Habitat segregation and ecological character displacement in cryptic African malaria mosquitoes.
Understanding how divergent selection generates adaptive phenotypic and population diversification provides a mechanistic explanation of speciation in recently separated species pairs. Towards this goal, we sought ecological gradients of divergence between the cryptic malaria vectors Anopheles coluzzii and An. gambiae and then looked for a physiological trait that may underlie such divergence. Using a large set of occurrence records and eco-geographic information, we built a distribution model to predict the predominance of the two species across their range of sympatry. Our model predicts two novel gradients along which the species segregate: distance from the coastline and altitude. Anopheles coluzzii showed a 'bimodal' distribution, predominating in xeric West African savannas and along the western coastal fringe of Africa. To test whether differences in salinity tolerance underlie this habitat segregation, we assessed the acute dose-mortality response to salinity of thirty-two larval populations from Central Africa. In agreement with its coastal predominance, Anopheles coluzzii was overall more tolerant than An. gambiae. Salinity tolerance of both species, however, converged in urban localities, presumably reflecting an adaptive response to osmotic stress from anthropogenic pollutants. When comparing degree of tolerance in conjunction with levels of syntopy, we found evidence of character displacement in this trait.
Institut de Recherche pour le Développement (IRD), UMR MIVEGEC (UM1, UM2, CNRS 5290, IRD 224) Montpellier, France ; Laboratoire de Recherche sur le Paludisme, Organisation de Coordination pour la lutte contre les Endémies en Afrique Centrale (OCEAC) Yaoundé, Cameroon ; Department of Animal Biology, Faculty of Sciences, University of Yaoundé I Yaoundé, Cameroon.
Billy
B
Tene Fossog
Institut de Recherche pour le Développement (IRD), UMR MIVEGEC (UM1, UM2, CNRS 5290, IRD 224) Montpellier, France ; Eck Institute for Global Health & Department of Biological Sciences, University of Notre Dame Notre Dame, IN, USA ; Centre International de Recherches Médicales de Franceville (CIRMF) Franceville, Gabon.
Diego
D
Ayala
SaBio, Instituto de Investigación en Recursos Cinegéticos (IREC), CSIC-UCLM-JCCM Ciudad Real, Spain.
Pelayo
P
Acevedo
Institut de Recherche pour le Développement (IRD), UMR MIVEGEC (UM1, UM2, CNRS 5290, IRD 224) Montpellier, France ; Laboratoire de Recherche sur le Paludisme, Organisation de Coordination pour la lutte contre les Endémies en Afrique Centrale (OCEAC) Yaoundé, Cameroon.
Pierre
P
Kengne
Faculty of Medicine, Universidad Nacional de Guinea Ecuatorial (UNGE) Bata, Equatorial Guinea.
Ignacio
I
Ngomo Abeso Mebuy
Institut de Recherche pour le Développement (IRD), UMR MIVEGEC (UM1, UM2, CNRS 5290, IRD 224) Montpellier, France ; Centre International de Recherches Médicales de Franceville (CIRMF) Franceville, Gabon ; Institut de Recherche en Ecologie Tropicale (IRET) Libreville, Gabon.
Boris
B
Makanga
Centre International de Recherches Médicales de Franceville (CIRMF) Franceville, Gabon.
Julie
J
Magnus
Laboratoire de Recherche sur le Paludisme, Organisation de Coordination pour la lutte contre les Endémies en Afrique Centrale (OCEAC) Yaoundé, Cameroon.
Parfait
P
Awono-Ambene
Department of Animal Biology, Faculty of Sciences, University of Yaoundé I Yaoundé, Cameroon.
Flobert
F
Njiokou
Sezione di Parassitologia, Dipartimento di Sanità Pubblica e Malattie Infettive, Università di Roma 'La Sapienza' Rome, Italy.
Marco
M
Pombi
Laboratoire de Recherche sur le Paludisme, Organisation de Coordination pour la lutte contre les Endémies en Afrique Centrale (OCEAC) Yaoundé, Cameroon.
Christophe
C
Antonio-Nkondjio
Institut de Recherche pour le Développement (IRD), UMR MIVEGEC (UM1, UM2, CNRS 5290, IRD 224) Montpellier, France ; Centre International de Recherches Médicales de Franceville (CIRMF) Franceville, Gabon.
Christophe
C
Paupy
Eck Institute for Global Health & Department of Biological Sciences, University of Notre Dame Notre Dame, IN, USA.
Nora J
NJ
Besansky
Institut de Recherche pour le Développement (IRD), UMR MIVEGEC (UM1, UM2, CNRS 5290, IRD 224) Montpellier, France ; Laboratoire de Recherche sur le Paludisme, Organisation de Coordination pour la lutte contre les Endémies en Afrique Centrale (OCEAC) Yaoundé, Cameroon.
Carlo
C
Costantini
Anopheles coluzzii; Anopheles gambiae; cryptic species; ecological character displacement; ecological speciation; habitat segregation; malaria vector; molecular forms; niche partitioning; saltwater tolerance; spatial ecology; species distribution modelling; urban pollution