Evolutionary Ecology

, Volume 23, Issue 1, pp 5–16 | Cite as

Inverting the null-hypothesis of speciation: a marine snail perspective

Original Paper


Speciation is currently an intensely debated topic, much more so than 20–30 years ago when most biologists held the view that new species (at least of animals) were formed through the split of evolutionary lineages by the appearance of physical barriers to gene flow. Recent advances have, however, lent both theoretical and empirical support to speciation in the presence of gene flow. Nevertheless, the allopatric hypothesis of speciation is still the default model. The consequence of this is that to support sympatric and parapatric modes of speciation all allopatric alternatives must be rejected, while an allopatric explanation is usually accepted without rejecting possible non-allopatric alternatives. However, classical cases of allopatric speciation can be challenged by alternative non-allopatric explanations, and this begs for a more respectful view of how to deal with all models of speciation. An appealing approach is studying parallel evolution of reproductive barriers, which allows for comparative approaches to distinguish between allopatric and non-allopatric events, and explicit tests of a suitable null-hypothesis. Parallel evolution of reproductive isolation in a strongly polymorphic marine snail species serves as an illustrative example of such an approach. In conclusion, a more balanced debate on allopatric and non-allopatric speciation is needed and an urgent issue is to treat both allopatric and nonallopatric hypotheses critically, rather than using allopatry as the default model of speciation.


Sympatric speciation Allopatric speciation Parallel speciation Incipient speciation Littorina saxatilis 



I am most grateful to the organizers of the Lund symposium on speciation, and to the participants in the meeting who contributed with insightful discussions on the topic of parallel speciation, in particular Olof Leimar, who explicitly suggested me to write a paper on the “inverted null-hypothesis” problem. Moreover, two anonymous reviewers, and Erik Svensson gave excellent critics and made me tighten up loose parts of my argumentation. The Swedish Research Council funded this work.


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© Springer Science+Business Media B.V. 2007

Authors and Affiliations

  1. 1.Department of Marine Ecology, Tjärnö Marine Biological LaboratoryGöteborg UniversityStromstadSweden

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