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Preliminary study of wing morphometry in relation to tsetse population genetics


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COMPARATIVE MORPHOMETRIC ANALYSIS of shape variation in the wings of different tsetse species reveals close accordance with the phylogenetics of these species indicated by DNA sequence analysis. In practice, the morphometric analysis is economical and simple to carry out, suggesting that this could become a useful surrogate or complementary tool for large-scale studies of tsetse population genetics, designed to identify discrete population targets amenable to local elimination.
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132 South African Journal of Science 101, March/April 2005 Research in Action
Preliminary study of wing
morphometry in relation to
tsetse population genetics
J.S. Patterson*and C.J. Schofield*
of shape variation in the wings of different
tsetse species reveals close accordance
with the phylogenetics of these species indi-
cated by DNA sequence analysis. In practice,
the morphometric analysis is economical and
simple to carry out, suggesting that this could
become a useful surrogate or complementary
tool for large-scale studies of tsetse population
genetics, designed to identify discrete popu-
lation targets amenable to local elimination.
Control of tsetse (Diptera, Glossinidae:
vectors of African trypanosomiasis) can
be achieved through a variety of tech-
niques, including traps, insecticide-
impregnated targets, live-baits, sequen-
tial aerial spraying (SAT), and sterile male
release (SIT) (see Hargrove1for review). In
most cases, however, the tsetse popula-
tions then tend to recover – either due to
flies surviving the initial interventions,
or immigration of flies from untreated
regions, or both. To achieve and sustain
local elimination of a target fly population,
it is therefore preferable to define the area
of intervention to include an entire
panmictic fly population, such that natural
immigration from neighbouring localities
is of low likelihood. This is most readily
achieved for isolated island populations,
as shown by the elimination of Glossina
pallidipes from the Island of Principe in
1914,2the eradication of G. pallidipes and
G. m. morsitans from Antelope Island,
LakeKariba,Zimbabwe, in 1984,1,3 and the
elimination of G. austeni from Unguja
Island of Zanzibar in 1997.4But for most
mainland populations of tsetse, the geo-
graphical limits of target tsetse popula-
tions are less easily definable.
Application of population genetics
techniques can reveal the existing level of
population differentiation in tsetse,
providing guidance on the distribution of
genetically defined sub-populations. In
essence, the population genetics models
are used to estimate rates of gene flow
between populations, which are taken as
a surrogate for the rate of migration of
individuals. Allozyme studies, for example,
have revealed high levels of genetic
differentiation within populations of
G. pallidipes and other species of the
morsitans group in East Africa,5suggest-
ing that these species exist as a series of
relatively isolated populations, each of
which might be targeted separately for
control interventions. Similarly, mito-
chondrial and microsatellite DNA analy-
ses also reveal a high level of population
structuring within species of the morsitans
group in southern and eastern Africa,6,7
and within some of the G. palpalis gam-
biense populations in West Africa.8,9
Extensive further studies of population
structuring in tsetse seem appropriateas a
guide to planning progressive control
interventions, as envisaged by the
AU-PATTEC initiative.10 In addition, such
studies could help in post-control moni-
toring for analysing the likely source of
survivors or immigrants into treatedareas
– as shown for Triatominae, vectors of
American trypanosomiasis.11 To minimize
the use of expensive techniques of DNA-
sequence analysis for such studies, we
present here a preliminary comparison
of geometric wing morphometry as an
inexpensive surrogate for genetic analy-
sis. This work was carried out at the level
of tsetse species and species-groups, as a
prelude to further studies of within-
species differentiation.
Materials and methods
The insects. Samples were received as
individuals or groups of flies in 70%
ethanol, from colonies maintained at the
FAO/IAEA laboratories in Seibersdorf,
Austria, and from the CIRDES laborato-
ries at Bobo Dioulasso, Burkina Faso.
Additional samples of G. p. gambiense
were collected by trapping along the Kou
valley, Burkina Faso (Table 1).
Wing morphometry. Wings were removed
and dry-mounted between two micro-
scope slides. The right wing of each speci-
men was photographed using a digital
camera. Images of each wing were subse-
quently digitized and 7 cartesian coordi-
nates (homologous landmarks defined by
vein intersections; Fig. 1) were recorded
automatically using TPSdig software
(version 1.39).12 The x, y coordinates were
subjected to generalized procrustes anal-
ysis (GPA)13 and subsequently to a
thin-plate spline analysis14 using TPSrelw
software (version 1.35)15 and TPS regr
(version 1.26),16 allowing visualization of
shape differences as deformation grids.
The analysis produces variables subdi-
vided into uniform and non-uniform
components of shape changes. To offset
the problem of small sample sizes, a prin-
cipal component analysis of the shape
variables delivers fewer shape compo-
nents (‘relative warps’), explaining most
of the shape variance within the data set.
The relative warps were subsequently
analysed by discriminant analysis. Size
differences were assessed using centroid
size (CS), an isometric estimator of size
derived from the GPA superimposition
procedure. Finally, mean Mahalanobis
distances were used in a cluster analysis to
construct a UPGMA dendrogram (Un-
weighted Pair Group Method with Arith-
metic Mean). Multivariate analyses and
graphs were completed using JMP®ver-
sion 4.0.5 (SAS Institute Inc. 2001) and
Intercooled STATA 8.2 for Windows (Stata
Corporation 2003)
DNA sequence comparison: For comparison
with the wing morphometry, we used
available partial sequences of the ribo-
somal DNA internal transcribed spacer-2
(ITS2) downloaded from GenBank
( (Table 1).
These sequences were aligned using
Clustal-X and analysed by Neighbor-
*Department of Infectious and Tropical Disease, London
School of Hygiene and Tropical Medicine, London WC1
E7HT, U.K.
Author for correspondence.
E-mail: Fig. 1. Slide-mounted tsetse wing showing landmarks used for morphometric analysis.
Research in Action South African Journal of Science 101, March/April 2005 133
Joining using the Kimura-2-parameter
model of base substitution to construct
phylogenetic trees with 1000 bootstrap
The first five relative warps (shape
components) accounted for 90.6% of the
variance in the total data set, and were
used as input for the discriminant analysis.
Regressing centroid size against the first
relative warp gave no significant correla-
tion (r= 0.002), suggesting that size is not
the primary factor influencing the major
shape differences. Figure 2 shows the
discrimination of the three main species
groups by wing morphometry. The
discriminant model gave correct reclassi-
fication scores of 100% for pooled mem-
bers of the fusca and morsitans groups
and 95.2% for palpalis (4.2% assigned to
morsitans group). These reclassification
scores were ‘almost perfect’ (kappa =
0.96).17 The first two canonical vectors
(CV) together accounted for 84% of the
total heterogeneity (CV1–56% and
CV2–28%). The thin-plate spline repre-
sentations (Fig. 2a,b) show that most of
the shape change is associated with a
relative elongation of the wing, and this
separates fusca from the morsitans and
palpalis species groups. Figure 2c,d show
that the secondary factor of shape change
is related to the relative arrangement of
vein junctions, and clearly discriminates
between the morsitans and palpalis
Analysis of the ITS2 sequences revealed
three major clades, with good bootstrap
support. These correspond to the three
species groups, and show clear congruence
with a cluster analysis of the morpho-
metric data (Fig. 3).
The 31 currently recognized species and
subspecies of Glossina are customarily
placed into three species groups which
are sometimes given subgeneric status18
the fusca group (subgenus Austenina),
palpalisgroup (subgenus Nemorhina), and
morsitans group (subgenus Glossina).
These groupings are based primarily on
morphological features of the adult
genitalia,19 although they also reflect
differences in distribution, habitat and
behaviour.20 Species of the fusca group
typically occur in lowland rain forests of
Westand Central Africa (exceptions being
G. longipennis and G. brevipalpis in drier
regions of eastern Africa); species of the
palpalis group are more usually associ-
ated with riverine vegetation, but also
extend into savanna regions between
river systems; while species of the morsi-
tans group are primarily associated with
drier savannas. In this study, the geomet-
ric analysis of wing morphometry suc-
cessfully recovered not only the species,
but also the three species-groups.
As initially shown by Solano et al.8for
G. p. gambiense, a degree of correlation can
Table 1.
specimens used in the study.
Species group Species Source of material for morphometry (n) ITS2 GenBank accession nos
morsitans G. morsitans s.l. FAO/IAEA, CIRDES (21) AF021360; AF021359; F021358
G. pallidipes FAO/IAEA (5) AF021357(1); AF021356(2)
G. swynnertoni FAO/IAEA (4) AF021355
palpalis G. palpalis gambiensis FAO/IAEA, CIRDES, and Kou valley (16) AF024505
G. fuscipes FAO/IAEA (4) AF021352
G. tachinoides CIRDES (4) AF021353
fusca G. brevipalpis FAO/IAEA (3) AF022361(1); AF022360(2)
Fig. 2. Discriminant analysis of the morphometric data, showing the distribution of specimens in the space defined by the first two canonical variates (CV1 and CV2).
a–d are thin-plate splines showing, by deformations from the mean, shape differences of the wings that correspond to the indicated species/species groups on both axes
(landmarks on the deformation grids are numbered as in Fig. 1).
134 South African Journal of Science 101, March/April 2005 Research in Action
be found between estimates of popula-
tion structuring based on analysis of
microsatellite DNA, and comparative
wing morphometrics. Using linear wing
morphometrics, these authors showed
clear separation between G. p. gambiense
populations of Senegal and Burkina Faso,
but not between populations within
Burkina Faso which were revealed by
comparative analysis of microsatellite
DNA sequences. Genetic separation of
the Senegal populations from those of
Maliwas also confirmed by Marquez et al.9
using comparisons of mitochondrial
DNA sequences. In our study, the very
high congruence over seven species and
subspecies between genetic comparisons
based on a ribosomal DNA sequence, and
phenetic comparisons based on geometric
morphometry, suggests that the geometric
analysis is a more sensitive surrogate
for the DNA sequence comparisons. It
appears, moreover, that wing shape may
represent a relatively neutral trait that is
not heavily modulated by ecological
adaptationor environmental constraints.
In practice, data collection for geometric
analysis of wing shape is relatively
simple. The wings can be dry mounted
between microscope slides and then
either scanned (using a computer scan-
ner) or photographed with a digital cam-
era. The resulting image can then be
processed using freely available software
or sent as an e-mail attachment to a refer-
ence laboratory for further analysis. Such
a procedure is simpler and much less
costly than current techniques for DNA ex-
traction and sequencing, and offers op-
portunities for rapid processing of large
samples of field-collected material cover-
ing the entire distributional range of tar-
get species and subspecies of tsetse. This
would permit detailed analysis of popula-
tion structuring to identify the geograph-
ical limits of discrete or panmictic
populations, which would represent
targets for control interventions that
would be least likely to suffer from
post-control reinvasion. In addition, as
shown for Triatominae,11 such studies
can also be used for post-intervention
monitoring, providing a way to confirm
whether any newly encountered tsetse
are survivors from the initial control
interventions (indicating a local control
failure) or are immigrants from a neigh-
bouring population of that species (per-
haps indicating a breakdown of control
In the context of the African Union
initiative to eliminate the problem of
tsetse and trypanosomiasis (AU-PATTEC),10
we believe that these techniques could
be particularly applicable for defining
geographical areas amenable to large-
scale elimination of the tsetse popula-
tions. There is a wealth of evidence that
tsetse control is feasible, but also that it is
difficult to sustain over the long term.1,21,22
By contrast, local elimination of tsetse is
sustainable, but generally held to be feasi-
ble only for geographically constrained
situations such as islands.1,2,4 The task of
population genetics studies is, in a sense,
to find and define those biogeographical
‘islands’ of tsetse distribution on main-
land Africa, and our study shows that this
may be feasible on a large scale using the
techniques of geometric morphometry,
with confirmation from smaller-scale
studies using the more expensive methods
of DNA sequence comparisons.
A summary of this work was presented as a poster at
the IX European Multicolloquium of Parasitology,
Valencia, Spain (18–23 July 2004). We thank Alan
Robinson (FAO/IAEA Laboratories), Abdoulaye
Gouro and Idrissa Kabore (CIRDES), and Tamboura
Issa (UCLT, Burkina Faso) for supplying the insects
used in this study, and Brian Williams for encourage-
ment and critical reading of the manuscript.
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Fig. 3. Comparison of Neighbor-Joining k2p linearized tree (left) with UPGMA cluster analysis of Mahalanobis
distances from wing morphometrics (right). Numbers indicate per cent bootstrap support from 1000 replicate
... This tool has shown considerable epidemiological significance for medically important insects such as the vectors of leishmaniasis and Chagas disease in Latin America [2] . In addition, the use of geometric morphometrics was established for comparisons of many samples with homologous landmarks, e.g. the vein-patterns on wings [3,4] . Also, the variation of morphometric features was used to determine how close or distant tsetse fly populations with factors such as size and rotation of the wings from the different populations [5] . ...
... Tsetse flies are classified based on a combination of distributional, behavioural, molecular and morphological characteristics to the Genus Glossina. It is grouped as the sole member of the family Glossinidae that is essentially one of the four families of blood-feeding obligate parasites [4] . They are in the order Diptera, the true flies. ...
Full-text available
Total sample of four hundred and eighty (480) tsetse flies (Glossina) were collected from three randomly selected Area Councils of Federal Capital Territory (FCT), Abuja namely: Abaji, Kwali and Gwagwalada. The multivariate morphometric analysis was made with MiScope microscope (Mag. 40-140x). The morphometric variables measured include: the length of body, proboscis, antennae, femur, tibia, tarsi, largest part of the body (abdomen) at the widest point and length and width of the forewing. Data were analyzed with parametric statistic tools of mean and standard deviation. The distribution and relation between them were subjected to two-step and hierarchical cluster analysis. Also, the dendrogram plot was used to show the phylogenetic relationship of the species. Results show the presence of two morphometrically distinct Glossina species in the FCT. Glossina tachinoides recorded 67.5% while G. morsitans was 32.5 % of collections. The distribution of species per Area Council showed majority of G. tachinoides i.e. 73.4%, 51.6% and 81.9% in Gwagwalada, Abaji and Kwali respectively while the remaining flies were G. morsitans. The correlation of morphometric features with sampling sites i.e. Area Councils gave insignificant negative correlations while highly significant correlations (p<0.01) were established between the morphometric variables of the tsetse flies. The Dendogram plot based on variations in morphometric features revealed linkages between the different samples collected. This gives an indication that the samples were of the same descent and shows that the morphometric based features can be engaged in classifying tsetse fly into species in FCT, Abuja.
... Similarly, the value of II-Zagreb index, Modified II-Zagreb index, Redefined Zagreb index values estimated different as per different species of insects which is showing the importance and capability of topological indices to differentiate insects. Identification of insects by molecular techniques is being recently used for the confirmatory test but the technique is very costly but estimation of morphological analysis is an easy method and no specific costly instruments required which made this technique important [14,15] . In the past research, wings were analyzed by estimating Cubital index of fore wing of bee species [11] . ...
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Insect are the important fauna of ecosystem and provide pollination service for the sexually reproducing plants and help in enhancing crop production for the human beings. Present study was totally concerned on the identification of order of insects by estimating Zagreb index, Harmonic index and inverse index. These indices were first time used to identify insect's order by the study of wings belonging to different insect species. Wing graph has been first time plotted and applied globally. Wings of Drosophila, Cicada, Apis, Musca species were amputed and permanent slides were prepared. Venation system of different wings was analyzed by using different vertices (cross-over of venation) and edges (part of vein between two vertices). Wing graphs were plotted with the help of wings photos and studied indices were calculated. The value of Zagreb index, Harmonic index and Inverse index were estimated specific for a particular insect order and insects can be differentiated and order of insects can be identified by using these indices this made this study significant for future study. Introduction Insects are hexapod invertebrates belonging to the Insecta class of Arthropoda phylum which was derived from word Insectum of Latin language. It was observed that all the members of insecta class have three pairs of legs, compound eyes, one pair of antennae, chitinous exoskeleton and body is divided into head, thorax and abdomen. Insects make over 90% of total life forms globally [5]. Insects made biological foundation for all land driven animals by contributing in nutrient cycle, seed dispersion, plant pollination and maintenance of soil structure [7]. This makes Insects important for the welfare of human being. There are several ways of indentifying insects by using entomological keys and research literature existed in the scientific world but first time in the present study, a new concept has been applied in identifying insect orders by calculating M-Polynomials and different Topological Indices with the help of vertices of wings venation. M-Polynomials express new findings of topological indices which have been used to correlate topological studies to the chemical properties of different chemicals or medical behaviour of drugs [10]. In the present study, it was used to identify insect orders as wings of different orders of insecta showed different venation pattern and venation vertices in the wings. This idea has been first time employed to identification of Insect orders. Photos of different kind of wings were used to demonstrate the behaviour of these polynomials.
... There are 31 recognized Glossina species and sub-species, divided into three groups (morsitans, palpalis and fusca) which have been given sub-generic status [99]. Recently, comparative gene sequence analysis and geometric wing morphometry have been proposed to help in the Glossina group identification [100]. The morsitans group that includes G. morsitans morsitans, G. m. submorsitans, G. pallidipes, G. longipalis and G. austeni is found mainly in the savannah ecosystems. ...
... Lower numbers of flies were available from Mozambique (n = 36), Kosi Bay (n = 31) and False Bay Park (n = 37) for G. brevipalpis and Mozambique (n = 14) and the Hluhluwe-iMfolozi Park (n = 13) for G. austeni. The right wings of 345 G. brevipalpis and 346 G. austeni females were removed, dry mounted between two microscope slides (Patterson & Schofield 2005) ...
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The effective control of tsetse flies (Diptera; Glossinidae), the biological vectors of trypanosome parasites that cause human African trypanosomosis and African animal trypanosomosis throughout sub-Saharan Africa, is crucial for the development of productive livestock systems. The degree of genetic isolation of the targeted populations, which indicate reinvasion potential from uncontrolled areas, will be critical to establish a control strategy. Molecular and morphometrics markers were used to assess the degree of genetic isolation between seemingly fragmented populations of Glossina brevipalpis Newstead and Glossina austeni Newstead present in South Africa. These populations were also compared with flies from adjacent areas in Mozambique and Eswatini. For the molecular markers, deoxyribonucleic acid was extracted, a r16S2 Polymerase chain reaction (PCR) was performed and the PCR product sequenced. Nine landmarks were used for the morphometrics study as defined by vein intersections in the right wings of female flies. Generalised Procrustes analyses and regression on centroid size were used to determine the Cartesian coordinates for comparison between populations. Both methods indicated an absence of significant barriers to gene flow between the G. brevipalpis and G. austeni populations of South Africa and southern Mozambique. Sustainable control can only be achieved if implemented following an area-wide management approach against the entire G. brevipalpis and G. austeni populations of South Africa and southern Mozambique. Limited gene flow detected between the G. austeni population from Eswatini and that of South Africa or Mozambique may imply that these two populations are in the proses of becoming isolated.
... In essence, the JOURNAL OF MEDICAL ENTOMOLOGY Vol. 43, no. 5 population genetics models are used to estimate rates of gene flow between populations, which are taken as a surrogate for the rate of migration of individuals (Patterson and Schofield 2005). Initial studies already showed evidence of strong structuring of G. palpalis populations in fragmented landscapes . ...
... This study is unique for including wing morphometric as a criterion to the quality of the mass-rearing procedure. Geometric morphometry using wings of Diptera species is a well-known tool for population studies (Lyra et al., 2010;Patterson and Schofield, 2005) and in this case is a definitive method to check if there are any deformations. Also in further studies, the wing samples from mass-reared adults should be compared with wild male wings in order to prevent a negative selection when mating. ...
The vector species Aedes albopictus (Skuse, 1894) was recorded in Turkey for the first time, near the Greek border, in 2011 and a high risk of expansion towards Aegean and Mediterranean coasts of Turkey was estimated. A preliminary study was planned to evaluate the possibility of creating a satellite mass rearing facility for this species and manage a larval rearing procedure by using the new mass-rearing technology proposed by the International Atomic Energy Agency (IAEA). For this purpose, the effects of different larval densities (1, 2, 3 and 4 larvae per ml) on the preimaginal development were evaluated by observing pupal, adult and male productivity using life cycle trials. Geometric morphometric analyses were also performed to define all phenotypic differences that occurred on the wing size and shape morphology of adult stage at the four different rearing conditions tested. A high pupation productivity was obtained with a larval density of 2 larvae/ml while adult emergence ratio was not affected by the densities tested. No significant difference was observed in shape of the wings among different densities in males and females. Nevertheless, a significant difference in female's centroid sizes was observed between the treatment groups 1-2 and 3-4 larvae/ml and in males centroid size reared at 1 larvae/ml versus the other densities.
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Wing geometric morphometrics has been applied to honey bees (Apis mellifera) in identification of evolutionary lineages or subspecies and, to a lesser extent, in assessing genetic structure within subspecies. Due to bias in the production of sterile females (workers) in a colony, most studies have used workers leaving the males (drones) as a neglected group. However, considering their importance as reproductive individuals, the use of drones should be incorporated in these analyses in order to better understand diversity patterns and underlying evolutionary processes. Here, we assessed the usefulness of drone wings, as well as the power of wing geometric morphometrics, in capturing the signature of complex evolutionary processes by examining wing shape data, integrated with geographical information, from 711 colonies sampled across the entire distributional range of Apis mellifera iberiensis in Iberia. We compared the genetic patterns reconstructed from spatially-explicit shape variation extracted from wings of both sexes with that previously reported using 383 genome-wide SNPs (single nucleotide polymorphisms). Our results indicate that the spatial structure retrieved from wings of drones and workers was similar (r = 0.93) and congruent with that inferred from SNPs (r = 0.90 for drones; r = 0.87 for workers), corroborating the clinal pattern that has been described for A. m. iberiensis using other genetic markers. In addition to showing that drone wings carry valuable genetic information, this study highlights the capability of wing geometric morphometrics in capturing complex genetic patterns, offering a reliable and low-cost alternative for preliminary estimation of population structure.
Conference Paper
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The geometric morphometrics of the wings has been an important method for the identification and evaluation of honey bee diversity patterns around the world. Honey bee populations of the Macaronesian archipelagos of Canaries and Madeira have been intensively surveyed for diversity using a variety of genetic markers. In contrast, honey bee populations inhabiting the Azorean archipelago have been largely undersampled. To fill this gap, we sampled 473 colonies from across the Azores and assessed diversity patterns using a geometric morphometrics approach. A total of 5 forewings were collected per colony, mounted in a slide and photographed with a stereomicroscope. Additionally, the forewings representing 711 colonies of A. m. iberiensis, 11 A. m. ligustica, 15 A. m. carnica and 12 A. m. caucasia were used as reference samples. To extract shape information, 19 anatomical landmarks were plotted across the veins’ intersections in the wing structures of all individuals. The analyses of wing shape were performed in MorphoJ using the Procrustes superimposition method. Shape differences were investigated through multivariate statistical analysis and Mahalanobis and Procrustes distances were used to construct a dendrogram of the morphological proximity. Results revealed the power of landmark-based methods to discriminate different honey bee populations from the Azores, and also to distinguish them from the subspecies of the reference collection. The wing geometric morphometrics patterns showed that while, overall, populations from the Azores exhibited a closer relationship with A. m. iberiensis, some populations, especially those from the islands of Graciosa, but also Terceira and Pico tended to cluster closer to A. m. ligustica, A. m. carnica. Several non-mutually exclusive factors can contribute to the observed wing patterns such as the recent human-mediated introductions of subspecies from Eastern Europe, and the founder effect resulting from honey bee introductions in historical times. Moreover, the particular insular environment and the barrier to gene flow due to geographical isolation possibly shaped the diversity patterns currently observed in the Azores.
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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.
The landmark-based geometric morphometric approach of relative warps (RW) was used to determine the population structures of the rice black bugs (RBB), Scotinophara coarctata, from the Philippines and in one site in Malaysia based on the shapes of the head and pronotum. The symmetric and asymmetric components were used to analyze the direction of shape change for each structure. However, multivariate analyses were conducted only on the symmetric components to infer the relationships among the RBB populations. The results showed that in many cases, the landmark configurations are continuous. Landmark configurations of the pronotum separated the RBB from Omar, Malaysia. Considerable shape differences between populations were also found locally within Luzon, Iloilo, Palawan and Mindanao based from the results of the analyses. The results of the current study strongly suggest the existence of morphological differences in the populations of RBB, which may indicate possible genetic differentiation. Such variability may have direct bearing on the management of the RBB as a pest of rice agroecosystem.
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It is important…to ask whether…the control and eradication of tsetse is really relevant to the present situation, whether it is now a marginal activity which could be dispensed with, or whether it is actually harmful.
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A method is described for optimizing models by linking simulation procedures with a non-linear regression programme. It is then possible to work towards a parsimonious model which contains those, and only those, variables required for an optimum fit. Using the observed values, and the predicted values from each simulation, the optimizing routine calculates the value of an appropriate loss function. It then makes small changes in the parameters governing the simulation, recalculates the predicted values and the first and second derivative of the loss function with respect to each parameter. The algorithm uses this information to minimize the loss function for a given formulation of the model. The model is improved by adding variables which can be shown statistically to improve the fit, and by removing those which do not. The use of the technique is illustrated with reference to a series of weekly estimates of the total numbers, births and survival probabilities of a population of male and female tsetse flies Glossina morsitans morsitans Westwood. Simulation involved following the lives of cohorts of flies, and of all their progeny, from the time they were deposited as larvae. Development and reproduction were regarded as fixed functions of temperature, but mortality rates of pupae and of adult flies depended on meteorological and biological variables, plus the level of trapping imposed on the population. Potential factors were added singly and the model thereby improved in an objective, stepwise manner. The best fit was achieved when effects on adult survival due to maximum temperature, various modes of trapping, and an annual cycle were included in the model. The optimized simulation technique has been used here in improving a model which describes a biological population but it could equally be used to improve models in any situation where data are fitted using simulation procedures.
The Glossinidae, or tsetse-flies, form a monogeneric family of the Diptera. The adults range in length from 6 to 14 mm and in all the 23 known species are various shades of brown — ranging from light yellowish brown to dark blackish brown. In some species the abdomen has alternate darker and lighter bands. Female flies give birth, at intervals of about nine days, to a single third-instar larva which rapidly burrows into the soil and transforms into a black puparium; according to the species, this varies in length from 3 to 8 mm.
Morphometrics is the statistical study of biological shape and shape change. Its richest data are landmarks, points such as 'the bridge of the nose' that have biological names as well as geometric locations. This book is the first systematic survey of morphometric methods for landmark data. The methods presented here combine conventional multivariate statistical analysis with themes from plane and solid geometry and from biomathematics to support biological insights into the features of many different organs and organisms. This book will be of value to applied statisticians and geometers, as well as to all biological and biomedical researchers who need quantitative analyses of information from biomedical images.
Glossina palpalis gambiensis Vanderplank (Diptera: Glossinidae) from West Africa (Senegal and Burkina Faso) were analysed for microsatellite DNA polymorphisms and size of the wings. In the overall sample a strong heterozygote deficiency was found at two polymorphic microsatellite loci. It led to a highly significant value of Fis (within-sample heterozygote deficit) in the western zone of Sideradougou area in Burkina Faso. Genetic differentiation was significant on a macrogeographic scale, i.e. between tsetse coming from Senegal and Burkina Faso. Wing measures also differed between these two countries; flies from Senegal appeared to be smaller. Microsatellite loci further allowed differentiation of populations of G. palpalis gambiensis trapped on the same hydrographic network a few kilometres apart. The results are interpreted as indicating that further investigations will allow the study of genetic variability of tsetse flies in relation to the dynamics of transmission of human and animal trypanosomoses.
To study the population structure of Glossina morsitans morsitans Westwood (Diptera: Glossinidae), polymerase chain reaction (PCR) and singlestrand conformational polymorphism (SSCP) methods were used to estimate mitochondrial DNA diversity at four loci in six natural populations from Zambia, Zimbabwe and Mozambique, and in two laboratory cultures. The Zambian and Zimbabwean samples were from a single fly belt. Four alleles were recorded at 12S and 16S1, and five alleles at 16S2 and COI. Nucleotide sequencing confirmed their singularities. Chi-square contingency tests showed that allele frequencies differed significantly among populations. Mean allele diversities in populations averaged over loci varied from 0.14 to 0.61. Little loss in haplotype diversity was detected in the laboratory cultures thereby indicating little inbreeding. Wright's fixation index F(ST) in the natural populations was 0.088+/-0.016, the correlation of haplotypes within populations relative to correlations in the total. A function of its inverse allows an estimate of the mean equivalent number of females exchanged per population per generation, 5.2. No correlation was detected between pairwise genetic distance measures and geographical distances. Drift explains the high degree of differentiation.
This paper presents a general statistical methodology for the analysis of multivariate categorical data arising from observer reliability studies. The procedure essentially involves the construction of functions of the observed proportions which are directed at the extent to which the observers agree among themselves and the construction of test statistics for hypotheses involving these functions. Tests for interobserver bias are presented in terms of first-order marginal homogeneity and measures of interobserver agreement are developed as generalized kappa-type statistics. These procedures are illustrated with a clinical diagnosis example from the epidemiological literature.
Gene diversity was investigated in four taxa of tsetse flies (Diptera: Glossinidae) including Glossina morsitans, G.m. centralis, G. Swynnertoni, and G. pallidipes. Histochemical tests were performed for 35-46 isozymes. Polymorphic loci were 20% in G. morsitans, 32% in G.m. centralis, 17.6% in G. swynnertoni, and 26% in G. pallidipes. Mean heterozygosities among all loci were 6.6% in G. morsitans morsitans, 6.0% in G.m. centralis, 7.1% in G. swynnertoni, and 6.8% pallidipes. Allozyme gene diversities were considerably less than those reported for many Diptera. The low gene diversities are probably related to small effective population sizes.