/uploads/2010/09/Tiglon20.jpg
Zedonk
• Donkey + Zebra
http://4.bp.blogspot.com/_p5mAt9Tofmg/TFf_sh1ENTI/AAAAAAAAAt4/ZM0AlU4z9gU/s320/zedonk+trimmed.jpg
What do all those creatures
have in common?
• Sterility.
• If two animals can produce offspring, that’s
not good enough.
• They need to produce fertile offspring that can
reproduce on their own.
• Until that point, they are considered separate
species.
Barriers
• So what are some barriers to reproduction?
– Pre-Zygotic Isolation (reproduction/conception preventers)
•
•
•
•
•
•
Geographic isolation
Ecological isolation
Temporal isolation
Behavioral isolation
Mechanical isolation
Gametic isolation
– Post-Zygotic Isolation (barriers to birthed offspring)
• Reduced hybrid viability
• Reduced hybrid fertility
Geographic Isolation
• Some kind of physical barrier preventing
interaction:
– Example: Harris’s Antelope Squirrel lives across a
canyon from a close relative, the White-Tailed
Antelope Squirrel.
Uh…hold on a sec.
• I can’t think of a good place
to put these two vocabulary
words so I’m puttin’ ‘em
here.
• Allopatric speciation is
when you get a new species
due to a geographic divide.
• Sympatric speciation is
when you get a new species
that lives in the same area.
Allopatric Speciation Case in Point
• The Mexico-United States
border.
• Jaguars range throughout
Central and South America,
and historically have been in
North America too.
• The construction of some of
the U.S. border fence has
isolated only a few (<5)
individuals in Arizona.
– Local extinction likely, but
allopatric speciation is a
possibility.
http://s1.reutersmedia.net/resources/r/?m=02&d=20071008&t=2&i=1901911&w=580&fh=&fw=&ll=&pl=&r=2007-1008T163501Z_01_N08297982_RTRUKOP_0_PICTURE0
Ecological Isolation
• No big physical barrier,
but the niches occupied
by each species are
different.
– Example: 2 species of
Thamnophis garter snake
live in the same area but
one is aquatic and one
terrestrial.
Temporal Isolation
• Time-based isolation – species’ breeding
schedules just don’t line up.
– Example: Eastern and Western Spotted Skunks
actually have an overlapping range but not
overlapping mating periods.
 Mates in Winter
Mates in Summer 
Eastern Spotted Skunk
Western Spotted Skunk
http://www.julielarsenmaher.com/wp-content/uploads/2012/09/Julie-Larsen-Maher-6637-Eastern-Spotted-Skunk-03-05-10.jpg
Behavioral Isolation
• Some kind of behavior or display is necessary
for mating.
– Example: Blue-tongued skinks are thought to have
blue tongues in part to identify one another.
http://www.lafebervet.com/wp-content/uploads/2011/05/BlueTongueSkink.jpg
Behavioral Isolation
• Other examples:
– Courtship displays.
– Mating calls.
Lacewing Courtship Calls
Differing Meadowlark Calls
Eastern Meadowlark
Western Meadowlark
Mechanical Isolation
• Morphological (shape) differences prevent
mating.
– Example: Monkey flowers attract different
pollinators but may live near one another.
– Example: Damselflies’ sex organs are differentlyshaped preventing interbreeding.
Male reproductive organs
of the Damsel fly
Gametic Isolation
• Sperm cannot fertilize eggs.
– Biochemical Barrier: Sperm
can’t penetrate eggs.
– Chemical Incompatibility:
Sperm can’t survive in female
reproductive tract.
– Example: Aquatic creatures that
release sperm into open water
only fertilize females of their
species.
Gametic Isolation
• Species may differ in chromosome number:
– Dog: 78 Chromosomes (39 pairs)
– Orangutan: 48 Chromosomes (24 pairs)
– Mouse: 40 Chromosomes (20 pairs)
– Strawberry: 56 Chromosomes (7 groups of 8 octoploid)
– Adders-tongue fern: 1200 or 1260 Chromosomes
Post-Zygotic Isolation
• Suppose a hybrid (offspring of two separate
species) actually is born. What could go wrong?
• Reduced Viability
– Offspring are frail/can’t survive well.
• Example: Interbred salamander species. Offspring often
don’t complete development.
• Reduced Fertility
– Offspring are sterile.
• Example: All those animals from before.
Aside: Chromosome Number
• Horses: 64 Chromosomes
• Donkeys: 62 Chromosomes
• Mules: 63 Chromosomes
• It’s amazing mules can even be born!
Back to the Species Definition
• All those breeding-related things really help
define a species…if it’s a sexually-reproducing
organism.
– No love for the asexual reproducers.
• Oh, pun!
• Fossils are also a bit of a challenge.
• Some alternate definitions could be useful.
Alternative Species Definitions
• Ecological Concept
– Defines species by role relative to other species.
• Morphological Concept
– Defines species by similar body structures.
• Genealogical Concept
– Defines species by similar DNA.
• Pluralistic Concept
– Some/all of the above.
Aside: Cows and Platypuses
• When you actually start
digging around in creatures’
DNA, you get surprising
results. Here are two:
– “Cows are 25% Snake” article
– Platypus DNA contains segments
associated with mammals, birds,
and reptiles.
• Plus they’ve got 10 sex
chromosomes. So there’s that.
http://1.bp.blogspot.com/-2zq5eXFKk5E/Tc6GeJUi5fI/AAAAAAAAAro/ad_I1NKNF8c/s1600/Platypus+003.jpg
Speciation Rate
• Over time, the splitting and
rise of new species is referred
to as adaptive radiation.
• The “radiation” part refers to
the diversification of
organisms as they speciate.
– Typically speciation is FAST.
• Exactly how fast/sudden
adaptive radiation occurs is a
matter of debate, however.
http://www.mcatzone.com/uploads/gloss/adaptive_radiation.gif
Gradualism vs.
Punctuated Equilibrium
• Gradualism is the idea that change
occurs very slowly but at a somewhat
constant rate.
– Supporters include Charles Darwin and
Charles Lyell.
• Punctuated equilibrium, on the other
hand, states that changes occur rapidly
when speciation occurs, but then does
not change much thereafter.
– Supporters include Stephen J. Gould and
Niles Eldredge.
Punctuated
Equilibrium?
• Time is on the X-axis.
• The yellow stripe highlights a
relatively brief period of
divergent evolution, which is
when species branch off from
one another.
– The opposite of divergent
evolution is convergent evolution,
and both terms typically refer to
traits of populations rather than
actual species.
– Bats and birds both developing
wings is a case of convergent
evolution because they evolved to
become more similar to one
another.
http://evolution.berkeley.edu/evosite/evo101/VIIBDiversityclades.shtml
Tie-In
• When two populations undergo divergent
evolution, it may lead to speciation
(macroevolution).
– Some structures may remain similar-looking,
which would qualify them as homologous
structures.
• On the other hand, two species undergoing
convergent evolution will likely develop
analogous structures.
Coevolution
• There’s also coevolution, which is not necessarily divergent or
convergent evolution (but could be).
• This is when you see two species evolving in lockstep with
one another.
• For example, the monarch butterfly (poisonous) and the
viceroy butterfly (harmless) have evolved together, with the
viceroy mimicking the monarch’s coloration.
Monarch
Viceroy
– More next unit…
The Kitchen Sink
Final Assorted Notes
• Evo-Devo
– Short for evolutionary developmental biology.
– A field that uses development stages in an individual’s
life to learn about evolutionary changes in the species.
– One thing that is often studied in Evo-Devo is…
• Paedomorphosis
– When adult organisms retain features that were
considered juvenile features in their ancestors.
• For example, amphibians are “supposed” to become landdwellers as they mature to adults.
• Some amphibians maintain gills even after sexual maturation.
Paedomorphosis
• Paedomorphosis occurs one of two ways:
– Progenesis is when sexual maturity occurs sooner, so
you get sexually-mature juveniles.
– Neoteny is when sexual maturity age doesn’t change,
but organisms take longer and longer to go through body
changes, so you get sexually-mature juveniles.
• Both of these represent forms of heterochrony:
– Evolution-produced changes in developmental timing in
an organism.
– The difference between them is what development
timing changes (progenesis = sexual maturity; neoteny =
everything else).
Closure
• Think back to middle school evolution.
• You learned about homologous and analogous
structures.
• Homologous structures are…?
– Structures that are similar because they developed in
a common ancestor.
– The fins of a whale and arms of humans are
homologous structures.
• Analogous structures are…?
– Structures that just look similar, but don’t have
common ancestor significance.
– Bird wings and bat wings evolved independently.
Closure: Cladogram Construction
• Now that we’ve all but concluded our evolution
unit, we can try a practice AP exam question.
– Construct a cladogram based on the following data, and
indicate where each character arose:
Character
Cat
Cow
Lactose
Protein A
Protein B
+
+
-
+
+
+
Horse Human
+
+
+
+
+
-
Pig
+
+
+
Casein
+
+
+
+ indicates presence of the character, - indicates absence
Character
Lactose
Cat
+
Cow
+
Protein A
Protein B
Casein
+
-
+
+
+
Horse Human
+
+
+
+
+
+
-
Pig
+
+
+
+
Protein B
and
Casein
Lactose and
Protein A
+ indicates presence of the character, - indicates absence
Cow
Horse
Lactose and Protein A are in all five
organisms, so it’s likely to have
arisen with their common ancestor.
Pig
Human
Cat
Protein B and casein are present in
cows, horses, and pigs, so it’s likely
that they are more closely related to
one another than to humans and
cats, who do not have them.
Closure Deux
• HHMI – Stickleback – Speciation