Habitat segregation and ecological character displacement in cryptic African malaria mosquitoes.

Billy Tene Fossog,Carlo Costantini,Julie Magnus,Marco Pombi,Pierre Kengne,Ignacio Ngomo Abeso Mebuy,Christophe Paupy,Pelayo Acevedo,Parfait Awono‐Ambene,Boris Makanga,Diego Ayala,Nora J Besansky,Flobert Njiokou,Christophe Antonio‐Nkondjio

doi:10.1111/eva.12242

Abstract

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.

Highlights

One of the major interests of evolutionary ecology is understanding the ecological forces that are responsible for the evolution and coexistence of closely related sympatric species
The long-term sympatric coexistence of cryptic species implies the presence of intrinsic biological differences that facilitate specialization and ecological niche partitioning, reducing the strength of interspecific competition (Szilagyi and Meszena 2009; Sobel et al 2010; Nosil 2012)
Using a large set of distribution records extracted across the study area from published and unpublished data, in conjunction with layers of geographic information that included climatic, spatial and anthropogenic variables, we developed an SDM mapping the relative probability of occurrence of the two species across Western and Central Africa

Summary

Introduction

One of the major interests of evolutionary ecology is understanding the ecological forces that are responsible for the evolution and coexistence of closely related sympatric species. Empirical genetic and ecological investigations have yet to provide a detailed understanding of the mechanisms responsible for the build-up of ecological and reproductive barriers during ongoing speciation (Sobel et al 2010; Nosil 2012). The long-term sympatric coexistence of cryptic species implies the presence of intrinsic biological differences that facilitate specialization and ecological niche partitioning, reducing the strength of interspecific competition (Szilagyi and Meszena 2009; Sobel et al 2010; Nosil 2012). Uncovering the nature of these differences is a fundamental goal in studies of speciation, and is critically important to biodiversity assessment, conservation efforts and control of economically and medically important insect pests (Coluzzi 1970; Ferguson et al 2010)

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