Scent of a break-up: phylogeography and reproductive trait divergences in the red-tailed bumblebee (Bombus lapidarius)

Pierre Rasmont,Maryse Vanderplanck,Thomas Lecocq,Jean-Yves Rasplus,Patrick Lhomme,Irena Valterová,Simon Dellicour,Denis Michez

doi:10.1186/1471-2148-13-263

Abstract

BackgroundThe Pleistocene climatic oscillations are considered as a major driving force of intraspecific divergence and speciation. During Ice Ages, populations isolated in allopatric glacial refugia can experience differentiation in reproductive traits through divergence in selection regimes. This phenomenon may lead to reproductive isolation and dramatically accentuates the consequences of the climatic oscillations on species. Alternatively, when reproductive isolation is incomplete and populations are expanding again, further mating between the formerly isolated populations can result in the formation of a hybrid zone, genetic introgression or reinforcement speciation through reproductive trait displacements. Therefore changes in reproductive traits driven by population movements during climatic oscillations can act as an important force in promoting pre-zygotic isolation. Notwithstanding, divergence of reproductive traits has not been approached in the context of climatic oscillations. Here we investigate the impact of population movements driven by climatic oscillations on a reproductive trait of a bumblebee species (Bombus lapidarius). We characterise the pattern of variation and differentiation across the species distribution (i) with five genes (nuclear and mitochondrial), and (ii) in the chemical composition of male marking secretions (MMS), a key trait for mate attraction in bumblebees.ResultsOur results provide evidence that populations have experienced a genetic allopatric differentiation, in at least three main refugia (the Balkans, Centre-Eastern Europe, and Southern Italy) during Quaternary glaciations. The comparative chemical analyses show that populations from the Southern Italian refugium have experienced MMS differentiation and an incipient speciation process from another refugium. The meeting of Southern Italian populations with other populations as a result of range expansion at a secondary contact zone seems to have led to a reinforcement process on local MMS patterns.ConclusionsThis study suggests that population movement during Quaternary climatic oscillations can lead to divergence in reproductive traits by allopatric differentiation during Ice Ages and by reinforcement during post-glacial recolonization.

Highlights

The Pleistocene climatic oscillations are considered as a major driving force of intraspecific divergence and speciation
When reproductive isolation is incomplete and formerly isolated lineages meet as a result of range expansion, further mating between the populations produces hybrids, resulting in the formation of a hybrid zone (e.g. [15,16]), genetic introgression (e.g. [17]) or reinforcement speciation through pre-zygotic isolation mechanisms (e.g. [18,19,20])
Phylogeography of the red-tailed bumblebee Phylogeographic structure is usually consistent with long-term isolation in multiple refugia during climatic oscillations (e.g. [5])

Summary

Introduction

The Pleistocene climatic oscillations are considered as a major driving force of intraspecific divergence and speciation. During Ice Ages, populations isolated in allopatric glacial refugia can experience differentiation in reproductive traits through divergence in selection regimes. This phenomenon may lead to reproductive isolation and dramatically accentuates the consequences of the climatic oscillations on species. We characterise the pattern of variation and differentiation across the species distribution (i) with five genes (nuclear and mitochondrial), and (ii) in the chemical composition of male marking secretions (MMS), a key trait for mate attraction in bumblebees Historic events such as climatic and topographic changes have triggered current patterns of biodiversity [1,2]. When reproductive isolation is incomplete and formerly isolated lineages meet as a result of range expansion, further mating between the populations produces hybrids, resulting in the formation of a hybrid zone (e.g. [15,16]), genetic introgression (e.g. [17]) or reinforcement speciation through pre-zygotic isolation mechanisms (e.g. [18,19,20])

Methods

Results

Discussion

Conclusion