TENE FOSSOG Billy1,2, KEGNE Pierre 1,2, KAMDEM Colince1,2, TOTO Jean-Claude1, AGBOR Jean-Pierre1,2, BESANSKY Nora J. 3,
ANTONIO-NKONDJIO Christophe1,2, COSTANTINI Carlo1,2.
INTRODUCTION
A previous study showed that in southern Cameroon, the M and S
To explain the unpredicted distribution of M in coastal villages, we hypothesized
molecular forms of Anopheles gambiae are spatially segregated, with M better adapted
to urban conditions and S to rural conditions in the region around Yaounde (Fig. 1A).
Statistical modelling using an index of urbanisation extracted from satellite imagery
as predictor allowed to correctly discriminate between M or S occurrences in the forest
region of southern Cameroon ≈70% of the time (Kamdem et al., in press). Discrepancies
from predictions were mostly concentrated in coastal localities where M occurred in small
rural villages far from urban centres (Fig. 2B) (Simard et al., 2009).
that this molecular form might have evolved greater tolerance to sodium chloride
(NaCl) the most abundant salt present in sea water.
AIMS
- Assess the level of tolerance of the two An. gambiae ss molecular forms M and S to
NaCl;
- Correlate the level of tolerance with the geographical origin of the molecular forms.
METHODS
 Field larval collections
- 2 localities in Yaounde (Fig. 1A): Locality A (rural area where S predominates), Locality B (urban area where M predominates) (Table 1A);
- 3 coastal localities in southern Cameroon (Fig. 1B) : Lolabe and Ebodje (where M predominates) and Eboundja (where S predominates) (Table 1B).
 Salinity tolerance test 24h larval survival in dilutions from 10% to 50% of sea water (35g/L of NaCl).
 rDNA analysis for identification of the molecular forms to confirm the distribution of molecular forms in different localities.
 Logistic regression in R to estimate lethal concentrations of NaCl for each form.
Figure 1A: Spatial segregation between the two
N
M
S
molecular forms - M and S - of An gambiae
following a rural-urban transect in Yaounde
B
(Kamdem et al., in press), showing the
A
localities A and B where the larvae tested
RURAL
Vegetation
Constructions
in this study were collected.
URBAN
YAOUNDE
Yaoundé
Figure 1B: Spatial distribution of M and S in the
CAMEROUN
1
coastal region of southern Cameroon
2
(Simard et al., 2009), and larval collection
points of the study
3
(1= Eboundja,
2=Lolabe 3=Ebodje ) .
M
S
SOUTH-COASTAL REGION
RESULTS & DISCUSSION
YAOUNDE
COASTAL AREA
Table 1B: Molecular forms identification by PCR
Table 1A: Molecular forms identification by PCR
M
S
Rural area
0 (0%)
196 (100%)
Urban area
256 (100%)
0 (0%)
M
1 (1.3%)
75 (97.4%)
242 (96.4%)
(1)Eboundja
(2) Lolabe
(3) Ebodje
Table 2B: lethal concentrations to NaCl of An. gambiae molecular forms (M & S) in the
coastal region of southern Cameroon .
Table 2B: lethal concentrations to NaCl of An. gambiae molecular forms (M & S) in
Yaounde.
M molecular form
S molecular form
YAOUNDE
Dose (% sea water)
Dose (% sea water)
LC 50
29.5 (±1.82)
LC 95
LC 99
S
76 (98.7%)
2 (2.6%)
9 (3.6%)
M molecular form
S molecular form
COASTAL AREA
Dose (% sea water)
Dose (% sea water)
24.8 (±0.28)
LC 50
35.5 (±1.47)
22.7 (±0.91)
43.6 (±3.57)
35.6 (±0.52)
LC 95
50.6 (±2.80)
32.5 (±1.59)
51.5 (±5.10)
41.7 (±0.74)
LC 99
59.1 (±4.03)
38.0 (±2.23)
(A)
(B)
1.0
(C)
(D)
1.0
99% mortality
99% mortality
4
4
0.8
0.8
0.4
M
0.2
0.6
0
0.4
-2
10
20
30
[NaCl] (% sea water)
40
50
60
0
-2
S
-4
0
M
0.2
S
0.0
logit(Mortality)
Mortality
0.6
2
Mortality
logit(Mortality)
2
0.0
0
10
20
30
40
50
60
-4
0
[NaCl] (% sea water)
Figure 2A: Dose response to NaCl of An. gambiae molecular forms (M & S) in Yaounde.
10
20
30
40
50
60
0
10
[NaCl] (% sea water)
20
30
40
50
60
[NaCl] (% sea water)
Figure 2B: Dose response to NaCl of An. gambiae molecular forms (M & S) in the coastal
region of southern Cameroon .
CONCLUSION
• In agreement with expectations, in both sites M is more tolerant to salinity than S (Fig. 2A & 2B);
• M tolerance on the coast is marginally greater than far from the coast.
• Physiological traits as tolerance to salts like NaCl (this study) or NH3 (Kamdem et al., in press) are associated to
the ability of M to occupy marginal habitats such as polluted urban centres and coastal habitats;
1. Laboratoire de Recherche sur le Paludisme, Organisation de
Coordination pour la lutte contre les Endémies en Afrique
Centrale (OCEAC), P.O. Box 288, Yaoundé, Cameroon.
• Differential salinity tolerance provides another phenotype potentially explain the ecological divergence of the
M and S molecular forms of An. gambiae.
2. Institut de Recherche pour le Développement (IRD), UMR 224
MIVEGEC, BP 64501, 34394 Montpellier, France
3. University of Notre Dame, USA