Date: ________________________
Name: __________________________
Phylogenetic Relationships
Through a system of classification
called cladistics, scientists construct
pylogenetic trees to group organisms
based on an analysis of shared derived
(apomorphic) traits, or synapomorphies.
What happens at a speciation event?
Does C share a common ancestry with A?
Which box is a common ancestor to B and C?
Clade: ___________________________________________________________________
Cladogram:________________________________________________________________________________
What information can we derive from the cladogram on right?
Learning Check:
a) Which groups are most closely related? _______________
b) Which groups are the most distantly related? ___________
c) What do the numbers 1through 7 represent? ____________
PRACTICE
I) Do B, C, and D represent a clade?
II) Which species is/are most closely related to F?
III) Which species is/are most closely related to D?
IV) If a new character (or trait) evolved at position 4, which
of the species in the tree would definitely not have the new
trait
A couple more definitions:
Synapomorphy: ________________________________________________________________________
Ingroup: ______________________________________________________________________________
Outgroup: _____________________________________________________________________________
Figure 1: This
phylogenetic tree
depicts the
evolutionary
relationships
among major
groups of
vertebrates.
a) At which point (letter), did the ray-finned fish split off from a species ancestral to all displayed groups?
b) At which point did a split into two lineages occur, with one giving rise to the mammals?
c) Using the phylogenetic tree, which of the following are more closely related to crocodiles? (turtles or birds)
d) Could crocodiles, lizards, snakes and turtles be grouped into a clade that did not include birds?
e) What is the most common ancestor (letter) for mammals, turtles and birds?
f) The ancestor to all vertebrates, at position A, had _______, while the ancestor of all non-fish vertebrates, at
position B, had evolved ___________.
g) Does the fact that monkeys and salamanders both possess tails indicate that monkeys are more closely related to
salamanders than they are to chimpanzees, which do not have tails? Explain.
h) Does a branch to the mammal lineage at position C imply that mammals existed at that time?
i)
Cladograms can provide information about the relative sequence in which species split. Which of the named
groups in the cladogram are not alive today? How is this shown?
j)
Birds and mammals are endothermic and have relatively large brains, yet as shown in Figure 1, mammals are no
more closely related to birds than they are to turtles or snakes. Consider the hypothesis that species B was an
ancient large brained endotherm. If this were the case, these traits must have been lost independently in the
organisms that gave rise to turtles, lizards and snakes, crocodiles, and most dinosaurs. Do you agree with the
hypothesis? If not, write a better hypothesis.
Practice Questions – Answer on a separate page!
1. Match the following terms with the phrases below: primary abiogenesis, adaptive radiation, clade, coevolution,
convergent evolution, divergent evolution, gradualism, hominid, punctuated equilibrium, synapomorphy
a) a group with a single common ancestor
b) theory that evolution is very slow at times
c) a shared derived trait
d) theory that life arose from inorganic molecules
e) very common evolutionary pattern in archipelagos
f) species usually dependent on each other for survival
g) species exhibit different genetic codes but similar outward appearance and behaviour
h) theory that the pace of evolution does not change significantly
i) species may exhibit similar genetic codes but have different outward appearance and behavior
j) includes Australopithecus afarensis
2. Examine the phylogenetic tree in Figure 1 and answer the following questions about it:
a) Which grouping of circles represent clades?
b) Which species is/are most closely related to the
following species?
i)
V
ii)
T
iii)
Q
c) If a new character (or trait) evolved at position 4, which
of the species in the tree would definitely not have the
new trait?
d) List all the numbered positions at which a derived
(apomorphic) character may have evolved.
e) Should you expect the ancestral species at position 5 to
resemble S or T more closely?
f) Along which path could a derived character evolve that would eventually be inherited by S?
g) Which species would you expect to be most ancient in appearance?
3. Examine the phylogenetic tree in figure 1.
SINEs (short interspersed nuclear
elements): Repeated DNA sequences of
300 base pairs in length that alternate
with lengths of DNA sequences found in
the genomes of higher organisms.
a) Which two species are most closely related? Explain.
b) Species B and D share a SINE which is not found in species A. What other species would you expect to also share
this trait? Explain.
c) List all species to which species C is most closely related.
ANSWERS:
f) The ancestor to all vertebrates, at position A, had fins, while the ancestor of all non-fish vertebrates, at position B, had
evolved four limbs.
g) Does the fact that monkeys and salamanders both possess tails indicate that monkeys are more closely related to
salamanders than they are to chimpanzees, which do not have tails? Explain.
No. Ancestral features cannot be used to determine the relationship of species or groups; for example, the vertebrate tail
is considered the ancient condition, while the lack of a tail is considered to be a derived condition.
h) Does a branch to the mammal lineage at position C imply that mammals existed at that time?
No. Only that a common ancestor to the mammals had branched from the previous lineage.
i) Cladograms can provide information about the relative sequence in which species split. Which of the named groups in
the cladogram are not alive today? How is this shown?
Dinosaurs, whose branch ends before reaching most recent times.
j) Birds and mammals are endothermic and have relatively large brains, yet as shown in Figure 1, mammals are no more
closely related to birds than they are to turtles or snakes. Consider the hypothesis that species B was an ancient large
brained endotherm. If this were the case, these traits must have been lost independently in the organisms that gave rise to
turtles, lizards and snakes, crocodiles, and most dinosaurs. Do you agree with the hypothesis? If not, write a better
hypothesis.
Even without examining the fossil evidence, it would seem highly unlikely that having a large brain and being
endothermic are ancient conditions. A more likely hypothesis is that having relatively large brains (in relation to other
non-mammalian vertebrates) and being endotherms are analogous features, or homoplasies, having evolved
independently and relatively recently in both mammals and birds.
Practice 1
a)
Clade
b) Punctuated
c)
Synapomorphy
d) Primary
abiogenesis
e)
Adaptive radiation
f)
Coevolution
g) Convergent
evolution
h) Gradualism
i)
divergent
Practice 2
A) Clades include: [U+V], [R+S], [R,S,T],
[R,S,T,U,V], [Q]
B) A) U, b) R + S equally, c) all other species
equally
C) Q, R, S, T
D) 2, 4, 7. The other events are nodes
where a speciation event occurred.
Apomorphic characters could arise
immediately after or immediately before
a node but not at the precise theoretical
nodal position.
E) You should not expect the ancestral
species to resemble either one more than
the other.
F) Any derived character that evolved
along the path from ‘1’ to ‘3’ to ‘5’ and
then onward to R, but forking up to the
right to ‘s’ would eventually have been
inherited by species ‘s’.
G) There is no reason to think that any
living species (Q,R,S,T,U,V) would
appear more ancient than any other.
Practice 3
a)
D + E are more closely
related. They share the
most recent common
ancestor.
b) C + E would be expected
to share the SINE. This is
because we would
conclude that both B + D
inherited the SINE form
their most common recent
ancestor. This species is
also an ancestor of C + E.
c)
D + E and equally closely
related to C.