Download Lizards Tree Solutions

The information that follows is intended as a guide to solutions to
the phylogenies based on different types of data. These are my
interpretations and are by no means definitive.
Below is one possible solution based on geographical distance and
island hopping. It does not take into account actual currents which
vary over time. There can be other reasonable solutions. The idea here
is to get the student thinking about the logic of the problem, not its
ultimate answer. The numbers indicate the chronological sequence.
atlantica
1
galloti
T enerife
3
galloti
Palma
5
galloti
Hierro
6
galloti
Gomera
4
stehlini
2
African Ancestor?
Below is a possible solution using island distribution and
morphology. In using body size, one is tempted to guess that
medium lizards of Palma could have been the immediate ancestors to
Gomera, and the small lizards of Gomera are ancestors to the small
lizards of Hierro. This could contradict the argument based on
distance. Again there is no one perfect answer. Ecologists and
geneticists have debated several hypotheses for years. Numbers imply
chronology.
atlantica
1
galloti
T enerife
3
= Common Ancestor
galloti
Gomera
5
galloti
Hierro
6
galloti
Palma
4
stehlini
2
?
The following solution uses DNA evidence from Table 2 to deduce
genetic distance. It is considered the most reliable criterion to
establish evolutionary kinship. Since all base pairs have an equal
chance for mutation and mutation rate is relatively constant even
though evolution rate is not. Note that north and south Tenerife
populations are listed as one. Either may be a source for new
colonization. The real surprise here is not the evolution of the smaller
forms, it is that stehlini on Gran Canaria appears to have the oldest
ancestry although atlantica is actually closer to Africa. This unexpected
surprise could could support the hypothesis that the Gallotia lizard
ancestor is European! As an extension, have students investigate the
currents along the Portugal coast.
stehlini
1
atlantica
3
Hierro
6
Gomera
4
4
Palma
5
9
Tenerife
2
G. galloti complex
15-17
= common
ancestor
36
Small nu mb ers ind icate
genetic d istance b etween
branch es .
Large numbers
indicate the
chronology of
speciation.
40
Table 2 Cytochrome b DNA sequence differences for populations of
Gallotia Lizards
1.
G.
stehlini
2.
G.
atlantica
3.
G. galloti
Palma
4.
G. galloti
N.
Tenerife
5.
G. galloti
S.
Tenerife
6.
G. galloti
Gomera
7.
G. galloti
Hierro
1.
G.
stehlini
2.
36
41
40
40
45
49
G.
atlantica
25
23
19
24
28
3.
G. galloti
Palma
8
10
19
19
4.
G. galloti
N.
Tenerife
6
19
21
5.
G. galloti
S.Tenerif
e
15
17
6.
G. galloti
Gomera
4
7.
G. galloti
Hierro