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Evolution of Postzygotic Reproductive Isolation in a Guild of Deceptive Orchids

Giovanni Scopece, Alex Widmer and Salvatore Cozzolino
The American Naturalist
Vol. 171, No. 3 (March 2008), pp. 315-326
DOI: 10.1086/527501
Stable URL: http://www.jstor.org/stable/10.1086/527501
Page Count: 12
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Evolution of Postzygotic Reproductive Isolation in a Guild of Deceptive Orchids
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Abstract

Abstract: The evolution of reproductive barriers is of central importance for speciation. Here, we investigated three components of postzygotic isolation—embryo mortality, hybrid inviability, and hybrid sterility—in a group of food‐deceptive Mediterranean orchids from the genera Anacamptis, Neotinea, and Orchis. In these orchids, pollinator‐mediated isolation is weak, which suggests that postpollination barriers exist. Based on crossing experiments and a literature survey, we found that embryo mortality caused complete reproductive isolation among 36.3% of the species pairs, and hybrid inviability affected 55.6% of the potentially hybridizing species pairs. Hybrid sterility was assessed experimentally for seven species pairs. A strong reduction of fertility in all investigated hybrids was found, together with clear differences between male and female components of hybrid sterility. Postzygotic isolation was found to evolve gradually with genetic divergence, and late postzygotic isolation (i.e., hybrid inviability and sterility) evolved faster than embryo mortality, which is an earlier postzygotic isolation stage. These results reveal that intrinsic postzygotic isolation strongly contributes to maintaining species boundaries among Mediterranean food‐deceptive orchids while establishing a prominent role for these reproductive barriers in the early stage of species isolation.

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