Title: Comparative morphometric and molecular genetic analyses of triatominae (Hemiptera: Reduviidae)
Abstract: Triatomine bugs (Hemiptera: Reduviidae: Triatominae)
are the
vectors
of
Chagas
disease
in South and Central America. Chagas disease
predominantly affects
poor
rural
communities with simply constructed housing susceptible to infestation
by triatomines.
Chagas disease is restricted to the Americas largely
due to the limited
distribution
of
triatomine bugs. The global diversity of triatomines is
-130
species,
of which
only
-10%
are known to occur outside the Americas, one species
(Triatoma
rubrofasciata)
is
tropicopolitan, and the others are concentrated on the Indian
subcontinent
(Linshcosteus
spp. ) and adjacent south east Asian island groups
(Triatoma
spp.
).
The main objectives of this PhD programme
were to:
a) assess the facility
of
morphometric approaches (measurement and
robust
statistical analysis
of
morphological
variation) in the study of population structure of
vector species
with proximal
domestic
and silvatic distributions to detect population
structure and give
information
on the
risk of
reinvasion, b) study interspecific and higher taxonomic level
relationships
of
New World
and Old World triatomine bugs. To these ends
geometric
morphometric
analyses
were
conducted in concert with molecular genetic analyses of mitochondrial
and
nuclear
DNA
sequences. The principal question being: Does the
relatively
low
cost
method
of
morphometrics reveal patterns consistent with
population
structure,
as
otherwise
determined by more expensive molecular genotyping
methods?
Or
are
such
patterns
disrupted by environmental effects and intraspecific convergent/divergent
morphological
evolution?
Combined morphometrics and molecular genetics
were used
to
study vector
populations
in three of the countries that continue to
be
most affected
by Chagas disease. In
Venezuela and Ecuador Rhodnius species (R.
prolixus and
R.
ecuadoriensis
respectively)
were studied, in areas where they occur in both domestic
and silvatic
environments,
and
in Paraguay T. infestans from a domestic and a
putative
silvatic
focus.
Head
and
wing
morphometrics were compared to mitochondrial
DNA
sequence
data to
assess the
population structure and disparity among
domestic
and silvatic samples
in
each
case.
The
results presented suggest that head shape variation
is
subject to
morphological
plasticity
and/or selective pressure and functional constraint
and
does
not
correlate
well with the
11 Abstract
phylogeny. However, in all examples, wing shape
was
found to
be
congruent
with the
phylogenetic patterns inferred from sequence analysis.
Consequently, it is
recommended
that wing shape and not head shape be used
in
morphometric
assessments
of
population
dynamics. It is also asserted here that if
population structure
is
suggested
by
morphometrics, it should be followed by
robust population
genetic
analysis.
As
such,
morphometrics could be used as a tool for
broad
surveillance to identify
areas of concern.
A further objective was to elucidate the
broader
phylogeny of
Triatominae
and their
relationships with other reduviid subfamilies.
To investigate the
debated
polyphyletic
origin of the Triatominae molecular approaches
were used.
Combined head and wing morphometric
and
molecular
genetic analyses
of
New
World
and Old World Triatominae have revealed patterns
of convergent
morphological
evolution (among New World and Old World Triatoma)
and
striking
examples
of
strongly divergent morphological evolution
(between
Old
World
Triatoma
and
Linshcosteus).
Applying a molecular clock based on the rate of
sequence
divergence for
a
fragment
of
ribosomal DNA (D2-28S), calibrated to the fossil
record and
vicariant
events
(the
divergence of ancestral lineages due to separation
by topographical
or ecological
barriers)
it has been possible to reconstruct a likely evolutionary
history for the
Triatominae
and
the Reduviidae as a whole.
The weight of evidence presented supports a
polyphylectic
origin
for blood-feeding for
the Triatominae. The apparent independent development
of
blood feeding
among the
main lineages of the Triatominae represented
by the
genera
Triatoma
and
Rhodnius
highlights a fundamental biological difference among
important
vector species.
This
difference is likely to become evident
in the
eventual post
genomic era
in
studies
of
vector/parasite interactions and it highlights the
importance
of sequencing
genomes
from
different vector genera.
Publication Year: 2007
Publication Date: 2007-01-01
Language: en
Type: dissertation
Access and Citation
Cited By Count: 6
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