Symbiosis and the Origin of Species - Insect Symbiosis - page 214

17

Symbiosis and
the Origin of Species

Seth R. Bordenstein

CONTENTS

Introduction ....................................................................................................................................283
DeÝning a Species and Symbiont..................................................................................................284

Wolbachia as a Model System for Symbiont-Induced Speciation................................................285

Abundance...............................................................................................................................285
Reproductive Alterations.........................................................................................................285
Reproductive Isolation ............................................................................................................286
Rapid Speciation .....................................................................................................................286
Cytoplasmic Incompatibility and Speciation.................................................................................287
Two Forms of CI ....................................................................................................................287
Four Models of CI-Assisted Speciation .................................................................................288
Model 1 (CI Alone).......................................................................................................288
Model 2 (CI Coupled with Genetically Based Isolation) ............................................291
Model 3 (Host Accommodation) ..................................................................................293
Model 4 (Reinforcement)..............................................................................................294
Asexuality, Sexual Degradation, and the Origin of Species .........................................................295
Skeptical Views on

Wolbachia -Assisted Speciation ......................................................................297

From Wallin to and Beyond.........................................................................................299

Acknowledgments ..........................................................................................................................299
References ......................................................................................................................................300

Wolbachia

It is a rather startling proposal that bacteria, the organisms which are popularly associated with disease,
may represent the fundamental causative factor in the origin of species.

Ivan E. Wallin, 1927

INTRODUCTION

In making his case for the bacterial nature of mitochondria, Ivan E. Wallin (1927) became the Ýrst
serious advocate of symbiont-induced speciation Ð the process by which symbiotic organisms
split one host species into two. In his book , Wallin reasoned

that the universality of bacterial-derived mitochondria reÞected the importance of bacterial sym-
bionts as building blocks of evolutionary change and ultimately new species. To Wallin, bacteria
were not just pathogenic agents but also heritable units that could generate large phenotypic changes
leading to new species. His views on microbial symbiosis were received as plausible at the time,
though they were quickly overshadowed by T. H. MorganÔs discovery of chromosomal genes and

Symbionticism and the Origin of Species