Parasites contribute to ecologically dependent postmating isolation in the adaptive radiation of three-spined stickleback.

Aliya El Nagar,Andrew D C Maccoll

doi:10.1098/rspb.2016.0691

Abstract

Spatial variation in parasitic infections is common, and has the potential to drive population divergence and the reproductive isolation of hosts. However, despite support from theory and model laboratory systems, little strong evidence has been forthcoming from the wild. Here, we show that parasites are likely to cause reproductive isolation in the adaptive radiation of three-spined stickleback. Adjacent wild populations on the Scottish island of North Uist differ greatly and consistently in the occurrence of different parasites that have substantial effects on fitness. Laboratory-reared fish are more resistant to experimental infection by parasite species from their own population. Furthermore, hybrid backcrosses between the host populations are more resistant to parasites from the parental population to which they are more closely related. These patterns provide strong evidence that parasites can cause ecological speciation, by contributing to selection against migrants and ecologically dependent postmating isolation.

Highlights

The ecological model of speciation, which proposes that reproductive isolation between populations occurs as a result of divergent adaptation to different environments, is widely accepted as a major explanation for how new species arise [1,2]
In order to infer a sufficient role of parasites in host speciation, we first show that the three necessary prerequisites for parasites to contribute to speciation are true for an adjacent pair of stickleback populations on North Uist, which we call Chadha Ruaidh (CHRU) and OBSM
We focus on the potential for parasites to contribute to reproductive isolation between an adjacent pair of waterbodies, Loch a Chadha Ruaidh (CHRU, 578360 N; 78120 W), which supports a freshwater population of stickleback, and Ob nan Stearnain (OBSM, 578360 N; 78100 W), a brackish lagoon 1.5 km distant

Summary

Introduction

The ecological model of speciation, which proposes that reproductive isolation between populations occurs as a result of divergent adaptation to different environments, is widely accepted as a major explanation for how new species arise [1,2]. In order to infer a sufficient role of parasites in host speciation, we first show that the three necessary prerequisites for parasites to contribute to speciation are true for an adjacent pair of stickleback populations on North Uist, which we call CHRU (from a small freshwater loch) and OBSM (from a brackish lagoon) (figure 1).

Results

Conclusion