Evolution__3rd_Edition

630 PART 5 / Macroevolution
The cophylogeny of pocket gophers
and lice ...
22.5.2 Parasites and their hosts may have cophylogenies
(a) Host Parasite
C
C
A
O. heterodus
B
O. cherriei
A
G. costaricensis
B
G. cherriel
C
E
E
D
O. underwoodi
O. cavator
G. setzeri
D
G. panamensis
D
F
O. hispidus
F
G. chapini
I
G
I
H
I
K
L
Z. trichopus
P. bulleri
C. castanops
C. merriami
G. personatus
G. breviceps
G. bursarius (a)
G. bursarius (b)
T. bottae
T. talpoides
In Sections 22.3.1 and 22.3.2 above, we saw that the phylogenies of flowering plant
taxa and the specialist insects that feed on them, or pollinate them, sometimes form
mirror images, or cophylogenies. Host taxa and their specialist parasites can show the
same pattern. Indeed, mirror-image phylogenies were first discovered in parasite–host
relations. Cophylogenies between parasites and hosts are sometimes referred to as
Fahrenholz’s rule.
Hafner et al.’s (1994) research on the rodent family Geomyidae (the pocket gophers)
and their ectoparasitic lice (Mallophaga) is a good example. Hafner et al. sequenced a
mitochondrial gene in 14 species of pocket gophers and their parasitic lice, and used the
data to construct the phylogenies of the two groups (Figure 22.8a). The phylogenies are
nearly mirror images, though there are some deviations. The deviations are probably
due to host switching. For example, at the bottom of the figure, the parasitism of
Thomomys bottae by Geomydoecus actuosi looks like host switching.
G. trichopi
G. nadleri
G. expansus
G. actuosi
G
G. texanus
G. ewingi
G
G
H
G. oklahomensis
I
G. geomydis
J
G. thomomyus
G. perotensis
K
T. minor
L
T. barbarae
Figure 22.8
Mirror-image phylogenies in parasites and hosts. (a) The
phylogenies of 14 species of pocket gophers (Geomyidae)
and 17 of their mallophagan parasites. The phylogenies were
reconstructed from the sequence of a mitochondrial gene
(cytochrome oxidase subunit 1) using the parsimony principle.
The phylogenies mainly form mirror images, but there are
several cases of probable host switching. A pocket gopher
(Geomys bursarius) and louse (Geomydoecus geomydis) are
also illustrated. (b) Test of simultaneity of speciation in
(b)
Chewing lice
Expected number of substitutions per site (×100)
2.0
All substitutions
F
4.0
Synonymous
changes
1.8
3.5
F
1.6
1.4
L
3.0
1.2
J
G
B
2.5
1.0
D 2.0
C
K
0.8
1.5
C
A
0.6
E
0.4
I
1.0
D
0.2 H
0.5
B
0
0 0.2 0.4 0.6 0.8
A
0
0 E 0.4 0.8 1.2
Pocket gophers
Expected number of substitutions per site (×100)
parasites and hosts. The estimated number of substitutions
in various branches in the host phylogeny are plotted against
the numbers in the mirror-image branches in the parasite
phylogeny. Letters on the graph refer to lettered branches in
(a). The clocks in the two taxa probably run at different rates
because of differences in generation times. If the speciation
events were really simultaneous, the points should fall on the
line. The fit is better when only synonymous changes are
counted. Redrawn, by permission, from Hafner et al. (1994).
© 1994 American Association for the Advancement of Science.
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