Testing alternative models for sexual isolation in natural populations of Littorina saxatilis: indirect support for by-product ecological speciation?
Article first published online: 29 JAN 2004
Journal of Evolutionary Biology
Volume 17, Issue 2, pages 288–293, March 2004
How to Cite
Cruz, R., Carballo, M., Conde-Padín, P. and Rolán-Alvarez, E. (2004), Testing alternative models for sexual isolation in natural populations of Littorina saxatilis: indirect support for by-product ecological speciation?. Journal of Evolutionary Biology, 17: 288–293. doi: 10.1111/j.1420-9101.2003.00689.x
- Issue published online: 29 JAN 2004
- Article first published online: 29 JAN 2004
- Received 27 March 2003; revised 11 November 2003; accepted 11 November 2003
- incipient speciation;
- Littorina saxatilis;
- mate choice;
- parallel speciation;
- size assortative mating
Two ecotypes of the rough periwinkle Littorina saxatilis occur at different shore levels, showing assortative mating for size and partial reproductive isolation when they meet at the mid-shore. This system represents a putative case of incomplete speciation in sympatry. Two processes contribute to the assortative mating: morph-specific microhabitat aggregation and mate choice. The estimation of mate choice coefficients in nature and a simulation of the aggregation effects on sexual isolation were used to disentangle these processes as well as to test alternative mechanisms of mate choice. Mate choice significantly increased the frequency of within-morph pairs and significantly decreased the frequency of between-morph pairs, whereas those pairs including at least one hybrid morph mated randomly. These results allow us to reject a discriminant mate choice and support a model of evolution of sexual isolation as a side-effect of size-assortative mating in a context of divergent natural selection for size in the population. This mechanism is more compatible with a model of incomplete by-product ecological speciation, as suggested by previous evidence.