Table of Contents
International Journal of Evolutionary Biology
Volume 2012, Article ID 247352, 10 pages
Review Article

170 Years of “Lock-and-Key”: Genital Morphology and Reproductive Isolation

Department of Zoology, University of Oklahoma, 730 Van Vleet Oval, Norman, OK 73019, USA

Received 19 July 2011; Accepted 6 September 2011

Academic Editor: Artyom Kopp

Copyright © 2012 John P. Masly. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The divergent genital morphology observed among closely related animal species has long been posited as a mechanism of reproductive isolation. Despite the intuitive appeal that rapidly evolving genitalia might cause speciation, evidence for its importance—or even its potential—in reproductive isolation is mixed. Most tests of genital structural isolation between species often fail to find convincing evidence that differences in morphology prevent copulation or insemination between species. However, recent work suggests that differences in genital morphology might contribute to reproductive isolation in less obvious ways through interactions with sensory mechanisms that result in lowered reproductive fitness in heterospecific matings. In this paper, I present a brief history of the “lock-and-key” hypothesis, summarize the evidence for the involvement of genital morphology in different mechanisms of reproductive isolation, discuss progress in identifying the molecular and genetic bases of species differences in genital morphology, and discuss prospects for future work on the role of genitalia in speciation.