AOBPreview originally published online on July 26, 2004
Annals of Botany 2004 94(3):419-426; doi:10.1093/aob/mch159
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Annals of Botany 94/3, © Annals of Botany Company 2004; all rights reserved
Genetic structure and outcrossing rates in Flourensia cernua (Asteraceae) growing at different densities in the South-western Chihuahuan Desert
1 Instituto de Ecología A. C., Ap. Postal 63, 91070 Xalapa, Veracruz, México, 2 Departamento de Ecología Evolutiva, Instituto de Ecología, UNAM, Apartado Postal 70-275, 04510 México D. F., México and 3 Instituto de Ecología A. C., Ap. Postal 63, 91070 Xalapa, Veracruz, México
* For correspondence. E-mail mferrer{at}miranda.ecologia.unam.mx
Received: 4 March 2004 Returned for revision: 13 April 2004 Accepted: 25 May 2004 Published electronically: 26 July 2004
• Backgrounds and aims Flourensia cernua is a partially self-incompatible, wind-pollinated shrub that grows in two scrub types of contrasting densities. It was anticipated that differences in plant density would affect the amount of genotype availability, and thus higher outcrossing rates and less genetic differentiation would be found at high-density sites.
• Methods At five high-density sites and at five low-density sites, 11 allozyme loci were analysed in adults. Outcrossing rates were estimated using five allozyme loci sampled from eight families from each scrub type.
• Key results High levels of genetic variation were found at all sites (ranging from P = 82–100 %, He = 0·33–0·45, and Ho = 0·4–0·59). Heterozygotes were found in excess (FIS = –0·15 ± 0·06 s.d.), suggesting that natural selection favours heterozygosity, and there was little differentiation between sites (FST = 0·08 ± 0·02 s.d.). Life history attributes, such as long-lived habit and wide geographic distribution, as well as the presence of a self-incompatibility system may explain these results. Outcrossing rates did not differ from 1·0 in both scrub types, and there was no genetic differentiation between scrub types (FST = –0·01 ± 0·004 s.d.).
• Conclusions The high rate of outcrossing favoured by partial incompatibility may generate unrestricted gene flow between scrub types and thus may explain the lack of differentiation between them. High heterozygosity could be expected in long-lived plants of arid zones as they confront a variable and stressing environment.
Key words: Density, outcrossing rates, genetic structure, genetic variability, heterozygosity excess, self-incompatibility, Flourensia cernua
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