Phylogeography
of the Seastar Linckia laevigata and its
obligate parasite Thyca crystallina
Bolanle Akinronbi, Marta Muñoz, Paul Barber
What is Phylogeography?
Phylogeography deals with the
historical, phylogenetic components of
the spatial distribution of gene lineages;
so that time and space are jointly
considered axes onto which gene
genealogies of interest are mapped
(Avise, 2000).
Linckia laevigata
Linckia laevigata is a species of sea star that lives on a coral reef.
Thyca crystallina
Thyca crystallina is a species of gastropod snails.
They are obligate parasites of the species Linckia laevigata.
Why Study Host-Parasite Relationships?
Information obtained from phylogeographic studies of HostParasite relationships can be used to better understand the
ecology of both host and parasite as well as provide information
about effective population sizes, dispersal distances, gene flow
rates and the factors that control these parameters. ( McCoy et
al). Knowledge thus obtained may then be applied on a grander
scale in areas such as conservation, vaccine development and
disease prevention.
These studies are also important for directing future studies of
cospeciation and coevolution of Host and parasite species
Previous comparative studies of HostParasite populations have revealed varying
results. In some cases both Host and parasite
show equal phylogeographic structure, in some
the host had more structure while parasites
were more structured in others. (McCoy et al
2005).
Coevolution Host and Parasites
Hafner et al (1994)
HYPOTHESIS
Linckia disperses as larvae and so
does its parasite Thyca, therefore it is
expected that they will have similar
patterns of phylogeography.
The aim of the study was twofold:
1. to investigate genetic relationships
within Linckia and Thyca populations
from different locations in the Indo-West
Pacific Ocean.
2. to compare patterns of phylogeography
between both Host-Parasite species
METHODS
 377 individuals of the host Linckia were
sampled in 25 populations from locations in
the coral reefs around the Indo-West Pacific
and 204 individuals of thyca were sampled
from 13 populations.
 DNA extraction using chelex
 PCR Amplification of the mitochondrial gene:
Cytochrome Oxidase 1 (COI)
 They were sequenced on a ABI 377 DNA
Sequencer
ANALYSIS
Individual haplotype definitions
were obtained using MacClade.
Genetic analysis was conducted
using PAUP and ARLEQUIN.
LINCKIA
LINCKIA
THYCA
LINCKIA
THYCA
Amova Data Showing Variation In Linckia
Source of
Sum of
V arianc e Percentage
variat ion
d.f.
Squares
C omponents Variation
------------------------------------------------------------------------------ -- -- - -- - -- -- - -- Indian vs. 1
3 5 .0 0 1
0 .1 3 1 0 8 V a
2 .9 3
Pacif ic
W it hin
Indian OR
Pacif ic
21
1 8 1 .8 2 8
0 .2 6 8 8 2 V b
6 .0 2
W it hin
373
1 5 1 7 .5 5 5
4 .0 6 8 5 1 V c
9 1 .0 5
populat ions
- -- -- - -- - -- -- - -- - -- -- - -- - -- -- - -- -- - -- - -- -- - -- - -- -- - -----------------------------T otal
395
1 7 3 4 .3 8 4
4 .4 6 8 4 1
- -- -- - -- - -- -- - -- - -- -- - -- - -- -- - -- -- - -- - -- -- - -- - -- -- - -----------------------------F ixation I ndic es
P values
FSC :
0 .0 6 1 9 8
0
FST :
0.08949
0
FC T :
0 .0 2 9 3 3
0 .0 1 2 7 1
- -- -- - -- - -- -- - -- - -- -- - -- - -- -- - -- -- - -- - -- -- - -- - -- -- - ------------------------------
Amova Data Showing Variation Across Indian Pacific
Source of
S um of
V arianc e Percentage
variat ion
d.f.
S quares
C omponents Variation
-----------------------------------------------------------------------------Indian vs.
Pacif ic
1
2 .2 2 9
- 0 .0 0 4 5 5 V a
-0.20
W it hin
Indian OR
Pacif ic
11
2 7 .1 5 3
0 .0 1 1 7 0 V b
0.51
W it hin
populat ions
192
4 3 9 .1 8 9
2 .2 8 7 4 4 V c
99.69
- -- -- - -- - -- -- - -- - -- -- - -- - -- -- - -- -- - -- - -- -- - -- - -- -- - -- - -- -- - -- - -- -- - -- T otal
204
4 6 8 .5 7 1
2 .2 9 4 5 9
- -- -- - -- - -- -- - -- - -- -- - -- - -- -- - -- -- - -- - -- -- - -- - -- -- - -- - -- -- - -- - -- -- - -- F ixation I ndic es
P Value
FS C :
0 .0 0 5 0 9
0.28152
FS T :
0 .0 0 3 1 2
0.30205
FC T :
- 0 .0 0 1 9 8
0.42522
Pairwise Fst values show inverse relationship
0.12
y = -0.0883x + 0.0363
0.1
2
R = 0.0624
Linkia
0.08
0.06
0.04
0.02
0
0
0.05
0.1
0.15
Thyca
0.2
0.25
0.3
CONCLUSION
What have we found?
Thyca is not coevolving with Linckia. Rather its
pattern of gene flow suggests that it may have
evolved ways to disperse beyond the dispersal
distances of its host, Linckia.
This may not be surprising given the difference in
terrestrial vs marine methods of Host - parasite
Dispersal.
It will be interesting to see in future
studies how the length of larval stages
in both Linckia and Thyca may have
influenced the differences observed in
their phylogeographic patterns.
ACKNOWLEDGEMENTS
I’d like to thank Paul Barber, Marta Munoz,
Elizabeth Jones and Eric Crandall for their support
and contributions towards this project.