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(American Journal of Botany. 2008;95:745-755.) doi: 10.3732/ajb.2007342 © 2008 Botanical Society of America, Inc.

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Strait of Gibraltar: an effective gene-flow barrier for wind-pollinated Carex helodes (Cyperaceae) as revealed by DNA sequences, AFLP, and cytogenetic variation¹

² Department of Molecular Biology and Biochemical Engineering, Pablo de Olavide University, Ctra. Utrera km 1, 41013 Sevilla, Spain ³ Botanic Garden of Madrid, CSIC, Pza. Murillo n° 2, 28014 Madrid, Spain

ABSTRACT

The Strait of Gibraltar is the most important barrier disconnecting the landmasses of Europe and Africa on the western Mediterranean extreme. Carex helodes is a wind-pollinated species endemic to the western Mediterranean. Because molecular and cytogenetic data allow the inference of its evolutionary history, we analyzed variations in chromosome number, including meiotic chromosome behavior, amplified fragment length polymorphism (AFLP) fingerprints, and nucleotide substitutions in plastid and nuclear DNA sequences. Cytogeographic results showed that the African populations have stabilized at a single chromosome number of 2n = 74, whereas the most frequent cytotype in Iberia is 2n = 72. Phylogenetic reconstructions of 17 sequences from nine closely related species revealed that C. helodes is monophyletic and that the Moroccan populations are embedded in the Iberian lineages. The haplotype network is also consistent with a European origin of the northern African haplotype. AFLP analysis also revealed hierarchical levels of genetic variation compatible with a founder effect process responsible for the African populations. All sources of evidence support the hypothesis that the Strait of Gibraltar has been an effective gene-flow barrier, generating two isolated evolutionary lineages after their dispersal. Recent connections between the two lineages appear unlikely, whereas active gene flow occurs among populations within the two lineages.

Key Words: AFLP • cytogeography • founder effect • genetic diversity patterns • ITS • long-distance dispersal • rps16 intron • western Mediterranean Basin

Received for publication 23 October 2007. Accepted for publication 3 April 2008.

FOOTNOTES

¹ The authors thank E. Cano for essential technical support; R. Piñeiro for helpful advice with analyses; C. Pendry for valuable comments on the manuscript; C. Rodríguez, M. Míguez, and F. Fernández for technical support; P. Jiménez, J. M. Marín, J. Bautista, and J. Fernández for plant materials; R. Rubio de Casas for analytical support; and two anonymous reviewers for contructive comments. This research was supported by the Spanish Ministry of Science and Technology (project CGL2005-06017-C02-02/BOS) and the Andalusian Government (P06-RMM-4128).

⁴ Author for correspondence (e-mail: amesclir{at}upo.es); present address: Department of Molecular Biology and Biochemical Engineering, Pablo de Olavide University, Ctra. Utrera km 1, 41013 Sevilla, Spain; fax: + 34-954349813

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