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The Journal of Heredity 2002:93(3)
© 2002 The American Genetic Association 93:193-200

Allozyme Diversity and Genetic Structure of the Leafy Cactus (Pereskia guamacho [Cactaceae])

J. M. Nassar, J. L. Hamrick, and T. H. Fleming

From the Biology Department, University of Miami, P.O. Box 249118, Coral Gables, FL 33124, and Instituto Venezolano de Investigaciones Científicas, Centro de Ecología, Apdo. Postal 21827, Caracas 1020-A, Venezuela (Nassar), Departments of Botany and Genetics, University of Georgia, 2502 Plant Sciences, Athens, GA 30602 (Hamrick), and Biology Department, University of Miami, P.O. Box 249118, Coral Gables, FL 33124 (Fleming).

Address correspondence to Jafet M. Nassar, IVIC-Biblioteca "Marcel Roche," 8424 NW 56 St., Suite CCS 00206, Miami FL 33166, or e-mail: jnassar{at}oikos.ivic.ve.

We examined levels of genetic variation and genetic structure in the leafy cactus (Pereskia guamacho) in arid and semiarid zones in Venezuela. We surveyed genetic diversity within 17 populations using 19 allozyme loci. Genetic diversity was relatively high at both the species (Ps = 89%, As = 3.26, APs = 3.53, Hes = 0.24) and population (Pp = 63%, Ap = 1.90, APp = 2.42, Hep = 0.20) levels. A significant deficit of heterozygote individuals was detected within populations in the Paraguana Peninsula region (FIS = 0.301). Relatively low levels of population differentiation were detected at macrogeographic (GST = 0.112) and regional levels (GST = 0.044 for peninsula region and GST = 0.074 for mainland region), suggesting substantial genetic exchange among populations; however, gene flow in this species seems to be regulated by the distance among populations. Overall, estimates of genetic diversity found in P. guamacho are concordant with the pattern observed for other cacti surveyed, namely high levels of polymorphism and genetic diversity with one common allele and several rare alleles per locus. Differences in gene dispersal systems between this species and other cacti studied were not reflected in the patterns of genetic diversity observed. The concentration of the highest estimates of genetic variation in northwestern Venezuela suggests a potential reservoir of plant genetic diversity within xerophilous ecosystems in northern South America.


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