1. National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, Maryland 20894, USA
2. Simon's Rock College, 84 Alford Road, Great Barrington, Massachusetts 01230, USA

Correspondence to: Fyodor A. Kondrashov² Correspondence and requests for materials should be addressed to F.A.K. (e-mail: Email: fedya@simons-rock.edu).

Abstract

Sympatric speciation, the origin of two or more species from a single local population, has almost certainly been involved in formation of several species flocks^{1, 2, 3, 4}, and may be fairly common in nature⁵. The most straightforward scenario for sympatric speciation requires disruptive selection favouring two substantially different phenotypes, and consists of the evolution of reproductive isolation between them followed by the elimination of all intermediate phenotypes⁶. Here we use the hypergeometric phenotypic model^{7, 8, 9, 10} to show that sympatric speciation is possible even when fitness and mate choice depend on different quantitative traits, so that speciation must involve formation of covariance between these traits. The increase in the number of variable lociaffecting fitness facilitates sympatric speciation, whereas the increase in the number of variable loci affecting mate choice has the opposite effect. These predictions may enable more cases of sympatric speciation to be identified.